33-2014 Stetina Ren. Nem. Resistance Annual Rep.

MISSISSIPPI SOYBEAN PROMOTION BOARD
PROJECT NO. 33-2014 (YEAR 2)
2014 Annual Report
Title of Project: Development of Reniform Nematode Resistant Lines from JTN-5203, PI 404166, and
02011-126-1-1-5-1-1 Soybean
Principal Investigator: Dr. Salliana R. Stetina (Sally.Stetina@ars.usda.gov)
BACKGROUND AND OBJECTIVES
Many soybean growers, in the Delta region of Mississippi in particular, are faced with the challenge of
producing a profitable crop in fields infested with reniform nematode (Rotylenchulus reniformis). The
soybean lines JTN-5203 (PI 664903), PI 404166, and 02011-126-1-1-5-1-1, previously identified by
project scientists as having resistance to Mississippi isolates of reniform nematode, will be used as
parents in crosses to transfer that resistance into soybean lines adapted for Mississippi.
The objectives of this project are to (1) develop F2 and F2:3 populations derived from crosses between PI
404166 or 02011-126-1-1-5-1-1 and soybean lines agronomically adapted for Mississippi, (2) evaluate
the F2 progeny from these crosses in phenotypic screening experiments for selection of reniform
nematode-resistant genotypes, and (3) advance resistant F2:3 lines from and earlier cross to JTN-5203 in
the breeding program using phenotypic assessments and marker assisted selection where available.
REPORT OF PROGRESS/ACTIVITY
Objective 1.
In 2013, reniform nematode-resistant soybean lines PI 404166 and 02011-126-1-1-5-1-1 were crossed to
lines adapted for Mississippi that have desirable agronomic traits such as high yield and very good seed
quality. F1 seeds were planted in soybean winter nurseries, and F2 seeds were received in the spring of
2014. A subset of F2 seeds from each cross was planted in the soybean nursery at Stoneville, MS in the
spring of 2014. The remaining subset of seeds from each cross was reserved to screen for reniform
nematode resistance after the crosses were confirmed to be true.
In July, segregation of agronomic traits such as flower color and pubescence were examined and seven
true crosses were confirmed:
04030-1-4-1-1 x 02011-126-1-1-5-1-1
04025-1-1-4-1-1 x 02011-126-1-1-5-1-1
DB04-10836 x 02011-126-1-1-5-1-1
DS97-94-9 x PI 404166
DS880 x PI 404166
LG01-5087-5 x PI 404166
DB04-18036 x PI 404166.
F3 seeds were harvested from agronomically superior plants from each of these crosses in the fall of
2014. A subset of the F3 seeds was used to screen for resistance to reniform nematode in growth
chamber assays, and the remaining seeds were retained to plant in the field in 2015.
Objective 2.
A subset of F2 plants from the cross 04025-1-1-4-1-1 x 02011-126-1-1-5-1-1 was evaluated in the growth
chamber for infection by reniform nematode. A susceptible check, a resistant check, 136 individual F2
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plants, and the parent lines were inoculated with 1,000 reniform nematodes (mixed vermiform stages).
Approximately 4 weeks later, most of the root system was removed from each plant for nematode
assessment. The distribution of phenotypes of the F2 plants (Figure 1) was skewed in favor of resistant
plants; 11 plants had resistance levels comparable to or greater than the resistant parent.
The plants were repotted in the greenhouse to allow production of F3 seeds and collection of DNA from
leaf tissue for marker analysis and/or development. Seeds were successfully harvested from 135
recovered plants in December 2014, and those of the most resistant lines were selected for inclusion in
2015 field plantings.
Based on molecular marker data collected during the fourth quarter of this project year, the resistance
identified in this population could be unique. Research from previous work done by this project team
(DS97-084-1 source of resistance) and other published reports in the literature identified putative loci
for resistance to reniform nematode on chromosome 18. However, when the phenotypic data from this
F2 population was analyzed, neither of the two markers from chromosome 18 was significantly
associated with the resistance, regardless of whether resistance was considered a binary or continuous
variable.
We are currently considering alternative approaches to identifying this locus, including additional
probing of the soybean genome using known markers and development of recombinant inbred lines
from susceptible and resistant individuals in this population that would eventually allow replicated
testing of each line for reaction to reniform nematode and improve the precision of the test.
Objective 3.
Advancement of F2:3 lines from the JTN-5203-derived population progressed as anticipated. We are
using two different approaches to identify reniform nematode-resistant plants and advance them in the
breeding program. In total, 15 resistant lines have been identified and advanced to the F4 generation at
this stage in the breeding program.
One approach is to screen for nematode resistance in the F2 generation, recover the best plants, and use
their seeds to plant the F3 generation in the field. A nematode screening for 228 F2 plants derived from a
cross to JTN-5203 was conducted during the 2013-2014 project year, and F2:3 seeds of the 10 most
resistant plants screened were planted in the 2014 nursery at Stoneville, MS. At harvest, F4 seeds were
successfully collected from all of the lines selected using this approach.
In the second approach, the best F2 plants from crosses to JTN-5203 were selected in the field based on
agronomic characteristics and F3 seeds were harvested in 2013. Ten F3 plants representing 20 different
F2 families were tested in the growth chamber during the summer of 2014 to determine if reniform
nematode-resistant lines occur in any of the F2:3 families; concurrently, the seeds from each F2:3 family
were grown in the field for advancement to the next generation and further evaluation of agronomic
properties.
For the growth chamber testing, a susceptible check, a resistant check, and 10 F3 plants representing
each F2 family were inoculated with 1,000 reniform nematodes (mixed vermiform stages).
Approximately 4 weeks later, the root system was removed from each plant and the number of
nematodes infecting the root system was determined. The five best F2:3 families demonstrated to
contain reniform nematode-resistant lines were selected for harvest in 2014 and advancement to the F4
generation. From an agronomic perspective, the F3 plants from the selected families looked very good.
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IMPACTS AND BENEFITS TO MISSISSIPPI SOYBEAN PRODUCERS
According to the National Agricultural Statistics Service, approximately 2,200,000 acres of soybean were
planted in Mississippi in 2014, primarily in the Delta region where reniform nematode is ubiquitous.
Based on the 2014 price-received estimate of $11.10 per bushel and average yield of 52 bushels per
acre, Mississippi soybean acreage had a potential value of $1,269,840,000. Even an average yield loss of
10% caused by reniform nematode translated to a potential annual loss of more than $126 million to
Mississippi growers. Losses to reniform nematode could be drastically reduced if resistant soybean
varieties adapted for Mississippi were available.
END PRODUCTS
The ultimate end products from this work will be soybean germplasm with putatively unique resistance
to reniform nematode derived from thee different soybean lines, and associated conference
presentations and journal publications describing the resistance. Intermediate products from this year
of the project are F2, F3, and F4 generation soybean lines with reniform nematode resistance that are
being advanced in a long-term breeding program.
Figure 1. Frequency distribution of F2 progeny from the cross 04025-1-1-4-1-1 (susceptible to reniform
nematode) x 02011-126-1-1-5-1-1 (resistant to reniform nematode) in a growth chamber screening. R
and S indicate the phenotypes of resistant and susceptible parents, respectively.
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