Blauer_wsu_0251E_10645 - Washington State University

Transcription

FACTORS AFFECTING TUBER ASCORBATE CONTENT, PHYSIOLOGICAL AGE,
TUBER SET AND SIZE DISTRIBUTION IN POTATO
(Solanum tuberosum L.)
By
JACOB MICHAEL BLAUER
A dissertation submitted in partial fulfillment of
the requirements for the degree of
DOCTOR OF PHILOSOPHY
WASHINGTON STATE UNIVERSITY
Program in Molecular Plant Sciences
MAY 2013
© Copyright by JACOB MICHAEL BLAUER, 2013
All Rights Reserved
© Copyright by JACOB MICHAEL BLAUER, 2013
All Rights Reserved
i
To the Faculty of Washington State University:
The members of the Committee appointed to examine the dissertation of
JACOB MICHAEL BLAUER find it satisfactory and recommend that it be accepted.
___________________________________
N. Richard Knowles, Ph.D., Chair
___________________________________
Amit Dhingra, Ph.D.
___________________________________
G.N. Mohan Kumar, Ph.D.
___________________________________
John K. Fellman, Ph.D.
ii
ACKNOWLEDGEMENTS
I would like to thank Prof. N. Richard Knowles and Dr. Amit Dhingra for giving
me the opportunity in 2008 to improve myself by working towards my Doctorate of
Philosophy degree in Molecular Plant Science in their laboratories. It is with their
generosity, patience, and guidance that this work was possible. Thank you to Dr. Mohan
Kumar for the hours of training and evaluation of my work to ensure quality of
experiments and to Dr. John Fellman for all the advice and always maintaining an open
door policy.
A special thanks to Dr. Lisa Knowles for the hours spent assisting with data
collection, technical advice, and training. To Dr. Mark Pavek for his role in maintaining
field quality for experiments in Othello, WA, and for also having an open door policy for
information and advice. Thanks to the rest of the WSU crew, but not limited to: Daniel
Zommick, Zachary Holden, Chris Hiles, Rudy Garza, Josh Rodriguez, Sergio Rodriguez,
Julio Ramirez, Nora Fuller, John Steinbeck, and Mark Weber for their help in the fields
and/or laboratory for data collection, planting, field maintenance, and harvest each year.
Finally, a very special thanks to my young family, Melanie, Rachel, Audrey, and
William for sacrificing time away from parents and grandparents for me to accomplish
this work. Additionally, for their patience and understanding of me being absent for
conferences and late hours and weekends in the laboratory.
You all will never fully understand my level of appreciation for all you have done
for me. Thank you.
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FACTORS AFFECTING TUBER ASCORBATE CONTENT, PHYSIOLOGICAL AGE,
TUBER SET AND SIZE DISTRIBUTION IN POTATO
(Solanum tuberosum L.)
Abstract
by Jacob Michael Blauer, Ph.D.
Washington State University
May 2013
Chair: N. Richard Knowles
Potatoes (Solanum tuberosum L.) are one of the most important food crops
globally and represent a multi-billion dollar market from production through retail.
Areas of fundamental importance to consumers and producers include improving the
nutritional quality of potatoes and enhancing their production value. The studies reported
here focus in three disparate areas: (1) understanding how vitamin C accumulates during
growth and development and is lost during storage in relation to expression of genes in
the biosynthetic and recycling pathways; (2) testing the hypothesis that tuber respiration
is the pacemaker of physiological aging in seed-potatoes; and (3) evaluating the efficacy
of seed-tuber age and gibberellins (GA) to alter apical dominance, tuber set, and size
distribution of five red/specialty cultivars to better meet the requirements of various
markets.
AsA concentration increased rapidly in tubers during the early stages of
tuberization and through bulking, reaching a maximum just prior to the attainment of
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physiological maturity, then fell during the maturation period as vines began to senesce.
AsA was lost rapidly from tubers following harvest and the rate of loss was affected by
genotype, tuber age, wounding, oxygen concentration, and sprouting; preventing this loss
has the potential of greatly increasing the contribution of potatoes to vitamin C in our
diet.
The importance of tuber basal metabolic rate in dictating the physiological age
(PAGE) and productive potential of seed was explored in chapter two. Seed-tubers given
high-temperature age-priming treatments at the beginning of storage maintained higher
respiration rates throughout storage until planting. Lowering the respiration rate of ageprimed seed during storage resulted in younger tubers. Respiration appears to be the
pacemaker of PAGE and production and storage conditions that affect respiration may
‘set the clock speed’ that will ultimately determine the PAGE at planting.
Methods for manipulating apical dominance, tuber set and size distribution of
specialty cultivars of potatoes were developed in chapter three. While aging treatments
were ineffective, pre-plant applications of GA to cut seed substantially increased crop
values, due to combined effects on apical dominance, tuber set, total yields and shifts in
tuber size distribution toward smaller size tubers with higher value.
v
TABLE OF CONTENTS
Page
Acknowledgements…………………………………………………………………….. iii
Abstract………………………………………………………………………………… iv
Table of Contents………………………………………………………………………. vi
List of Tables…………………………………………………………………………... viii
List of Figures………………………………………………………………………….. ix
Abbreviations...………………………………………………………………………… x
Attributions…………………………………………………………………………….. xii
Forward…..…………………………………………………………………………….. 1
References………………………………………………………………………... 6
CHAPTER 1: TUBER ASCORBATE CONTENT IN RELATION TO GENE EXPRESSION DURING
DEVELOPMENT AND STORAGE OF POTATO TUBERS (Solanum tuberosum L.)
Abstract…………………………………………………………………………... 8
Introduction……………………………………………………………………..... 10
Materials and methods………………………………………..………………….. 12
Results……………………………………………………..……………………... 21
Discussion ………………..…………………………………………..………….. 30
Acknowledgements………………………………………………………………. 37
References……………………………………………..…………………………. 38
Figures and Tables.….…………………………..……………………………….. 46
CHAPTER 2: EVIDENCE THAT TUBER RESPIRATION IS THE PACEMAKER OF
PHYSIOLOGICAL AGING IN SEED POTATOES (Solanum tuberosum L.)
Abstract……………………………………………..……………………………. 66
Introduction…………………………………………..…………………………... 68
Materials and methods…………………………………………………………… 71
Results…………………………………………………………….……………... 75
Discussion..……………..……………………………………………………….. 83
Acknowledgements……..……………………………………………………….. 86
References….…………………………………………………………………….. 87
Figures and Tables……..………………………………………………………… 91
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CHAPTER 3: MANIPULATING STEM NUMBER, TUBER SET AND SIZE DISTRIBUTION IN
SPECIALTY POTATO CULTIVARS
Abstract…………………………………………………………………………... 106
Introduction………………………………………………………………………. 108
Materials and methods………………………………………………………........ 110
Results……………………………………………………………………………. 115
Discussion ……..………..……..………………………………………………… 127
Acknowledgements………………………………………………………………. 130
References……….……………………………………………………………….. 131
Figures and Tables……………………………………………………………….. 135
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LIST OF TABLES
Page
1.
Ch. 1, Table 1. Genes of Interest in Vitamin C Metabolism…………...…….
46
2.
Ch. 1, Table 2. AsA Levels during Wound Healing……..…………...……...
47
3.
Ch. 2, Table 1. Effects of Temperature on Sprout Growth……………...…...
91
4.
Ch. 2, Table 2. Effects of Timing of Age-priming on Production……….......
92
5.
Ch. 2, Table 3. Effects of Oxygen on Production Potential………………….
93
6.
Ch. 3, Table 1. Dates for Materials and Methods……………………………
135
7.
Ch. 3, Table 2. Yield Results for 2009 CW, YG, & C....…………………….
136
8.
Ch. 3, Table 3. Yield Results for 2009 RL & S……......…………………….
137
9.
Ch. 3, Table 4. Yield Results for all Cultivars 2010…………………………
138
10. Ch. 3, Table 5. Yield Results for all Cultivars 2011…………………………
139
11. Ch. 3, Table 6. A, B, C Yields & Returns for all Cultivars 2011……………
140
12. Ch. 3, Table 7. Yield Results for all Cultivars 2012…………………………
141
13. Ch. 3, Table 8. A, B, C Yields & Returns for all Cultivars 2012……………
142
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LIST OF FIGURES
Page
1.
Ch. 1, Fig. 1. AsA Biosynthesis and Recycling Pathways..……………..…....
48
2.
Ch. 1, Fig. 2. Stages of Tuberization……………………………………….....
49
3.
Ch. 1, Fig. 3. Plant Growth & Development Profiles………………………....
51
4.
Ch. 1, Fig. 4. Changes in AsA during Tuber Development & Storage...……...
53
5.
Ch. 1, Fig. 5. AsA Gene Expression during Tuber Development…………......
55
6.
Ch. 1, Fig. 6. Transcript Levels during Tuber Development…...…………......
57
7.
Ch. 1, Fig. 7. Gene Expression for AsA Recycling…..……………………….
59
8.
Ch. 1, Fig. 8. AsA Loss during Storage……………...…………...…………...
60
9.
Ch. 1, Fig. 9. Low O2 Attenuates AsA Loss...…………….…………………..
61
10.
Ch. 1, Fig. 10. AsA Transcript Levels in Response to Wounding.....………...
62
11.
Ch. 1, Fig. 11. Effects of Tuber Age and Wounding on AsA Content………..
63
12.
Ch. 1, Fig. 12. Histochemical Staining of AsA in Relation to Transcripts……
65
13.
Ch. 2, Fig. 1. Effects of Age-priming Temperatures on Respiration Rate...…..
95
14.
Ch. 2, Fig. 2. Effects of Timing of Age-priming on Productivity...…………..
97
15.
Ch. 2, Fig. 3. Effects of Timing of Age-priming on Tuber Size Distribution...
99
16.
Ch. 2, Fig. 4. Age-priming affects Tuber Respiration.…..……………………
101
17.
Ch. 2, Fig. 5. Effects of Low O2 Storage on Tuber Size Distribution……...…
103
18.
Ch. 2, Fig. 6. Effects of Low O2 Storage on Tuber Respiration...…………….
105
19.
Ch. 3, Fig. 1. Tuber Diameter & Weight Relationships…………..…………... 144
20.
Ch. 3, Fig. 2. Age-induced Shifts in Tuber Size Distribution (2009).………...
146
21.
Ch. 3, Fig. 3. GA Affects Tuber Size Distributions (2010)..…...……...……...
148
22.
Ch. 3, Fig. 4. GA Affects Tuber Size Distributions (2011)……….…………..
150
23.
Ch. 3, Fig. 5. Effects of GA on Plant Emergence (2012)……...……………...
152
24.
Ch. 3, Fig. 6. GA Affects Tuber Size Distributions (2012)……….…...……...
154
ix
Abbreviations
APX, Ascorbate peroxidase
AsA, Ascorbate, Ascorbic Acid, Vitamin C
C, Chieftain
CV, Cultivar
CW, Cal White
Cyt, Cytochrome
DAP, Days after planting
DAH, Days after harvest
DBP, days before planting
DD, Degree days
DHA, Dehydroascorbate
DHAR, Dehydroascorbate reductase
DMSO, Dimethyl Sulfoxide
DW, Dry weight
FW, Fresh weight
GA, GA3, Gibberellic acid
GGP1, GDP-L-galactose phosphorylase/guanyltransferase
GGP2, GDP-L-galactose phosphorylase/guanyltransferase
G6PI, Glucose-6-phosphate isomerase
GR, Glutathione reductase
GPP, L-galactose-1-phosphate phosphatase
GME1, GDP-mannose-3’, 5’-epimerase 1
GMP1, GDP-mannose pyrophosphorylase 1
GMP2, GDP-mannose pyrophosphorylase 2
L-GalLDH, L-galactono-1, 4-lactone dehydrogenase
L-GalDH, L-galactose dehydrogenase
MDHAR1, Monodehydroascorbate reductase 1
MDHAR2, Monodehydroascorbate reductase 2
x
PAGE, Physiological Age
PGR, Plant Growth Regulator
PMI, Mannose-6-phosphate isomerase
PMM, Phosphomannomutase
RB, Russet Burbank
RL, Red La Soda
ROS, Reactive oxygen species
RR, Ranger Russet
S, Satina
SOD, Superoxide dismutase
YG, Yukon Gold
xi
Attributions
Chapter 1: Changes in ascorbate and associated gene expression during development and
storage of potato tubers (Solanum tuberosum L.).
Blauer, Jacob M.: Graduate student, the major contributor of research findings and writer
of manuscript with and under the direction of Dr. N. Richard Knowles.
Kumar, G.N. Mohan: Assisted in graduate and experimental training of Jacob M. Blauer
for completion of work and reviewer of manuscript for submission.
Knowles, Lisa O.: Assisted in graduate and experimental training of Jacob M. Blauer,
assisted in data collection including sugar evaluations, and reviewer of manuscript for
submission for publication.
Dhingra, Amit: Assisted in graduate and experimental training of Jacob M. Blauer for
completion of work, reviewed experimental results, and reviewed manuscript for
submission for publication.
Knowles, N. Richard: Graduate student advisor for Jacob M. Blauer. Oversaw all
training and experiments of work herein, and writer of manuscript in conjunction with
Jacob M. Blauer.
Chapter 2: Evidence that tuber respiration is the pacemaker of physiological aging in
seed potatoes (Solanum tuberosum L.). Journal of Plant Growth Regulation.
assisted in data collection and experimental setup, oversaw age-prime timing study, and
reviewer of manuscript for submission for publication.
xii
Jacob M. Blauer.
Chapter 3: Manipulating stem number, tuber set and size distribution in specialty potato
cultivars.
assisted in data collection, and reviewer of manuscript for submission for publication.
Jacob M. Blauer.
xiii
FORWARD
Today the potato is grown throughout the world and represents a multi-billion dollar
industry with close to two billion dollars of potatoes produced in the Pacific Northwest alone
(Anon, 2012). It is grown commercially for seed, processing (French fries, mashed, shreds, etc),
and for the fresh market. The aim of this work is three fold which, (1) focuses on the nutritional
value of potato tubers through vitamin C, (2) potato seed production as if effects subsequent
markets through physiological aging, and (3) the manipulation of the tuber size distribution
through the use of plant growth regulators in specialty cultivars.
In recent years the potato has received bad publicity due to the high carbohydrate content
and thought to contribute to diabetes and obesity (Carollo, 2011), but recent public opinions are
beginning to change and it is being recognized again as a nutrient dense food crop (Kramer,
2011). Because of the bad publicity the potato had received at the initiation of this work, we
aimed to address some of the health issues and potential benefits of a diet with potatoes, thus a
complete study on vitamin C metabolism in the potato tuber was completed and constitutes the
first chapter. As a side note, each chapter of this work is written in manuscript format and each
has been submitted for review for publication in peer-reviewed journals as indicated at the
heading of each chapter.
In plants, vitamin C is synthesized via four pathways (Galacturonate; Myo-inositol; LGulose; and the L-Galactose Smirnoff-Wheeler) with the L-Galactose Smirnoff-Wheeler
pathway proposed as the main biosynthetic pathway in plants/potatoes (Bulley et al., 2009;
Smirnoff et al., 2001; Ishikawa et al., 2006). Chapter one, the Smirnoff-Wheeler biosynthetic
pathway was evaluated to determine the complete kinetic accumulation of vitamin C in the
potato tuber from tuberization through growth and development and through storage. The
1
kinetics of vitamin C were further evaluated during sprouting in long-term storage and under
various stresses such as low oxygen storage, wound healing, extreme long-term chronological
age, and under heat stress in storage (aging treatments). In addition to the quantification of
vitamin C, we also evaluated the semi-quantitative changes in gene expression through RT-PCR
of the Smirnoff-Wheeler pathway during all the stages of the tuber lifecycle and during the
indicated stresses. Furthermore, vitamin C is recycled through Halliwell-Asada cycle where it is
reduced by glutathione for the scavaging of free radicals in the cell (Noctor and Foyer, 1998);
semi-quantitative changes in gene expression of this pathway were also measured. Generally,
our findings were consistent with previous results in that vitamin C levels peak at the end of the
growing season and are highest at harvest with a rapid loss during storage (Review: Love and
Pavek, 2008). We further showed that tubers do have the ability to synthesize their own vitamin
C in situ during rapid cellular division events such as tuberization, sprouting and wound healing,
and that there is a maintenance metabolism level of vitamin C that is required during long-term
storage that further promotes de novo synthesis of vitamin C, though the level is relatively low
and the regulating signals/cues are still not known. To our knowledge, this is the first complete
evaluation of vitamin C metabolism in the potato tuber to be conducted and submitted for
publication.
In addition to the nutritive properties of potatoes, one production issue of potatoes is the
inconsistent performance of seed potatoes in different growing regions as affected by the total
yield, plant emergence/establishment rates, stem number production, number of tubers set, and
the size distribution of tubers. Each market has different ideal parameters for each of these areas
and the environment, growing region, and cultivar selection only further clouds the issue. It is
believed that the physiological status (physiological age, PAGE) of the seed tuber at the time of
2
planting can have a dramatic effect on the emergence rate, stem number, tuber set and size
distribution (Knowles and Knowles, 2006; Struik, 2007), therefore much work has gone into
identifying markers of PAGE in the potato seed tuber, pre-plant, to better predict the overall
performance.
Over the years, there have been a number of indicators identified, but each one is either
only effective after planting (stem number accounting) (Iritani, et al., 1983) or in the case of
degree day (DD) accounting (O’Brien, et al., 1983), has not proven as reliable as previously
thought. DD accumulation is estimated by counting the heat units accumulated beyond standard
storage temperatures (typically 4°C) over time. Struik (2006) found that the timing of the heat
unit accumulation could have almost as dramatic an effect on the PAGE as just PAGE alone.
For this reason chapter two was conducted which focuses on the phenomenon of PAGE and
identifies respiration as the ‘pacemaker’ of aging in potato seed tubers and its subsequent effects
on the following year’s crop. We demonstrate that the intensity, timing, and duration of the heat
unit accumulation plays a critical role in dictating the true physiological status of the seed tuber
and thus the seed performance and economic return. Generally, tubers that acquired the same
DD accumulation can have dramatically varying PAGEs depending upon when and how extreme
the heat treatment was. Tubers essentially ‘remember’ the heat units they received and this is
reflected in their resting respiration rate across various storage temperatures. The differences in
the respiratory output can be directly correlated to changes in the stem number, tuber set, size
distribution and economic returns for the seed, processing, and fresh pack industries.
The final and third chapter was initiated in response to local growers in the state of
Washington wanting information clarifying the stem number to tuber set and size distribution
relationship in specialty cultivars of potatoes (Yukon Gold, Red La Soda, Cal White, Satina, and
3
Chieftain). Initially, it was thought that the yield size profile could be manipulated through
physiological aging as demonstrated in long-russet cultivars (Knowles and Knowles, 2006), but
it was found during the first year that these specialty potatoes were recalcitrant to physiological
aging. Therefore, we employed the use of plant growth regulators (PGRs) to obtain the desired
responses. Overall, we found the use of gibberellic acid (GA3) as a seed treatment, pre-plant,
was a very effective tool in altering the stem number, tuber set, size distribution and economic
returns in these five cultivars and that the application rate had substantial affects. The overall
effectiveness, it is important to point out, is highly dependent upon the final intended market.
While we focused on the seed and baby potato industries, we believe that the results of this work
will be beneficial for the processing industries and in other cultivars as well. Furthermore, it is
hoped the additional information will be of benefit to the chemical industry because while there
are GA3 products on the market, our findings suggest that half to 4 times the recommended rates,
depending upon the desired outcome and the cultivar, should be used.
In summation, it is believed that the findings in these three chapters will be of importance
to the potato world (industry and research) because first, we demonstrate the first complete
evaluation of the kinetics of vitamin C in the potato tuber throughout the entire lifecycle and
through various stresses with the corresponding changes in gene expression for biosynthesis and
recycling. It is hoped that this information will further improve targeted research to enhance
vitamin C content and retention in potato tubers long-term. Secondly, while impractical on a
commercial basis, respiration is a good indicator of PAGE in seed tubers, thus their performance
potentials. This has implications for improving seed potato handling practices short-term, and
long-term, for improving storage CO2 monitoring commercially which would be a step closer
toward tailored seed to improve the stem number, tuber set and size distribution in long-russet
4
cultivars for improved economic returns for varying cultivars, growing regions, and individual
markets. Finally, while not all cultivars of potatoes respond to physiological aging the same,
chapter three demonstrates that PGRs, specifically GA3, may currently be used, in addition to
altered agronomic practices, to improve the stem number, tuber set, size distribution and
economic returns of some cultivars for various industries when used at the correct rates.
5
References
Anonymous. 2012. United States Department of Agriculture, National Agricultural Statistics
Service. February 2012. Text and Media. 30 November, 2012. Crop Values 2011
Summary. <http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?
documentID=1050>., Washington D.C., U.S.A.
Bulley, S.M., Rassam, M., Hoser, D., Wolfgang, O., Schunemann, N., Wright, M., MacRae, E.,
Gleave, A., Laing, W. 2009. Gene expression studies in kiwifruit and gene overexpression in Arabidopsis indicates that GDP-L-galactose guanyltransferase is a major
control point of vitamin C biosynthesis. Journal of Experimental Botany 60 (3), 765-778.
Carollo, Kim and Lara Salahi. abcnews.go.com. 22 June 2011. Text & Media. 19 March 2012.
<http://abcnews.go.com/Health/healthy-weight-study-diet-lifestyle-leadsuccess/story?id=13893779#.T2e2TfUgW8A>.
Iritani, W.M., Weller, L.D., Knowles, N.R. 1983. Relationship between stem number, tuber set
and yield of Russet Burbank potatoes. American Journal of Potato Research 60:423-431.
Ishikawa, T., Dowdle, J., Smirnoff, N. 2006. Progress in manipulating ascorbic acid biosynthesis
and accumulation in plants. Physiology Plantarum 126, 343–355.
Knowles, N.R., Knowles, L.O. 2006. Manipulating stem number, tuber set, and yield
relationships for northern- and southern-grown potato seed lots. Crop Science 46: 284296.
Kramer, S. diabeticsurvivalkit.com. 8 May 2011. Text and Media. 28 November 2012.
<http://diabeticsurvivalkit.com/2011/05/08/diabetes-potatoes-glycemic-indes-diabetescontrol/>.
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Love, S.L., Pavek, J.J. 2008. Positioning the potato as a primary food source of vitamin C.
American Journal of Potato Research 85: 277-285.
Noctor, G., Foyer, C.H. 1998 Ascorbate and glutathione: keeping active oxygen under control.
Annual Review of Plant Physiology and Plant Molecular Biology 49: 249-279.
O’Brien, P.J., Allen, E.J., Bean, J.N., Griffith, R.L., Jones, S.A., Jones, J.L. 1983. Accumulated
day-degrees as a measure of physiological age and the relationships with growth and
yield in early potato varieties. The Journal of Agricultural Science 101(3):613-631.
Smirnoff, N., Conklin, P.L., Loewus, F.A. 2001. Biosynthesis of ascorbic acid in plants: a
renaissance. Annual Review of Plant Physiology and Plant Molecular Biology 52, 43767.
Struik, P.C., van der Putten, P.E.L., Caldiz, D.O., Scholte, K. 2006. Response of stored potato
seed tubers from contrasting cultivars to accumulated day-degrees. Crop Science
46:1156-1168.
Struik, P.C. 2007. The canon of potato science: 40. Physiological age of seed tubers. Potato
Research 52:295-304.
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CHAPTER 1
Changes in ascorbate and associated gene expression during development and storage of
potato tubers (Solanum tuberosum L.)1
Abstract
Reducing postharvest loss of AsA in potato (Solanum tuberosum L.) tubers could greatly
increase their contribution to vitamin C in our diet. Knowledge of developmentally linked
changes in AsA content in relation to associated gene expression (from tuberization through
bulking, maturation and storage) will facilitate elucidation of the mechanisms regulating tuber
AsA content, and is a prerequisite to developing high vitamin C retaining genotypes. Transcript
levels of genes in the Smirnoff-Wheeler pathway increased as field grown tubers developed to 10
g, suggesting de novo synthesis in situ contributes to AsA content early in development.
Transcript of GGP (GDP-L-galactose phosphorylase/guanylyltransferase), a potential rate
limiting step in AsA biosynthesis, increased as tubers developed from non-tuberized stolons to
the 0.6-1.5-g tuber stage, in parallel with an increase in AsA concentration. High levels of GGP
expression continued through 84 DAP (~54-g tubers) when 75% of the final AsA concentration
of fully mature (240-g) tubers had been established. Expression levels of other key genes in the
AsA pathway were also temporally correlated with AsA accumulation during tuberization and
early bulking. Tuber AsA concentration began to fall during vine senescence and continued to
decline progressively through maturation and storage, consistent with low levels of gene
expression, and losses reached 65% over an 8.5-month storage period. The rate of loss was
genotype-dependent. Storage of tubers under reduced O2 attenuated AsA loss, suggesting a
regulatory role for oxidative metabolism in AsA loss/retention. Wounding of tubers induced
AsA biosynthesis and recycling, indicating metabolic competence for AsA synthesis in the
detached organ. Crop breeding and postharvest handling strategies for enhancing content and
8
retention of tuber AsA will evolve from a better understanding of the metabolic regulation of
these processes.
1
Blauer, J.M., Kumar, G.N.M., Knowles, L.O., Dhingra, A., Knowles, N.R., 2012. Changes in
ascorbate and associated gene expression during development and storage of potato tubers
(Solanum tuberosum L.). Postharvest Biology and Technology. 78: 76-91.
9
1. Introduction
The high consumption rate of potatoes makes them a significant dietary source of vitamin
C (ascorbic acid, ascorbate, AsA). A 148-g tuber supplies approximately 45% of the
recommended daily requirement (Pennington and Wilkening, 1997). While other vegetables and
fruits (such as citrus) contain higher levels of AsA, potatoes contribute as much AsA (20%) to
the typical American diet as citrus fruits (18%) (McCay et al., 1975). Ascorbate content in
cultivated potatoes ranges from about 11 to 40 mg 100 g-1 FW (Dale et al., 2003; Love et al.,
2003; Love and Pavek, 2008). Moreover, the heritability of AsA content is high, indicating that
levels can and indeed have been increased through traditional breeding approaches (Pavek and
Corsini, 2004; Love and Pavek, 2008). Rapid loss during storage, however, is one of the most
important factors affecting the AsA content of tubers (Love and Pavek, 2008). Therefore,
strategies to enhance the contribution of potatoes as a dietary source of vitamin C should couple
breeding and biotechnological approaches for increased content and postharvest retention with
the development of handling and storage practices that attenuate postharvest losses. A detailed
understanding of the kinetics of AsA accumulation and loss in relation to the metabolic pathways
that modulate AsA levels during tuber ontogeny and storage will further these goals.
Four pathways have been implicated in the biosynthesis of AsA (Galacturonate; Myoinositol; L-Gulose; and L-Galactose Smirnoff-Wheeler) with the L-Galactose Smirnoff-Wheeler
pathway proposed as the main route in most plant tissues (Fig. 1A) (Smirnoff et al., 2001; 2004;
Ishikawa et al., 2006; Bulley et al., 2009). In ripening tomatoes, transcription of L-galactose-1phosphate phosphatase (GPP) in the Smirnoff-Wheeler pathway correlated with overall
production of AsA (Ioannidi et al., 2009). However, in kiwi fruit and Arabidopsis, GDP-Lgalactose phosphorylase/guanyltransferase (GGP) was identified as a rate limiting step for AsA
10
synthesis (Bulley et al., 2009). Bulley et al. (2012) demonstrated a 2-2.5-fold increase in AsA
concentration of tubers by upregulating GGP1, establishing a key regulatory step in the
Smirnoff-Wheeler pathway for AsA synthesis in potatoes.
AsA recycling to control oxidative stress occurs through the Halliwell-Asada pathway
(AsA-glutathione (GSH) cycle, Fig. 1B) (Noctor and Foyer, 1998), where AsA has a role in the
elimination of superoxide (O2-) and peroxide (H2O2) from cells. The balance and regulation of
enzymes in this pathway are important in maintaining AsA and GSH pools (Karuppanapandian
et al., 2011). In general, activity of the AsA-GSH cycle increases with oxidative stress in
potatoes (Kumar and Knowles, 1996; Zabrouskov et al., 2002), possibly increasing the demand
for AsA. Over-expression of GSH reductase increased AsA levels in poplar (Foyer et al., 1995)
and up-regulation of dehydroascorbate reductase (DHAR) increased AsA levels 2-4-fold in corn
(Chen et al., 2003) and 1.3-1.6-fold in potato tubers (Goo et al., 2008). Qin et al. (2011) further
achieved elevated AsA levels in tubers by over-expressing cytosolic DHAR but not chloroplastic
DHAR. Defining the extent to which the AsA-GSH cycle modulates AsA levels in potatoes may
facilitate developing genotypes with improved recycling capabilities for preservation of AsA
during long-term storage.
Herein we provide a comprehensive developmental study that profiles changes in AsA in
relation to transcript levels of genes in the L-Galactose Smirnoff-Wheeler and Halliwell-Asada
pathways throughout development and storage of field-grown tubers. Tuber AsA levels
following harvest were affected by genotype, O2 concentration, tuber age, wounding, sprouting
and daughter tuber formation.
11
2. Materials and methods
2.1. Ascorbate and associated transcript levels during tuber development
2.1.1. Tuber production
Tubers for all studies except those involving low O2 storage, wound-healing, and
sprouting/daughter tuber development were grown at the Washington State University Research
and Extension Unit, Othello, WA (46o 47.277’ N. Lat., 119o 2.680’ W. Long.) according to
commercial practices for long-season russet cultivars in the Columbia Basin. Certified (G3,
generation three from nuclear stock) seed-tubers of cvs. Ranger Russet, Premier Russet,
Defender, GemStar Russet, Summit Russet, and Russet Burbank were obtained directly from
growers in October and stored at 4oC (95% RH) until planting. The seed-tubers were hand cut
(50-64-g seed pieces) in early April and suberized at 9°C (95% RH) for 3-5 days prior to
planting. Seed pieces were planted 20-cm deep in a Shano silt loam soil (Lenfesty, 1967) with a
custom built two-row assist-feed planter as described by Weeda et al. (2009). Rows were 90 m
long and 86 cm apart with seedpieces spaced 25 cm apart within each row. The number of rows
ranged from two to four depending on the study. A linear-move irrigation system maintained
soil moisture at a minimum 65% field capacity as monitored by soil tensiometers positioned
throughout the field. Pre-plant and in-season fertilizer was applied based on soil tests and petiole
analyses, respectively, according to commercial recommendations for long-season russet
potatoes in the Columbia Basin. Applications of herbicides, insecticides, and fungicides
followed standard practices. Detailed meteorological data for the 2009 and 2010 growing
seasons at the WSU Othello, WA research site are available from the Washington Agricultural
Weather Network, AgWeatherNet (weather.wsu.edu/awn.php).
12
2.1.2. Tuber developmental stages
Eighteen stages of tuber development were sampled from field plots of cv. Ranger Russet
in 2009 and 2010 to characterize ascorbate accumulation in relation to expression of genes in the
Smirnoff-Wheeler pathway and the ascorbate-glutathione (AsA-GSH) cycle (Halliwell-Asada
pathway). The earliest stages of tuber development (stages I-VIII) ranged from non-tuberized
stolons (stage I) to 5-10-g tubers (stage VIII) and were collected from whole plants harvested
with root systems intact during tuberization (ca. 50 days after planting) as described by Weeda et
al. (2009) (Fig. 2). Multiple samples of each of the eight stages were pooled from different
plants to give three replicates of each stage (at least five tubers per replicate for stages V-VIII
and 20-100 stolons/tubers per replicate for stages I-IV). The replicate samples of stages I to VIII
were frozen intact in liquid N2 and stored at -80°C until further analysis.
Ranger Russet plants and tubers were also hand harvested from two center rows (flanked
by outside guard rows) at approximately 13-day intervals from 63 to 168 days after planting
(DAP) to further profile AsA accumulation and gene expression (Smirnoff-Wheeler pathway and
AsA-GSH cycle) throughout tuber bulking (ca. 60-145 DAP) and maturation (ca. 145-168 DAP).
Four replicates, each consisting of the foliage and tubers of four consecutive plants, were
selected at random from within the two 90-m center rows for each harvest. Foliar (above
ground) fresh weight (FW), tuber number and tuber fresh weight were recorded. Foliar and tuber
fresh weights, specific gravity, sucrose and reducing sugar (glc + fru) levels were plotted versus
DAP to fully define the developmental stages and physiological maturity of tubers used for
subsequent AsA and gene expression analyses.
13
2.1.3. Preparation of tuber samples
Twenty tubers were sampled at each harvest in four replicates of five tubers each for
analysis of sucrose and reducing sugar concentrations. The tubers at each harvest were chosen to
represent the average tuber fresh weight (g/tuber) at that point in the growing season. Tubers
were cut in half longitudinally along the apical to basal axis. A thin slice (ca. 1.5 mm thick,
periderm attached) was taken from the cut surface of one of the tuber halves with an electric
slicer (Sunbeam Products Inc., Boca Raton, FL). The longitudinal slice was then halved along
the apical to basal axis and one half retained to represent an individual tuber. Collectively, the
longitudinal tissue slices from the five tubers making up each replicate were cut into apical and
basal halves, which were immediately frozen at -80oC. The tissue samples were lyophilized,
ground with mortar and pestle, sieved through a 60-mesh (0.246 mm) screen, and stored until the
end of the growing season for analysis of soluble carbohydrates.
Tubers for analysis of AsA and transcript levels were washed with deionized H2O
containing 0.1% SDS (3 tubers per sample, 4 replicates). All utensils for tissue sampling were
rinsed with 70% EtOH and RNaseZAP (Ambion®). Tissue samples were prepared as described
above with minor modifications. A longitudinal center slice (3-5 mm thick, periderm intact) was
hand cut from each tuber and divided into two equal longitudinal halves, one of which was
discarded. The halves from three tubers were combined, diced, flash frozen under liquid N2, and
held at -80°C until further processing. Once all the tissue samples had been collected, half of
each frozen sample was weighed and lyophilized to determine the dry weight percentage. The
samples were analyzed within one week of lyophilization. Preliminary work showed no loss of
AsA from lyophilized tissue during this time period. The remaining frozen tissue was held at 80°C for extraction of RNA and semi-quantitative analysis of gene expression.
14
2.1.4. Carbohydrate analyses
Sucrose, glucose and fructose were extracted from 500 mg of lyophilized tissue with 6
mL of triethanolamine HCl (TEA) buffer (30 mM, pH 7.0) followed by successive additions of
300 µL of 85 mM K4[Fe(CN)6]·3·H2O (Carrez I), 300 µL of 250 mM ZnSO4·7 H2O (Carrez II),
and 500 µL of 0.1 mM NaOH with vortexing after each addition as described in Knowles et al,
(2009a). Following centrifugation (10,000 x g, 15 min), the supernatant was stored at -20oC
until analysis. All reagents were from Sigma-Aldrich (St. Louis, MO, USA).
Glucose (Glc) and fructose (Fru) were estimated by modifying the methods of Bergmeyer
et al. (1974) and Bernt and Bergmeyer (1974) as detailed in Knowles et al, (2009a). The
stoichiometric reduction of NADP as each hexose is enzymatically converted to 6phosphogluconate (using glucose-6-phosphate dehydrogenase, hexokinase and phosphoglucose
isomerase) was monitored at A340. A separate incubation of the extract with invertase facilitated
total glucose (free glucose plus that hydrolyzed from sucrose via invertase) determination. The
difference between moles total glucose and moles free glucose was used as a measure of sucrose
(Bergmeyer and Bernt 1974). Quantification was based on standard curves of glucose, fructose
and sucrose.
2.1.5. Ascorbate analysis
One hundred milligrams of lyophilized tuber tissue was extracted with 1.0 mL 6% (w/v)
trichloroacetic acid and centrifuged at 11,000 x g for 6 min (4ºC). Reduced, oxidized and total
AsA were analyzed as described by Gillespie and Ainsworth (2007) using a microplate reader
(PowerWavex, Bio-Tek Instruments, Inc., Winooski VT, USA). The referenced protocol exploits
the reduction of iron(III) to iron(II) by ascorbate in solution. The Fe+2 generated forms a colored
complex (A525) with bipyridine. The total AsA (reduced + oxidized) was obtained by reduction
15
of dehydroascorbate in one aliquot of extract with dithiothreitol prior to the assay. A second
aliquot was assayed directly. Oxidized ascorbate was calculated by subtraction of reduced AsA
from total AsA. Quantitation of AsA was achieved by linear regression from a standard curve of
0.05-1.0 mM authentic ascorbic acid.
2.1.6. RNA extraction and semi-quantitative RT-PCR
RNA extraction followed the methods of Kumar et al. (2007) with minor modifications.
Frozen tuber tissue (200 mg fresh weight amalgamated from four replicates of three tubers per
replicate) was ground to a fine powder in liquid nitrogen (mortar and pestle). RNA was
extracted with 1.0 mL Tris Buffer (0.1 M, pH 9.6) containing 0.2 M NaCl, 0.65% (w/v) Na2SO3,
1% (w/v) SDS and 0.1% (v/v) β-mercaptoethanol. The extract was centrifuged twice (14,000 x
g, 5 min, 23oC) to remove debris and interfering starch. The supernatant was de-proteinized with
an equal volume of acidic phenol (pH 4.3) and centrifuged as above. This procedure was
repeated and the resultant upper phase was extracted twice with equal volumes chloroform:isoamyl alcohol (24:1, v/v) and centrifuged as above. RNA in the upper phase was precipitated
with 0.1 vol of 3 M NaOAc (pH 5.2) and 1 mL absolute EtOH at -80°C. RNA was pelleted at
14,000 x g for 5 min and washed with 70% (v/v) EtOH four times. The EtOH was evaporated
(65°C, 2 min) and RNA was dissolved in 50 µL nuclease-free water by warming at 65°C for 2
min. The RNA was quantified at A260 and its integrity ascertained on a 1.0% (w/v) agarose gel.
Genes encoding enzymes in the Smirnoff-Wheeler pathway (AsA synthesis) and
Halliwell-Asada cycle (AsA oxidation and recycling) from tomato (Ioannidi et al., 2009) were
blasted against genes for potato on the Sol Genomics Network (www.solgenomics.net; Boyce
Thompson Institute for Plant Research, Ithaca, NY). Cytoplasmic ribosomal protein L2 (woundhealing study) and 18S rRNA (all other studies) served as internal reference genes (Nicot et al.,
16
2005), as their expression was relatively constant throughout tuber development and storage.
Transcript levels of the internal reference genes were plotted over time for direct comparison
with transcript levels of genes in the Smirnoff-Wheeler and Halliwell-Asada pathways. Primers
were designed using Primer3 software (http://frodo.wi.mit.edu/) and were synthesized either by
Invitrogen (Carlsbad, CA) or Sigma-Aldrich (St. Louis, MO). Following DNase treatment
(TURBO DNA-freeTM Kit, Ambion, Inc., Foster City, CA, USA), cDNA was synthesized using
the RevertAidTM First Strand cDNA Synthesis Kit with oligo(dT)18 primer (Fermentas Inc., Glen
Burnie, MD, USA). PCR was accomplished using the Promega GoTaq® Green Master Mix
(Promega Corp., Madison, WI, USA) following the manufacturer’s protocol. Samples were
initially denaturated at 95°C for 2 min, followed by 30-40 cycles of 45 s at 95°C, 45 s at primer
specific annealing temperature (see Table 1) and 1 min at 72°C. Final extension was
accomplished at 72°C for 5 min. The forward and reverse primer sequences, gene accession
numbers and amplified PCR product lengths are provided in Table 1. PCR products were
visualized on a 1.0% agarose gel and normalized band intensities (against image background)
were determined using Kodak Molecular Imaging Software (Version 4.0) for semi-quantitative
comparison of transcript levels.
2.2 Postharvest studies
2.2.1 Loss of ascorbate as affected by genotype
Tubers for postharvest AsA retention studies were produced at the WSU Othello
Research and Extension Unit as described previously. Cultivars Premier Russet, Russet
Burbank, Summit Russet, GemStar Russet, Ranger Russet and Defender were selected to
represent a broad range in genotype-dependent ascorbate content (ca. 17-35 mg AsA 100 g-1 FW;
Love et al., 2005; 2006; Novy et al., 2006; 2008) at maturity (harvest) and to subsequently
17
identify high and low AsA-retaining phenotypes during storage. Tubers were harvested at full
maturity (150-180 DAP) and wound-healed at 12oC (98% RH) for 14 d following harvest.
Tubers were sampled at ca. 30-d intervals over 258 days of storage at 9oC (95% RH) for analysis
of ascorbate. The tubers were treated with 0.75 mmol kg-1 3-nonen-2-one (Bedoukian Research,
CT) to inhibit sprouting as needed (2-3 times) over the 8.5-month storage interval (Knowles and
Knowles, 2012).
2.2.2. Storage temperature and controlled atmosphere studies
Ranger Russet certified seed-tubers were obtained from a commercial grower at harvest
to investigate the effects of storage temperature and oxygen concentration on changes in AsA
content over a 163-d storage period. The tubers were initially stored at 4 and 32oC (95% RH) for
21 days (Oct. 28 - Nov. 18) with samples (4 replicates, 3 tubers/replicate) taken at 0, 1, 3, 5, 8,
11, 14, 17, and 21 days for determination of AsA. At day 21 (Nov. 18), all tubers were
transferred to 19-L sealed plastic chambers at 4oC (95% RH). The chambers were equipped with
inlet and outlet ports through which an atmosphere of either 3.5% or 21% O2 (CO2-free air,
balance N2) was provided continuously at ca. 80-100 mL min-1 for the remainder of the 163-d
storage interval. The outlet air was analyzed for respiratory CO2 with an infra-red gas CO2/H2O
analyzer (LI-COR, model LI-6262, LI-COR, Inc. Lincoln NB, USA) as described in Knowles et
al. (2009a) The 3.5% O2 atmosphere was generated using a custom built, Permea nitrogen
generator (Permea Inc., St. Louis, MO, USA). Tubers were sampled (4 replicates, 3
tubers/replicate) at 22, 23, 24, 28, 35, 67, 94, 129, 158, and 163 days of storage for AsA
determination. An additional study was performed to evaluate the effects of 3.5% and 21% O2
atmospheres on AsA loss from cvs. Ranger Russet and Premier Russet during the initial 30 days
of storage at constant temperature (9oC, 95% RH) directly following harvest.
18
2.2.3. Glutathione, GR, DHAR, MDHAR, and APX determinations
Total, reduced and oxidized glutathione, glutathione reductase (GR), dehydroascorbate
reductase (DHAR), mono-dehydroascorbate reductase (MDHAR), and ascorbate peroxidase
(APX) activities were compared in tubers stored at 3.5 and 21% O2 as an indicator of HalliwellAsada pathway activity. Glutathione was determined via the methods of Akerboom and Sies
(1981) and Nair et al. (1991). Enzyme activities were evaluated as described in Zabrouskov et
al. (2002) and Murshed et al. (2008).
2.2.4. Wound-induced ascorbate production and associated gene expression
Studies were conducted to evaluate changes in the competence of tubers for woundinduced AsA biosynthesis as affected by storage time (tuber age). A short term study compared
wound-induced AsA synthesis of Ranger Russet tubers stored for 0 and 7 months (4oC, 95%
RH). Russet Burbank tubers were used for a longer term study, involving 0-, 12- and 24-monthold tubers (4oC, 95% RH). For both studies, tubers (~150-200g) were blocked for size into three
replicates (4 tubers per replicate). Three longitudinal center slices were cut (3-5 mm thick) from
each tuber and randomly assigned to a wound healing treatment (0, 1, or 2 days). The slices
were rinsed with distilled deionized water and placed on a foam mat (Grip-It Shelf and Drawer
Liner, MSM Industries, Smyrna, TN, USA) on moist filter paper in Petri dishes (15-cmdiameter) to wound heal (Kumar et al., 2010). The dishes were covered with lids containing two,
1-cm-diameter holes for air circulation and placed in the dark at 21°C for 0, 1 or 2 days.
Treatments (tuber age x three periods of wound-healing) were arranged factorially in randomized
complete block designs. Following incubation, tissue samples were diced into small pieces, flash
frozen (liquid N2) and stored at -80°C for analysis of AsA and transcript levels (SmirnoffWheeler pathway) via semi-quantitative PCR as described previously.
19
2.2.5. AsA production during sprouting and daughter tuber formation
Ranger Russet certified seed-tubers were obtained from a commercial grower at harvest
(early October) to investigate whether AsA and gene transcript levels (Smirnoff-Wheeler
pathway) change during sprouting and daughter tuber formation. The tubers were subjected to
various temperature priming treatments over a 176-day storage period (95% RH) to stimulate
production of etiolated sprouts and daughter tubers at the end of storage. Sprouting was induced
by incubating non-dormant tubers at 16oC in the dark for 8 days following 168 days of storage at
4oC (95% RH). Daughter tubers were induced to develop in response to two, non-consecutive
high temperature priming treatments at 32oC (95% RH) imposed from 120-142 days (return to
4oC) and 168-176 days of storage. Non-sprouted control tubers were stored at 4oC for 176 days.
Sprouts and daughter tubers were excised, weighed and frozen in liquid N2. Longitudinal
slices of tissue from the corresponding mother tubers were sampled as previously described.
Levels of gene expression (Smirnoff-Wheeler pathway) and AsA were determined using frozen
and lyophilized tissues, respectively. There were four replicates (one tuber per replicate) of five
tissue types (non-sprouted control tubers; sprouts and associated mother tubers; daughter tubers
and associated mother tubers). AsA data were subjected to analysis of variance (ANOVA) with
means separated by LSD (P<0.05). Complete longitudinal sections (3-5 mm thick) of mother
tubers with sprouts or daughter tubers still attached were prepared for in situ histochemical
staining of ascorbate following the method of Tedone et al. (2004). Images of the stained
sections were recorded on a CanoScan 4200F high resolution flatbed color image scanner
(Canon USA, Inc., Lake Success NY).
20
2.3. Data analysis and presentation
Foliar and tuber growth, tuber carbohydrate, specific gravity, AsA and selected transcript
level data were subjected to ANOVA with tuberization stage and DAP or days after harvest as
independent variables. Sums of squares were partitioned into polynomial (linear, quadratic, etc.)
trends and the data plotted accordingly. Coefficients of determination are reported along with
significance levels (P-values) for the correlation coefficients where appropriate. Postharvest
studies of the effects of temperature, O2 concentration, tuber age and wounding on changes in
tuber AsA levels over time entailed randomized complete block designs with treatments arranged
factorially with time. Main effects and interactions were partitioned in ANOVA and means were
separated by LSD (P<0.05) where appropriate. The statistical programs for data analysis
included SAS (Version 9.2; SAS Institute, Cary, NC) and SigmaPlot (Version 11.0; Systat
Software Inc., San Jose, CA).
3. Results
3.1. Tuber developmental profile
Field plots of cv. Ranger Russet potatoes were established at the Washington State
University Irrigated Agriculture Research and Extension Center (Othello, WA) to profile
changes in ascorbate accumulation in relation to expression of genes in the Smirnoff-Wheeler
and Halliwell-Asada pathways during tuber development from pre-tuberization, through
tuberization (ca. 50 DAP) and bulking (ca. 63-145 DAP), to maturation (ca. 145-168 DAP).
Consistent with previous results for cv. Ranger Russet in the Columbia Basin (Knowles et al.
2008; Weeda et al. 2009), the trend in foliar fresh weight was cubic (Y= -87.5 + 2.65X – 2.02e2
X2 + 4.62e-5X3, R2= 0.97, P<0.001) with a maximum at 100 DAP (Fig. 3A). The harvest index
21
(tuber fresh weight divided by foliar plus tuber fresh weight) was 45% at 100 DAP, favoring
foliar (source) growth over tuber (sink) growth, which is an ideal source/sink relationship at this
stage of crop development for achieving maximum yield potential of cv. Ranger Russet in the
Columbia Basin (Knowles et al., 2008). Foliar biomass declined linearly from 116 DAP to
season end, while tuber yield continued to increase through 168 DAP (Fig. 3A). Average tuber
fresh weight increased from 12 to 240 g tuber-1 from 63 to 158 DAP (Fig. 3B). Tuber growth
during this period was sigmoidal and best described by a cubic polynomial (Y = 117.2 – 6.18X +
0.090X2 – 2.89e-4X3, R2= 0.98, P<0.001).
Changes in sucrose, reducing sugars (glc + fru) and specific gravity (dry matter) were
measured in tubers as components of physiological maturity (Knowles, et al., 2009a,b). Sucrose
concentration fell precipitously during bulking from an average of 61 mg g-1 dry wt at 63 DAP to
7.2 mg g-1 dry wt at 131 DAP (Fig. 3B). Reducing sugars showed similar trends, reaching a low
of 0.26 mg g-1 dry wt by 131 DAP (Fig. 3C). Specific gravity increased to a maximum of 1.093
at 162 DAP, which equates to tuber dry matter and starch content of approximately 23% and
16.4%, respectively (Hassel et al., 1997; Kleinkopf et al., 1987). Tuber physiological maturity
(PM) was calculated as the average DAP to reach maximum yield, maximum specific gravity,
minimum sucrose, and minimum reducing sugars in the basal ends of tubers (Knowles et al.,
2008; 2009b). Tubers harvested at PM retain postharvest quality the longest in storage. PM was
achieved 148 DAP, which is consistent for Ranger Russet tubers grown commercially in the
Columbia Basin. Final yield (83 tonne ha-1), trends in foliar and tuber development, tuber
carbohydrate content, and attainment of PM were characteristic of a well-managed crop in the
Columbia Basin (Knowles et al., 2008).
22
3.2. Changes in ascorbate during tuber development and storage
Non-tuberized stolons (Stages I and II) contained approximately 11.8 mg 100 g-1 FW
total ascorbate (Fig. 4). Total ascorbate concentration increased 60% (to 18.9 mg 100 g-1 FW) as
tubers developed from stage II to VI (1.5-2.5-g tubers) in parallel with an increase in reduced
ascorbate. Ascorbate accumulation rate then diminished as tubers developed to stage VIII (5-10
g), reaching 19.9 mg 100 g-1 FW. As a percentage of total AsA, reduced AsA remained constant
throughout the tuberization phase of development at ca. 54%.
While the increase in total AsA concentration during tuberization was substantial, stage
VIII tubers contained only 53% of the maximum ascorbate concentration of fully developed
tubers (37.7 mg 100 g-1 FW) (Fig. 4A), which was approximately 43-fold less ascorbate than
fully developed tubers on an absolute (mg tuber-1) basis. From 63 to 148 DAP (PM), total AsA
increased at an average rate of ca. 1 mg tuber-1 d-1 (from 2.4 to 86 mg tuber-1) (Fig. 4B). Total
AsA concentration increased 85% during bulking from 63 to approximately 136 DAP (Fig. 4A),
then decreased through PM (148 DAP, see Fig. 3C) to harvest at 163 DAP (Fig. 4A). Thus, as a
function of tuber fresh weight (Fig. 3B), AsA concentration (Fig. 4A) increased to a maximum
(37.7 mg 100 g-1 FW) as tubers developed to 209 g tuber-1 at 136 DAP, then decreased to 34.8
mg 100 g-1 FW with further development to 241 g tuber-1 (AsA = 16.3 + 0.409 (FW) – 7.202e3
(FW)2 + 9.396e-5(FW)3 – 6.773e-7(FW)4 + 2.432e-9(FW)5 – 3.41e-12(FW)6; R2= 0.99, P<0.001).
This decrease in AsA coincided with a 15.8 tonne ha-1 loss in foliar growth as vines senesced
during the maturation period (Fig. 3A). Reduced AsA followed the same trend as total AsA,
accounting for ca. 80-85% of total AsA during bulking and maturation (Fig. 4A).
Tuber AsA concentration continued to decline in storage at 9oC (Fig. 4A) and the trend
was best described by a second degree polynomial (AsA = 33.4 – 0.144(DAH) + 2.225e-
23
4
(DAH)2, R2= 0.94, P<0.001). From 13 to 259 days of storage, total ascorbate concentration fell
65% (from 31.6 to 11.1 mg 100 g-1 FW) with half this decrease occurring over the initial 78 days
of harvest. The postharvest changes in reduced AsA concentration mirrored total AsA. Reduced
AsA accounted for 80% of total AsA 13 days after harvest and decreased to 71% by 259 days
after harvest. Dehydro (oxidized) ascorbate decreased from 6.4 to 3.0 mg 100 g-1 FW over the
8.5-month storage period.
3.3. Gene expression during tuber development
In contrast to the constant transcript levels of the reporter gene (18S rRNA), expression of
genes in the Smirnoff-Wheeler pathway of AsA biosynthesis changed significantly with tuber
development (Figs. 5 and 6). The first five steps of this pathway (glc-6-P to GDP-L-galactose)
are non-specific to AsA, producing precursors essential to a number of pathways including AsA
(Loewus, 1999), synthesis of cell wall polysaccharides (Smirnoff, 1996), and protein
glycosylation (Hoeberichts et al., 2008). With the possible exception of the gene encoding PMI,
genes modulating these initial steps were expressed throughout tuberization and transcript levels
were significantly correlated with developmental stage (I-VIII) (Fig. 6, R2= 0.68-0.94, P<0.050.01). Transcript levels of G6PI, PMI, PMM, GMP1, GMP2 and GME1-3 increased as tubers
developed from stage I (non-tuberized stolons) to stages IV-V (1.5-g tubers), then decreased
through stage VIII (Figs. 5 and 6). Transcript levels of PMI, PMM, and GMP2 changed the
most, increasing 6.1-, 2.7- and 10.1-fold, respectively, through stage V. The subsequent
downward trends in expression of G6PI, PMM, GMP1, GMP2, and GME1-3 during the latter
stages of tuberization continued during tuber bulking; with transcript levels reaching a low from
116 to 131 DAP. G6PI, GMP2, GME2 and GME3 transcript levels then increased during the
maturation phase of tuber development from ca. 131 to 168 DAP.
24
The last four steps of the Smirnoff-Wheeler pathway (GDP-L-galactose to AsA) are
believed to be specific to AsA biosynthesis (Bulley et al., 2009; Ioannidi et al., 2009) (Fig. 5).
GGP1, GGP2, GPP, L-GalDH, and L-GalLDH were facultatively expressed during tuberization
and, similar to the initial non-specific steps of this pathway, their transcript levels were highly
correlated (R2= 0.86-0.97, P<0.05-0.001) with developmental stage and AsA content (Figs. 5
and 6). Relative transcript levels of these genes increased 2.3-6.5-fold during development from
non-tuberized stolons to stage V tubers, then decreased 40 to 73% through stage VIII. The
decrease in expression continued during the early stages of bulking with relatively little
transcript detected beyond 91 to 102 DAP.
Developmental changes in the expression of genes for AsA recycling (Halliwell-Asada
cycle) are presented in Fig. 7. Expression of GRcyt was minimal and MDHAR2 was nondetectable throughout tuber development. In contrast, transcript levels of the other AsA
recycling genes [DHAR, MDHAR1, APX, superoxide dismutase (cytoplasmic, SODcyt),
ascorbate oxidase (AsAox)] increased substantially as tubers developed to stage V and then
decreased through stage VIII (R2= 0.81-98, P<0.05) (Fig. 7). Expression of these genes
continued to decline during bulking and maturation, reaching a low as early as 91 DAP.
Transcript levels of DHAR and MDHAR1 then remained relatively constant as tubers matured
from 131 to 168 DAP, while the increase in APX transcript was more substantial during this
period.
3.4. Postharvest loss of AsA – genotype, temperature, oxygen, tuber age, and wounding
Total AsA concentrations in tubers at harvest (ca. 160 DAP) varied by genotype (Fig. 8).
Ranger Russet tubers had the highest concentration (31.7 mg 100 g-1 FW), followed by Defender
(30.1 mg 100 g-1 FW), GemStar (23.8 mg 100 g-1 FW), Premier (23.5 mg 100 g-1 FW), Summit
25
(19.4 mg 100 g-1 FW), and Russet Burbank (17.3 mg 100 g-1 FW) (LSD0.05 = 2.5). Total AsA
concentrations fell most rapidly in all cultivars over the first ca. 75 days of storage at 9oC (95%
RH), followed by attenuation in the rate of loss through 240-250 days. Hence, the declines were
best described by second or third degree polynomials (R2 = 0.94-0.99, P<0.001). Rates of loss
over the initial 75 days of storage averaged 136 (Summit), 121 (Ranger), 117 (Defender), 99
(GemStar), 91 (Premier) and 90 (Burbank) micrograms total AsA 100 g-1 FW per day. Declines
ranged from 59% (Russet Burbank) to 65% (Ranger Russet) over the entire 8-month interval.
Premier Russet, Defender, and Ranger Russet had the highest AsA concentrations (11.5, 11.3,
11.1 mg 100 g-1 FW, respectively) at the end of storage, while GemStar, Summit and Russet
Burbank had the lowest (9.7, 7.9, and 7.1 mg 100 g-1 FW, respectively) (LSD0.05 = 1.2).
The postharvest declines in reduced AsA paralleled total AsA (Fig. 8) in all cultivars.
Reduced AsA averaged 86-89% of total AsA for all cultivars except Ranger Russet (avg = 79%)
throughout the storage period. Dehydroascorbate (oxidized) accounted for 14.2% of total AsA
and decreased (46% on average) in all cultivars except Premier Russet over the 8-month period.
The effects of storage temperature and oxygen concentration on AsA loss from tubers over
a 162-day storage interval were evaluated in Ranger Russet. Tubers were held at 4oC (Fig. 9A)
or 32oC (Fig. 9B) under ambient O2 (21%) for the initial 21 days of storage. Samples were then
stored at 4oC under 3.5% or 21% O2 for the remainder of the storage period. The most rapid loss
in AsA occurred during the initial 21 days of storage (21% O2); tuber AsA concentration fell 360
µg 100 g-1 FW per day on average (P<0.01) over this initial period regardless of storage
temperature. Low oxygen significantly (P<0.01) attenuated the loss in AsA from 21 to 162 days.
Reduced AsA decreased in parallel with total AsA at each temperature and O2 level, and
accounted for approximately 89% of total AsA on average over the 162-day period (data not
26
shown). Similar to total and reduced AsA, dehydroascorbate decreased (ca. 50%) during the
initial 21 days of storage at each temperature, but only averaged ca. 7.8% of total AsA over this
period (data not shown). Dehydroascorbate was maintained at very low levels from 21 to 162
days at 4oC and no effects of O2 were apparent.
AsA-GSH recycling enzyme activities (MDHAR, DHAR, APX and GR) were compared
at 21 and 129 days of storage at 21 and 3.5% O2 when the effect of low oxygen on preserving
AsA levels was maximum (see Fig. 9). Enzyme activities were not affected by time or O2
concentration despite a 4-fold increase in total glutathione (from 101 ±7.4 to 431 ±21.8 nmoles
g-1 FW, P<0.05) from 21 to 129 days at 21% O2. Total glutathione was ca. 25% lower (329
±17.0 nmoles g-1 FW) in tubers stored for 129 days at 3.5% O2 versus 21% O2. GR, DHAR,
MDHAR, and APX activities averaged 31.8 ±1.4, 671 ±4, 164 ±4.7, and 1534 ±75 nmoles min-1
mg-1 protein, respectively.
An additional study was conducted to assess whether low oxygen could slow the rapid
decline in AsA from harvest through the initial 30 days of storage using Ranger Russet and
Premier Russet tubers. When Ranger Russet tubers were stored at 21% O2 (9oC), AsA declined
25% from 27.3 mg 100 g-1 FW to a low of 20.5 mg 100 g-1 FW within the first 20 days (R2=
0.71, P<0.05). In contrast, AsA concentration remained constant (25 mg 100 g-1 FW) in tubers
stored at 3.5% O2. Similarly, the total AsA concentration in Premier Russet tubers fell 27%
(from 16.4 to 11.9 mg 100 g-1 FW; R2=0.97, P<0.01) when stored at 21% O2 but remained
constant at 16.0 mg 100 g-1 FW at 3.5% O2. These results extend those presented in Fig. 9 to
include another cultivar and the effects of low oxygen on the initial rapid loss of AsA from
freshly harvested tubers and indicate that AsA loss during storage is tied to oxidative
metabolism.
27
Wounding of 1-month-old tubers stimulated substantial AsA biosynthesis (Table 2) in cv.
Ranger Russet tubers. Ascorbate concentration increased 37% within 48 h of wounding,
correlating with increased expression of genes in the Smirnoff-Wheeler pathway (Fig. 10).
G6PI, GMP1, GMP2, GME2, GME3, GGP1, GPP, L-GalDH, and L-GalLDH transcript levels
increased within 24 h in response to wounding. The wound-induced increases in GGP1 and GPP
transcripts are particularly relevant as potential rate limiting steps in AsA biosynthesis (Bulley et
al., 2009; Ioannidi et al., 2009). Reduced AsA also increased in response to wounding and
averaged 90% of total AsA (data not shown).
Consistent with the results of Fig. 8, 7-month-old tubers had a substantially lower (58%)
concentration of total AsA (10.9 mg 100 g-1 FW) than freshly harvested tubers (26.0 mg 100 g-1
FW); however, AsA more than doubled within 48 h of wounding (Table 2). The wound-induced
increase in AsA was transitory as evident by the sigmoidal (cubic) trend over the 6-day wound
healing period (AsA = 10.7 + 15.2(days) – 5.71(days)2 + 0.556(days)3, R2= 0.99, P<0.01).
Maximum AsA concentration (22.9 mg 100 g-1 FW) was estimated at 43 h after wounding. AsA
concentration then declined 29% to reach a relatively constant level from 4 to 6 days after
wounding. Despite the significant decline, AsA concentration remained ca. 51% higher 6 days
after wounding compared with the non-wounded 7-month-old tubers.
Wound-induced AsA synthesis was also affected by tuber age (storage time). Tubers
stored for 12 and 24 months at 4oC had 39% less AsA than freshly harvested tubers (Fig. 11).
The rate of AsA synthesis in response to wounding decreased from an average of 8.2 mg 100 g-1
FW per day in freshly harvested and 12-month-old tubers to 5.4 mg 100 g-1 FW per day in 24month-old tubers (age x time, P<0.05).
3.5. Sprout and daughter tuber development
28
Changes in AsA concentration in relation to gene expression (Smirnoff-Wheeler pathway)
were further assessed during sprouting and daughter tuber formation following 176 days of
storage. Ranger Russet tubers were subjected to age priming temperatures of 16 and 32oC for
various intervals over the storage period to induce sprouting and formation of daughter tubers,
respectively (see Section 2.2.5). Control tubers were held at 4oC for the entire 176-day storage
period. The age priming treatments were effective in hastening sprouting and inducing daughter
tuber formation (Fig. 12A). Tubers were clearly non-dormant after 176 days at 4oC as indicated
by peeping (1-2-mm-long) sprouts; however, the low temperature greatly inhibited sprout
growth. In contrast, a brief period of storage at 16oC (from 168-176 days) stimulated sprouting,
resulting in 1.5 ±0.31 g sprout FW per tuber on average. Priming at 32oC stimulated formation
of daughter tubers (1.48 ±0.10 g FW per tuber) complete with a well-developed native periderm.
Histochemical staining with AgNO3 revealed AsA within the vasculature (phloem) of
tubers, associated sprouts and daughter tubers (Fig. 12B), as originally demonstrated by Tedone
et al. (2004). Consistent with previous results (Fig. 9), temperature (i.e. age priming treatments)
had no effect on the AsA concentration of mother tubers, which averaged 13 mg 100 g-1 FW
(Fig. 12C) over all three treatments. The 6-month-old tubers stored at 4oC expressed GGP1,
GPP, L-GalDH, and L-GalLDH at relatively low levels, which is consistent with that observed
for 7-month-old tubers (data not shown) in the wounding study (see Table 2). In contrast,
transcript levels were non-detectable in sprouted tubers. Low levels of gene expression were,
however, detected in mother tubers that produced daughter tubers (Fig. 12C). Sprouts and
daughter tubers clearly showed the highest levels of expression of GGP1, GPP, L-GalDH, and LGalLDH, consistent with their higher concentrations of AsA.
29
4. Discussion
The high per capita consumption of potatoes makes them a significant source of dietary
vitamin C (McCay et al., 1975; FAO, 2008). Chu, et al. (2002) estimated that AsA from
potatoes accounts for about 13.3% of their total anti-oxidant activity. However, as demonstrated
herein, the AsA content of tubers varies substantially with developmental stage (Fig. 4),
genotype (Fig. 8), storage duration (Figs. 4, 9 and 11; Table 2), and stress (Table 2, Fig. 11).
Since information on these variables is often lacking, it is difficult to accurately establish the
contribution of potato to the recommended daily allowance (RDA) of vitamin C. For example,
AsA content of cv. Ranger Russet tubers reached maximum concentration (37.7 mg 100 g-1 FW)
at 136 DAP when tubers had developed to 209 g FW, 12 days prior to achieving physiological
maturity (PM) and a final FW of 240 g tuber-1 (Figs. 3 and 4A). On an absolute basis, a 209-g
tuber at this stage of development provides about 88% (78.8 mg AsA; Fig. 4B) of the U.S. daily
requirement of vitamin C for an adult male (90 mg AsA) (Anon., 2010) and this decreased to
51% (45.9 mg AsA) and 29% (26.1 mg AsA) by approximately 3.5 and 8.5 months of storage,
respectively. In contrast to fully grown and physiologically mature tubers, the same portion
(209-g) of immature baby potatoes (ca. 10-66-g FW stage), also known as salad potatoes or
creamers, provides only 46-67% of the recommended daily requirement, depending on tuber
mass. The broad range of AsA content during tuber ontogeny and storage thus indicates
extensive scope for improving the contribution of potatoes to vitamin C nutrition.
AsA is synthesized via the L-Galactose Smirnoff-Wheeler pathway in tomato (Ioannidi et
al., 2009) and potato (Bulley et al., 2012). Recycling of AsA through the Halliwell-Asada
pathway to mitigate oxidative stress also affects AsA levels (Chen et al., 2003; Goo et al., 2008;
Qin et al., 2011). The work presented herein defines the dynamics of AsA content in relation to
30
the expression of genes in these biosynthetic and recycling pathways during tuber ontogeny and
identifies factors (genotype, tuber age, stress) and conditions (storage temperature, O2
concentration) that affect decline in AsA content following harvest.
Tubers are a sink for AsA transported from foliage during development (Tedone et al.,
2004). However, the extent to which AsA synthesis occurs in situ during tuberization, bulking
and maturation remains unresolved. Transcript levels of key genes in the Smirnoff-Wheeler and
Halliwell-Asada pathways increased during tuberization (through stage V) and remained
relatively high through early tuber development, then decreased through bulking and maturation
(Figs. 5-7). Additionally, total AsA and the ratio of reduced to oxidized AsA began to increase
at tuberization stage V (Fig. 4), which correlated with increasing transcript levels of GRcyt,
DHAR, MDHAR1, APX, SOD and AsAox (Fig. 7). This upregulation of the Halliwell-Asada
pathway is likely a response to the relatively high metabolic activity (Viola et al., 2001 and
references therein) associated with cell division and expansion (Xu et al., 1998) during the
tuberization phase of development. AsA pool size has been shown to correlate directly with
DHAR expression in leaf tissue (Chen and Gallie, 2006; 2005).
Collectively, our data suggest that synthesis of AsA in situ likely contributes significantly
to initial tuber AsA levels during tuberization. Substantially reduced expression of GGP, GPP,
L-GalDH and L-GalLDH during bulking and maturation (Figs. 5 and 6), coupled with the
decline in tuber AsA during the onset and progression of vine senescence (Figs. 3 and 4),
suggests that translocation from foliage also contributes significantly to AsA accumulation in
tubers during bulking until vine senescence. While it is not possible to estimate the proportion of
AsA contributed by tubers versus foliage from our studies, Viola et al. (1998) showed that tubers
developing from single-stem cuttings synthesize AsA during early development in culture, which
31
is consistent with the enhanced gene expression indicated in Figs. 5-7. It is also relevant that
sucrose stimulates AsA synthesis (Viola et al., 1998) and the highest sucrose concentrations in
tubers occurred during the earliest stages of tuber development (Fig. 3B). Studies designed to
quantify the translocation of labeled AsA and its precursors from source leaves to tubers during
development, similar to those presented by Badejo et al. (2012) for tomato, will provide
unambiguous evidence for the relative contributions of foliar- versus tuber-derived AsA.
The rapid loss of AsA in tubers, which began during maturation under senescing vines
and continued through storage (Figs. 3A and 4), was consistent with non-detectable or greatly
diminished transcript levels of key genes in the Smirnoff-Wheeler pathway (Figs. 5 and 6).
Reduced or lack of ability to synthesize AsA in situ, coupled with loss of foliar-derived AsA
during vine senescence and AsA catabolism by tubers in maintaining cellular homeostasis, likely
account for the progressive loss of AsA with time following the attainment of physiological
maturity and throughout storage. The decline in AsA concentration began ca. 136 DAP when
vine fresh weight had decreased to about 78% of maximum (22% senesced) and continued
through the tuber maturation phase as foliar growth further declined to 28% of maximum (i.e.
72% senesced) at 168 DAP (Figs. 3 and 4A). Vines thus appeared to cease being a source of
AsA for translocation to tubers (sinks) during the latter stages of bulking and early maturation
but prior to the cessation of tuber growth. These results suggest that tuber AsA is primarily
foliar-derived during bulking and maturation; however, unequivocal evidence for this awaits
further work with radiotracers to quantify translocation.
Tuber AsA concentration declined most rapidly during the initial 25-50 days of storage at
9oC and the rate of decline attenuated as the AsA concentration approached a maintenance level
that appeared to be genotype-dependent (Fig. 8). We demonstrate that (1) the rate of AsA loss is
32
cultivar dependent, (2) tubers appear to maintain a relatively low but steady-state concentration
of AsA late in storage and this maintenance level appears to be genotype-dependent (Fig. 8), and
(3) AsA loss was more sensitive to atmospheric oxygen than storage temperature (Fig. 9).
Interestingly, tuber AsA concentrations at harvest (zero-time, Fig. 8) correlated (P<0.05) with
cultivar-dependent differences in tuber respiration; cultivars with high respiration rates tended to
have higher levels of AsA and vice versa (Knowles, unpublished). This relationship would fit
with a greater need to detoxify reactive oxygen species (ROS) during periods of high metabolic
activity. However, storage at 3.5% O2 reduced respiration 3-fold (see below) and halted AsA
loss (Fig. 9 and see Section 3.4), which suggests that postharvest AsA levels are not entirely
dictated by basal metabolic rate. AsA also serves as a precursor for other metabolites (Ishikawa
et al., 2006; Debolt et al., 2007) and it is possible that reduced O2 slows their synthesis thus
helping to maintain AsA concentration.
Significant differences among cultivars in the rate of AsA loss during storage underscore
the importance of breeding for enhanced retention and for using existing genotypes to define
important AsA retention mechanisms. Ranger Russet had the highest initial AsA level, second
highest rate of loss over the first 2.5 months of storage (-121 µg 100 g-1 FW day-1) and highest
percentage loss (65%) over the 8.5-month storage period (Fig. 8). Russet Burbank and Summit
Russet had the lowest initial and final AsA levels and Summit lost AsA more rapidly (-136 µg
100 g-1 FW day-1) from 0 to 75 days of storage than all the cultivars. The relatively rapid initial
decrease in AsA concentration following harvest attenuated with time in storage in all cultivars
(Figs. 8 and 9). This trend is consistent with a similar decline in tuber respiration rate (basal
metabolism) from harvest through wound healing and dormancy (Schippers, 1977; Pringle et al.,
2009). As tuber intermediary metabolism slows postharvest, the need to deal with ROS directly
33
or through the AsA-GSH (Halliwell-Asada) pathway decreases and this may account for much of
the postharvest drop in AsA levels. We speculate that the lower steady state concentrations of
total AsA in tubers later in storage (e.g. Fig. 8, Premier Russet, Summit Russet, and Russet
Burbank) likely reflect the minimum levels needed for ‘maintenance metabolism’ in the
metabolically inactive tubers. Maintaining this basal level may involve AsA synthesis; however,
the extent and significance of turnover of biosynthetic enzymes in this process remains to be
established. While transcript levels of Smirnoff-Wheeler pathway genes were non-detectable by
ca. 1 month after harvest (zero-time samples in Fig. 10), relatively low levels were apparent in
the zero-time samples of 7-month-old tubers from table 2 (data not shown) and in the 6-monthold control tubers (stored at 4oC) of Fig. 12.
As a key antioxidant involved in modulating the redox potential of cells, regulation of
ascorbate level is likely at least partly tied to oxidative metabolism (respiration and the
AsA/GSH pathway). Indeed, storage in 3.5% O2 reduced the respiration rate of tubers from ca.
2.1 to 0.66 mg CO2 kg-1 h-1, slowed AsA loss and ultimately improved AsA retention by 35%
following 160 days of storage relative to tubers stored continuously at 21% O2; temperature had
little effect (Fig. 9). The minimal effect of storage temperature on loss of AsA is also
demonstrated by the data in Fig. 12 where tubers were exposed to high temperature priming
treatments to induce sprouting and daughter tuber development.
In contrast to low O2, wounding increases the respiration rate of tubers substantially
(Dizengremel, 1985) and also induced expression of genes in the Smirnoff-Wheeler pathway
(Fig. 10) resulting in synthesis of AsA (Table 2; Fig. 11). The wound-induced increase in GGP1
transcript (Fig. 10) is particularly relevant as a potential rate limiting step in AsA biosynthesis,
which agrees with Bulley et al. (2009) who showed a direct correlation between increased
34
transcript level of GGP1 and AsA concentration in Arabidopsis and kiwi fruit. Additionally,
Bulley et al. (2012) demonstrated that over-expression of GGP1 resulted in a 2-3-fold increase in
AsA in potatoes (cv. Ranger Russet). Tubers therefore have the metabolic competence for AsA
synthesis postharvest which, if expressed in intact (non-wounded) tubers, would likely prevent or
at least attenuate AsA loss, resulting in maintenance of higher levels throughout storage.
Ascorbate content and transcript levels of genes in the Smirnoff-Wheeler pathway were
low in tubers after 6 months of cold storage (4oC) and during daughter tuber formation.
Ascorbate synthesis, however, was greatly upregulated in sprouts and daughter tubers developing
from the 6-month-old tubers (Fig. 12); likely a response to stimulate and support the demands of
cell division (Liso et al., 1998). Histochemical staining showed AsA localized in areas of
vascular tissue continuous with the attached sprouts and daughter tubers, which may indicate
translocation from the mother tubers; however, this remains to be established. The low transcript
levels in non-dormant control and mother tubers implies continued AsA synthesis for
maintenance metabolism during cold storage and perhaps may be necessary to support longer
survival of the mother tubers during production of daughter tubers. GGP1, GPP, L-GalDH and
L-GalLDH transcripts were not detected in sprouting tubers; downregulation of AsA synthesis
during sprouting may help facilitate the mobilization of tuber reserves to promote sprouting and
rapid plant establishment. Further work is needed to determine the relevance of these differences
in gene expression to sprouting and daughter tuber formation.
5. Conclusions
Ascorbate synthesis in potato tubers appears to be largely driven by the elevated
metabolic requirements accompanying cell division (e.g. during tuberization, wound periderm
35
development, and in etiolated sprouts and daughter tubers). AsA concentration increased rapidly
in tubers during the early stages of tuberization and through bulking, reaching a maximum just
prior to the attainment of physiological maturity, then fell during the maturation period as vines
began to senesce. Transcript levels of genes in the Smirnoff-Wheeler pathway in tubers
increased during tuberization and early development and then decreased during bulking and
maturation. These results suggest that most of the AsA in tubers is translocated from foliage;
however, the actual contributions of foliar- and tuber-derived AsA to the AsA concentration in
mature tubers remain to be established. Up-regulation of GGP in the Smirnoff-Wheeler pathway
effectively increased total AsA content in tubers (Bulley et al., 2012).
AsA is lost rapidly from tubers following harvest and the rate of loss was cultivardependent; preventing this loss has the potential of greatly increasing the contribution of potatoes
to vitamin C in our diet. The postharvest loss of AsA was not affected by temperature but was
significantly reduced by storage of tubers in low O2. Low O2 storage can thus be used to
effectively dissect the mechanism(s) responsible for postharvest loss of AsA at the molecular
level. Although AsA concentration of stored tubers is markedly lower than the maximum
achieved at physiological maturity, the reduced AsA level is evidently adequate for mitigation of
oxidative stress due to respiration, including the enhanced respiration which occurs at elevated
temperatures. Wounding induced transcription of genes in the Smirnoff-Wheeler pathway and
substantially increased total AsA concentration, the extent of which depended on tuber age, thus
further demonstrating the ability of stored tubers to produce AsA in situ when given an
appropriate stimulus for cell division (e.g. wound periderm development; see Liso et al., 1998).
While AsA content is heritable, the greatest potential for improving potato tubers as a
source of vitamin C is clearly to improve postharvest retention. This study is the first to
36
comprehensively characterize the dynamics of AsA change in relation to semi-quantitative trends
in gene expression in field grown tubers from tuberization through bulking and maturation,
storage, early sprout development, and daughter tuber formation. Our results will hopefully spur
more fundamental studies to understand the regulation of AsA synthesis and metabolism in
tubers throughout development and storage, which will ultimately lead to strategies for the
development of higher AsA retaining genotypes.
Acknowledgements
Financial support from the USDA/ARS, Washington State Potato Commission, WSU
Agricultural Research Center, and WSU Molecular Plant Sciences Program is gratefully
acknowledged.
37
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variety with good fresh market and frozen processing qualities. American Journal of Potato
Research 82, 425-432.
Love, S.L., Novy, R.G., Whitworth, J.L., Corsini, D.L., Pavek, J.J., Mosley, A.R., Pavek, M.J.,
Knowles, N.R., Brown, C.R., James, S.R., Hane, D.C., Miller, J.C., 2006. GemStar Russet:
a potato variety with high yield, good culinary quality, excellent fresh market appearance,
and resistance to common scab. American Journal of Potato Research 83, 171-180.
Love, S.L., Pavek, J.J., 2008. Positioning the potato as a primary food source of vitamin C.
American Journal of Potato Research 85, 277-285.
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Love, S.L., Salaiz, T., Shafii, B., Price, W.J., Mosley, A.R., Thornton, R.E., 2003. Ascorbic acid
concentration and stability in North American potato germplasm. Acta Horticulturae 619,
87-93.
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& Smith, O. eds., Potato Processing. 3rd ed., pp. 235-273. West Port, Conn., AVI.
Murshed, R., Lopez-Lauri, F., Sallanon, H., 2008. Microplate quantification of enzymes of the
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45
Table 1. Forward (F) and reverse (R) primer sequences for the amplification of transcripts of
enzymes involved in the synthesis (Smirnoff-Wheeler pathway) and regeneration of ascorbate
(Halliwell-Asada cycle).
Gene
G6PI
PMI
GMP-1
GMP-2
GME-1
GME-2
GME-3
GGP-1
GGP-2
GPP
L-GalDH
L-GalLDH
APX
AsA Ox
MDHAR-1
MDHAR-2
DHAR
SOD
GR
18S rRNA
L2
Encoded protein
Glucose-6-P isomerase
Phosphomannose
isomerase
GDP-mannose
pyrophosphorylase
GDP-mannose
pyrophosphorylase
GDP-mannose-3’5’epimerase
GDP-L-galactose
phosphorylase/
guanylyltransferase
GDP-L-galactose
phosphorylase/
guanylyltransferase
L-Galactose-1-P
phosphatase
L-Galactose
dehydrogenase
L-galactono-1,4-lactone
dehydrogenase
Ascorbate peroxidase
Ascorbate oxidase
Monodehydroascorbate
reductase
Monodehydroascorbate
reductase
Dehydroascorbate
reductase
Cytoplasmic superoxide
dismutase
Glutathione reductase
Internal control
Cytoplasmic ribosomal
protein L2
Primer Sequence
F: GTCATGGAGTCTCTGGGGAA
R: CCAGGTTGGTGATAAGCGTT
F: ATGGAGGCTGATGGTCTGTC
R: CGGGTTTGTGGTTATCATCC
Accession Annealing
(oC)
SGN56
U270973
bp
341
SGNU279092
55
478
F: AATTGGCTTCAGGACCACAC
R: TCCTTGTGGGGCAAAACTAC
SGNU270618
57
316
F: AACACAACCAGGGCCAATAG
R: AGCGACTGGGAGAGTTGAAA
SGNU279970
58
385
F: GAAGCTTGCTGTCCAACACA
R: AGAGGGATTGGCTTCCAGTT
SGNU268615
59
309
F: GCCCTCACTTCCACTGACAA
R: GGTTCTTGCCATCAAAGCTG
SGNU271148
57
199
F: CGGAGGGAGCCTAATTCAAC
R: TAGTCCTCAGCTTCGATGGC
SGNU288060
59
265
F: GAGGCCAACTGAGTTTCGAG
R: TCTCTGCATAGCACTGTGGG
SGNU268513
58
632
F: GCAATAAAACCACATCTCCC
R: CCAAGAACAGGACCGATGTT
SGNU271705
55
338
F: CCCTTCGAATGTGTGGTTCT
R: GCATGATTTGATCGCTGCTA
SGNU273059
59
370
F: TGGCAGCTCAGACATTGCAG
R: CGAGGGACCCAAATTCAATA
SGNU274917
56
399
F: AGAATCCCCAATTCCCAATC
R: TCATCCACAAGCTGCTGAAC
SGNU272974
55
484
F: AGCCCATTAGGGAGCAGTTT
R: GGTCACAGAGGAGAGCCTTG
F: TGTGGAGCCATTTGTGGTAA
R: CGTTCACCCTGTTTTGTGTG
F: AGCTGGATATGCGGCTAGAA
R: CCGATCTTCTCAGGAAATCT
SGNU268593
55
399
SGNU276734
59
341
SGNU278793
55
360
F: AAGGGTACAGTGGCTGTTGG
R: GCTGAGCAGGCTGTCAAGGC
SGNU270762
55
314
F: CTACCCGAGACACAACACGA
R: GCAGGCTCTCCTTGATGAAC
SGNU281276
56
319
F: TTCAAGGGTGACCTGAGATC
R: ACGCACCTCATCTTCAGGAG
SGNU268852
57
264
F: TCTCATCCCCGTACCTCATC
R: GAGGGTGCTCCAGTCATGTT
F: GGGCATTCGTATTTCATAGTCAGAG
R: CGGTTCTTGATTAATGAAAACATCCT
F: GGCGAAATGGGTCGTGTTAT
R: CATTTCTCTCGCCGAAATCG
SGNU269464
55
210
X67238
58
101
39816659
55
121
46
Table 2. Wound-induced total ascorbate
biosynthesis in tissue slices from freshly
harvested and 7-month-old Ranger Russet
tubers. Tissue slices were wound healed at
21oC (98% RH) for 1 to 6 days. Letters
indicate significant differences (P<0.05)
between means within a column (tuber age).
Each value represents 12 tubers.
*,**P<0.05 and 0.01, respectively, for the
indicated trends.
Days after
Wounding
Ranger Russet
Months in Storage (4oC)
1
7
-1
mg AsA 100 g FW
0
26.0 a
10.9 a
1
28.0 a
20.3 c
2
35.6 b
23.2 c
4
-
15.6 b
6
-
16.5 b
Linear
*
ns
Quadratic
-
**
Cubic
-
**
47
Fig. 1. (A) Smirnoff-Wheeler pathway for AsA biosynthesis; (B) Halliwell-Asada (AsA-GSH
cycle) pathway for AsA recycling adapted from Noctor and Foyer (1998) and Bulley et al.
(2009).
48
Stages of Tuberization
10 mm
I
IV
II
III
V
VI
VII
I
II
Hooked stolon with no apparent swelling.
III
Stolon terminal continues to swell until the hook is completely open;
developing tuber is less than twice the diameter of the stolon.
IV
Tuber continues to swell; developing tuber is approximately twice the
diameter of the stolon.
V
VI
VII
VIII
VIII
Slight swelling below the apex results in apical hook beginning to straighten.
0.6 – 1.5 g tuber
1.5 – 2.5 g tuber
2.5 – 5.0 g tuber
5.0 – 10.0 g tuber
Fig. 2. Descriptions of the eight stages of tuber development sampled during tuberization of cv.
Ranger Russet potatoes for determination of AsA and associated gene expression. Stages I-VIII
ranged from non-tuberized stolons (Stage I) to 5- to 10-g tubers (stage VIII) and were collected
from field-grown plants at approximately 50 days after planting as described in Weeda et al.
(2009).
49
Fig. 3. (A) Foliar and tuber development of cv. Ranger Russet potatoes grown under late-season
management at Othello, WA. Changes in average tuber FW and tuber sucrose concentration (B),
and reducing sugars (glucose and fructose) and specific gravity (C) were analyzed to fully define
the developmental stages of tubers used for AsA analysis and associated gene expression during
bulking and maturation (see Figs. 4-7). Tuber physiological maturity (PM) was estimated at 148
DAP as the average of DAP to achieve maximum tuber yield and specific gravity, and minimum
sucrose and reducing sugar concentrations in tubers. The tubers sampled for AsA and transcript
analyses are identified by DAP in A and B (small font) and cross referenced to Figs. 4-7.
Cumulative degree days corresponding to DAP are shown (A). Foliar, tuber yield and average
tuber wt (g tuber-1) data are the average of four replicates of four plants per replicate harvested at
each sampling (n=16 plants). Sucrose, reducing sugars, and specific gravity were determined on
four replicates (5 tubers/replicate) at each harvest date (n=20 tubers).
coefficients.
50
***
P<0.001 for correlation
Cumulative Degree Days (7.2oC base)
1169 1713 2260 2761 3169 3433
100
Ranger Russet
70
60
60
50
50
40
40
30
30
R2= 0.97***
20
63
50
70
B 100
83 91 102
90
116
131
147
0
110 130 150 170 190
280
Days After Planting
90
240
g tuber-1
80 Basal
200
70
2
R = 0.98***
60
50
160
Apical
120
40
80
30
40
20
10
Sucrose
63
0
18
-1
20
Reducing Sugars (mg g dry wt )
50
C
70
Apical
83 91 102
90
-1
10
168
116
131
147
-1
0
20
foliar
growth
Tuber Yield (tonne ha )
80
70
10
-1
90
tuber
yield
80
Tuber Weight (g tuber )
-1
Foliar Growth (tonne ha )
90
Sucrose (mg g dry wt )
3497
0
168
110 130 150 170 190
1.100
Days After Planting
1.095
16
Gravity
1.090
1.085
14
1.080
12
R2= 0.99***
1.075
10
1.070
8
1.065
6
Basal
1.060
4
PM = 148 DAP
2
Glc + Fru
Basal
Apical
0
50
70
90
1.055
1.050
1.045
110 130 150 170 190
Days After Planting
51
Specific Gravity
A 100
677
Fig. 4. (A) Changes in total, reduced, and oxidized AsA in cv. Ranger Russet tubers during
tuberization, bulking, maturation, and storage. Tuberization stages I-VIII are defined in Fig. 2.
The DAP indicated for tubers sampled during bulking and maturation correspond to those
labeled in the growth and development profiles in Figs. 3A and B.
**,***
P<0.01 and 0.001,
respectively, for correlation coefficients (ns, not significant). (B) Changes in total AsA on a per
tuber (absolute) basis during bulking, maturation and storage. This plot was derived from the
tuber growth (g tuber-1) and AsA concentration polynomial models in Figs. 3B and 4A,
respectively. RDA, recommended daily allowance of vitamin C (see Discussion).
52
A
45
35
o
Bulking & Maturation
Storage at 9 C
45
40
Total AsA
Reduced AsA
Oxidized AsA
35
2
R = 0.93**
30
30
2
R = 0.94**
25
25
20
20
R2= 0.94**
15
R2= 0.96**
2
R = 0.95**
15
2
R = 0.94**
10
10
5
2
2
R = 0.49ns
R = 0.47ns
63
0
I II III IV V VI VIIVIII
Stage
5
2
R = 0.54ns
83 91 102 116 131 147 168
0
30 240
60 270
90 120
150 360
180 390
210 420
240 450
60 80 100 120 140 160180 210
300 330
Days after Planting
o
Days after Harvest (9 C)
100
90
-1
Total Ascorbate (mg tuber )
-1
Ascorbate (mg 100 g FW)
40
Tuberization
B
80
100
96% RDA
90
88% RDA
80
70
70
60
60
51% RDA
50
50
40
40
30
30
20
20
29% RDA
10
10
0
0
30 240
60 270
90 120
150 360
180 390
210 420
240 450
60 80 100 120 140 160180 210
300 330
Days after Planting
53
o
Fig. 5. Developmentally-linked changes in transcript levels of genes encoding enzymes in the
Smirnoff-Wheeler pathway of AsA biosynthesis during tuberization, bulking and maturation of
potato tubers (cv. Ranger Russet). 18S rRNA served as internal reference gene (35 cycles). The
changes in tuber AsA concentrations are shown in Fig. 4. Tuberization stages I-VIII are defined
in Fig. 2. Each bulking and maturation stage corresponding to the indicated DAP are defined in
Fig. 3 by tuber weight, specific gravity, sucrose, and reducing sugar content during tuber
development through the 168-day growing season. A semi-quantitative analysis of transcript
levels is presented in Fig 6.
54
Tuberization Stages
Bulking & Maturation (DAP)
I
II
III IV
V VI VII VIII
63
76
Smirnoff-Wheeler Pathway
83 91 102 116 131 147 161 168
18S rRNA
Glucose-6-Phosphate
G6PI
Fructose-6-Phosphate
PMI
PMM
GMP 1
Mannose-6-Phosphate
Mannose-1-Phosphate
GMP 2
GME 1
GME 2
GDP-Mannose
GDP-L-Galactose
GME 3
GGP 1
GGP 2
L-Galactose-1-Phosphate
L-Galactose
GPP
L-Galactono-1,4-lactone
L-GalDH
L-GalLDH
55
Ascorbate
Fig. 6. Semi-quantitative analysis of transcript levels of selected genes in the Smirnoff-Wheeler
pathway of AsA biosynthesis during tuberization, bulking and maturation of cv. Ranger Russet
tubers from the agarose gels shown in Fig. 5. Expression of 18S rRNA (yellow squares) was not
affected by tuber development and hence served as internal reference gene. The tuber
developmental stages are defined in Figs. 2 and 3.
correlation coefficients.
56
*,**,***
P<0.05, 01 and 0.001, respectively, for
Stage
Tuberization
Days
after
Bulking
& Planting
Maturation
120
GME2
18S rRNA
GME2
100
R2= 0.91**
60
18S rRNA
40
100
80
Stage
Tuberization
40
18S rRNA
40
20
GME3
R = 0.85**
120
GME3
18S rRNA
80
18S rRNA
60
40
60
R2= 0.93**
18S rRNA
40
L-GalDH
2
R = 0.95***
2
R = 0.88**
120
100
18S rRNA
80
60
GGP1
2
Stage
Stage
Days after Planting
57
161
168
147
131
116
102
76
83
91
I II III IV V VI VII VIII
63
161
168
147
131
116
102
63
76
83
91
Days after Planting
1
2
3
4
5
6
7
8
0
76
83
91
63
1
2
3
4
5
6
7
8
120
L-GalLDH
100
R = 0.81**
R = 0.74*
0
Days
after&Planting
Bulking
Maturation
140
18S rRNA
GGP1
40
20
2
Stage
Tuberization
160
18S rRNA
80
60
18S rRNA
40
20
R2= 0.86*
L-GalLDH
0
Stage
76
83
91
R = 0.84*
20
180
63
18S rRNA
2
140
0
161
168
147
131
116
102
76
83
91
63
Days
after
Planting
Bulking
& Maturation
Relative Transcript Level
60
18S rRNA
80
1
2
3
4
5
6
7
8
GMP2
100
40
Stage
Tuberization
160
GMP2
161
168
18S rRNA
80
1
2
3
4
5
6
7
8
Days after
Planting
Bulking
& Maturation
140
120
1
2
3
4
5
6
7
8
161
168
147
131
116
102
76
83
91
63
1
2
3
4
5
6
7
8
Stage
Tuberization
160
147
100
R = 0.79**
180
161
168
120
20
0
131
L-GalDH
2
180
147
1
2
3
4
5
6
7
8
140
20
0
116
Days
after
Planting
Bulking
& Maturation
161
168
60
Stage
Tuberization
Days after Planting
161
168
R2= 0.82**
180
160
2
100
147
GMP1
18S rRNA
80
140
18S rRNA
GPP
20
161
168
147
131
116
102
76
83
91
Days
after
Planting
Bulking
& Maturation
GMP1
100
2
R = 0.94**
2
R = 0.97***
60
GPP
160
140
18S rRNA
0
180
102
120
147
Days after
Planting
Bulking
& Maturation
Bulking
& Planting
Maturation
Days
after
Stage
Tuberization
140
R2= 0.66*
63
161
168
147
131
116
102
76
83
91
63
1
2
3
4
5
6
7
8
Stage
Tuberization
1
2
3
4
5
6
7
8
180
0
160
R2= 0.80**
160
140
80
161
168
147
131
116
102
76
83
91
63
0
20
PMM
0
131
R = 0.68*
GGP2
GGP2
131
2
0
120
20
2
131
18S rRNA
18S rRNA
40
116
PMM
20
60
102
80
60
80
116
18S rRNA
18S rRNA
R = 0.93***
120
180
GME1
1
2
3
4
5
6
7
8
161
168
147
131
116
102
140
40
40
Days&after
Planting 180
Bulking
Maturation
160
Stage
Tuberization
76
83
91
63
160
100
18S rRNA
60
R = 0.80**
1
2
3
4
5
6
7
8
180
80
100
20
2
0
18S rRNA
120
102
20
100
116
40
120
140
102
18S rRNA
60
R2= 0.92**
76
83
91
18S rRNA
80
63
G6PI
100
Tuberization
160
GME1
140
180
76
83
91
R2= 0.76**
Tuberization
63
G6PI
120
140
160
Bulking & Maturation 180
Tuberization
160
1
2
3
4
5
6
7
8
180
Fig. 7. (A) Developmentally-linked changes in transcript levels of genes encoding enzymes in
the Halliwell-Asada (AsA-GSH) recycling pathway during tuberization, bulking and maturation
of potato tubers (cv. Ranger Russet). 18S rRNA served as internal reference gene (35 cycles).
The tuber developmental stages are defined in Figs. 2 and 3. A semi-quantitative analysis of
transcript levels is presented in (B).
*,**,***
P<0.05, 01 and 0.001, respectively, for correlation
coefficients.
58
Tuberization Stages
A
Bulking & Maturation (DAP)
I
II
III IV
V VI VII VIII
63
76
83 91 102 116 131 147 161 168
18S rRNA
GR cytoplasmic
DHAR
MDHAR 1
MDHAR 2
APX
SOD cytoplasmic
AsA Ox
35 Cycles
180
160
140
140
120
18S rRNA
100
80
60
18S rRNA
40
GRcyt
2
R = 0.88***
GRcyt
R2= 0.86**
0
R = 0.98***
80
60
18S rRNA
40
40
20
159
168
146
131
116
102
76
84
91
63
1
2
3
4
5
6
7
8
20
Tuberization
140
120
18S rRNA
100
80
60
18S rRNA
SOD
40
20
2
R2 = 0.68*
SOD
R2 = 0.88***
R = 0.88**
0
Stage
Tuberization
180
Tuberization
159
168
146
131
116
102
76
84
91
1
2
3
4
5
6
7
8
Days after Planting
63
159
168
146
131
116
102
76
84
91
1
2
3
4
5
6
7
8
63
0
160
160
140
MDHAR1
120
100
80
18S rRNA
2
R = 0.89*
18S rRNA
40
AsA ox
120
100
80
AsA ox
18S rRNA
R2 = 0.81*
60
18S rRNA
40
MDHAR1
20
2
R = 0.63*
0
20
R2 = 0.96***
Stage
Days after Planting
59
Stage
159
168
146
131
116
102
159
168
146
131
116
102
76
84
91
63
0
1
2
3
4
5
6
7
8
Mean Intensity
60
180
DHAR
2
18S rRNA
60
R2 = 0.79**
18S rRNA
160
100
140
18S rRNA
80
Days after Planting
140
180
APX
100
159
168
146
131
116
102
76
84
91
63
1
2
3
4
5
6
7
8
Stage
Tuberization
160 DHAR
120
R2 = 0.86**
120
0
180
APX
76
84
91
20
Tuberization
63
Tuberization
160
1
2
3
4
5
6
7
8
180
B
35 Cycles
Days after Planting
10 Oxidized
2
R = 0.95***
5
20
15
R2=0.97***
10
5
R2=0.96***
Oxidized
0
50
o
20
15
Reduced
50
100 150 200 250 300
25
Total
Reduced
Oxidized
-1
Total
Reduced
Oxidized
Total
R2= 0.94***
10
2
20
Total
15
Reduced
10
R2=0.99***
R = 0.88***
5
Oxidized
2
5
R2= 0.28ns
R =0.99***
Oxidized
0
50
100 150 200 250 300
o
0
R2=0.89***
50
25
20
100 150 200 250 300
Russet
Days after Harvest
(9oC)Burbank
30
Total
Reduced
Oxidized
Total
15
10
Reduced
R2=0.98***
5
R2=0.99***
Oxidized
R2=0.94***
0
0
R2=0.99***
5
Oxidized
Summit
Days after Harvest
(9oC) Russet
30
25
-1
30
2
R =0.99***
10
0
0
100 150 200 250 300
Reduced
15
R =0.52*
0
Premier
Days after Harvest
(9 C) Russet
Total
Reduced
Oxidized
20
2
2
R = 0.54**
0
Total
-1
Reduced
25
-1
R2= 0.94***
Total
Reduced
Oxidized
GemStar Russet
30
Reduced
Defender
Total
25
-1
20
15
Total
Reduced
Oxidized
25
30
Ranger Russet
Total
-1
30
R2=0.58*
0
0
50
100 150 200 250 300
Days after Harvest (9oC)
0
50
100 150 200 250 300
Days after Harvest (9oC)
Fig. 8. Postharvest changes in total, reduced and oxidized AsA in tubers of six potato cultivars
over a 250-day storage period at 9oC (95% RH).
*,**,***
correlation coefficients (ns, not significant).
60
P<0.05, 01 and 0.001, respectively, for
-1
Total Ascorbate (mg 100 g FW)
A 35
Ranger Russet
30
35
30
o
4C
B
o
32oC 4 C
Ranger Russet
R2= 0.58**
R2= 0.79***
25
25
20
20
R2= 0.67**
3.5% O2
3.5% O2
R2= 0.81***
15
15
21% O2
21% O2
R2= 0.94***
10
R2= 0.93***
10
0
20 40 60 80 100 120 140 160
0
Days in Storage
20 40 60 80 100 120 140 160
Days in Storage
Fig. 9. Effects of temperature and low oxygen atmosphere on total AsA loss from cv. Ranger
Russet tubers over a 162-day storage period at 4oC (97% RH). Tubers were held under normal
O2 (21%, grey circles) from day zero to twenty at 4oC (left) or 32oC (right). Samples were then
placed at 3.5% O2 (red squares) or maintained at 21% O2 (blue diamonds) for the remainder of
the storage period at 4oC. The greatest loss in AsA occurred during the initial 20 days and was
not affected by temperature (4oC vs 32oC). Low oxygen significantly (P<0.01) slowed the loss
of AsA from 20 to 162 days.
**,***
P<0.01 and 0.001, respectively, for correlation coefficients.
61
Days after
Wounding
0 1 2
Smirnoff-Wheeler Pathway
Glucose-6-Phosphate
L2
G6PI
Fructose-6-Phosphate
PMI
PMM
Mannose-6-Phosphate
GMP 1
Mannose-1-Phosphate
GMP 2
GDP-Mannose
GME 1
GME 2
GDP-L-Galactose
GME 3
L-Galactose-1-Phosphate
GGP 1
GGP 2
L-Galactose
GPP
L-Galactono-1,4-lactone
L-GalDH
L-GalLDH
Ascorbate
Fig. 10. Wound-induced changes in transcript levels of genes encoding enzymes in the
Smirnoff-Wheeler pathway of AsA biosynthesis in 1-month-old tubers (cv. Ranger Russet).
Cytoplasmic ribosomal protein L2 served as internal reference gene (35 cycles). Tissue slices
were wound-healed at 21oC (98% RH) for 0, 1 or 2 days. AsA concentration increased
significantly (P<0.05) over the 48-h healing interval as presented in Table 2.
62
-1
Total Ascorbate (mg 100 g FW)
Russet Burbank
32
Freshly harvested
28
24
Stored 12 months
20
16
Stored 24 months
12
8
0
1
2
o
Days After Wounding (23 C)
Fig. 11. Tuber age (storage duration) affects wound-induced AsA synthesis. Tissue slices from
tubers (cv. Russet Burbank) stored for 0, 12 or 24 months at 4oC (95% RH) were wound-healed
at 21oC (98% RH) for 0, 1 or 2 days. Tuber age, healing time and their interaction were
significant at P<0.05, 0.01 and 0.05, respectively.
63
Fig. 12. Effects of sprouting and daughter tuber formation (A) on AsA concentrations and
transcript levels (C) of genes encoding enzymes in the last four steps of the Smirnoff-Wheeler
pathway. 18S rRNA served as internal reference gene (40 cycles). Image has been inverted for
better resolution. Tubers (cv. Ranger Russet) were stored for 176 days in the dark following
harvest. Control tubers (A, top left) were held continuously at 4oC (95% RH). Etiolated sprouts
(A, top middle) were induced by raising the storage temperature to 16oC over the last 8 days of
storage. Daughter tubers (A, top right) developed in response to two, non-consecutive high
temperature priming treatments at 32oC (95% RH). (B) Histochemical staining of AsA in
longitudinal sections of tubers with attached sprouts or daughter tubers. Arrows indicate
vascular connections with sprouts and daughter tubers.
64
(A)
A
B
C
1 cm
1 cm
1 cm
(B)
(C)
Tuber
Tuber Sprout
Mother Daughter
Tuber
Tuber
GPP1
GPP
L-GalDH
L-GalLDH
18S rRNA
12.3 a
12.6 a
28.8 b
14.1 a
Total AsA (mg 100 g-1 FW)
65
58.8 c
CHAPTER 2
Evidence that tuber respiration is the pacemaker of physiological aging in seed potatoes
(Solanum tuberosum L.)1
Abstract
Storage temperatures greater than 4ºC (i.e. heat-unit accumulation) increase respiration and
accelerate physiological aging of seed tubers. The degree of apical dominance is a good
indicator of physiological age (PAGE). As seed age advances, apical dominance decreases,
resulting in more stems, greater tuber set and shifts in tuber size distribution. Here we provide
evidence that tuber respiration rate is the ‘pacemaker’ of aging. Tubers exposed to a brief high
temperature age-priming treatment initially in storage, followed by holding at 4ºC for the
remainder of a 190-200-day storage period, maintained a higher basal metabolic (respiration)
rate throughout storage compared with tubers stored the entire season at 4ºC. Tubers thus
‘remembered’ the age-priming treatment as reflected by their elevated metabolic rate. Moreover,
reducing the respiration rate of age-primed seed by subsequently storing at 3.5% O2 (4ºC) until
planting significantly attenuated effects of the aging treatment on apical dominance, tuber set and
size distribution. The effect of the age-priming treatment on the magnitude of the respiratory
response was the same whether given at the beginning or toward the end of storage. However,
moving the age-priming treatment progressively later in the storage season effectively decreased
its impact on plant growth and development. These results underscore the importance of time in
the aging process. Exposure of seed to a high temperature age priming treatment at the
beginning or end of storage elevated respiration (the pacemaker) to the same extent; however,
the timing of these treatments resulted in vastly different physiological ages. The longer the
66
respiration rate of tubers remains at an elevated level, the greater their PAGE at planting. Thus,
an accurate but impractical measure of PAGE may be the respiratory output from vine kill to
subsequent planting. Respiration appears to be the pacemaker of PAGE and production and
storage conditions that affect respiration may ‘set the clock speed’ that will ultimately determine
the PAGE at planting.
1
Submitted to the Journal of Plant Growth Regulation Nov. 8, 2012.
Blauer, J.M., Knowles, L.O., Knowles, N.R., 2012. Evidence that tuber respiration is the
pacemaker of physiological aging in seed potatoes (Solanum tuberosum L.). Journal of Plant
Growth Regulation. (In Review).
67
Introduction
Tuber maturity at harvest interacts with storage temperature and time to affect the
physiological age (PAGE) and productive potential of seed potatoes at planting (Knowles and
Knowles 2006; Struik 2007). Storing seed tubers at temperatures greater than 4°C (i.e. heat-unit
accumulation) accelerates aging (Caldiz 2009). Apical dominance, tuber set, tuber size
distribution, yield and economic return are greatly affected by differences in seed PAGE
(Knowles and Knowles 2006). The degree of apical dominance (stem number per seedpiece) is
an excellent indicator of seed PAGE. As seed age advances, apical dominance decreases,
resulting in more stems per plant. While cultivars vary in the extent of their response to seed
aging, in general, tuber set per plant increases with stems resulting in a decrease in average tuber
size (Iritani 1968; O’Brien et al. 1983; Van Loon 1987; Eshel et al. 2012).
The ability to optimize tuber set and size distribution in relation to market requirements is
of great importance to the potato industry and may be accomplished by manipulating the average
number of stems per seedpiece (i.e. apical dominance) without compromising total yield
(Knowles and Knowles 2006). Since the values of seed, fresh-market, and processing potatoes
are dictated in part by the specific array of tuber size classes, manipulating tuber size profiles by
varying the PAGE of seed lots can significantly affect returns. The aging responses of seedtubers to accumulated degree days (DD) in storage and the target stem numbers for particular
size distributions are cultivar-dependent (Moll 1994) and have recently been determined for
many mainstream and newly released long-russet cultivars in the Columbia Basin of WA (e.g.
Ranger Russet, Russet Burbank, Premier Russet, Russet Norkotah) (Knowles and Knowles 2004;
2006; 2011).
68
To date, no physiological or biochemical indices have been identified that adequately
resolve differences in seed age prior to planting, which greatly diminishes the scope for using
PAGE as a management option to alter tuber size distribution, yield and quality. Age-induced
differences in crop development, however, are clearly evident after planting. Developmental
indicators of advanced PAGE include more rapid sprouting leading to earlier emergence and
plant establishment, reduced apical dominance, increased tuber set, and shift in tuber size
distribution toward smaller tubers (Iritani et al. 1983; Iritani and Thornton 1984; Knowles and
Botar 1991; 1992). Until recent years, cumulative degrees days (DD) were thought to be a good
measure of seed PAGE (Struik 2007). However, the temperature at which DD accumulate
(Knowles and Knowles 2006) and the timing of heat unit accumulation by seed (Struik 2006)
significantly affect the onset of sprouting and the degree of apical dominance, two key indicators
of seed PAGE. Effects of seed PAGE on overall yield can range from substantial increases
(Knowles and Botar 1992), to no effects, to significantly reduced yields, and depend on a number
of factors including cultivar, the extent of aging, and length of the growing season.
Aging is an oxidative process that affects the hormonal regulation of apical dominance in
tubers (Kumar and Knowles 1993a; 1996a; 1996b). Higher temperature (e.g. >4oC) and/or
prolonged storage elevate basal metabolism (van Es and Hartmans 1981; Kumar and Knowles
1996a), which likely accelerates tuber aging. Elucidation of age-induced alterations in tuber
physiology and metabolism may lead to the identification of biochemical and/or molecular
markers for estimating the relative PAGE of seed. Long-term storage studies (e.g. >10 months)
at 4oC have documented effects on membrane architecture and integrity (Knowles and Knowles
1989; Zabrouskov and Knowles 2002a; 2002b), oxidative stress metabolism (Kumar and
Knowles 1993; Zabrouskov et al. 2002c), auxin transport in relation to apical dominance (Kumar
69
and Knowles 1993a), protein synthesis and catabolism (Kumar and Knowles 1993b; Kumar et al.
1999; Weeda et al. 2011), wound healing (Kumar and Knowles 2003; Kumar et al. 2007; Kumar
et al. 2010), and respiration (Kumar and Knowles 1996a). The higher respiration of older tubers
is fully coupled and cyt-mediated (Kumar and Knowles 1996a; Zabrouskov et al. 2002c). The
progressive increase in respiration rate of tubers during prolonged storage (at 4oC) fuels agedependent and energy intensive changes in metabolism, many of which are consequences of
increasing oxidative stress (Kumar and Knowles 1996b).
In contrast to aging during long-term storage at constant temperature, relatively little is
known about the effects of high temperature-induced aging (age priming) on tuber metabolism
over a typical 200-day commercial storage season. Clearly, exposure to higher temperatures
(>4oC) increases tuber respiration rate (van Es and Hartmans 1981), but how does this effect
relate to PAGE? Respiration is indicative of overall metabolic rate (Makarieva et al. 2008) and
may be the ‘pacemaker’ of PAGE. An accurate measure of PAGE in potato tubers may thus be
the total respiratory output from vine-kill through storage to planting. To test this hypothesis, we
studied the effects of brief, high temperature-induced age-priming treatments on tuber respiration
over a ca. 200-day storage season in relation to in-season developmental indicators of PAGE
(emergence, apical dominance, tuber set, size distribution). Fundamental questions included: (1)
is the PAGE established during the relatively brief period of exposure of seed to high
temperature priming, or is the post aging storage period at 4oC also important in contributing to
the ultimate PAGE? (2) Does the sensitivity of seed-tubers to high temperature aging treatments
change from harvest through storage to planting? (3) How does high temperature priming affect
tuber respiration rate during and after treatment and how does this relate to PAGE? Seed-tubers
were subjected to an age priming treatment at various times throughout a 190-200-day storage
70
period and respiration rates and in-season developmental indicators of PAGE were compared
with non-aged tubers. Storage of seed in 3.5% O2 was used to modify age-induced changes in
tuber respiration rate to further define the importance of respiration in the aging process.
Collectively, our data indicate that respiration is indeed the pacemaker that controls and reflects
the rate of aging. Treatments that alter the basal metabolic rates of tubers even for short periods
have the potential of producing tubers of different PAGEs.
Materials and Methods
Plant material
Certified seed potatoes (cvs. Ranger Russet and Russet Burbank) were acquired from
commercial seed growers in October immediately following harvest in each year of study. Seed
tubers were hand-selected from bulk storage piles to acquire the desired size range of 113 to 170
g per tuber. The tubers were then wound-healed at approximately 12oC (95% RH) for 10 days
prior to various age priming treatments (see below) imposed at different times during 190-200
days of storage.
Seed aging during storage
With exception of the age-timing study, age priming treatments were given immediately
following wound healing as described in Knowles and Knowles (2006) by storing seed tubers at
12, 22 or 32oC (95% RH) for various periods until the desired number of degree days (DD) was
reached. A degree day is defined as one day at one degree above the base temperature of 4oC.
Control seed had no additional aging imposed after the initial wound healing period and is
indicated as 80-DD seed. Seed was stored at 4oC (95% RH) except during wound healing and
71
the age-priming treatments during the main storage period. The duration of storage ranged from
ca. 190 to 200 days depending on the year of study.
Assessing tuber respiration as an indicator of metabolic rate
Seed tubers in replicates were sealed into chambers with a continuous flow of air
containing 21% or 3.5% O2 (balance N2). Tuber respiration rates were determined by CO2
analysis at 5-h intervals with an automated gas sampling system as described in Knowles et al.
(2009). The outflow from each chamber was directed through an LI-6262 infrared gas analyzer
(LI-COR, Inc., Lincoln, Nebraska). Tuber respiration was monitored at 4oC during the main
storage period, at 22oC during growth of etiolated sprouts at the end of storage, or at 32oC during
age priming, depending on the study. Respiration rate is reported as mg CO2 kg-1 h-1 ±SE and is
equivalent to the rate of O2 consumption (molar basis), given that the RQ=1 (carbohydrate as
substrate) for potatoes in storage (van Es and Hartmans 1981). While basal metabolic rate is
generally expressed in terms of energy output of an organism at rest (Makarieva et al. 2008), in
plants, and particularly non-photosynthetic plant organs, it is directly proportional to the aerobic
dark respiration rate (Reich et al. 2006; Makarieva et al. 2008). Hence, the terms basal
metabolic rate and respiration rate are used interchangeably throughout this work.
Age priming studies – temperature, timing, and low O2
Effects of the temperature of age-priming on the respiration rates of seed tubers were
determined in relation to developmental indicators of PAGE. ‘Russet Burbank’ seed tubers were
given 450 DD (4oC base) at three temperatures (12, 22 and 32oC) directly following harvest and
then held at 4oC (95% RH) in the dark for the duration of storage (ca. 200 days) as described
above. At the end of March, sample tubers of each age were placed in 12.6-L Plexiglas
chambers to begin respiration measurements at 4oC. On April 25, the storage temperature was
72
raised to 22oC to simulate growing conditions and stimulate sprouting, and respiration was
continuously monitored until May 16. Sprout number, dry weight and sprout length were
measured as indicators of tuber PAGE.
Additional studies were conducted to assess the role of respiration in the aging process.
The first study evaluated the effects of timing of an age-priming treatment during storage on
tuber respiration rates in relation to developmental indicators of PAGE and yield. Four age
priming treatments of 600 DD (21 days at 32oC, 95% RH) were imposed on ‘Ranger Russet’
seed-tubers at different times spaced evenly throughout a 194-day storage period beginning 172,
128, 84, or 39 days before planting (DBP). The seed was stored at 4oC (95% RH) before and
after each of the 21-day age-priming treatments. The effects of all four treatments plus a nonaged control (80 DD) on various developmental and productivity indicators of PAGE were
assessed in field trials (see below). A randomized complete block design (five age priming
treatments) with five replicates was used during each year of the 3-yr study (2009-11).
Respiration rates of the 600 DD seed primed 172 and 39 DBP were compared with that from
non-aged (80 DD) control seed during the 2009-10 and 2010-11 storage seasons. Results for the
two seasons were comparable and the 2010-11 data are presented herein.
A second study assessed the impact of low O2 storage in mitigating the effects of a high
temperature age-priming treatment on respiration rates and subsequent developmental indicators
of PAGE in field studies. Approximately 50 kg each of ‘Ranger Russet’ and ‘Russet Burbank’
seed tubers were age-primed for 600 DD (21 d at 32oC) in storage immediately following harvest
and wound-healing (ca. 172 DBP). An equivalent quantity of seed served as non-aged controls
(80 DD). Directly following the age-priming treatments, tubers of both ages were divided
between two 190-L food-grade plastic barrels in 4oC storage. One barrel received a constant
73
flow (900 mL min-1) of house air (21% O2, balance N2) and the other was supplied with house air
filtered through a hollow-fiber membrane nitrogen generator (Permea Inc., St. Louis, Missouri),
which reduced the O2 concentration to 3.5%. The seed tubers remained in these conditions until
planting in April. Respiration rates of samples of the 80- and 600-DD ‘Ranger Russet’ seed in
both the 21% and 3.5 % O2 atmosphere treatments were monitored from December 8 through
April 18 at 4oC. Four replicates of six tubers were sealed into 3.9-L glass jars with a constant
flow (ca. 80 mL min-1) of each atmosphere. The field trial for evaluation of this seed was a three
factor factorial (two cultivars, two seed ages, and two O2 levels) planted in a randomized
complete block design with five replicates during each year of the 4-yr study (2008-11).
Respiration results are presented for the 2010-11 storage season and are comparable to those
obtained in 2009-10.
Evaluations of seed productivity
Seed was removed from 4°C storage in April each year, hand cut into 50- to 64-g seed
pieces and blocked for tuber portion (apical or basal) before suberizing at 9°C (95% RH) for 3 to
5 days prior to planting. Seedpieces were planted 20 cm deep in a Shano silt loam soil (Lenfesty
1967) with a custom-built two-row assist-feed planter at the Washington State University
Irrigated Agriculture Research and Extension Center in Othello, WA (46° 47.277’ N. Lat., 119°
2.680’ W. Long.). Treatments were arranged in randomized complete block designs for the
various field experiments. Individual plots consisted of 24 seed pieces spaced 25 cm apart in
rows spaced 86 cm apart. The plots were located under a linear move irrigation system which
maintained soil moisture at a minimum of 65% of field capacity as determined by soil
tensiometers positioned throughout the field. Pre-plant and in-season fertilizer, insecticide and
fungicide applications were based on standard practices for long-season russet potatoes in the
74
Columbia Basin. The time course of plant emergence and aboveground stem numbers were
determined each year prior to row closure. The duration of growth was approximately 155 days
at which time the vines were mechanically mowed. Harvest occurred approximately 7 to 14 days
later in late September of each year. Individual tuber weights were obtained for calculations of
total yield, U.S. no. 1 yield (>113-g tubers), marketable yield (U.S. no. 1 + <113-g tubers), yield
of individual tuber size categories, and tuber number for each plot.
Data analysis and presentation
Growth and yield data were subjected to analysis of variance (ANOVA). Sums of squares
were partitioned into single degree-of-freedom contrasts for main effects (cultivar, seed age,
timing of age priming, aging temperature, O2 concentration) and interactions, including
polynomial trends (linear, quadratic) as appropriate. Coefficients of determination are reported
along with significance levels (P-values) for the correlation coefficients. Trends in
developmental and yield data were similar from year to year. Hence, 3- and 4-yr averages are
presented for the timing of age priming and cultivar x age x low oxygen studies, respectively.
Treatment effects on yield and tuber size distributions were summarized in polygonal plots.
Tuber respiration data were subjected to ANOVA with time as repeated measure and P-values
are reported for the effects of seed age, low O2, and their interaction. Respiration and selected
growth and yield data are plotted versus time ±SE.
Results
Aging temperature affects basal metabolic rate
Effects of the temperature of age priming at the beginning of storage on tuber respiration
rates at the end of storage were evaluated in relation to apical dominance and sprout growth, two
75
developmental indicators of PAGE. Russet Burbank seed-tubers were given 450 DD by priming
seed samples for 13, 20 and 48 days at 12, 22 and 32oC, respectively, directly following woundhealing at the beginning of storage in October. The seed was subsequently held at 4oC (95%
RH) for the remainder of a ca. 200-day storage period. Respiration rates of the seed-tubers were
compared while still at 4oC from March 30 to April 25 (Fig. 1). Despite the constant number of
DD, seed subjected to the three age priming treatments had significantly different basal
metabolic (respiration) rates during the final 27 days of storage at 4oC. The basal respiration
rates of seed primed at 32 and 22oC averaged 2.54 and 2.31 mg CO2 kg-1 h-1, respectively, over
this period, which was 85 and 77% higher than that of seed given 450 DD at 12oC (P<0.01) (Fig.
1 inset). Sprouts within all eyes (nodes) of the tubers were peeping (<2 mm in length) on April
25 but sprout growth was inhibited at 4oC and no differences were apparent due to priming
treatment.
The storage temperature was increased to 22oC on April 25 to determine whether priming
treatments affected respiration rates during early sprout development. Respiration rates
increased rapidly and substantially as tubers acclimated to the higher temperature and then
decreased to new basal metabolic rates at 22oC (Fig. 1). The seed primed at 12oC acclimated to
the temperature change more rapidly, reaching the higher steady-state rate of respiration sooner
at 22oC than seed primed at 22 and 32oC. The acclimation responses lasted approximately 8, 10
and 12 days for seed primed at 12, 22 and 32oC, respectively. The final basal respiration rates (at
22oC) of seed primed at 12, 22 and 32oC averaged 6.63, 8.52 and 9.49 mg CO2 kg-1 h-1 (averaged
from 35-48 d, 37-48 d, and 39-48 d for seed primed at 12, 22 and 32oC, respectively). Seed
primed at 32 and 22oC thus maintained 43% and 29% higher basal rates of respiration (P<0.01)
than seed primed at 12oC during early sprout development. Storage at 22oC in the dark for the
76
final 21 days (April 25 to May 16) stimulated sprouting. Sprout number, length and dry weight
all increased with priming temperature (Table 1), reflecting different physiological ages, despite
the constant number of DD.
Timing of high temperature age priming affects PAGE
Studies to assess how the sensitivity of seed to temperature-induced accelerated aging
changes during a typical 190-200-day storage season were conducted in 2009, 2010, and 2011.
‘Ranger Russet’ seed-tubers were acquired at harvest and wound-healed at 12oC (95% RH) for
10 days. The seed was then stored at 4oC, except for a brief (21-day) age-priming treatment at
32oC (95% RH) on Oct. 23 (172 days before planting, DBP), Dec. 6 (128 DBP), Jan 19 (84
DBP), and Mar. 5 (39 DBP). These treatments thus resulted in four, 600-DD seed lots, each
receiving the same accelerated aging treatment at different times during the 190 to 200-day
storage periods. Except for the wound healing period, control seed was stored the entire season
at 4oC. The effects of these treatments on key developmental indicators of PAGE, including
plant emergence, apical dominance (stem numbers), tuber set, tuber size distribution, and yield,
were assessed in field trials over the 3-yr study period.
When imposed early in the storage season (172 DBP), the 600 DD aging treatment was
most effective in hastening plant emergence, increasing stem numbers (i.e. decreasing apical
dominance), increasing tuber set per plant, and decreasing average tuber size (Fig. 2A-C, Table
2). Plant emergence at 32 days after planting (DAP) decreased from 52 to 21% as the 600-DD
age priming treatment was moved progressively through the storage season from 172 DBP to 39
DBP. Plant emergence was slowest from the control (non-aged) seed (17% by 32 DAP).
However, regardless of treatment, emergence had reached 100% by 40 DAP. Similar trends in
apical dominance and tuber set per plant were evident; stem number and tuber set were lower
77
with later age-priming treatments. In contrast, average tuber fresh weight increased 29% from
ca. 154 g tuber-1 to 199 g tuber-1 as the timing of age priming was moved from 172 to 0 DBP
(Fig. 2D). The yield of U.S. No. 1 tubers (>113 g) increased by 11.2 MT ha-1 (from 69.5 to 80.7
MT ha-1) as the timing of age priming moved from 172 to 0 DBP. Marketable yield (U.S. No. 1
+ <113-g tubers) averaged 90 MT ha-1 and was not affected by seed age.
A constant marketable yield (Fig. 2D) in conjunction with substantial effects of the
timing of age priming on tuber set and average weight (Fig. 2C) reflects significant shifts in
overall tuber size distribution (Table 2). Tuber size distribution profiles of the 600-DD seed
primed at 172 or 39 DBP were compared with that of non-aged seed on a percent of marketable
yield basis. The non-aged control seed (80 DD, 0 DBP in Fig. 3) averaged 2.9 stems per
seedpiece and produced a significantly higher percentage of >284-g tubers and a lower
percentage of <170-g tubers than either of the 600-DD seed treatments (P<0.01) (Fig. 3). In
contrast, seed primed 172 DBP averaged 5.5 stems and the increased tuber set (Fig. 2C, Table 2)
associated with this decrease in apical dominance shifted the yield profile away from larger
(>284-g) tubers to favor higher percentage yield of tubers less than 170 g (P<0.01) (Fig. 3).
However, seed primed 39 DBP performed as physiologically younger seed, producing fewer
stems and a tuber size distribution favoring larger size tubers than seed primed 172 DBP
(P<0.01). The tuber size distribution of seed aged 39 DBP was thus intermediate to that
characteristic of non-aged seed and seed primed 172 DBP. These data indicate that the efficacy
of a high temperature-induced accelerated aging treatment in stimulating PAGE changes from
harvest to planting. Therefore, the ultimate PAGE (as defined by subsequent effects on crop
growth and development) for a given number of DD at a particular temperature, depends on the
timing of exposure to the aging treatment during storage.
78
The extent to which the timing of age priming (600 DD, 32oC, 21 days) affected the
metabolic rate of ‘Ranger Russet’ tubers was determined by comparing the respiration rates of
seed aged 172 and 39 DBP with that of non-aged (80 DD) seed over the final 131 days of
storage. Seed primed 172 DBP had a 28% higher rate of respiration than non-aged seed from 66
(Dec. 8) to 194 days (Apr. 18) of storage at 4oC (2.46 vs. 1.92 mg CO2 kg-1 h-1, P<0.01) (Fig. 4).
This metabolic response of ‘Ranger Russet’ tubers to high temperature-induced aging early in
storage was thus consistent with that characterized for ‘Russet Burbank’ (Fig. 1). Increasing the
storage temperature from 4oC to 32oC 39 DBP induced a 12-fold increase in respiration rate
within the first 24 h (from 2.1 to 26.0 mg CO2 kg-1 h-1, P<0.01), followed by a 50% decrease
over the next 7 days as tubers established a new basal metabolic rate of 12.9 mg CO2 kg-1 h-1 at
the higher temperature during the 21-day priming period (Fig. 4). This acclimation response was
similar to that demonstrated for cv. Russet Burbank tubers when the temperature was increased
from 4oC to 22oC at the end of the storage season (Fig. 1). Following the 21-day priming
treatment at 39 DBP, the temperature was lowered to 4oC (at 171 days), resulting in an
immediate decrease in respiration rate from 12.9 to 1.6 mg CO2 kg-1 h-1 (P<0.01) (Fig. 4). The
respiration rate of the age-primed seed then increased 49% over the next 10 days (P<0.01) as the
seed established a new basal metabolic rate at 4oC, which was equal to that displayed by the seed
subjected to the same 32oC age-priming treatment administered 172 DBP. From 182 to 194 days
in storage, the respiration rates of seed aged 172 and 39 DBP averaged 2.48 and 2.40 mg CO2 kg1
h-1, respectively, and were not significantly different (Fig. 4 and inset). Hence, regardless of
whether the age priming treatment was given at the beginning of storage (172 DBP) or end of
storage (39 DBP), tubers responded with an equivalent increase in metabolic rate. The only
difference between the two aging treatments was the length of time the basal metabolic rate
79
remained elevated. Relative to non-aged (80 DD) seed, the seed aged 172 DBP maintained a
28% higher basal metabolic rate for at least 131 days of storage at 4oC (Dec. 8 to Apr. 18). In
contrast, seed aged 39 DBP maintained a 28% higher basal metabolic rate over the final 2 weeks
of storage at 4oC compared with non-aged seed. As demonstrated by the developmental data in
Table 2 and Figs. 2 and 3, the 600 DD seed aged 39 DBP was physiologically younger than the
seed aged 172 DBP. Collectively, these results suggest that tuber respiration rate is the
‘pacemaker’ of aging; the longer the basal metabolic rate remains elevated prior to planting, the
more advanced the PAGE.
Effects of low oxygen storage on PAGE
To further elucidate the role of basal metabolic rate in dictating the PAGE of seed, seedtubers were age-primed for 600 DD (32oC, 21 days) 172 DBP and then stored at 21 or 3.5% O2.
The low O2 treatment was imposed to counter the increase in respiration rate induced by the age
priming treatment. Effects on respiration rates and developmental indicators of PAGE were
evaluated.
Storage in 3.5% O2 altered the PAGE of the 80- and 600-DD seed-tubers, as evidenced
by significant effects on in-season development and yield over the 4-yr study period. Overall,
the reduced oxygen atmosphere resulted in PAGE’s characteristic of younger seed-tubers than
when stored under normal (21% O2) atmospheric conditions (Table 3). Consistent with previous
results, age-primed (600 DD) seed of both cultivars stored at 21% O2 produced increased stems
(83% on average), resulting in increased tuber set per plant (27% on average) and lower average
tuber weight (22% on average) compared with non-aged (80 DD) seed (P<0.01). Total and
marketable (U.S. no. 1 + <113-g tubers) yields were not affected by age-priming in ‘Ranger
Russet’; however, the 600-DD ‘Russet Burbank’ seed produced ca. 9% lower yields than the
80
non-aged seed at 21% O2. Tuber size distributions produced by the 600 DD seed of both
cultivars stored in 21% O2 shifted as a percentage of marketable yield to favor increased yields
of tubers <170 g relative to non-aged seed (P<0.01) (Fig. 5, Table 3).
Storage of the 80- and 600-DD seed in 3.5% O2 effectively increased apical dominance
(reduced stem numbers) by 13 and 26%, respectively, relative to the same treatments stored in
21% O2 (Age x O2, P<0.01) (Table 3). This interaction was also apparent for the number of
tubers set per plant; storage of seed in 3.5% O2 decreased tuber set by an average of 0.8 tubers
(P<0.05) in plants produced by 600 DD seed versus no change in 80-DD seed. The result of the
age-attenuating effects of 3.5% O2 on stem numbers and tuber set was a 7% increase in tuber
weight (P<0.01) averaged across cultivar and seed age. Oxygen concentration had no effects on
total and marketable yields. However, relative to the 600-DD ‘Ranger Russet’ and ‘Russet
Burbank’ seed stored at 21% O2, tuber size distributions from plants produced by the 600 DD
seed stored at 3.5% O2 favored higher yields of >284-g tubers as a percentage of marketable
yield (Fig. 5). The age-primed, 600 DD seed of both cultivars stored under low O2 thus behaved
as physiologically younger seed when compared with that stored under ambient (21%) O2.
The PAGE-modifying affects of low O2 storage, as demonstrated by effects on apical
dominance, tuber set and size distribution (Table 3, Fig. 5), were compared with the effects of
low O2 on tuber metabolic rates during storage. Storage in 3.5% O2 reduced the respiration rates
of seed substantially and to the same extent regardless of DD accumulation (29% on average,
2.19 mg CO2 kg-1 h-1 vs 1.55 mg CO2 kg-1 h-1; P<0.01) (Fig. 6 and inset). While the 600 DD
age-primed seed stored at 3.5% O2 maintained a comparable (non significantly different) basal
respiration rate to 80 DD seed stored at 21% O2 through most of storage, its PAGE was
significantly more advanced. The inability of low O2 storage to completely counter the advanced
81
PAGE induced by the 600-DD treatment is attributable to the substantially high respiration rate
(ca. 4-fold increase) and associated aging experienced by the seed during the 21-day priming
treatment at 32oC 172 DBP. Tuber metabolic (respiration) rate thus appears to be the pacemaker
that at least partly controls the rate of aging. Treatments that modify tuber respiration rate (e.g.
temperature, low O2) also affect the rate of aging and the ultimate PAGE.
In an additional study, seed given 600 DD (ca. 172 DBP) and held under 3.5% oxygen
for 148 days at 4oC, was then moved to 21% oxygen and stored an additional 17 days to
determine any residual effects of the initial age-priming treatment on metabolic rate upon return
to normal atmosphere conditions. Respiration rate of the age-primed seed while at 3.5% O2 was
approximately equal to that of the 80 DD seed at 21% O2 (average = 2.11 mg CO2 kg-1 h-1)
immediately prior to restoring the O2 to 21%. After 5 days (153 days total storage) at 21% O2,
respiration of the age-primed seed had increased to become 42% higher than the 80 DD (21%
O2) seed and 12% higher than the 600 DD seed stored continuously at 21% O2. Twelve days
later (165 days total storage) the 600 DD seed previously held at 3.5% O2 had a respiratory
output within 0.09 mg CO2 kg-1 h-1 of the 600 DD seed stored continuously at 21% O2 and 29%
greater than the 80 DD control seed stored at 21% O2. While the metabolic rate of the 600 DD
age-primed seed was temporarily reduced by storage in low O2, the tubers ‘remembered’ the
initial (172 DBP) age priming treatment as indicated by restoration of the age-induced increase
in tuber respiration rate upon return to 21% O2. These results are thus similar to those in the
timing of age priming study where the 600 DD treatment induced the same increase in basal
metabolic rate regardless of whether given at the beginning (172 DBP) or end (39 DBP) of
storage (Fig. 4). Storage of the age-primed seed in 3.5% O2 reduced the respiration rate over
time, thus resulting in a younger PAGE. These results support respiration as the pacemaker of
82
PAGE. The longer the basal respiration rate of tubers remains high during storage, the more
advanced the PAGE. Altering the length of time age-primed seed maintains a high metabolic
rate, either by lowering the O2 concentration or moving the priming treatment later in storage,
significantly modifies the PAGE as assessed by developmental and productivity indicators of
PAGE in the field.
Discussion
Developing robust measures of PAGE for seed potatoes will likely require a deeper
understanding of the physiological responses of tubers to environmental conditions following
their growth. Accurate assessment of PAGE before planting would facilitate targeting seed lots
to specific growing regions to fulfill production goals for tuber size distribution and yield in
relation to market requirements. To date, many studies have focused on developing methods for
predicting PAGE (Coleman 2000; Struik 2006) but environmental and cultural conditions often
confound the results and have a direct impact on the true PAGE (Caldiz 2009). Most proposed
measures of PAGE incorporate either physical aspects of the growing and postharvest
environments into thermal indices (e.g. temperature, time, DD) or rely on various developmental
indices (e.g. sprouting capacity; incubation period) (Coleman 2000 and references therein),
without factoring in the physiological responses of tubers over time. Better elucidation of the
physiological bases of aging may lead to the development of more effective measures of PAGE.
We demonstrated that temperature, timing, and duration of exposure of seed-tubers to age
priming treatments alters tuber metabolic rate, which in turn affects the ultimate PAGE. Degree
day accumulation above the 4oC base temperature accelerates aging; however, in the absence of
information on temperature, DD are inadequate for describing the PAGE of seed tubers. The
temperature at which DD accumulate is of paramount importance in dictating the final PAGE
83
and associated productive potential of seed for a particular cultivar (Knowles and Knowles
2006). Hence, soil temperature during maturation of tubers under dead vines at season end, field
heat during harvest, and storage temperature during wound healing and the main holding period
collectively affect tuber metabolic rate and, potentially, the definitive PAGE.
The studies reported herein demonstrate unequivocally that seed responds to high
temperature age priming treatments with higher metabolic rate, not only concurrent with the high
temperature exposure but also after the temperature has been lowered to the base level of 4oC.
Aging induced by high temperature priming thus has two components – the accelerated aging
that occurs directly as a result of the increased metabolic rate during incubation at the elevated
temperature and a latent effect wherein the high temperature has affected changes in tuber
metabolism such that respiration remains relatively high, even after the age-priming stimulus has
been removed. In essence, tubers have ‘remembered’ the high temperature age priming
treatment as reflected by their elevated metabolic rate after the aging stimulus has been removed.
The duration of the age priming treatment (i.e. length of time the high temperature
treatment is applied) and the subsequent duration of storage before planting (latent period) likely
interact to define the PAGE at planting. In terms of the effects of the high temperature priming
treatment on basal metabolic rate, seed-tubers were just as responsive at the end of storage as
they were at the beginning of storage. Therefore, it is inaccurate to say that tubers are less
responsive to an age-priming treatment late in the storage season. In addition to the actual
temperature, the important factors dictating PAGE are the duration of exposure (incubation)
during the high temperature priming treatment and the duration of the latent period following the
age priming treatment. When stored for ca. 200 days, seed given the same priming treatment
progressively later in storage (e.g. 39 DBP) was physiologically younger than seed primed early
84
(e.g. 172 DBP) in storage and four distinct PAGE’s were created by simply moving the age
priming treatment later toward planting. Likewise, manipulating the higher metabolic rate of
age-primed seed by storing in 3.5% O2, lowered the otherwise age-enhanced basal respiration
rate during the latent period, thus reducing the total duration of high basal metabolic rate during
the storage period, which attenuated the aging process and resulted in distinctly younger seed
lots as characterized by the growth and productivity data from field trials. Hence, respiration
rate appears to be the ‘pacemaker’ of aging and the duration it is maintained at a specific level is
critical for determining PAGE of seed potatoes. An accurate measure of seed PAGE may thus
be the total respiratory output integrated over time from vine kill (when tubers cease growing)
through maturation, wound healing and storage to planting. It is worth reiterating that cultivars
vary in their sensitivity to high temperature-induced age priming. Cultivars Ranger Russet and
Russet Burbank are highly sensitive whereas Chieftain and Satina (and others) are relatively
insensitive (Knowles and Knowles 2006). The nature of these differences in relation to
respiratory metabolism is currently under investigation.
Conclusions
While PAGE of potato tubers is affected by numerous environmental and cultural
conditions as well as genotype, the basal metabolic rate over time, as indicated by the respiration
rate may provide a good measure of PAGE. To date, accounting of heat unit accumulation has
been considered one of the better measures of PAGE, but the relative intensity, duration and
timing of the heat can dramatically alter the PAGE. Respiratory output from vine-kill through
storage to planting is a core physiological response that reflects exposure to these variables and
when combined with information on heat unit accumulation may be more indicative of PAGE.
Tuber respiration rate appears to be the ‘pacemaker’ (clock) of aging in potato tubers and
85
additional work to define the mechanism(s) by which age priming treatments enhance tuber
metabolic rate may lead to the development of more robust biochemical or molecular markers of
physiological age. Such markers would be useful to facilitate management decisions to optimize
yield and tuber size distribution or in breeding programs to select cultivars with differential
resistance to environmental conditions that promote aging.
Acknowledgements
We gratefully acknowledge financial support from the Washington State Department of
Agriculture Specialty Crop Block Grant Program, USDA-ARS State Partnership Potato
Program; Washington State Potato Commission; and the Washington State University
Agricultural Research Center to NRK.
86
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90
Table 1. Effects of high-temperature age-priming
treatments at the beginning of storage on sprout
development of ‘Russet Burbank’ tubers at the end of
storage. Seed-tubers were given 450 degree days (4oC)
base) at 12, 22 and 32oC in October directly following
harvest. The tubers were then stored at 4oC until April 25.
The temperature was then increased to 22oC to stimulate
growth of etiolated sprouts over the final 3 weeks of
storage (until May 16). *,**P<0.08 and 0.05 for
correlation coefficient, respectively. Tuber respiration
rates are shown in Fig. 1.
Priming
Temperature
Russet Burbank Sprout Growth
Number
Dry wt
Length
C
no. tuber-1
mg tuber-1
cm tuber-1
12
2.5 ±0.5
120 ±6
3.7 ±0.8
22
3.5 ±0.5
180 ±14
5.2 ±0.1
32
5.0 ±1.0
267 ±28
7.1 ±2.3
0.99*
0.99**
0.99*
o
R2
91
92
U.S. no. 1 yield >113g.
NS
87.7
89.9
91.3
91.5
90.1
0.01
5.4
68.7
71.8
75.9
76.3
80.8
0.01
0.01
0.10
0.05
1.7
19.0
17.9
15.1
14.8
9.2
0.05
0.01
0.01
2.2
21.1
22.1
19.7
20.1
14.0
Significance levels for polynomial trends (P<0.01, 0.05 or 0.10; NS, non-significant)
d
Polynomial trend
c
Linear
Quadratic
Cubic
Deviations
Plant emergence at 32 DAP.
b
a
0.01
0.10
d
0.01
0.5
14.2
c
LSD0.05
5.5
4.9
4.5
4.1
2.9
52
41
28
21
17
172
128
84
39
0
Oct 23
Dec 6
Jan 19
Mar 5
-
92
0.10
2.9
28.3
28.6
30.8
30.6
30.2
0.01
1.8
6.1
6.7
8.0
7.6
10.7
0.01
2.2
4.0
4.3
5.6
6.2
8.3
0.01
0.10
3.3
9.1
10.1
11.8
11.9
17.7
Tuber Yields (MT ha-1) (3-yr average 2009-11)
Stems
plant-1 Total U.S. #1b <113 g 113-170 g 170-284 g 284-340 g 340-397 g >397 g
DBP
Emerg.a
(%)
Date
Age Priming
U.S. #1 + <113-g Tubers
0.01
0.2
0.1
0.2
0.3
0.3
0.1
0.01
0.01
0.05
0.05
8.2
154
158
169
172
202
0.01
0.05
0.9
12.6
12.5
11.8
11.6
9.8
0.01
0.05
39
572
568
540
532
448
Culls g tuber-1 plant-1 1000’s ha-1
plotted in Fig. 2. Tuber size distributions of early and late age priming treatments are compared with the non-aged control Fig. 3.
interval. Data are averaged over three growing seasons (2009-11) in the Columbia Basin of WA. Emergence, stem number, tuber set and yield data are
was stored the entire season at 4oC. The four aged seed lots each accumulated 600 degree days (4oC base) at different times over the 200-day storage
given to separate samples on Oct. 23 (172 days before planting, DBP), Dec. 6 (128 DBP), Jan 19 (84 DBP), and Mar. 5 (39 DBP). Control (non-aged) seed
and wound-healed at 12oC (95% RH) for 10 days. The seed was then stored at 4oC, except for brief (21-day) age priming treatments at 32oC (95% RH)
Table 2. Timing of age priming during the storage season affects developmental indicators of PAGE. ‘Ranger Russet’ seed-tubers were acquired at harvest
93
U.S. no. 1 yield >113g.
d
0.05
0.01
0.01
0.01
0.01
0.01
0.5
3.2
2.8
5.9
4.1
2.6
2.3
4.7
3.7
0.01
0.01
0.01
4.9
82.5
85.2
75.5
71.7
90.8
92.1
91.0
92.4
0.01
0.01
0.05
0.01
5.2
70.2
74.0
56.0
56.9
81.6
83.8
74.9
79.4
0.01
0.01
0.01
0.01
0.01
1.3
11.6
10.8
18.3
13.1
8.1
7.3
15.9
12.2
0.05
0.01
0.01
0.01
0.01
1.7
16.6
17.0
20.7
18.4
11.4
10.6
19.4
17.4
93
0.01
0.05
2.8
30.5
29.6
23.8
24.7
27.6
26.0
30.7
30.3
0.01
0.01
1.9
8.7
9.0
4.8
5.7
12.1
12.2
8.4
9.0
0.01
0.01
0.10
1.5
5.4
6.4
2.5
3.0
8.9
8.5
5.4
7.0
0.01
0.01
0.01
0.01
0.10
3.0
8.9
11.9
4.2
5.2
21.7
26.5
10.8
15.6
0.05
1.1
0.6
0.4
1.2
1.6
1.1
1.0
0.3
0.8
0.01
0.01
0.01
0.01
7.4
175
182
142
155
217
229
166
182
0.05
0.01
0.01
0.01
0.01
0.5
10.3
10.2
12.5
11.9
9.1
8.8
12.1
11.1
0.01
0.10
0.10
0.01
0.01
0.01
22
468
465
526
451
414
399
550
504
U.S. #1 + <113-g Tubers
Tuber Yields (MT ha-1) (4-yr average 2008-11)
Stems
plant-1 Total U.S. #1b <113 g 113-170 g 170-284 g 284-340 g 340-397 g >397 g Culls g tuber-1 plant-1 1000’s ha-1
Significance levels for the various sources of variation (P<0.01, 0.05 or 0.10)
d
Sources of variation
c
8.6
LSD0.05
0.01
0.01
21
21
15
20
47
37
67
71
21
3.5
21
3.5
CV
Age
Oxygen
CV x Age
CV x O2
Age x O2
CV x Age x O2
c
600
80
21
3.5
21
3.5
Emerg.a
(%)
Plant emergence at 33 DAP.
b
a
RB
80
RR
600
Age
CV
O2
(%)
tuber size distributions are summarized in Fig. 5 for selected treatments of each cultivar.
period. The field plots were maintained under late season management and tops were mowed at ca. 155 DAP. The effects of seed age and O2 concentration on
until planting in mid-April. Plant emergence and above ground stem numbers were assessed ca. 33 and 55 days after planting, respectively, over the 4-yr study
DD). Following the 600-DD age priming treatments, the 80- and 600-DD seed of each cultivar was stored at 4oC in an atmosphere of 21 or 3.5% O2 (balance N2)
(95% RH) for the remainder of a ca. 200-day storage period (80 DD non-aged control seed) or given an age priming treatment at 32oC (95% RH) for 21 days (600
Ranger Russet (RR) and Russet Burbank (RB) seed-tubers. Seed-tubers were initially wound-healed at 12oC for 10 days following harvest and then placed at 4oC
Table 3. Effects of seed age and oxygen concentrations during storage on plant emergence, stem numbers, tuber set, yields, and tuber size distributions of cvs.
Fig. 1. Effects of high temperature age priming treatments at the beginning of storage on
respiration rates of cv. Russet Burbank tubers at the end of storage. Seed-tubers were woundhealed at 12oC for 10 days directly following harvest in late September and then stored at 12, 22
and 32oC (95% RH) for 48, 20 and 13 days, respectively, to accumulate 450 DD. Following age
priming, the seed was held at 4oC until April 25 (ca. 200-day storage period). Respiration rates
were compared from March 30 to April 25 at 4oC (inset). Note that tubers primed at higher
temperatures at the beginning of storage had higher respiration rates at the end of storage. The
storage temperature was increased to 22oC on April 25 and respiration rates were quantified
during the early stages of sprouting until the study was terminated on May 16. Gray bars are
±SE (shown every 28 h to retain clarity). Apical dominance and sprout growth data are
presented in Table 1.
94
(mg CO2 kg h )
-1
o
-1
-1
-1
Tuber Respiration (mg CO2 kg h )
24 Russet Burbank
22
450 DD
3.0
450 DD
12oC, 48 d
20
22oC, 20 d
32 C
32oC, 13 d
2.5
18
16
22 C
2.0
14
12 C
12
Apr 25
1.5 Mar 30
10
0
4
8
12
16
20
24
28
Days
8
6
Apr 25
May 16
4 Mar 30
4oC
22oC
2
0
0 4 8 12 16 20 24 28 32 36 40 44 48
o
o
Days
95
Fig. 2. Plant emergence (A), stem numbers (B), tuber set and average tuber FW weight (C), and
total and marketable (U.S. no. 1 + <113-g tubers) yields (D) depend on the timing of an age
priming treatment (21 days at 32oC) during the storage season (190-200 days). ‘Ranger Russet’
seed-tubers were acquired at harvest and wound-healed at 12oC (95% RH) for 10 days. The seed
was then stored at 4oC, except for brief (21-day) age priming treatments at 32oC (95% RH) given
to separate samples on Oct. 23 (172 days before planting, DBP), Dec. 6 (128 DBP), Jan 19 (84
DBP), and Mar. 5 (39 DBP). Control (non-aged) seed was stored the entire season at 4oC. The
four aged seed lots each accumulated 600 degree days (4oC base) at different times over the 190200-day storage intervals. Data are averaged over three growing seasons (2009-11) in the
Columbia Basin of WA. Bars indicate ±SE. **P<0.01 for correlation coefficients; ns, not
significant. Tuber size distributions for seed aged 172 and 39 DBP versus non-aged seed are
presented in Fig. 3.
96
Ranger Russet
5.5
Stems per Seedpiece
50
40
30
2
R = 0.99**
20
10
Oct 23
Dec 6
Jan 19
Mar 5
172
128
84
39
2
R = 0.97**
3.5
0
210
(Days Before
Planting)
-1
tubers plant
2
R = 0.93**
12.0
11.5
180
11.0
170
10.5
g tuber
160
-1
2
150
Oct 23
Dec 6
Jan 19
Mar 5
172
128
84
39
Dec 6
Jan 19
Mar 5
172
128
84
39
0
(Days Before Planting)
R = 0.93**
9.5
Oct 23
D 110 Ranger
Russet of Aging Treatment
Beginning
200
190
9.0
4.0
2.5
Begining of Aging Treatment
12.5
10.0
4.5
3.0
C 13.5
13.0
5.0
0
100
Tuber Yield (MT/ha)
0
Tubers per Plant
B 6.0
Ranger Russet
-1
% Plant Emergence (32 DAP)
60
A
90
2
R = 0.50ns
Marketable Yield
80
R2 = 0.96**
70
US #1 Yield
60
50
Oct 23
Dec 6
Jan 19
Mar 5
172
128
84
39
Beginning of Aging Treatment
Beginning of Aging Treatment
97
0
Fig. 3. Polygonal plots illustrating the effects of aging seed-tubers at the beginning or end of a
190-200-day storage season on the tuber size distributions produced by cv. Ranger Russet seedtubers in the Columbia Basin of WA. Seed-tubers were acquired at harvest and wound-healed at
12oC (95% RH) for 10 days. The seed was then stored at 4oC, except for brief (21-day) age
priming treatments at 32oC (95% RH) given to separate samples on Oct. 23 (172 days before
planting, DBP) and Mar. 5 (39 DBP). Control (non age-primed) seed was stored the entire
season at 4oC. The aged seed lots each accumulated 600 DD (4oC base) during storage. The
yield axes for the six tuber weight classes ranges from 0 to 32% of marketable yield (U.S. no. 1 +
<113 g tubers), which was not affected by treatment (inset). For clarity, only the <113-g tuber
yield axis is labeled. Note that the non age-primed control seed (blue polygon) produced the
fewest number of stems (P<0.01). Seed aged 172 DBP (red polygon) produced the most stems
(5.5), which resulted in the greatest shift in tuber size distribution toward smaller tubers
(P<0.01). Imposing the age-priming treatment 39 DBP (green polygon) resulted in less stems
than the 172-DBP treatment (P<0.01) and a size distribution profile favoring larger size tubers.
Other developmental and yield indicators of PAGE are presented in Table 2 and Fig. 2. Data are
averaged over three growing seasons (2009-11). Respiration rates of the 600 DD seed primed
172 and 39 DBP are compared with that of non-aged seed in Fig. 4.
98
< 113g
32
% Yield
Ranger Russet
28
24
5.5 stems
20
>397g
113-170g
16
12
Age
Priming
(DBP)
Yield
(MT ha-1)
0
90
172
88
39
91
4.1 stems
8
2.9 stems
4
0
170-284g
340-397g
284-340g
99
Fig. 4. Effects of aging seed-tubers at the beginning or end of a 194-day storage season on the
basal metabolic (respiration) rates of tubers during storage. Seed-tubers were acquired at harvest
and wound-healed at 12oC (95% RH) for 10 days (80 DD). The seed was then stored at 4oC,
except for a brief (21-day) age priming treatment at 32oC (95% RH) on Oct. 23 (172 days before
planting, DBP) or Mar. 5 (39 DBP). The aged seed lots thus accumulated 600 DD (4oC base)
during storage. The non age-primed control seed was stored the entire season at 4oC (80 DD).
Tuber respiration rates were compared over the final 131 days of storage from Dec. 8 to April
18. The 600 DD tubers primed 172 DBP had a higher respiration rate than non-aged tubers over
the entire assessment period (P<0.01). The inset table compares the average respiration rates at
4oC before and after the 39 DBP priming treatment. Letters indicate mean separation by LSD at
P<0.01 and 0.05 for the 66-150 and 182-194 day storage periods, respectively. Note that
administering the age priming treatment 39 DBP induced tubers to establish a new basal
respiration rate over the final two weeks of storage equal to that of seed primed 172 DBP. Gray
bars are ±SE (shown every 40 h to retain clarity). The upward drift in respiration rates from ca.
145 to 173 days in storage was in response to a ca. 1oC increase in storage temperature caused by
a temperature control valve malfunction, which was subsequently fixed. Developmental, yield
and tuber size distribution data are presented in Table 2 and Figs. 2 and 3.
100
-1
-1
Tuber Respiration (mg kg h )
24.0
20.0
16.0
12.0
Ranger Russet
3.6
1.6
DBP
Respiration
(mg kg-1 h-1)
66-150
80
600
600
-172
39
1.85a
2.36b
1.97a
80
600
600
-172
39
1.89a
2.48b
2.40b
32oC
600 DD
39 DBP
600 DD
172 DBP
4oC
4 oC
2.4
2.0
DD
182-194
3.2
2.8
Days
80 DD
Dec 8
Apr 18
60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Days in Storage (4oC)
101
Fig. 5. Polygonal plots illustrating the shifts in tuber size distribution of 600-DD ‘Ranger
Russet’ (A) and ‘Russet Burbank’ seed stored at 21 and 3.5% O2 versus non-aged (80 DD) seed.
Seed-tubers were acquired at harvest and wound-healed at 12oC (95% RH) for 10 days. The
seed was then stored at 4oC, except for a 21-day age priming treatment at 32oC (95% RH)
administered 172 days before planting (DBP). Yields for the six tuber weight classes are
expressed as percent of marketable yield (U.S. no. 1 + <113 g tubers), which was not affected by
DD or O2 concentration for ‘Ranger Russet’ (inset A). Marketable yield of the 600 DD ‘Russet
Burbank’ seed was 12% lower compared with the non-aged 80 DD seed (inset B; letters indicate
P<0.05). For clarity, only the <113-g tuber yield axes are labeled. The non age-primed control
seed (blue polygons) produced the fewest number of stems (P<0.01). Seed aged 172 DBP (red
polygons) produced the most stems (4.7 and 5.9 for ‘Ranger Russet’ and ‘Russet Burbank’,
respectively), which resulted in the greatest shifts in tuber size distribution toward smaller tubers.
Storing the age-primed 600-DD seed at 3.5% O2 (green polygons) resulted in fewer stems than
the 600 DD seed stored at 21% O2 (P<0.01) and a size distribution profile favoring larger tubers.
The developmental, yield and tuber size distribution data are presented in Table 3 with ANOVA
results. Data are averaged over four growing seasons (2008-11) in the Columbia Basin of WA.
Tuber respiration rates during storage are shown in Fig. 6.
102
< 113 g
Ranger Russet
% Yield
A
< 113 g
32
Russet Burbank
28
B
24
20
>397 g
% Yield
4.7 stems
113-170 g
>397 g
16
3.7 stems
Seed Age
Yield
[O2] (MT ha-1)
(DD)
80
600
21%
21%
90
91
600
3.5%
92
12
Seed Age
Yield
[O2] (MT ha-1)
(DD)
8
4
2.6 stems
0
340-397 g
170-284 g
284-340 g
80
600
21%
21%
82a
74b
600
3.5%
70b
3.2 stems
36
32
28
24
20
16
12
8
4
0
5.9 stems
4.1 stems
340-397 g
170-284 g
284-340 g
103
113-170 g
Fig. 6. Effects of seed age (DD) and oxygen concentrations on the basal metabolic (respiration)
rates of ‘Ranger Russet’ seed-tubers during storage. Seed-tubers were initially wound-healed at
12oC for 10 days following harvest and then placed at 4oC (95% RH) for the remainder of a 194day storage period (80 DD non-aged seed) or given an age priming treatment at 32oC (95% RH)
for 21 days (600 DD) starting 172 DBP. Following age priming, the 80- and 600-DD seed was
stored at 4oC in an atmosphere of 21 or 3.5% O2 (balance N2) until planting in mid April. Tuber
respiration rates were compared over the final 131 days of storage. The inset table compares the
respiration rates averaged over time. Letters indicate mean separation by LSD (P<0.01). The
effects of DD (age) and O2 concentration were significant at P<0.01. Gray bars are ±SE (shown
every 40 h to retain clarity). The upward drift in respiration rates from ca. 145 to 173 days in
storage was in response to a ca. 1oC increase in storage temperature caused by a temperature
control valve malfunction, which was subsequently fixed. The developmental, yield and tuber
size distribution data are presented in Table 3 and Fig. 5.
104
-1
-1
Tuber Respiration (mg kg h )
4.4
Ranger Russet
DD
[O2]
Respiration
(mg kg-1 h-1)
3.6
80
3.2
600
21
3.5
21
3.5
1.92b
1.40a
2.46c
1.70ab
4.0
2.8
2.4
2.0
600 DD
21% O2
80 DD
21% O2
1.6
600 DD
3.5% O2
1.2
80 DD
3.5% O2
0.8
Dec 2
Apr 18
0.4
60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Days in Storage (4oC)
105
CHAPTER 3
Manipulating Stem Number, Tuber Set and Size Distribution in Specialty Potato Cultivars1
Abstract
Controlling tuber size distribution in potato production can substantially increase crop value.
Tuber set and size development are directly related to the number of stems produced per
seedpiece (degree of apical dominance). As stem number increases, tuber set increases and
average tuber size decreases. For many cultivars, manipulating seed physiological age is an
effective method to alter tuber set and size distribution. However, as demonstrated here,
cultivars Cal White, Red La Soda, Chieftain, Yukon Gold, and Satina were largely insensitive to
high temperature-induced age-priming treatments. Gibberellins (GA) break dormancy and
reduce apical dominance in potato and thus also have potential for altering tuber set and size
development. When applied to cut seed of the five cultivars, GA hastened plant emergence,
increased stem numbers and tuber set, and decreased average tuber size. The optimum
concentration of GA for shifting tuber size distribution to maximize crop value without
decreasing total yield depended on cultivar. Total yields decreased substantially in all cultivars
with 10 mg L-1 GA but lower concentrations (0.5-4 mg L-1) either increased yields of Red La
Soda, Yukon Gold, Chieftain and Satina by 11, 13, 15, and 24%, respectively, or had no effect
(Cal White). GA-induced increases in tubers per hectare ranged from zero (Cal White, Satina) to
36% (Chieftain) and associated increases in yields of premium priced creamer (C size; 10-66-g,
28-51-mm diameter) potatoes ranged from 0 to 140%, depending on cultivar and duration of the
growing season. Tuber yields and the efficacy of GA in shifting size distributions were highly
dependent on length of the growing season. Increases in total crop value ranged from 7 to 30%
(Chieftain) with the optimum concentration of GA, which varied by cultivar. Effective use of
106
GA to alter tuber size distribution for increased value depends on cultivar, concentration, and
harvest timing.
1
To be submitted to the American Journal of Potato Research 2013.
Blauer, J.M., L.O. Knowles, and N.R. Knowles. 2013. Manipulating Stem Number, Tuber Set
and Size Distribution in Specialty Potato Cultivars. American Journal of Potato Research. (In
draft).
107
Introduction
The degree of apical dominance (i.e. stem number per seedpiece), tuber set, and tuber size
distribution are directly correlated in potato (Solanum tuberosum L.). As stem numbers increase,
plants set more tubers and average tuber size decreases (Iritani et al. 1983; Knowles and
Knowles 2006). Since tubers are packed and marketed according to size (weight and/or
diameter), which largely determines crop value, developing methods to reliably manipulate and
control apical dominance, tuber set and size distribution are important to the potato industry.
Fresh market potatoes are graded according to weight and/or diameter and are often
packed into 22.7-kg (50-lb) cartons with returns dependent on carton count. Tubers less than 51mm diameter (‘creamers’) bring a premium price as baby potatoes for their higher nutritive
values and for use in the gourmet restaurant trade. In the seed industry, smaller tubers result in
less waste and ‘blind’ seedpieces when cut for planting, and premiums are often paid for small
single-drop (whole) seed. Optimal tuber size distributions thus depend on the market (seed,
fresh, processing). Target stem number and tuber set relationships exist for every production
region and market niche, where size distribution can be optimized for maximum profitability of a
particular cultivar in relation to the climatic constraints of the growing environment (Knowles
and Knowles 2006).
Adjusting seed spacing (between and within-row) (Arsenault et al. 2001; Bussan et al.
2007; Iritani et al. 1972), cultivar selection (Struik et al. 1990), and manipulating the
physiological age of seed-tubers (Caldiz 2009; Knowles and Knowles 2006; Struik et al. 2006)
are effective methods for altering tuber set and size distribution. Flexibility in choosing a
cultivar is often limited, however, as selection is frequently dictated by market demand and
growers respond accordingly. Similarly, while manipulating the physiological age of seed is
108
effective for many russet cultivars, some cultivars are recalcitrant to aging treatments and no two
cultivars perform alike (Knowles and Knowles 2006; and data herein).
Plant growth regulators (PGR) offer an alternative approach to altering stem number,
tuber set and size distribution relationships (Knowles et al. 1985; Struik et al. 1999). Several
auxin- and GA-based PGR products that affect tuber set and size development are commercially
available; however, lack of cross-market efficacy data has restricted their use to particular
markets (e.g., seed potatoes) and application rates have not been optimized for individual
cultivars in relation to specific requirements for tuber size. Cultivar response is fundamental for
defining application rates to effectively control apical dominance, tuber set and size distribution
without negatively affecting overall yields. A better understanding of cultivar-dependent
responses is critical for using PGRs to manipulate tuber size distribution for added value.
Here we report the extent to which seed physiological age and GA treatment of cut seed
can be used as potential management techniques to manipulate tuber size distribution for added
value in the production of five specialty potato cultivars (red/yellow) for seed and fresh markets.
The main beneficiaries of the work are seed potato growers and growers of red/yellow skin and
specialty potatoes for wholesale and retail domestic and export markets. In contrast to many
russet cultivars, apical dominance, tuber set and size development in cultivars Cal White, Yukon
Gold, Chieftain, Red La Soda, and Satina were relatively insensitive to heat-unit based storage
treatments designed to accelerate the physiological age of seed. However, GA applied to cut
seed prior to planting effectively altered stem number, tuber set and size distributions. GA
application rates need to be tailored in relation to cultivar, desired size distributions, and length
of growing season to maximize crop values based on market requirements. The results provide a
basis for redefining label rates and expanding the scope of registration of commercially available
109
products for use on potatoes destined for seed, fresh and processing markets. The use of GA to
increase yields of tubers in specific size classes is an effective approach to minimizing waste and
maximizing crop value.
Materials and Methods
Seed tubers, storage, aging and GA treatments
The effects of seed age and GA treatments on stem numbers, tuber set, and tuber size
distribution of cultivars Satina, Cal White, Yukon Gold, Red La Soda, and Chieftain were
evaluated in field trials at the Washington State University (WSU) Research and Extension Unit,
Othello, WA (46o 47.277’ N. Lat., 119o 2.680’ W. Long.) over a 4-yr period from 2009 to 2012.
Certified (G3, from nuclear stock) seed-tubers of each cultivar were acquired from a commercial
grower in October in each year of the 4-yr study (Table 1). Seed treatments depended on year
and are defined below. Detailed meteorological data for the 2009, 2010, 2011 and 2012 growing
seasons at the Othello, WA research site are available from the Washington Agricultural Weather
Network, AgWeatherNet (weather.wsu.edu/awn.php).
The effects of storage degree days (designed to advance the physiological age of seedtubers) on apical dominance, yields and tuber size distributions of the five cultivars were
evaluated in 2009. Aging treatments followed the methods of Knowles and Knowles (2006).
Briefly, all seed received a wound healing period at 12oC (95% RH) for 10 days (80-DD)
following harvest. Seed-tubers were then stored for 13-, 22-, and 46-days at 32, 22, and 12oC
(95% RH), respectively, resulting in the accumulation of 450-degree days (DD) at each
temperature. Seed samples were also stored for 29-, 45-, and 102-days at 32, 22, and 12oC (95%
RH), respectively, to accumulate 900-DD at each temperature. After the aging treatments, seed-
110
tubers were held at 4oC (95% RH) until planting. Control (young) seed-tubers (80-DD) were
stored at the base temperature of 4oC continuously following wound healing. At the end of
storage, seed-tubers were cut and planted into replicated field plots according to the schedule in
Table 1 and as described below (see field plot design and maintenance). These combinations of
time and temperature defined the seven age treatments, which were evaluated separately for each
cultivar in randomized complete block designs (five replicates) in the 2009 field trials.
In 2010, the effects of seed-tuber age and GA on apical dominance, tuber set, yields and
tuber size distributions were evaluated in two-factor factorial experiments consisting of two tuber
ages (80- and 900-DD) and two GA concentrations (0 and 10 mg L-1) arranged in randomized
complete block designs for each cultivar (five replicates). Seed-tubers of the five cultivars were
acquired in the fall and wound healed at 12oC (95% RH) for 10-days as described above. The
resulting 80-DD control (young) seed was then stored at 4oC (95% RH) until planting (Table 1).
A subset of the 80-DD seed was given an additional ca. 820-DD by storing at 18oC (95% RH)
for 51 days to create the 900-DD advanced age treatment. Following the aging treatments, seedtubers were stored at 4oC (95% RH) until cutting and treating with GA in April. GA3 (90%,
Sigma-Aldrich, St. Louis, MO) was solubilized (100 mg mL-1) in dimethyl sulfoxide (DMSO),
which was then used to prepare 12-L of 10 mg L-1 GA3 solution in water containing 0.1% Tween
20 (polyoxyethylene (20) sorbitan monolaurate). Cut seed was briefly rinsed in water prior to
immersing in the GA3 treatment solution for 5 min at room temperature. Control seed (0 mg L-1
GA3) was similarly treated with equal concentrations of DMSO solution containing 0.1% Tween
20. The seed was then air dried at room temperature and held at 9oC until planting (Table 1).
Apical dominance, tuber set, yield and tuber size distribution responses to a broad range
of GA concentrations were evaluated in 2011 and 2012. Seed-tubers were acquired in October
111
and stored at 4°C (95% RH) until cutting, treating and planting in April (Table 1). The cut seed
was wound healed at 9oC (95% RH) for 3 days in 2011 and 2 days in 2012 prior to treating with
0, 2, 4, and 8 mg L-1 GA3 in 2011 and 0, 0.5, 1, 2, and 4 mg L-1 GA3 in 2012. GA was applied as
described above. The effects of GA concentration were evaluated separately for each cultivar,
with treatments arranged in randomized complete block designs (five replicates) for field trials in
both years (see field plot design and maintenance).
Field plot design and maintenance
Following storage, seed-tubers (ca. 110-180-g each) were hand cut (50-64-g seed pieces),
blocked for apical and basal portions, treated as described above, and planted 20-cm deep in a
Shano silt loam soil (Lenfesty 1967) with a two-row assist feed-planter at the WSU Othello, WA
research unit, as previously described (Knowles and Knowles 2006). Rows were spaced 86-cm
apart with seed planted 25-cm apart within each row. A 1.3-m alley was left between each
treatment plot. Treatment plots were flanked on either side by guard rows of non-treated seed.
Twenty four seedpieces were planted per treatment plot and treatments were arranged in
randomized complete block designs (separate experiments for each cultivar) with five replicates
in all years. A single hill (i.e. one seedpiece) of cultivar All Blue was planted at the beginning
and end of each treatment plot to maintain interplant competition at the ends of plots and to
facilitate harvesting individual plots in the fall. Soil moisture was maintained with a linear-move
irrigation system at a minimum of 65% field capacity with the aid of soil tensiometers positioned
throughout the field. Pre-plant and in-season applications of fertilizer followed standard
practices for potato production in the Columbia Basin and were adjusted as needed based on soil
tests and petiole analyses, which were taken at ca. 7- to 10-day intervals starting post emergence
and extending through mid-July each season. Herbicide, insecticide, and fungicides were
112
applied according to standard practices. The time course of plant emergence and stem numbers
(Table 1) were determined prior to row closure, which occurred ca. mid June each year.
Harvesting and sorting
Vine-kill and harvest timing (Table 1) followed commercial practices for early season
production of the five cultivars in the Columbia Basin and, in 2011 and 2012, were aided by
hand digs to estimate and maximize the yields of smaller tubers (<113-g and C-size) while
maintaining commercially acceptable overall yields. Vines were cut with a flail type mower 90to 115-days after planting (DAP) (Table 1) and sprayed with diquat® to enhance desiccation.
Plots were harvested with a single-row mechanical harvester 10- to 22-days later (102- to 134DAP), depending on year and cultivar. Tubers were washed, individually weighed and counted
with a computer controlled sorter, and treatment effects on yields and tuber size distributions
were assessed on a 22.7-kg (50-lb) carton count basis as well as for “A”, “B” and “C” grades,
which are based on tuber diameter. The following tuber weight classes were compiled: <113-g,
113-198-g, 198-241-g, 241-298-g, 298-397-g, >397-g, and U.S. number twos (#2’s). The 198241-g, 241-298-g and 298-397-g tuber weight classes correspond to 100, 90-80, and 70-60 tuber
count (22.7-kg) cartons, respectively. Total yield included the combined weights of all
categories. U.S. number one yield was equal to the sum of all categories except #2 and undersize
(<113-g) tubers, and marketable yield included U.S. number one plus undersize tubers.
Tuber yield data were also sorted into A, B, and C grades, which correspond to 56-87-,
51-56-, and 28-51-mm diameters, respectively (averaged across cultivars). Since tubers were
sorted by weight, relationships between tuber diameter and weight were modeled for each
cultivar to facilitate translation of the A, B, and C diameter categories to weight ranges for
sorting the data (Fig. 1). Ninety-five to ninety-nine percent of the variation in tuber diameter
113
was accounted for by differences in tuber fresh weight. Tuber diameter can thus be predicted for
each cultivar by solving the line equations for a particular tuber weight. Given these
relationships, A-, B-, and C-size (“creamer size”) tuber diameters corresponded to average tuber
weight ranges of 92-360-g, 67-91-g, and 10-66-g, respectively, across cultivars. Yield data were
thus sorted accordingly to evaluate the effects of treatments on tuber size distributions based on
estimated differences in tuber diameter.
Data analysis, presentation, and estimation of economic returns
The effects of seed age and GA on plant emergence, stem number, tuber number per plant
and per hectare, average tuber weight, and the yields of various tuber size classes (tuber size
distribution) were evaluated separately for each cultivar. Data were subjected to analysis of
variance (ANOVA) and sums of squares were partitioned into single degree-of-freedom
contrasts for main effects and interactions in the case of factorial experiments (age x GA), or into
linear, quadratic, and cubic polynomial trends for single-factor studies involving GA
concentrations. Polygonal plots were used to compare the effects of seed age (DD) and GA
concentrations on shifts in tuber size distributions relative to non-treated controls for each
cultivar.
Crop values (F.O.B. shipping point and/or delivered sales, shipping point basis) were
estimated for the effects of GA concentrations on yields of A-, B-, and C-size tubers in 2011 and
2012. Overall crop values were estimated using the average prices corresponding to the 5 day
period coinciding with harvests, averaged over the five year period from 2007-2011, as quoted
on the USDA Agricultural Marketing Service website for Columbia Basin (WA) and Umatilla
Basin (OR) shipping points (www.marketnews.usda.gov). The 5-yr average prices for A-, B-,
and C-sizes for round red cultivars (Red La Soda, Chieftain) were $13.64, $15.80, and $27.71
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U.S. dollars per 22.7-kg carton, respectively. Yukon Gold, Satina and Cal White were valued
based on prices for yellow type potatoes, which averaged $14.62, $12.36, and $26.03 U.S.
dollars per 22.7-kg carton for A-, B-, and C-sizes, respectively (5-yr average). Crop values are
expressed as percent increase or decrease relative to non-treated control seed.
Results
The relationships between weight and diameter of tubers of the five cultivars were
modeled to facilitate translation of data depending on the grading priorities of various markets
(seed, fresh, processing). Tuber diameter was highly correlated (P<0.001) with tuber weight for
all cultivars (Fig. 1). For all cultivars, the increase in tuber diameter per unit tuber weight was
greatest as tuber weight increased from about 10- to 128-g (Fig. 1). Chieftain and Satina had the
narrowest ranges of tuber weight and diameter relative to the other cultivars. Chieftain tubers
did not exceed 420-g and 93-mm in diameter. Likewise, the size limit for Satina tubers was
about 326-g and 86-mm diameter. In contrast, the largest tubers of Cal White, Yukon Gold, and
Red La Soda were 738-, 585-, and 588-g, respectively, with diameters from 100- to 105-mm.
Ninety to ninety-seven percent of the variation in tuber diameters could be predicted by
differences in tuber weight for Satina, Chieftain, Cal White, Yukon Gold, and Red La Soda.
Tuber diameter can thus be estimated for each cultivar by solving the line equations (Fig. 1) for a
given tuber weight. Direct comparison of the cultivars for tuber diameter/weight relationships
appear in the bottom right graph of Fig. 1. Except for Cal White, diameter/weight relationships
were similar, indicating that a single model would suffice for translating weights to diameter
(and vice versa) for these cultivars.
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In 2009, tubers were stored at 12, 22, and 32oC for various periods to accumulate 80-,
450- and 900-degree days (DD) at the beginning of storage. The effects of these age priming
treatments on plant emergence, apical dominance, tuber set, yields, and tuber size distributions
were evaluated for each cultivar. Plant emergence and establishment occurred from 25- to 47days after planting (DAP) for all cultivars regardless of treatment. At 31-DAP, plant emergence
from the control seedlots was 5% for Chieftain, 16% for Yukon Gold, 18% for Red La Soda,
22% for Cal White, and 49% for Satina (Tables 2 and 3). Effects of the age priming treatments
on emergence varied by cultivar. When given 450-DD, percent emergence at 31-DAP increased
linearly with temperature for Red La Soda (Table 3) but remained relatively constant for the
other cultivars (Tables 2 and 3). When given 900-DD, percent emergence increased linearly
with temperature for Cal White and Satina but decreased for Yukon Gold, Chieftain, and Red La
Soda (Tables 2 and 3). Effects of the storage treatments on final emergence were also cultivardependent. Cal White, Red La Soda and Satina achieved 100% emergence regardless of DD or
temperature. Yukon Gold and Chieftain seed-tubers given 900-DD at 32oC (29-days of storage)
only achieved about 60% plant emergence, characterizing increased sensitivity of these cultivars
to high temperature early in the storage season.
In contrast to many russet skin cultivars, the aging treatments did not reduce apical
dominance substantially in any of the specialty cultivars, as evidenced by relatively small
increases in stems per seedpiece (Tables 2 and 3). Significant (P<0.05) changes in stem number
were observed in Cal White, Red La Soda, Chieftain, and Satina; however, the age priming
treatments only induced changes ranging from 0.3 to 1.3 stems per seedpiece over non-aged seed
(80-DD). By contrast, these aging treatments more than doubled the stem numbers of Ranger
Russet, Russet Burbank, and Umatilla Russet seed-tubers (range = 2.5 to 6.0 stems per
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seedpiece) (Knowles and Knowles 2006; Knowles unpublished data). While a broader range of
stem numbers is required to effectively model the relationships among stem numbers, tuber set,
and tuber size distribution for these specialty cultivars, differences in tuber set and size
distribution were achieved in four of five cultivars (Tables 2 and 3).
Accumulation of 900-DD at 32oC (29 days) significantly reduced total and U.S. No. 1
yields of all cultivars relative to the other aging treatments. Chieftain and Yukon Gold were
most sensitive to this 900-DD treatment, averaging 53% and 42% decline in total yield relative to
the average of all other treatments, respectively (Table 2). Furthermore, 450 DD at 32oC reduced
the total yield of Yukon Gold by 5.6 MT ha-1 relative to the 80 DD control seed, but had no
effect on Chieftain, indicating that Yukon Gold may be more sensitive to high temperature for
decline in seed productivity than Chieftain. Information on the sensitivity of these cultivars to
high temperatures is relevant to managing seed during the maturation period under dead vines in
warmer growing regions. Prolonged maturation periods in warm soils could negatively affect
yield potentials of all five cultivars. Total and U.S. #1 yields were not affected by the other
aging treatments, indicating wide tolerance of the specialty cultivars to accumulated degree days
at more moderate temperatures (12-22oC) following harvest. Average total yields across all
treatments except 900 DD (32oC) were: Red La Soda, 79.4 MT ha-1; Cal White, 75.6 MT ha-1;
Satina, 73.7 MT ha-1; Chieftain, 64.7 MT ha-1; Yukon Gold, 55.0 MT ha-1.
Tuber size distributions of Chieftain and Satina were similar and favored high yields of
<198-g tubers and very low yields of >241-g tubers (Fig. 2, Tables 2-3). In contrast, the tuber
size profile of Cal White favored >298-g tubers with relatively low yields of 241-298- (90-80,
22.7-kg carton count), 198-241- (100 count), 113-198-, and <113-g tubers. Relative to Cal
White, Chieftain and Satina, the marketable yields (U.S. #1 + <113-g tubers) of Yukon Gold and
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Red La Soda were more evenly distributed among a greater number of tuber size classes (Fig. 2,
Tables 2-3). The tuber size distribution profiles depicted in Fig. 2 are diagnostic for the cultivars
when grown under early season management for 106-days (planting to vine kill) in the central
Columbia Basin.
Changes in tuber set and size distribution were compared for age priming treatments that
induced the greatest differences in stem number for each cultivar, without affecting marketable
yields. These treatments were: 450-DD, 12oC vs. 450-DD, 32oC for Chieftain, Satina, and Red
La Soda; 450-DD, 32oC vs. 900-DD, 12oC for Cal White; and 450-DD, 12oC vs. 900-DD, 22oC
for Yukon Gold (Fig. 2). Red La Soda, Satina and Chieftain were the most sensitive cultivars for
increasing tuber set (number) per plant, tuber number per hectare, and decreasing average tuber
size with increasing stems (Fig. 2 and inset tables). The tuber size distribution of Red La Soda
changed the most per unit increase in stems. A 26% increase in stem number (from 2.7 to 3.4
stems/plant) resulted in a 14% increase in tuber set (from 7.7 to 8.8 tubers/plant = 52,000 more
tubers per hectare) and a 14% decrease in average tuber size (from 226- to 194-g tuber-1) (Fig. 2,
Table 3). These changes significantly decreased the yields of greater than 298-g tubers and
increased the yields of 198-241-, 113-198-, and <113-g tubers. A substantial shift in tuber size
distribution thus occurred with the 0.7 stem number increase, as illustrated by the blue and red
polygons for Red La Soda (Fig. 2).
The specialty cultivars were clearly resistant to the broad range of DD-based treatments
designed to accelerate the physiological age of seed, decrease apical dominance and shift tuber
size distribution. Defining the relationships among stem numbers, tuber set, and size distribution
requires seed lots expressing a wider range of apical dominance than that produced by the age
priming treatments in 2009. A different approach to reducing apical dominance was tested for
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the 2010 growing season. The effects of age priming (900-DD at 18oC) in combination with preplant treatment of cut seed with GA (10 mg L-1) on plant emergence, apical dominance, tuber set
and size distribution were evaluated in 2010.
As in 2009, plant emergence in 2010 occurred from 25- to 47-days after planting (DAP)
for all cultivars regardless of treatment. At 33-DAP, plant emergence from the young, 80-DD
seed was 59% for Red La Soda, 51% for Yukon Gold, 48% for Satina, 37% for Cal White, and
37% for Chieftain (Table 4). Storage of seed for 900-DD at 18oC had little effect on plant
emergence for most cultivars (except Red La Soda where 900-DD hastened emergence).
Relative to the non-treated 80- and 900-DD seed, GA treatment significantly hastened plant
emergence of all cultivars. All cultivars had achieved 95 to 100% plant emergence by 55-DAP
(time of stem counts), except Cal White seed stored for 900-DD (final emergence ranged from
88-95%).
Consistent with results in 2009, the 900-DD age priming treatment did not reduce apical
dominance in the specialty cultivars in 2010. The 900-DD seed of each cultivar produced the
same number of stems as the 80-DD seed (Table 4), underscoring the resistance of these cultivars
to high temperature-induced accelerated aging during storage. On average, Satina produced the
most stems (3.7) followed by Cal White (3.4), Red La Soda (3.3), Chieftain (2.8) and Yukon
Gold (1.8) in the control (non-GA treated) plots. In contrast, GA treatment greatly reduced
apical dominance in all cultivars, increasing stems from 1.8 to 5.4 in Yukon Gold, 2.8 to 6.4 in
Chieftain, 3.3 to 6.1 in Red La Soda, 3.6 to 6.7 in Satina, and 3.3 to 5.2 in Cal White, when
averaged across DD. The GA-induced reduction in apical dominance was equal for the 80- and
900-DD seed of all cultivars except Red La Soda (Table 4). GA had a greater effect on
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increasing stems of the 900-DD Red La Soda seed when compared with the 80-DD seed (Age x
GA, P≤0.005).
Despite the lack of effect of seed age on stem numbers, age affected yields and tuber size
distributions of most cultivars. Total and U.S. #1 yields of Red La Soda were reduced by 10.1
and 10.6 MT ha-1, respectively, by the aging treatment (Table 4). The total yield from 900-DD
Chieftain seed was also lower than 80-DD seed (by 9.9 MT ha-1); however, U.S. #1 yield was
unaffected by the aging treatment. Total and U.S. #1 yields of the other cultivars were not
affected by storage degree days. However, aging decreased the yields of >298-g tubers in Red
La Soda, decreased the yield of <113-g tubers but increased the yield of 298-397-g tubers in
Satina, decreased the yield of 113-198-g Chieftain tubers, decreased the yield of >397-g Yukon
Gold tubers, and increased the yields of 113-198-g and 241-298-g tubers of Yukon Gold.
GA treatment of seed resulted in the greatest effects on yields, tuber set, average tuber
size, and tuber size distributions compared with non-treated seed (Table 4). Relative to nontreated seed, GA increased tuber set per plant and decreased average tuber fresh weight for Red
La Soda, Cal White, Yukon Gold, and Chieftain. For all cultivars, GA reduced the yields of
larger tubers and increased the yields of smaller tubers. This effect was apparent regardless of
whether the tubers were sorted into weight categories corresponding to 22.7-kg carton counts
(Table 4, Fig. 3) or sorted based on “A”, “B” and “C” tuber diameters (converted to weight
equivalents) (data not shown).
Tuber size distributions of Chieftain, Red La Soda, and Satina from 80-DD seed were
similar and favored high yields of 113-198-g tubers and relatively low yields of >298-g tubers
(Fig. 3 blue polygons). In contrast, the tuber size profile from 80-DD Cal White seed favored
241- to >397-g tubers with relatively low yields of 198-241- (100 count), 113-198-, and <113-g
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tubers. The tuber size distribution profile from 80-DD Yukon Gold seed favored 113-397-g
tubers with 113-198- and 298-397-g (70-60 count) tubers dominating the profile.
The GA-induced shift in tuber size distribution is clearly evident in the polygonal
diagrams of Fig. 3. In addition to increasing stems, tubers per plant and per hectare, and
decreasing average tuber weight, GA also reduced marketable yields (U.S. #1 + <113-g tubers)
(Fig. 3 table insets). Yukon Gold was the most sensitive to GA-induced reduction of marketable
yield (-28%), followed by Satina (-22%), Red La Soda (-16%), Chieftain (-12%), and Cal White
(-9.6%). GA also resulted in elongation of the tubers (increased length/width ratio), the extent of
which was cultivar-dependent. Yukon Gold and Cal White responded to GA treatment with
increased yields of #2 grade tubers (Table 4), which characterizes their increased sensitivity to
elongation and pointed ends as a result of GA treatment. The negative effects on yields and
tuber shape were likely due to the relatively high concentration of GA (10 mg L-1).
Lower concentrations of GA (0, 2, 4, and 8 mg L-1) were tested in 2011 to determine if
tuber size distributions could effectively be altered while maintaining the yield potentials and
tuber shapes characteristic of the five cultivars. Plant emergence was completed from
approximately 25- to 57-days after planting (DAP) for all cultivars in 2011. At 35-DAP, plant
emergence from non-treated seed was 0% for Chieftain and Red La Soda, 2% for Satina, 3% for
Yukon Gold, and 5% for Cal White (Table 5). In contrast, plant emergence in 2010 averaged
46% at 33-DAP for the non-treated 80-DD seed. The slower emergence in 2011 was a
consequence of an unusually cool spring/early summer. Relative to non-treated seed, GA
significantly hastened plant emergence and the responses were concentration-dependent and best
defined by first or second degree polynomials (Table 5). Satina was the most sensitive cultivar
to GA-induced stimulation of plant emergence; attaining 66 and 87% by 35-DAP when treated
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with 2 and 8 mg L-1 GA, respectively. Plant emergence from the 8 mg L-1 GA-treated seed of
Cal White, Red La Soda, Yukon Gold, and Chieftain was 81, 66, 35, and 14%, respectively, at
35-DAP. All cultivars had achieved 100% plant emergence by 57-DAP.
On average, non-treated seed of Satina produced the most stems (3.3) followed by Red
La Soda and Cal White (2.9), and Yukon Gold and Chieftain (2.4) (Table 5). GA significantly
reduced apical dominance (increased stems) in all cultivars and the effect was concentrationdependent. The GA-induced increase in stems was greatest for Cal White (2.9-5.3 stems, 83%
increase) followed by Yukon Gold (2.4-4.0 stems, 66% increase), Chieftain (2.4-3.9 stems.
63%), Satina (3.3-4.9 stems, 48%), and Red La Soda (2.9-3.8 stems, 31%). Except for Red La
Soda, the largest increases in stem number over control were apparent with only 2 mg L-1 GA
(increases over non-treated seed ranged from 50-75% depending on cultivar). The greatest
change in stem number for Red La Soda was observed between 0 and 4 mg L-1 GA. Increasing
GA levels higher than 2 or 4 mg L-1 did not result in further increases in stem number. Hence,
the dose-dependent effect of GA on apical dominance should be defined further by screening
concentrations between 0 and 2-4 mg L-1 for all of these cultivars.
Total yields of non-treated seed were greatest for Red La Soda followed by Cal White,
Chieftain, Satina and Yukon Gold in 2011 (Table 5). U.S. #1 yields followed the same trend
except for Yukon Gold, which produced a 46% higher yield than Satina. Treatment of seed with
GA significantly affected yields, tuber set, average tuber size, and tuber size distributions
compared with non-treated seed. At 8 mg L-1, GA decreased total, U.S. #1 (>113-g), and
marketable (U.S. #1 + <113-g) yields for all cultivars except Satina where total yield was
unaffected but U.S. #1 yield decreased 36%. However, lower concentrations of GA (2 and 4 mg
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L-1) either had no effect on total and marketable yields (4 cultivars) or significantly increased
these yields (Satina).
Relative to non-treated seed, GA increased tuber set per plant and decreased average
tuber fresh weight in all cultivars (Table 5). Maximum tuber set per plant was achieved with 2-4
mg L-1 GA. For all cultivars, GA reduced the yields of larger tubers and increased the yields of
smaller tubers. This effect was apparent regardless of whether the tubers were sorted into weight
categories corresponding to 22.7-kg carton counts (Table 5) or sorted based on “A”, “B” and “C”
diameters (converted to weight equivalents) (Table 6). Tuber size profiles produced by nontreated seed were dominated by a high percentage of 113-198-g tubers and a relatively low
percentage of tubers greater than 241-g (Fig. 4). Satina produced the smallest tubers compared
with the other cultivars, with negligible yield of tubers over 241-g.
The GA-induced shift in tuber size distribution is clearly evident in the polygonal
diagrams of Fig. 4. At the ideal concentrations of 2 or 4 mg L-1 (depending on cultivar), GA
increased stems, tubers per plant and per hectare, and decreased average tuber size without
reducing marketable yields (U.S. #1 + <113-g tubers) (Fig. 4 and table insets). For all cultivars,
GA treatment decreased the percentage of 198-g and greater tubers, and increased the percentage
of tubers less than 198-g. Red La Soda showed the greatest GA-induced shift in tuber size
distribution followed by Cal White, Chieftain, Yukon Gold, and Satina. While concentrations of
GA higher than those specified in Fig. 4 also shifted tuber size distributions (Tables 4, 5 and 6),
the decrease in marketable yield would likely offset any potential increases in value afforded by
higher yields of smaller size tubers. Higher concentrations of GA (e.g. 8-10 mg L-1) stimulated
elongation of tubers (increased length/width ratio) and the extent of this response was cultivardependent. Yukon Gold and Cal White responded to increasing GA concentration with
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increased yields of #2 grade tubers (Table 5), which partly reflects their increased sensitivity to
elongation and pointed ends as a result of GA treatment. The greatest decreases in apical
dominance, increases in tuber set and shifts in tuber size distribution occurred at the lowest
concentrations of GA. Hence, low concentrations of GA are effective in altering tuber size
distribution while maintaining yield potential and tuber shape in these cultivars.
Additionally, economic returns (overall crop values) were not solely dependent upon the
largest shifts in tuber size distribution among “A”, “B”, and “C” grades (Table 6). All cultivars
produced the highest overall crop values at 2 mg L-1 GA. Increases in total value over nontreated seed ranged from 5.3% (Yukon Gold) to 26.7% (Satina) with 2 mg L-1 GA. The total
values of Cal White, Chieftain and Red La Soda increased 11.8, 9.2, and 6.4%, respectively, at
this concentration. Increases in the values of creamer (C-size, 10-66-g) potatoes were substantial
with GA treatment for all cultivars, ranging from 48 to 145% when compared with non-treated
seed. The GA-induced increases in the values of “B” size (67-91-g) tubers ranged from 1.9 to
124%, depending on cultivar and GA concentration. Crop values of “A” size (92-360-g) tubers
decreased with increasing GA concentration for all cultivars.
Since the greatest effects of GA on apical dominance, tuber set and size distributions in
2011 were apparent at the lowest rates (2 and 4 mg L-1), 0.5 and 1 mg L-1 were included during
the 2012 growing season to resolve tuber yield responses at even lower concentrations. Plant
emergence began approximately 23 DAP and 100% emergence was achieved in all cultivars
regardless of GA treatment by 42 DAP (Fig. 5). The rate of plant emergence from non-treated
seed was cultivar-dependent; Cal White and Red La Soda plants emerged more rapidly than the
other cultivars over the first ca. 31 days, averaging 36% compared with 13% from the other
cultivars (Table 7, Fig. 5). GA significantly hastened plant emergence and the effects were
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concentration-dependent and best described by second degree polynomials for all cultivars at ca.
31-DAP. Satina and Red La Soda were the most sensitive to GA-induced stimulation of plant
emergence, attaining 93% and 94% by ca. 31-DAP when treated with 4 mg L-1 GA. In contrast,
emergence from the GA-treated (4 mg L-1) seed of Cal White, Yukon Gold, and Chieftain was
77, 63, and 60%, respectively, at ca. 31-DAP.
Non-treated seed of Red La Soda produced the most stems (3.8) followed by Cal White
(3.5), Satina (3.3), Chieftain (2.0), and Yukon Gold (1.4) (Table 7). GA significantly reduced
apical dominance in all cultivars and the effect was concentration-dependent. The increase in
stems was greatest for Chieftain (2.0 to 5.2 stems) followed by Red La Soda (3.8 to 5.9 stems),
Yukon Gold (1.4 to 3.2 stems), Cal White (3.5 to 5.1 stems), and Satina (3.3 to 4.8 stems) as GA
increased from 0 to 4 mg L-1.
Total yields for non-treated seed were greatest for Satina (44.0 MT ha-1) followed by Red
La Soda (42.0 MT ha-1), Cal White (41.3 MT ha-1), Chieftain (36.2 MT ha-1), and Yukon Gold
(34.2 MT ha-1) (Table 7). The trends in total yield with increasing GA concentration for most
cultivars were quadratic, with yields increasing as GA concentration increased from 0 to 1-2 mg
L-1, and then decreasing marginally. Relative to non-treated seed, GA did not reduce total yields
significantly at any concentration. Based on the quadratic polynomials, maximum GA-induced
increases in total yields were 1.5 MT ha-1 for Satina at 1.3 mg L-1 (Yield = 45.4 + 2.40[GA] –
0.95[GA]2, R2= 0.80, P<0.05); 5.8 MT ha-1 for Chieftain at 2.2 mg L-1 (Yield = 36.4 + 5.15[GA]
– 1.14[GA]2, R2= 0.99, P<0.01); 2.1 MT ha-1 for Red LaSoda at 1.6 mg L-1 (Yield = 43.6 +
2.59[GA] – 0.79[GA]2, R2= 0.57, P<0.05); 3.2 MT ha-1 for Cal White at 1.9 mg L-1 (Yield = 40.9
+ 3.36[GA] – 0.86[GA]2, R2= 0.73, P<0.05); and 0.2 MT ha-1 for Yukon Gold at 0.7 mg L-1
(Yield = 35.5 + 0.61[GA] – 0.43[GA]2, R2= 0.70, P<0.05).
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U.S. #1 tuber yields (>113-g tubers) decreased linearly with increasing GA concentration
except for Satina, where yield increased with 0.5 mg L-1 but then decreased as GA concentration
increased to 4 mg L-1 (Table 7). The decreases in U.S. #1 yields were offset by GA-induced
increases in yields of <113- and 113-198-g tubers, characterizing an overall shift in tuber size
distribution toward higher yields of smaller size tubers, which was partly a consequence of GAinduced increases in tuber set for Yukon Gold, Chieftain and Red La Soda. GA had no effect on
tuber set of Cal White and Satina. On average, tuber weight decreased linearly with increasing
GA concentration, reflecting the increased tuber set and shift toward smaller tubers. The shifts
in tuber size distributions with GA-induced increases in stem number are clearly evident in
Figure 6 where marketable yields (U.S. #1 + <113-g) remained unaffected by GA. GA treatment
resulted in a higher percentage of <198-g tubers at the expense of 198-298-g tubers for Cal
White, higher percentage of <113-g tubers at the expense of 113-298-g tubers for Yukon Gold,
and higher percentage of <113-g tubers at the expense of 113-198-g tubers for Chieftain, Red La
Soda, and Satina (Fig. 5).
The size distribution shifts toward higher percentages of <113-g tubers were even more
apparent when data were sorted based on “A”, “B” and “C” tuber diameters, which correspond to
ca. 92-360-g, 67-91-g, and 10-66-g tubers, respectively (Table 8). The relatively short growing
season in 2012 (90 days) virtually eliminated yields of >360-g tubers for all cultivars relative to
the 2009-11 growing seasons, which averaged 111-days. Yields of C-size tubers increased and
A-size tubers decreased with increasing GA concentration for all cultivars. Based on the linear
or quadratic polynomials, yields of “C” size tubers increased 32% in Satina, 48% in Cal White,
76% in Red LaSoda, 89% in Yukon Gold, and 96% in Chieftain with 4 mg L-1 GA.
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The GA-induced changes in tuber size distribution affected crop value. Except for Red
LaSoda, all cultivars produced the highest overall crop values with 0.5 to 2 mg L-1 GA (Table 8).
Maximum increases in total crop value over non-treated seed were 7.1% for Satina (0.5 mg L-1),
7.3% for Cal White (1 mg L-1), 12% for Red La Soda (4 mg L-1), 13.6% for Yukon Gold (0.5 mg
L-1) and 30% for Chieftain (2 mg L-1). Increases in the values of creamer (C-size, 10-66-g)
potatoes were substantial with GA treatment for all cultivars, ranging from 15% (Satina) to
116% (Yukon Gold) when compared with non-treated seed. Similarly, maximum increases in
the values of “B” size (67-91-g) tubers ranged from a low of 5.7% (Satina) to a high of 77%
(Yukon Gold), with all cultivars showing increases. Values of “A” size (92-360-g) tubers
decreased with increasing GA concentration for all cultivars.
Discussion
Controlling tuber size distribution can potentially increase returns to growers, packers
and processors by increasing yields of the more lucrative tuber size classes and reducing waste.
To date, it has been demonstrated that various cultivars, especially long-season russet varieties,
are highly responsive to heat-induced accelerated aging treatments during storage for decreasing
apical dominance, increasing tuber set and shifting tuber size distribution (Knowles and
Knowles, 2006). The timing, duration and intensity of such age-priming treatments interact with
genotype to dictate efficacy (Knowles et al. 2011; see Chapter 2).
In contrast to many russet cultivars, Cal White, Yukon Gold, Chieftain, Red La Soda, and
Satina were relatively resistant to high temperature-induced aging for decreasing apical
dominance, increasing tuber set, and reducing tuber size. Accumulation of degree days (>4oC)
during storage at 12, 22 and 32oC by seed of these cultivars increased stem numbers, tuber set
127
and shifted tuber size distributions in some cases; however, the changes were inconsistent, the
effects on overall tuber size distribution marginal, and some treatments (900-DD, 32oC)
significantly reduced total and marketable (U.S. #1 + <113-g tubers) yields (Tables 2-4; Fig. 2).
These five cultivars are thus recalcitrant to heat-induced accelerated aging for manipulating tuber
size distribution without affecting overall yields.
Tuber set and size distribution are highly correlated with the degree of apical dominance
expressed by seed-tubers. As stem numbers increase (reduced apical dominance), tuber set
increases and average tuber size decreases (Knowles and Knowles 2006). Apical dominance is
regulated by auxin, cytokinins and gibberellins. Auxin imposes apical dominance (Leyser 2005
and references therein), cytokinins are involved in lateral bud formation (Tanaka 2006), and
gibberellins promote internode elongation (Nagai et al. 2010) of lateral buds during sprouting
(Carerra et al. 2001). Auxin produced by an actively growing dominant sprout is translocated to
lateral buds, thus suppressing the growth of sprouts from other nodes (eyes) on the tuber (Kumar
and Knowles 1993). Apical dominance decreases progressively as the physiological age of
tubers advances and can be restored in older seed-tubers by treating the seed with auxin prior to
planting (Knowles et al. 1985; Mikitzel and Knowles 1990; Kumar and Knowles 1993; Knowles
et al. 2012). In addition to regulating stem elongation, GAs have a role in dormancy break
(Suttle 2004 and references therein) and commercial products are registered to break tuber
dormancy to facilitate the early evaluation of potato seed in virus testing programs (Allen et al.
1992; Anon 1999; Bryan 1989; Goth 1974; Rappaport 1957). Emergence from dormancy is
gradual in tubers (Suttle 2004 and references therein) and the degree of apical dominance
decreases with advancing age (Krijthe 1962). Furthermore, in addition to hastening dormancy
break, GA has been shown to increase stem numbers in several cultivars (Holmes et al. 1970;
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Marinus, J.K. and B.A. Bodlaender 1978). GA was thus evaluated as a seed treatment for its
efficacy in decreasing apical dominance and shifting tuber size distributions of Cal White,
Yukon Gold, Chieftain, Red La Soda, and Satina in this study.
GA decreased apical dominance, increased tuber set, decreased average tuber size, and
either increased or decreased total yields of the five cultivars, depending on concentration. At
greater than ca. 4 mg L-1, GA decreased yields, while concentrations greater than ca. 2 mg L-1
produced elongated (misshapen) tubers that were graded as #2’s (Tables 4, 5 and 7). This latter
effect was evident in cultivars Cal White and Yukon Gold only, reflecting their increased
sensitivity to GA-induced elongation of internodes relative to the other cultivars. The optimum
concentrations for decreasing apical dominance, to the extent needed to change tuber size
distribution and increase overall crop value based on “A”, “B”, and “C” grades, were less than or
equal to 2 mg L-1 GA (Tables 6 and 8). Pre-plant applications of GA to cut seed is thus an
effective technique for altering stem number, tuber set and size distribution in cultivars that are
otherwise resistant to heat-induced age-priming, but concentration is critical to avoid negative
effects on yield and tuber shape.
In addition to concentration, the effects of GA on tuber size distributions and crop values
depended on cultivar and length of the growing season. For example, when grown 115-days in
2011, 2 and 4 mg L-1 GA significantly increased total yields of Satina which, when combined
with the substantial shift toward higher yields of <113-g (especially C size) tubers, increased
crop values by 20 to 27% (Table 6). These effects would be beneficial for seed and baby potato
markets. However, when only grown for 90-days in 2012, overall yields of “C” size tubers were
37% lower on average than in 2011 and 0.5 mg L-1 GA increased crop value the most, but only
by 7% (Table 8). In contrast, percentage returns for GA-treated Red La Soda and Chieftain seed
129
were much greater in 2012 (90-day season) than 2011 (115-day season), even though total yields
were ca. 36% less in 2012 than 2011. The lower overall yields from an earlier harvest do not
necessarily represent loss to the grower. The potential economic advantage to being first to
market with the ideal tuber size profile in relation to demand needs to be considered in
determining how best to use GA in potato production.
Collectively, these studies demonstrate that the use of pre-plant applications of GA to cut
seed can substantially increase crop values, due to a combination of effects on total yields and
shifts in tuber size distributions toward smaller size (especially <113-g) tubers. It is relevant to
note that while GA-based products are commercially available, some are only registered for use
in seed potato production and recommended application rates are only half to a quarter of those
found to be optimal for changing tuber size distribution of the five cultivars reported here.
Additionally, economic returns were determined based solely on USDA prices for Columbia and
Umatilla Basin shipping points, since these were the most relevant to our production site at
Othello, WA. Returns to growers would be substantially different if contracts specified a fixed
return for total yield, and for the packing houses, depending on the retail market and packaging
strategy (e.g. 22.7-kg cartons versus 0.45- to 2.26-kg poly bags). More in depth economic
analyses are thus warranted to fully evaluate the potential advantages/disadvantages of using GA
to alter tuber size profiles for added value in potato production.
Acknowledgements
We thank the Washington State Department of Agriculture (Specialty Crop Block Grant
Program), the Washington State Seed Potato Commission, and the WSU Agricultural Research
Center for financial support.
130
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134
Table 1. Principal dates of seed acquisition and handling, treatment applications (aging and
GA), planting, in-season data collection, and harvest for field studies conducted at Othello,
WA on cultivars Chieftain, Cal White, Red La Soda, Satina, and Yukon Gold from 2009 to
2012.
Study Year
Activity
Seed acquisition
Seed aging periods
Seed cutting
GA treatments
Planting
Emergence data
collected
Stem
counts
Vine kill
Harvest
Growing degree days1
2009
2010
2011
2012
10/8/08
10-21 – 1/19
4/8
n/a
4/14
5/11 – 6/9
6/16–18
7/22 YG
7/29 C,CW,RL,S
8/13 C,CW,YG
8/14 RL,S
1958 & 2149
10/26/09
10-14 – 12/4
4/7
4/7
4/14
5/4–24
6/8
7/28 YG
8/5 C,CW,RL,S
8/11 YG
8/26 C,CW,RL,S
1712 & 1902
10/10/10
n/a
4/5
4/8
4/11
5/10 – 6/7
6/16 & 6/20
7/25 YG,S,CW
7/29 C,RL
8/4 CW,S,YG
8/8 C,RL
1494 & 1587
10/15/11
n/a
4/9
4/11
4/13
5/7–23
6/5
1
7/12
7/24 C,CW
7/25 RL,S,YG
1286
Cumulative growing degree days (7.2oC base) at Othello, WA calculated from planting to harvests for the
indicated cultivars.
135
Table 2. Effects of seed storage degree days and temperature on stem numbers, yield and grade of cultivars Cal White, Yukon
Gold, and Chieftain potatoes. Seed-tubers were stored at 12, 22, and 32oC for 450 and 900 degree days (DD) directly after harvest.
Storage temperatures were then lowered to 4oC for the remainder of a 198-day storage season. Dates for seed treatments and
production activities are given in Table 1. ANOVA results (P levels) for the effects of DD, temperatures (Temp), and their
interactions are presented for each cultivar (LSD, least significant difference (P<0.05); ns, not significant; TLT, temperature linear
trend; TDEV, deviations from linearity).
Tuber Yield (MT ha-1) (2009)
Age
Cultivar
(DD)
Cal
White
80
450
900
Temp
Stems
Emerg.
U.S. #1 <113g
(C) (%) 31 DAP plant-1
12
12
22
32
12
22
32
LSD0.05
DD450 vs. 900
TLT
TDEV
DD450/900 x TLT
DD450/900 x TDEV
Yukon
Gold
80
450
900
12
12
22
32
12
22
32
LSD0.05
DD450 vs. 900
TLT
TDEV
DD450/900 x TLT
DD450/900 x TDEV
Chieftain
80
450
900
12
12
22
32
12
22
32
LSD0.05
DD450 vs. 900
TLT
TDEV
DD450/900 x TLT
DD450/900 x TDEV
U.S. #1 Tubers + <113 g
113198g
198- 241- 298>397g #2’s
241g 298g 397g
Total
g tuber-1
Tubers
plant-1
1000s ha-1
7.5
7.9
9.8
9.1
6.5
8.0
7.2
10.0
11.8
11.3
10.1
9.0
11.1
9.3
18.4
16.1
18.1
12.3
13.8
17.4
12.2
23.1
24.4
22.9
22.3
30.7
23.7
14.9
0
0.1
0.1
0.2
0
0.4
0.1
75.1
76.0
77.3
72.4
75.3
77.3
65.7
253
257
249
231
264
247
210
6.6
6.5
6.9
6.9
6.3
6.9
6.9
300
296
314
316
289
313
314
22
34
37
33
28
37
55
3.1
3.2
3.4
3.4
2.7
3.3
3.0
70.8
71.7
72.4
66.1
70.8
72.6
59.4
4.3
3.9
5.0
5.7
4.3
4.4
6.2
11.7
11.7
10.2
12.4
11.0
12.5
15.8
16.3
0.45
6.3
1.5
3.3
2.6
2.7
4.6
6.0
0
6.1
24
0.7
34
ns
0.05
ns
0.05
ns
0.05
ns
0.1
ns
ns
ns
0.01
0.01
ns
ns
ns
0.01
ns
ns
ns
0.1
0.05
ns
0.1
ns
0.05
ns
ns
ns
ns
0.1
ns
ns
ns
ns
ns
0.1
0.01
ns
ns
ns
0.01
ns
0.05
ns
ns
ns
ns
ns
ns
ns
0.01
0.05
ns
ns
ns
0.01
ns
ns
ns
ns
0.1
ns
ns
ns
ns
0.1
ns
ns
ns
16
14
22
22
33
32
26
1.7
1.7
1.8
2.2
1.8
2.0
1.7
49.8
50.4
48.2
43.7
51.1
52.2
28.0
5.0
5.1
5.9
5.2
4.7
5.5
3.2
11.3
10.9
11.2
10.5
11.8
10.8
6.3
0.3
0.3
0.5
0.9
1.0
0.8
0.5
55.1
56.5
54.9
49.5
56.0
58.1
31.8
207
210
196
203
213
208
206
5.8
5.8
6.0
5.3
5.8
6.1
5.8
264
265
276
240
263
278
154
16
0.1
ns
ns
0.05
ns
0.3
ns
0.05
ns
0.05
0.05
4.0
0.01
0.01
0.01
0.01
0.01
1.5
0.05
ns
0.05
ns
ns
2.7
ns
0.01
ns
0.01
ns
1.4
ns
0.01
0.01
0.05
ns
2.6
0.05
0.01
0.1
ns
0.1
2.4
ns
0.01
0.01
0.01
0.01
2.4
ns
0.1
ns
0.05
ns
0
4.5
ns
ns
ns
ns
ns
0.01
0.01
0.01
0.01
0.01
16
ns
ns
ns
ns
ns
0.5
ns
ns
0.01
ns
ns
33
0.01
0.01
0.01
0.01
0.05
5
3
2
5
37
24
3
2.5
2.2
2.6
2.9
2.9
2.5
1.7
49.1
48.9
53.6
49.5
53.1
51.6
24.9
12.1
12.8
12.8
15.6
13.3
14.3
5.8
26.7
26.7
30.0
29.4
27.6
29.8
10.6
9.3
9.7
11.0
10.7
11.5
11.3
4.3
7.6
7.5
8.6
5.3
7.2
6.1
3.8
4.6
4.1
3.4
2.9
5.9
4.3
4.6
1.0
0.8
0.8
1.5
1.1
0.2
2.1
0.1
0.2
0
0.3
0.4
0.1
0.4
61.6
61.9
66.8
65.2
66.6
66.1
30.7
147
148
146
138
148
142
154
9.1
9.2
10.0
10.4
9.8
10.2
7.1
415
419
454
473
447
465
200
18
0.01
0.05
ns
0.01
ns
0.4
0.05
0.05
ns
0.01
ns
8.1
0.01
0.01
0.01
0.01
ns
2.6
0.01
0.05
0.05
0.01
0.01
3.9
0.01
0.01
0.01
0.01
0.01
3.7
ns
0.05
0.1
0.01
ns
2.4
0.05
0.01
0.1
ns
ns
2.7
0.1
ns
ns
ns
ns
0.5
ns
ns
0.1
ns
ns
0
ns
ns
ns
ns
ns
7.8
0.01
0.01
0.01
0.01
0.01
10
ns
ns
ns
0.05
0.1
0.8
0.01
0.05
0.01
0.01
0.01
41
0.01
0.01
0.01
0.01
0.01
7.1 8.9 12.2 10.3
5.6 11.5 13.2 9.3
6.8 8.7 12.8 8.6
5.2 6.1 12.1 9.7
6.4 8.0 13.5 11.4
7.1 9.0 15.5 9.8
3.7 4.6 6.0 7.5
136
Table 3. Effects of seed storage degree days and temperature on stem numbers, yield and grade of cultivars Red La Soda and
Satina potatoes. Seed-tubers were stored at 12, 22, and 32oC for 450 and 900 degree days (DD) directly after harvest. Storage
temperatures were then lowered to 4oC for the remainder of a 198-day storage season. Dates for seed treatments and production
activities are given in Table 1. ANOVA results (P levels) for the effects of DD, temperatures (Temp), and their interactions are
presented for each cultivar (LSD, least significant difference (P<0.05); ns, not significant; TLT, temperature linear trend; TDEV,
deviations from linearity).
Age
Cultivar
(DD)
Red
La Soda
80
450
900
Temp
Stems
Emerg.
U.S. #1 <113g
(C) (%) 31 DAP plant-1
12
12
22
32
12
22
32
LSD0.05
DD450 vs. 900
TLT
TDEV
DD450/900 x TLT
DD450/900 x TDEV
Satina
80
450
900
12
12
22
32
12
22
32
LSD0.05
DD450 vs. 900
TLT
TDEV
DD450/900 x TLT
DD450/900 x TDEV
U.S. #1 Tubers + <113 g
113198g
198- 241- 298>397g #2’s
241g 298g 397g
Total
g tuber-1
Tubers
plant-1
1000s ha-1
18
15
33
41
73
28
47
2.8
2.7
3.3
3.4
2.9
2.9
2.7
73.3
73.1
73.1
69.3
75.3
72.2
58.7
6.5
5.7
6.2
7.8
6.1
6.7
8.8
17.6
14.8
19.9
20.2
17.8
19.0
19.1
10.3
8.9
11.8
12.4
10.6
11.8
9.3
13.6
14.5
15.0
13.1
15.5
13.2
12.2
18.7
18.5
16.4
13.0
16.0
18.0
12.2
13.1
16.4
9.9
10.6
15.6
10.1
6.0
0.2
0.2
0
0.2
0
0
0.3
80.0
78.9
79.4
77.1
81.6
79.1
67.5
212
226
204
194
214
204
183
8.3
7.7
8.6
8.8
8.3
8.5
8.3
379
351
390
403
380
389
374
13.9
0.01
ns
0.01
0.01
0.01
0.5
0.05
ns
ns
0.05
ns
6.3
0.1
0.01
0.1
0.01
ns
1.9
ns
0.01
ns
ns
ns
3.9
ns
0.05
ns
ns
ns
3.2
ns
ns
ns
0.05
ns
3.6
ns
0.1
ns
ns
ns
4.6
ns
0.01
ns
ns
ns
6.6
ns
0.05
ns
ns
ns
0
ns
ns
ns
ns
ns
6.7
ns
0.01
ns
0.05
ns
17
ns
0.01
ns
ns
ns
0.9
ns
ns
ns
0.1
ns
44
ns
ns
ns
0.1
ns
49
53
62
58
38
61
68
3.9
3.7
3.8
5.2
3.4
4.0
4.3
48.9
51.6
46.4
47.5
49.8
52.2
35.2
23.8
21.1
24.9
28.0
21.0
21.5
27.8
33.0
33.0
32.5
35.0
31.2
31.4
24.2
8.0
9.4
7.8
5.6
10.3
9.1
4.3
5.2
5.4
4.3
3.8
5.7
6.4
4.5
2.6
2.9
1.6
1.9
2.0
3.3
1.7
0
0.9
0.2
1.2
0.5
1.9
0.5
0.6
1.1
1.2
0.9
1.0
1.0
0.7
73.5
73.8
72.2
76.7
71.3
74.4
63.9
121
125
117
114
124
128
104
13.2
12.8
13.4
14.7
12.6
12.8
13.3
602
583
611
670
570
582
605
12
ns
0.01
0.1
0.01
ns
0.6
0.05
0.01
0.1
ns
0.05
7.2
ns
0.01
ns
0.05
0.01
4.5
ns
0.01
ns
ns
ns
2.8
0.01
0.05
ns
0.01
0.01
3.2
ns
0.01
ns
ns
ns
2.9
ns
ns
ns
ns
ns
2.8
ns
ns
ns
ns
ns
1.2
ns
ns
ns
ns
0.05
0
ns
ns
ns
ns
ns
5.2
0.01
ns
ns
0.01
0.01
11
ns
0.01
ns
ns
0.05
1.2
0.05
0.01
ns
ns
ns
55
0.05
0.01
ns
ns
ns
137
Table 4. Effects of seed age (degree days, DD) and GA on plant emergence, stem numbers, yield, tuber set and size distributions
of cultivars Cal White, Yukon Gold, Chieftain, Red La Soda, and Satina in 2010. Seed-tubers were stored at 18°C for 80 and 900
DD directly after harvest and then held at 4°C for the remainder of the storage season. Dates for seed treatments and production
activities are given in Table 1. ANOVA results (P levels) for the effects of seed age, GA, and their interaction are presented for
each cultivar (LSD, least significant difference (P<0.05); ns, not significant).
Age
GA
Stems
Emerg.
Cultivar
U.S. #1 <113g
(DD) (mg L-1) (%) 33 DAP plant-1
Cal
White
80
900
Yukon
Gold
80
900
Chieftain
80
900
Red
La Soda
80
900
Satina
80
900
U.S. #1 Tubers + <113 g
113198g
198- 241- 298>397g #2’s
241g 298g 397g
Total
g tuber-1
Tubers
plant-1
1000s ha-1
0
10
0
10
37
90
39
77
3.4
5.3
3.3
5.1
101.1
82.0
95.7
82.3
6.0
12.7
7.0
12.4
16.5
25.3
16.4
23.9
13.9
12.9
11.7
12.7
19.5
12.7
17.2
15.7
25.8
17.6
22.6
16.7
25.4
13.3
27.6
13.3
0.5
4.6
0.3
3.7
107.6
99.3
103.1
98.4
236
185
235
184
10.1
11.3
10.8
11.9
454
513
440
514
LSD0.05
Age
GA
Age x GA
23
ns
0.01
ns
0.8
ns
0.01
ns
8.4
0.05
0.01
ns
1.7
ns
0.01
ns
3.9
ns
0.01
ns
2.2
ns
ns
ns
3.2
ns
0.01
0.05
3.7
0.05
0.01
ns
5.2
ns
0.01
ns
2.3
ns
0.01
ns
7.8
ns
0.05
ns
16
ns
0.01
ns
1.0
0.05
0.01
ns
44
ns
0.01
ns
0
10
0
10
51
83
58
84
1.5
5.2
2.1
5.6
63.7
32.5
66.1
33.4
6.5
17.7
7.0
19.6
13.6
22.0
19.2
22.3
12.4
5.2
13.0
4.9
11.5
3.5
15.3
4.0
18.6
1.6
14.2
2.0
7.4
0.2
4.5
0.3
0.8
7.9
0.2
6.7
70.8
58.1
73.3
59.6
208
122
193
119
7.7
9.1
8.3
10.0
337
416
378
448
LSD0.05
Age
GA
Age x GA
18
ns
0.01
ns
1.0
0.1
0.01
ns
5.4
ns
0.01
ns
3.1
ns
0.01
ns
5.1
0.05
0.01
ns
2.8
ns
0.01
ns
3.2
ns
0.01
ns
4.8
0.05
0.01
ns
2.8
0.05
0.01
0.1
2.1
ns
0.01
ns
4.5
ns
0.01
ns
14
0.01
0.01
ns
1.2
0.05
0.01
ns
47
0.05
0.01
ns
0
10
0
10
37
82
51
70
2.7
6.2
2.9
6.6
87.2
62.5
79.4
53.8
15.8
26.9
13.9
29.8
35.0
34.5
30.7
30.5
18.8
11.3
15.9
8.3
16.5
9.8
14.5
8.0
11.4
5.3
13.8
4.1
5.7
1.6
4.5
2.7
0.7
0.7
0.6
0.4
103.8
90.1
93.9
83.8
163
128
166
118
14.3
15.6
12.9
16.3
636
711
566
718
LSD0.05
Age
GA
Age x GA
22
ns
0.01
0.1
0.8
ns
0.01
ns
10.5
0.1
0.01
ns
5
ns
0.01
ns
4.3
0.01
ns
ns
4.5
ns
0.01
ns
4.7
ns
0.01
ns
5.1
ns
0.01
ns
3.2
ns
0.05
ns
0.9
ns
ns
ns
8.3
0.05
0.01
ns
18
ns
0.01
ns
2.5
0.05
0.05
ns
61
ns
0.01
0.1
0
10
0
10
59
89
77
87
3.2
5.4
3.4
6.7
92.6
51.1
82.0
45.7
17.5
38.3
17.8
41.7
34.7
32.1
36.5
29.6
16.6
9.2
15.8
6.8
16.0
5.6
14.3
5.9
14.7
3.8
9.9
3.2
10.6
0.5
5.6
0.2
0.9
0.5
1.1
0.1
111.2
89.9
101.1
87.4
165
104
155
99
14.7
18.7
14.1
19.5
671
854
645
888
LSD0.05
Age
GA
Age x GA
18
0.01
0.01
ns
0.7
0.01
0.01
0.05
8.7
0.01
0.01
ns
3.9
0.01
0.01
ns
8.1
ns
0.1
ns
3.8
ns
0.01
ns
4.1
ns
0.01
ns
4.6
0.01
0.01
ns
2.6
0.05
0.01
ns
0.9
ns
0.05
ns
8.3
0.1
0.01
ns
15
0.01
0.01
ns
1.6
ns
0.01
ns
79
0.1
0.01
ns
0
10
0
10
48
95
59
89
3.7
7.2
3.6
6.2
81.4
50.9
86.1
57.4
21.3
27.1
16.4
24.9
40.8
30.9
36.5
28.5
16.6
9.1
18.4
9.8
14.3
6.1
15.5
8.5
8.4
4.3
11.8
7.2
1.3
0.6
3.9
3.5
0.6
0.4
0.4
0.2
103.3
78.2
102.9
82.3
144
117
159
126
15.7
14.7
14.2
14.5
716
668
646
660
LSD0.05
Age
GA
Age x GA
20
0.01
0.01
ns
0.8
ns
0.01
ns
6.1
0.01
0.01
ns
4.4
0.01
0.01
ns
7.8
0.05
0.01
ns
2.9
0.01
0.01
ns
3.3
0.01
0.01
ns
3
0.01
0.01
ns
2
0.01
ns
ns
0.7
ns
ns
ns
6.1
ns
0.01
ns
10
0.01
0.01
ns
1.6
0.01
ns
ns
72
0.01
ns
ns
138
Table 5. Effects of GA on plant emergence, stem numbers, yield, tuber set and size distributions of cultivars Cal White,
Yukon Gold, Chieftain, Red La Soda, and Satina in 2011. Dates for seed treatments and production activities are given in
Table 1. ANOVA results (P levels) for polynomial trends of the effects of GA concentration on growth and yield parameters
are presented for each cultivar (LSD, least significant difference (P<0.05); ns, not significant).
GA
Stems
Emerg.
Cultivar
U.S. #1 <113g
(mg L-1) (%) 35 DAP plant-1
Cal
White
Yukon
Gold
Chieftain
Red
La Soda
Satina
U.S. #1 Tubers + <113 g
113198g
198- 241- 298>397g #2’s
241g 298g 397g
Total
g tuber-1
Tubers
plant-1
1000s ha-1
0
2
4
8
5
47
57
81
2.9
4.5
4.4
5.3
51.3
46.4
40.6
31.6
8.7
16.0
17.1
16.1
22.6
24.2
23.3
19.1
8.9
9.1
7.7
4.8
9.6
7.9
6.5
4.5
6.8
3.4
3.0
2.7
3.4
1.9
0.2
0.5
2.4
2.6
4.7
8.3
62.5
65.0
62.3
55.8
158
130
117
107
8.5
10.6
10.8
9.7
386
485
494
440
LSD0.05
linear
quadratic
deviations
22
0.01
0.05
ns
0.7
0.01
0.1
0.05
5.6
0.01
ns
ns
2.9
0.01
0.01
ns
2.6
0.01
0.05
ns
2.6
0.01
ns
ns
2.9
0.01
ns
ns
2
0.01
0.05
ns
1.2
0.01
0.01
ns
3.1
0.01
ns
ns
5.4
0.01
0.1
ns
17
0.01
0.05
ns
0.9
0.1
0.01
ns
42
0.1
0.01
ns
0
2
4
8
3
10
31
35
2.4
4.2
4.3
4.0
41.7
38.6
29.4
20.4
10.0
13.5
13.9
13.6
19.4
23.8
19.9
15.0
8.7
7.3
4.9
3.6
7.1
5.3
3.1
0.8
4.9
2.2
1.4
1.0
1.5 2.2
0.0 4.7
0.2 7.7
0.0 11.1
53.8
56.7
51.1
45.1
138
125
110
98
8.2
9.4
8.6
7.6
373
418
390
342
LSD0.05
linear
quadratic
deviations
26
0.05
ns
ns
0.9
0.01
0.01
ns
5.2
0.01
ns
ns
1.9
0.01
0.01
ns
2.5
0.01
0.01
0.01
2.8
0.01
ns
ns
1.7
0.01
ns
ns
1.3
0.01
0.01
ns
1.3
0.1
ns
ns
3.8
0.01
ns
ns
4.5
0.01
0.1
0.1
9
0.01
ns
ns
1.1
0.05
0.05
0.1
51
0.1
0.05
ns
0
2
4
8
0
8
8
14
2.4
3.6
3.8
3.9
43.3
37.4
34.1
25.6
14.5
22.1
22.4
21.6
25.1
24.9
23.1
18.8
6.6
5.5
5.8
3.9
6.7
4.1
3.6
2.0
3.9
2.5
1.2
1.0
1.0
0.5
0.4
0.0
2.2
0.9
3.0
1.7
60.1
60.3
59.6
48.9
132
107
101
94
9.8
12.5
12.4
11.4
442
559
559
504
LSD0.05
linear
quadratic
deviations
11
0.05
ns
ns
0.6
0.01
0.01
ns
5.6
0.01
ns
ns
5.4
0.05
0.05
ns
4.2
0.01
ns
ns
1.7
0.01
ns
ns
2.5
0.01
ns
ns
2.1
0.01
ns
ns
0.6
0.01
ns
ns
1.4
ns
ns
0.01
7.8
0.01
ns
ns
10
0.01
0.01
ns
2.2
ns
0.05
ns
96
ns
0.05
ns
0
2
4
8
0
15
29
66
2.9
3.1
3.7
3.8
58.3
52.2
43.5
35
10.5
17.2
20.9
24.2
24.9
27.3
25.8
22.6
10.0
7.8
7.1
6.8
11.7
9.1
4.8
3.7
7.3
6.7
4.6
1.7
4.3
1.2
1.3
0.2
1.9
0.9
1.4
1.3
70.6
70.4
65.9
60.5
161
131
117
105
9.6
11.6
12.1
12.5
435
530
552
570
LSD0.05
linear
quadratic
deviations
15
0.01
ns
ns
0.5
0.01
ns
ns
6.3
0.01
ns
ns
4.2
0.01
0.05
ns
5.8
ns
ns
ns
2.6
0.05
ns
ns
3.7
0.01
ns
ns
3.9
0.01
ns
ns
1.5
0.01
0.1
0.1
2.5
ns
ns
ns
5.4
0.01
ns
ns
17
0.01
0.05
ns
1.6
0.01
0.05
ns
73
0.01
0.05
ns
0
2
4
8
2
66
77
87
3.3
5.1
5.0
4.9
28.5
28.7
24.4
18.2
25.6
37.9
37.7
34.1
22.3
26.0
22.1
16.1
3.5
1.9
1.7
1.2
1.2
0.9
0.6
0.6
1.2
0.0
0.0
0.2
0.4
0.0
0.0
0.0
0.1
0.4
0.4
0.5
54.0
66.8
62.5
52.7
96
87
83
78
12.3
16.8
16.5
14.7
563
767
751
670
LSD0.05
linear
quadratic
deviations
21
0.01
0.01
0.1
0.4
0.01
0.01
0.01
3.6
0.01
ns
ns
3.4
0.01
0.01
0.05
3.7
0.01
0.05
0.1
1.7
0.05
ns
ns
1
ns
ns
ns
0.5
0.01
0.01
0.1
0
ns
ns
ns
0.4
0.05
ns
ns
3.4
0.01
0.01
0.01
4
0.01
0.01
ns
0.8
0.01
0.01
0.01
37
0.01
0.01
0.01
139
Table 6. Effects of GA on plant emergence, stem numbers, yield, and economic returns of cultivars Cal White, Yukon
Gold, Chieftain, Red La Soda, and Satina in 2011. Dates for seed treatments and production activities are given in Table
1. The weight ranges for A, B and C tuber size classes were estimated from Fig. 1. Crop values are expressed as percent
change in average prices corresponding to the 5-day period coincident with harvest from 2007-2011 as quoted by the
USDA Agricultural Marketing Service (www.marketnews.usda.gov). ANOVA results (P levels) for polynomial trends of
the effects of GA concentration on growth and yield parameters are presented for each cultivar (LSD, least significant
difference (P<0.05); ns, not significant).
GA
Stems
Emerg.
Cultivar
U.S. #1
Cal
White
Yukon
Gold
Chieftain
Red
La Soda
Satina
C’s
B’s
A’s
(10-66 g) (67-91 g) (92-360 g)
Crop Value (% control)
>360g
#2’s
Total
C’s
B’s
A’s
Total
0
83.8
117
120
0
89.3
103
113
0
1.4
-7.3
-29.2
0
11.8
7.6
-11.0
0
48.1
52.7
69.8
0
24.0
25.3
1.9
0
-1.0
-21.8
-41.5
0
5.3
-11.6
-27.8
0
108
143
145
0
35.3
37.6
22.0
0
-8.5
-15.6
-33.0
0
9.2
7.7
-7.4
0
49.7
66.5
125
0
56.4
124
105
0
-3.2
-13.1
-24.2
0
6.4
4.3
0.3
0
53.1
61.4
56.5
0
44.9
51.3
36.1
0
12.8
-3.0
-24.4
0
26.7
19.5
2.9
0
2
4
8
5
47
57
81
2.9
4.5
4.4
5.3
60.1
62.5
57.6
47.7
2.6
4.8
5.7
5.8
2.7
5.1
5.5
5.8
49.1
49.8
45.5
34.8
5.6
2.5
0.6
1.2
2.4
2.6
4.8
8.3
62.3
64.8
62.1
55.8
LSD0.05
linear
quadratic
deviations
22
0.01
0.05
ns
0.7
0.01
0.1
0.05
6.1
0.01
0.05
ns
0.8
0.01
0.01
ns
1.3
0.01
0.01
ns
5.6
0.01
0.1
ns
1.8
0.01
0.01
ns
3.1
0.01
0.01
0.01
5.4
0.01
0.1
ns
0
2
4
8
3
10
31
35
2.4
4.2
4.3
4.0
52.2
51.8
43.3
33.8
2.9
4.3
4.4
4.9
3.5
4.3
4.3
3.5
43.3
42.8
33.8
25.3
2.6
0.4
0.7
0.1
2.2
4.7
7.6
11.1
54.0
56.5
50.9
45.1
LSD0.05
linear
quadratic
deviations
26
0.05
ns
ns
0.9
0.01
0.01
ns
6.9
0.01
n
ns
1.0
0.01
0.1
ns
1.3
ns
0.1
ns
5.2
0.01
ns
0.1
1.7
0.05
ns
ns
3.8
0.01
ns
ns
5.4
0.01
ns
ns
0
2
4
8
0
8
8
14
2.4
3.6
3.8
3.9
57.6
59.4
56.5
47.1
3.3
6.9
8.0
8.1
5.7
7.7
7.9
7.0
47.5
43.5
40.1
31.8
1.2
1.2
0.5
0.1
2.2
0.9
3.0
1.7
59.9
60.3
59.4
48.9
LSD0.05
linear
quadratic
deviations
11
0.05
ns
ns
0.6
0.01
0.01
ns
8.3
0.01
ns
ns
1.9
0.01
0.01
ns
2.5
ns
ns
ns
6.7
0.01
ns
ns
0.8
0.01
ns
ns
1.4
ns
ns
0.01
7.8
0.01
ns
ns
0
2
4
8
0
15
29
66
2.9
3.1
3.7
3.8
68.8
69.5
64.3
59.2
3.7
5.6
6.2
8.4
3.6
5.7
8.2
7.5
56.5
54.7
49.1
42.8
6.0
2.2
2.0
0.5
1.9
0.9
1.4
1.3
71.5
69.0
67.0
60.5
LSD0.05
linear
quadratic
deviations
15
0.01
ns
ns
0.5
0.01
ns
ns
5.8
0.01
ns
ns
2.2
0.01
ns
ns
2.1
0.01
0.05
ns
5.4
0.01
ns
ns
2.7
0.01
ns
ns
2.5
0.1
0.05
ns
5.8
0.01
ns
ns
0
2
4
8
2
66
77
87
3.3
5.1
5.0
4.9
53.8
66.4
61.9
52.2
7.9
12.1
12.7
12.4
8.9
12.9
13.4
12.1
36.8
41.5
35.6
27.8
0.3
0
0
0
0.1
0.4
0.4
0.5
53.8
66.8
62.3
52.7
LSD0.05
linear
quadratic
deviations
21
0.01
0.01
0.1
0.4
0.01
0.01
0.01
3.6
0.01
0.01
0.01
1.3
0.01
0.01
0.1
1.8
0.05
0.01
ns
3.6
0.01
0.01
0.05
0.3
0.1
0.1
ns
0.4
0.05
ns
ns
3.4
0.01
0.01
0.01
140
Table 7. Effects of GA on plant emergence, stem numbers, yield, tuber set and size distributions of cultivars Cal White,
Yukon Gold, Chieftain, Red La Soda, and Satina in 2012. Dates for seed treatments and production activities are given in
Table 1. ANOVA results (P levels) for polynomial trends of the effects of GA concentration on growth and yield parameters
are presented for each cultivar (LSD, least significant difference (P<0.05); ns, not significant).
GA
Stems
Emerg.
Cultivar
U.S. #1 <113g
Cal
White
Yukon
Gold
Chieftain
Red
La Soda
Satina
U.S. #1 Tubers + <113 g
113198g
198- 241- 298>397g #2’s
241g 298g 397g
Total
g tuber-1
Tubers
plant-1
1000s ha-1
0
0.5
1
2
4
38
52
72
81
77
3.5
4.0
4.6
4.5
5.1
27.8
28.7
28.0
28.2
22.2
12.6
11.4
15.2
13.4
13.5
16.3
17.6
18.4
17.3
15.2
5.9
5.7
4.5
5.3
4.4
4.0
3.1
2.8
3.2
2.1
1.5
1.8
1.7
2.3
0.5
0.3
0.5
0.6
0.2
0.0
0.8
0.9
1.5
2.1
4.8
41.3
41.0
44.6
43.8
40.5
116
119
110
112
103
7.6
7.5
8.6
8.2
7.6
348
341
394
373
348
LSD0.05
linear
quadratic
cubic
18
0.01
0.01
ns
0.5
0.01
0.1
0.05
4.2
0.01
0.1
ns
3.2
ns
ns
ns
2.2
0.1
0.05
ns
ns
ns
ns
ns
ns
ns
ns
ns
1.1
0.05
0.05
ns
ns
ns
ns
ns
1.5
0.01
ns
ns
4.9
0.05
0.05
ns
12
0.05
ns
ns
1.1
ns
0.1
ns
51
ns
0.1
ns
0
0.5
1
2
4
18
41
50
57
63
1.4
2.2
2.4
2.8
3.2
22.6
21.2
17.7
13.7
9.7
9.8
14.0
14.6
15.6
15.0
15.0
15.8
14.3
11.4
8.3
4.0
4.3
2.6
1.5
1.0
2.7
1.1
0.9
0.3
0.2
0.9
0
0
0.5
0.2
0
0
0
0
0
1.9
2.6
3.3
5.0
6.6
34.2
37.8
35.6
34.2
31.3
114
95
91
84
76
6.3
8.1
7.7
7.7
7.2
286
370
353
352
329
LSD0.05
linear
quadratic
cubic
14
0.01
0.01
0.1
0.5
0.01
0.05
ns
3.5
0.01
0.1
ns
2.7
0.01
0.01
ns
2.6
0.01
ns
ns
0.9
0.01
0.01
ns
1.5
0.01
0.05
ns
0.6
ns
ns
0.01
ns
ns
ns
ns
2.1
0.01
ns
ns
3.9
0.01
ns
ns
11
0.01
0.05
ns
1.2
ns
0.05
0.1
53
ns
0.05
0.1
0
0.5
1
2
4
10
33
39
61
60
2.0
2.9
3.3
4.3
5.2
10.4
7.4
8.3
6.9
5.1
25.6
31.5
32.2
34.8
33.7
10.0
7.2
8.3
6.5
4.5
0.5
0.1
0.1
0.3
0.2
0
0.1
0
0.1
0
0
0
0
0.1
0
0
0
0
0
0.5
0.1
0
0.1
0.1
0.1
36.2
38.9
40.7
41.9
38.9
68
61
62
59
54
11.7
14.3
14.5
16.0
16.3
532
640
654
712
722
LSD0.05
linear
quadratic
cubic
17
0.01
0.01
ns
0.7
0.01
0.05
ns
2.6
0.01
ns
ns
3.4
0.01
0.01
ns
2.6
0.01
ns
ns
0.4
ns
ns
0.1
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
3.9
ns
0.01
ns
5
0.01
ns
ns
1.5
0.01
0.01
ns
59
0.01
0.01
ns
0
0.5
1
2
4
33
63
80
88
94
3.8
4.4
4.5
4.9
5.9
20.3
21.9
21.9
16.5
13.0
21.6
24.4
24.0
27.6
28.3
17.0
17.9
17.7
14.5
11.7
2.0
2.3
2.7
1.6
1.1
0.9
1.3
0.8
0.3
0.1
0.4
0.5
0.6
0.1
0.1
0
0
0.2
0
0
0.1
0.4
0.3
0.2
0.3
42.0
46.7
46.1
44.2
41.6
88
90
91
77
71
10.6
11.3
11.1
12.7
12.7
483
515
507
578
577
LSD0.05
linear
quadratic
cubic
20
0.01
0.01
0.05
0.8
0.01
ns
ns
4.4
0.01
ns
0.1
4.3
0.01
ns
ns
3.5
0.01
ns
ns
1.3
0.05
ns
ns
0.8
0.01
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
3.2
0.1
0.05
0.05
10
0.01
ns
0.05
1.5
0.01
ns
ns
69
0.01
ns
ns
0
0.5
1
2
4
12
49
68
78
93
3.3
4.1
4.6
4.6
4.8
20.8
26.9
22.2
21.8
14.0
23.1
21.9
23.7
23.5
25.6
17.8
23.8
19.2
19.2
12.7
2.3
2.0
2.2
1.7
1.4
0.7
0.7
0.8
0.8
0.2
0
0.4
0
0.1
0.1
0
0
0
0
0
0.1
0
0.6
0.3
0.3
44.0
48.8
46.5
45.7
40.1
89
97
92
91
79
10.9
11.0
11.0
11.0
11.1
495
503
499
500
504
LSD0.05
linear
quadratic
cubic
20
0.01
0.01
0.05
0.7
0.01
0.05
0.1
5.1
0.01
0.05
ns
3.7
0.1
ns
ns
4.0
0.01
0.05
ns
2.0
ns
ns
ns
0.8
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
0.5
ns
ns
ns
4.5
0.01
0.05
ns
8
0.01
0.05
ns
1.1
ns
ns
ns
49
ns
ns
ns
141
Table 8. Effects of GA on plant emergence, stem numbers, yield, and economic returns of cultivars Cal White, Yukon
Gold, Chieftain, Red La Soda, and Satina in 2012. The weight ranges for grading into A, B, and C tuber size classes,
which are commercially defined by tuber diameter, were estimated from Fig. 1. Crop values are expressed as percent
change in average prices corresponding to the 5-day period coincident with harvest from 2007-2011 as quoted by the
USDA Agricultural Marketing Service (www.marketnews.usda.gov). ANOVA results (P levels) for polynomial trends of
the effects of GA concentration on growth and yield parameters are presented for each cultivar (LSD, least significant
difference (P<0.05); ns, not significant). Dates for seed treatments and production activities are given in Table 1.
GA
Stems
Emerg.
Cultivar
U.S. #1
Cal
White
Yukon
Gold
Chieftain
Red
La Soda
Satina
C’s
B’s
A’s
(10-66 g) (67-91 g) (92-360 g)
Crop Value (% control)
>360g
#2’s
Total
C’s
B’s
A’s
Total
0
8.7
43.3
36.2
58.3
0
-11.7
16.8
10.7
0.0
0
-1.4
0.7
-2.1
-18.5
0
-1.1
7.3
3.8
-7.5
0
89.7
82.4
94.1
116
0
54.1
63.4
77.3
69.6
0
0.0
-14.4
-27.1
-47.5
0
13.6
2.5
-5.1
-20.5
0
51.3
64.1
92.3
108
0
15.0
20.0
30.0
20.0
0
-18.3
-17.1
-29.3
-51.2
0
15.7
22.2
30.4
25.3
0
3.2
9.7
51.6
67.7
0
23.3
30.0
36.7
40.0
0
8.1
4.8
-16.1
-24.2
0
9.1
10.2
11.4
12.0
0
-25.9
-10.2
-6.7
15.4
0
-5.4
5.2
3.3
5.7
0
26.6
6.5
-20.3
-1.6
0
7.1
1.6
-13.1
4.3
0
0.5
1
2
4
38
52
72
81
77
3.5
4.0
4.6
4.5
5.1
40.4
39.9
43.3
41.2
35.6
2.8
3.1
4.1
3.9
4.5
4.4
3.9
5.1
4.9
4.4
32.7
32.3
33.0
32.1
26.7
0.5
0.6
1.1
0.6
0
0.8
0.9
1.5
2.1
4.8
41.2
40.8
44.6
43.5
40.4
LSD0.05
linear
quadratic
cubic
18
0.01
0.01
ns
0.5
0.01
0.1
0.05
5.0
0.05
0.05
ns
1.0
0.01
ns
ns
1.5
ns
ns
ns
3.9
0.01
ns
ns
ns
ns
ns
ns
1.5
0.01
ns
ns
4.8
ns
0.1
ns
0
0.5
1
2
4
18
41
50
57
63
1.4
2.2
2.4
2.8
3.2
32.3
35.6
32.3
29.6
24.4
1.5
2.9
2.8
3.0
3.3
4.4
6.7
7.1
7.7
7.4
26.1
26.1
22.3
19.0
13.7
0.3
0
0
0
0
1.9
2.6
3.3
4.9
6.6
34.1
38.3
35.4
34.5
30.9
LSD0.05
linear
quadratic
cubic
14
0.01
0.01
0.1
0.5
0.01
0.05
ns
4.0
0.01
ns
ns
0.9
0.01
0.1
0.1
1.8
0.05
0.01
ns
3.8
0.01
ns
ns
ns
ns
ns
ns
2.11
0.01
ns
ns
3.5
0.01
ns
ns
0
0.5
1
2
4
10
33
39
61
60
2.0
2.9
3.3
4.3
5.2
35.9
38.6
40.1
41.5
38.3
8.7
13.2
14.4
16.8
18.2
9.0
10.3
10.8
11.7
10.8
18.4
15.0
15.2
13.0
9.0
0
0
0
0
0.5
0.1
0
0.1
0.1
0.1
36.1
38.6
40.4
41.7
38.6
LSD0.05
linear
quadratic
cubic
17
0.01
0.01
ns
0.7
0.01
0.05
ns
3.9
ns
0.01
ns
2.5
0.01
0.01
ns
2.5
ns
ns
ns
3.6
0.01
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
3.7
ns
0.01
ns
0
0.5
1
2
4
33
63
80
88
94
3.8
4.4
4.5
4.9
5.9
41.5
45.5
45.7
43.5
42.1
6.9
7.2
7.6
10.5
11.7
6.7
8.3
8.7
9.2
9.4
27.8
30.0
29.1
23.3
21.1
0
0
0.3
0.1
0
0.1
0.4
0.3
0.2
0.3
41.7
46.0
46.2
43.5
42.4
LSD0.05
linear
quadratic
cubic
20
0.01
0.01
0.05
0.8
0.01
ns
ns
4.2
ns
ns
0.1
3.2
0.01
ns
ns
1.8
0.05
0.1
ns
4.7
0.01
ns
0.05
ns
ns
0.1
ns
ns
ns
ns
ns
4.1
ns
ns
0.05
0
0.5
1
2
4
12
49
68
78
93
3.3
4.1
4.6
4.6
4.8
43.9
48.6
45.7
45.3
39.7
7.7
5.7
6.9
7.2
8.9
8.2
7.8
8.7
8.5
8.7
27.8
35.1
30.2
29.7
22.2
0.2
0
0
0
0
0.1
0
0.6
0.3
0.3
44.0
48.6
46.4
45.7
40.0
LSD0.05
linear
quadratic
cubic
20
0.01
0.01
0.05
0.7
0.01
0.05
0.1
4.2
0.01
0.05
ns
1.8
0.05
ns
ns
2.2
ns
ns
ns
5.1
0.01
0.05
ns
ns
ns
ns
ns
0.5
ns
ns
ns
4.4
0.01
0.05
ns
142
Fig. 1. Changes in tuber diameter with increasing tuber weight for five specialty cultivars.
***Correlation coefficents associated with the indicated coefficients of determination were
significant (P<0.001). Sample sizes (n) ranged from 740-1621 tubers.
143
110
110
Cal White
-1
90
80
70
Y = 12.7835(X)0.3127
R2 = 0.96***
60
50
40
30
20
10
0
50
40
30
20
n = 781
0
100 200 300 400 500 600 700 800
-1
Red La Soda
100
Tuber Diameter (mm tuber )
90
-1
-1
60
110
-1
Chieftain Tuber Weight (g tuber )
80
0.3290
Y = 12.7932(X)
2
R = 0.97***
70
60
50
40
30
20
90
80
70
Y = 14.2426(X)0.3130
2
R = 0.90***
60
50
40
30
20
10
n = 1,270
0
0
0
100 200 300 400 500 600 700 800
Satina
n = 1,079
0
110
Tuber Weight (grams)
100 200 300 400 500 600 700 800
-1
100
100
90
-1
-1
0.3159
Y =13.4457(X)
R2 = 0.97***
70
0
10
80
100 200 300 400 500 600 700 800
100
110
90
10
n = 740
0
110
Yukon Gold
100
-1
100
80
0.3204
Y = 13.5380(X)
R2 = 0.93***
70
60
50
40
30
20
90
80
70
60
50
Cal White
Yukon Gold
Chieftain
Red LaSoda
Satina
40
30
20
10
10
n = 1,621
0
0
100 200 300 400 500 600 700 800
0
0
100 200 300 400 500 600 700 800
Tuber Weight (g tuber-1)
-1
144
Fig. 2. Polygonal plots showing changes in tuber size distributions with increased stem number
per seedpiece of five specialty cultivars in 2009. The yields of <113-g, 113-198-g, 198-241-g
(100 count), 241-298-g (90-80 count), 298-397-g (70-60 count), and >397-g U.S. No. 1 tubers
are plotted on the six axes for each cultivar. The fifty-pound carton counts (22.7-kg) associated
with selected grades are indicated. Shifts in position of red polygons relative to blue polygons
illustrate the effect of increased stem number on tuber size distribution for each cultivar.
Marketable (Mkt) yields, tuber set, and average tuber size (corresponding to each polygon) are
shown in the inset tables. Only those treatments (storage degree days and temperature) that
induced the greatest difference in stem number for each cultivar, without affecting marketable
yield, were compared. *,**P≤0.05 and 0.01, respectively.
145
< 113 g
Cal White
%
< 113 g
Yukon Gold
40
Changes in Tuber Size Distribution
with GA Treatment of Seed
30
35
% 25
30
20
25
> 397 g
113 – 198 g
> 397 g
20
15
Mkt Yield (MT ha-1)
Stems plant-1
Tubers plant-1
Tubers ha-1
g tuber-1
Treatment
450DD (32ºC) 900DD (12ºC)
71.9
75.3ns
3.4
2.7*
6.9
6.3ns
315,800
288,900ns
231.4
263.7*
10
1.7 stems
3.4 stems
5
Mkt Yield (MT ha-1)
Stems plant-1
Tubers plant-1
Tubers ha-1
g tuber-1
0
70 - 60 count
298 – 397 g
Treatment
450DD (12ºC) 900DD (22ºC)
55.6
57.8ns
1.7
2.0ns
5.8
6.1ns
265,100
277,700ns
209.8
207.7*
0
70 - 60 count
298 - 397 g
100 count
198 – 241 g
100 count
198 - 241 g
90 - 80 count
241 - 298 g
< 113 g
Chieftain
% 40
ha-1)
Mkt Yield (MT
Stems plant-1
Tubers plant-1
Tubers ha-1
g tuber-1
Treatment
450DD (12ºC) 450DD (32ºC)
61.6
65.1ns
2.2
2.9**
9.2
10.4*
419,100
472,700*
147.8
138.3*
2.9 stems
113 - 198 g
ha-1)
Mkt Yield (MT
Stems plant-1
Tubers plant-1
Tubers ha-1
g tuber-1
0
100 count
198 - 241 g
< 113 g
% 40
5.2 stems
30
113 - 198 g
3.7 stems
20
Mkt Yield (MT ha-1)
Stems plant-1
Tubers plant-1
Tubers ha-1
g tuber-1
Treatment
450DD (12ºC) 450DD (32ºC)
72.7
75.6ns
3.7
5.2**
12.8
14.7*
583,200
669,900*
124.9
113.5*
10
0
70 - 60 count
298 - 397 g
70 - 60 count
298 - 397 g
100 count
198 - 241 g
90 - 80 count
241 - 298 g
146
3.4 stems
10
Treatment
450DD (12ºC) 450DD (32ºC)
78.8
77.1ns
2.7
3.4**
7.7
8.8*
351,100
403,000*
225.6
194.1*
5
0
2.7 stems
100 count
198 - 241 g
90 - 80 count
241 - 298 g
50
> 397 g
15
2.2 stems
90 - 80 count
241 - 298 g
Satina
113 - 198 g
> 397 g
10
70 - 60 count
298 - 397 g
% 25
20
30
20
< 113 g
30
Red La Soda
50
> 397 g
10
2.0 stems
5
90 - 80 count
241 - 298 g
113 - 198 g
15
2.7 stems
Fig. 3. Effects of GA on yield, stems per plant, tuber set, and tuber size distributions of five
fresh market cultivars in 2010. Seed was cut and treated by immersing in 10 mg L-1 GA prior to
planting. The yields of <113-g, 113-198-g, 198-241-g (100 count), 241-298-g (90-80 count),
298-397-g (70-60 count), and >397-g U.S. No. 1 tubers are plotted on the six axes for each
cultivar. The fifty-pound carton counts (22.7-kg) associated with selected grades are indicated.
Shifts in position of the red polygons relative to the blue polygons illustrate the effect of GA on
tuber size distribution for each cultivar. Marketable (Mkt) yields, stem number, tuber set, and
average tuber size are shown in the inset tables. Data are averaged for two ages of seed (80- and
900-DD). *,**P≤0.05 and 0.01, respectively.
147
< 113 g
30
Cal White
< 113 g
Yukon Gold
% 25
20
> 397 g
5.2 stems
15
113 - 198 g
> 397 g
3.3 stems
10
Treatment
control
GA
Mkt Yield (MT ha-1) 104.9
94.7ns
Stems plant-1
3.3
5.2**
Tubers plant-1
10.4
11.6*
Tubers ha-1
447,100 513,450**
g tuber-1
235.5
184.5**
5
Mkt Yield (MT ha-1)
Stems plant-1
Tubers plant-1
Tubers ha-1
g tuber-1
0
70 - 60 count
298 - 397 g
Treatment
control
GA
71.6
51.7**
1.8
5.4**
8.0
9.6*
357,450 431,800**
200.6
120.3**
35
30
6.4 stems
25
> 397 g
Mkt Yield (MT ha-1)
Stems plant-1
Tubers plant-1
Tubers ha-1
g tuber-1
10
Mkt Yield (MT ha-1)
Stems plant-1
Tubers plant-1
Tubers ha-1
g tuber-1
5
0
70 - 60 count
298 - 397 g
100 count
198 - 241 g
90 - 80 count
241 - 298 g
%
35
6.7 stems
30
25
> 397 g
Treatment
control
GA
80.0**
Stems plant-1
3.6
6.7**
Tubers plant-1
15.0
14.6ns
Tubers ha-1
681,000 663,950ns
g tuber-1
151.8
121.4**
3.6 stems
113 - 198 g
20
15
10
5
0
70 - 60 count
298 - 397 g
% 40
6.0 stems
Treatment
control
GA
105.1
88.4**
3.3
6.0**
14.4
19.1**
657,650 871,000**
159.9
101.4**
100 count
198 - 241 g
90 - 80 count
241 - 298 g
148
113 - 198 g
20
10
0
3.3 stems
70 - 60 count
298 - 397 g
100 count
198 - 241 g
90 - 80 count
241 - 298 g
< 113 g
40
Satina
50
> 397 g
2.8 stems
15
Treatment
Control
GA
98.2
86.5**
2.8
6.4**
13.6
16.0ns
600,750 714,500**
164.8
122.9**
100 count
198 - 241 g
30
113 - 198 g
20
1.8 stems
< 113 g
Red La Soda
40
%
113 - 198 g
90 - 80 count
241 - 298 g
< 113 g
Chieftain
5.4 stems
70 - 60 count
298 - 397 g
100 count
198 - 241 g
90 - 80 count
241 - 298 g
45
40
%
35
30
25
20
15
10
5
0
fresh market cultivars during 2011. Seed was cut and treated by immersing in GA (2 or 4 mg L1
) prior to planting. The yields of <113-g, 113-198-g, 198-241-g (100 count), 241-298-g (90-80
count), 298-397-g (70-60 count), and >397-g U.S. No. 1 tubers are plotted on the six axes for
each cultivar. The fifty-pound carton counts (22.7-kg) associated with selected grades are
indicated. Shifts in position of the red polygons relative to the blue polygons illustrate the effect
of GA on tuber size distribution for each cultivar. Marketable (Mkt) yields, stem number, tuber
set, and average tuber size are shown in the inset tables. Only those GA concentrations that
induced the greatest difference in stem number for each cultivar, without negatively affecting
marketable yield, were compared. *,**P≤0.05 and 0.01, respectively.
149
< 113 g
Cal White
%
35
30
Treatment
control GA (4 mg L-1)
57.6ns
-1
Stems plant
2.9
4.4**
Tubers plant-1
8.5
10.8**
Tubers ha-1
385,700 494,000**
g tuber-1
158.1
116.7**
%
4.4 stems
25
> 397 g
< 113 g
Yukon Gold
40
113 - 198 g
> 397 g
20
15
Treatment
52.0ns
Stems plant-1
2.4
4.2**
Tubers plant-1
8.2
9.4*
Tubers ha-1
373,100 417,600*
g tuber-1
138.1
124.8*
10
5
0
2.9 stems
70 - 60 count
298 - 397 g
70 - 60 count
298 - 397 g
100 count
198 - 241 g
> 397 g
Treatment
Control GA (4 mg L-1)
56.6ns
Stems plant-1
2.4
3.8**
Tubers plant-1
9.8
12.4**
Tubers ha-1
441,800 559,200**
g tuber-1
131.5
101.1**
45
40
%
35
30
25
20
15
10
5
0
100 count
198 - 241 g
2.4 stems
113 - 198 g
> 397 g
Treatment
Mkt Yield (MT ha-1)
68.8
64.4ns
Stems plant-1
2.9
3.7**
Tubers plant-1
9.6
12.1**
Tubers ha-1
435,400 552,000**
g tuber-1
161.3
117.0**
60
5.1 stems
113 - 198 g
30
3.3 stems
20
10
0
70 - 60 count
298 - 397 g
100 count
198 - 241 g
90 - 80 count
241 - 298 g
150
113 - 198 g
20
15
10
5
0
2.9 stems
100 count
198 - 241 g
90 - 80 count
241 - 298 g
40
Treatment
66.5**
Stems plant-1
3.3
5.1**
Tubers plant-1
12.3
16.8**
Tubers ha-1
562,700 766,800**
g tuber-1
96.3
86.9**
3.7 stems
70 - 60 count
298 - 397 g
< 113 g
> 397 g
%
35
25
100 count
198 - 241 g
% 50
40
30
90 - 80 count
241 - 298 g
Satina
< 113 g
Red La Soda
3.8 stems
70 - 60 count
298 - 397 g
113 - 198 g
90 - 80 count
241 - 298 g
< 113 g
Chieftain
4.2 stems
2.4 stems
90 - 80 count
241 - 298 g
45
40
35
30
25
20
15
10
5
0
Fig. 5. Plant emergence (%) from cultivars Red La Soda, Satina, Cal White, Yukon Gold, and
Chieftain as affected by gibberellin (GA). The seed was cut (50-64-g seedpieces), treated April
11, 2012 by immersing for 5 min in solutions of GA, and planted at the WSU Othello Research
Unit on April 13, 2012. *,**P≤0.05 and 0.01, respectively. Bars are ±SE.
151
Red LaSoda 2012
100
90
90
80
80
70
60
Control
0.5 mg L-1 GA
-1
1 mg L GA
2 mg L-1 GA
4 mg L-1 GA
50
40
30
20
Emergence (%)
Emergence (%)
100
35
40
45
30
Satina 2012 Days After Planting
100
80
70
60
Control
0.5 mg L-1 GA
-1
1 mg L GA
2 mg L-1 GA
4 mg L-1 GA
50
40
30
Emergence (%)
90
80
40
45
30
50
0.0 0.5 1.0
100
90
90
80
80
60
Control
0.5 mg L-1 GA
1 mg L-1 GA
2 mg L-1 GA
4 mg L-1 GA
50
40
30
20
2.0
4.0
Cal White 2012 GA (ppm)
70
60
50
R2= 0.98**
31 DAP
40
30
20
10
10
0
0
25
30
35
40
45
50
Yukon Gold 2012
Days After Planting
0.0 0.5 1.0
100
90
80
80
70
60
Control
0.5 mg L-1 GA
1 mg L-1 GA
2 mg L-1 GA
4 mg L-1 GA
50
40
30
20
Emergence (%)
90
2.0
4.0
Yukon Gold 2012GA (ppm)
70
60
50
31 DAP
40
2
R = 0.94**
30
20
10
10
0
0
25
100
R2= 0.94*
20
Cal White 2012
Days After Planting
70
28 DAP
40
0
35
4.0
50
10
30
2.0
GA (ppm)
60
0
25
Satina 2012
70
10
100
R2= 0.94*
0.0 0.5 1.0
90
100
31 DAP
40
50
Emergence (%)
Emergence (%)
30
20
Emergence (%)
50
0
25
Emergence (%)
60
10
0
30
35
40
45
50
0.0 0.5 1.0
Chieftain 2012
Days After Planting
100
90
90
80
80
70
60
Control
0.5 mg L-1 GA
1 mg L-1 GA
2 mg L-1 GA
4 mg L-1 GA
50
40
30
20
Emergence (%)
Emergence (%)
70
20
10
100
Red LaSoda 2012
Chieftain 2012
2.0
4.0
GA (ppm)
70
60
50
33 DAP
40
2
30
R = 0.98**
20
10
10
0
0
25
30
35
40
45
50
Days After Planting
0.0 0.5 1.0
2.0
4.0
-1
GA (mg L )
152
fresh market cultivars during 2012. Seed was cut and treated by immersing in GA (0, 0.5, 1, 2,
or 4 mg L-1) prior to planting. The yields of <113-g, 113-198-g, 198-241-g (100 count), 241298-g (90-80 count), 298-397-g (70-60 count), and >397-g U.S. No. 1 tubers are plotted on the
six axes for each cultivar. The fifty-pound carton counts (22.7-kg) associated with selected
grades are indicated. Shifts in position of the red polygons relative to the blue polygons illustrate
the effect of GA on tuber size distribution for each cultivar. Marketable (Mkt) yields, stem
number, tuber set, and average tuber size are shown in the inset tables. Only those treatments
that induced the greatest difference in stem number for each cultivar, without affecting
marketable yield, were compared. *,**P≤0.05 and 0.01, respectively.
153
< 113 g
Cal White
> 397 g
Treatment
43.2ns
Stems plant-1
3.5
4.6**
Tubers plant-1
7.6
8.6ns
Tubers ha-1
347,900 393,600ns
-1
g tuber
116.1
109.9ns
45
40
%
35
30
25
20
15
10
5
0
< 113 g
Yukon Gold
113 - 198 g
> 397 g
Treatment
29.3ns
Stems plant-1
1.4
2.8**
Tubers plant-1
6.3
7.7*
Tubers ha-1
285,700 351,900*
g tuber-1
113.7
84.0**
3.5 stems
100 count
198 - 241 g
< 113 g
Treatment
Control GA (4 mg L-1)
38.8ns
Stems plant-1
2.0
5.2**
Tubers plant-1
11.8
16.3**
Tubers ha-1
531,500 721,500**
g tuber-1
68.2
53.9**
5.2 stems
113 - 198 g
45
0
100 count
198 - 241 g
100 count
198 - 241 g
70
% 60
5.9 stems
40
70
4.8 stems
113 - 198 g
40
30
3.3 stems
20
10
0
70 - 60 count
298 - 397 g
100 count
198 - 241 g
90 - 80 count
241 - 298 g
154
113 - 198 g
3.8 stems
20
10
0
70 - 60 count
298 - 397 g
100 count
198 - 241 g
90 - 80 count
241 - 298 g
50
Treatment
39.9ns
-1
Stems plant
3.3
4.8**
Tubers plant-1
10.8
11.1ns
Tubers ha-1
494,700 504,100ns
g tuber-1
88.6
79.1*
> 397 g
Treatment
Mkt Yield (MT ha-1)
41.9
41.3ns
Stems plant-1
3.8
5.9**
Tubers plant-1
10.6
12.7*
Tubers ha-1
483,300 576,700*
g tuber-1
87.5
71.3**
15
< 113 g
> 397 g
0
30
2.0 stems
30
% 60
10
50
90 - 80 count
241 - 298 g
Satina
20
< 113 g
Red La Soda
70 - 60 count
298 - 397 g
1.4 stems
70 - 60 count
298 - 397 g
60
> 397 g
113 - 198 g
30
90 - 80 count
241 - 298 g
90
% 75
2.8 stems
40
90 - 80 count
241 - 298 g
Chieftain
% 50
4.6 stems
70 - 60 count
298 - 397 g
60

Blauer_wsu_0251E_10645 - Washington State University

Transcription

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