AERGC Spring 2015 Newsletter

Association of Education and Research Greenhouse Curators
Spring 2015
Volume 27, No.1, Spring 2015
FINAL
DRAF
T
Plant Profiles
In this Issue
The Genus Drymonia
Jonathan Ertelt
Vanderbilt University
The genus Drymonia is in the Gesneriaceae, the family most well-known (perhaps)
for African violets. This genus belongs in
more collections even if a bit of a challenge
to keep controlled, and depending on the
species, not wandering.
In this Issue
The Genus Drymonia
1
Cultivation of Parasitic Flower Plants
for Research and Teaching
4
How Do Plants Affectthe Performance
of Natural Enemies?
9
Help Wanted
10
Simulating Winter in a Mediterranean
Climate
11
Drymonia affin conchocalyx - A specimen yet
to be definitively identified This is tough, low
elevation grower.
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Drymonia ‘Fransisco Pizzaro’ – a shrubby, rare
hybrid in this genus, with large paired leaves
and numerous showy flowers. The tags indicate crosses made last year.
To review of some of the familial characteristics exhibited in this genus, the plants,
and particularly the leaves or flowers, can be
quite hairy. The leaves are generally found in
pairs opposite each other on the stem, and the
stems in this genus can be stout and shrubproducing. Or the stems can be thinner, producing vining lianas with stems that can
actually become quite stout themselves over
time. These are perennial plants with fibrous
roots. All members of the family have fibrous roots, but some have modified stems
forming typically underground tubers, rhizomes, or structures referred to as scaly rhizomes.
The flowers are zygomorphic, generally
slipper-shaped in this genus. While there are
exceptions, the flowers complete and perfect
with five sepals, a floral tube opening out to
five petal lobes, 4 paired stamens, and a
stigma leading back to a two-carpelled fruit.
Drymonia fruits are often more impressive
than the flowers. Opening at maturity as
display fruits, theya are a type of fleshy
capsule often with a brightly colored interior
to the fruit helping to advertise the ripe seeds.
An interesting characteristic of the flowers in this family is that they are protandrous.
Though the flowers are complete and perfect, they are male flowers first and then
female. And this floristic dimorphism is very
noticeable in the genus Drymonia, wherein
the individual flowers are relatively shortlived, usually lasting 2 or 3 days. When the
flowers first open the anthers are prominently displayed, but after a day or so the coiling
filaments pull these back. By the middle of
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Volume 27, No.1, Spring 2015
AERGC Newsletter
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Drymonia affin conchocalyx - 2nd day female. t.
Like most in the Gesneriad family, these flowers are protandrous (male first and then female). Here, the anthers have been pulled back
by the filaments curling up, while the stigma
has elongated and grown forward towards the
opening of the floral tube. The stigma indicates
that the flower is now female and has been
open for at least the second day.
the second day the typically bilobed stigma
is there instead, presenting a female flower.
The pollinating hummingbirds or bees
do not get dusted with pollen as it bumps into
the male flower’s open anthers. Instead, in
Drymonia the anthers (as always, with a few
exceptions) open only at apical pores, the
pollinators get pollen shaken or poured onto
their head or back as they push under the
anthers toward their nectar reward, tipping
the anthers like salt & pepper shakers in the
process.
These anthers, while not strictly unique,
are certainly unusual and would be enough
to warrant the inclusion of this genus of
epiphytic lianas and shrubs in the “educational interest” category. I thoroughly enjoy
demonstrating the salt & pepper shaker aspect by either pushing into the bottom of the
flower with a pencil tip, or pulling the anthers out with a pair of tweezers and then
tipping them over pouring out the pollen. But
it is what happens after pollination / fertilization - which is easily accomplished once
both male and female flowers are present on
a flowering plant - that firmly pins this genus
to the educational highlights board. The
question of whether the display fruit is a
dehiscing berry or a fleshy capsule has challenged many of my students over the years.
It is officially categorized as the latter but
I’ve never seen a paper explaining why. It is
a curiosity, and with several species as already mentioned, the display fruit is at least
as showy as the flowers. Members of this
genus grow readily, and if pollinated, fruit
readily as well.
Drymonia species do tend to lean towards the large size, but can be pruned as
needed. The shrubby species such as D. kil-
Page 2
Jonathan Ertelt
lipii and D. chiribogana do not require as
much pruning. D. strigosa and a few other
less commonly grown species are medium in
size - generally not quite upright shrubby, but
not given to the quickly elongating stems of
the vining liana-type species. One of the
most wide-spread species of the family in
terms of native habitat is perhaps the most
commonly cultivated vining type, D. serrulata, but there are numerous others. While
some of the species can be grown with care
under lights or in a window, most just require
too much space. And the large size is relative, and not so difficult for greenhouses as it
Drymonia coccinea 'umecta' -a specimen from
upper elevations with more constant moisture.
The 'umecta' tag indicates that this one can be
quite slimy. An hypothesis is that the slime is
produced to help inhibit fungal pathogens that
might destroy immature fruit.
might be for hobbyists, windowsill growers
and those that grow under lights.
Of course, like so many other exciting
tropicals, there are species yet to be named
and others that are quite challenging to grow.
There are currently at least three varieties,
possibly species, grown collectively as D.
coccinea, though there are some unique
FINAL DRAFT
AERGC Newsletter
characteristics to each, as we will see. And
there’s a species that had been so difficult to
bloom that it was named D. pudica (‘pudica’
meaning shy or bashful) that we have now
discovered will bloom readily with cooler
temperatures of the upper elevation rain forests, commonly known as cloud forest. (I am
very proud to report that one of my volunteers has submitted an article on this species
which will be coming out in the first issue,
2015, of Gesneriads, entitled “Drymonia pudica; An exploration of the shy Drymonia.”)
In addition to the potential teaching aspects, these plants offer attractive flowers
and fruits along with the ease of propagation.
Size might be a challenge for some, pruning
is of course an option. So, try to find a Drymonia species or two to add to your collection. Enjoy, and Good Growing.
Drymonia pudica 1st flr, 1st day - The shy Drymonia needs the cool/cold to initiate flower
buds/inflorescences. The anthers within the
corolla, indicate the first day of blooming for
this protandrous species.
Volume 27, No.1, Spring 2015
Drymonia pudica display fruit in calyx – This
fruit, harvested from the plant with the large
surrounding calyx, is displaying the black seed
mass midst whitish funicular tissue, the inside
of the fruit shiny bright pink/purple, reflexing
back to expose the seeds.
Jonahan Ertelt is the Greenhouse Manager for
the Department of Biology at Vanderbilt University in Nashville, TN. Contact Jonathan via email at jonathan.ertelt@vanderbilt.edu.
The AERGC 2015 Annual Meeting
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The Ohio State University
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Page 3
FINAL DRAFT
AERGC Newsletter
Volume 27, No.1, Spring 2015
Plant Cultivation
Cultivation of Parasitic Flower Plants for Research and Teaching
From the Laboratory of Claude dePamphalis
Penn State University
Approximately 1% of all flowering plant
species are parasitic. Displaying extremes of
specialization and development, parasitic
plants are cherished botanical oddities. Apart
from their appeal to botanists for their curious
lifestyle, they have also been studied extensively, due to their economic impact or extremeness of adaptations. Aside from
taxonomic studies, which have shown multiple independent evolutionary origins of
parasitism1, parasitic plants are generally
classified depending upon their attachment
points or by their degree of host dependence.
The connection organ, called a haustorium,
can attach to stems, as do the Mistletoes, or to
roots, as do Beechdrops (Epifagus). Endophytic parasites, like Rafflesia, grow inside
their hosts and only emerge to flower. Rafflesia, which exclusively parasitizes vines in the
grape family, produces the largest flower of
any angiosperm! It is also useful to divide
parasites based upon their host dependence.
One way is to describe the dependence on he
host for carbon, or alternatively, on levels of
parasite photosynthesis. Hemiparasites still
photosynthesize, while holoparasites have
lost photosynthesis and rely completely upon
the host for carbon. Curiously, some holoparasites are thought to synthesize small
amounts of chlorophyll. The role chlorophyll
plays in a non-photosynthetic, obligate, holoparasite like Phelipanche is unclear2.
grown and studied at Penn State, and in the
labs of our collaborators. These plants represent a wide range of parasite types, including
widely varying plant structures and growth
rates. One of the primary hurdles in cultivation of parasitic plants is creating ideal conditions for the parasite to establish with a host
that are also amenable to research goals.
Orobanchaceae
Contributed by
Loren Honaas and Claude dePamphilis
Consisting of 90 genera and ca. 1800
species3, this family represents a special case
in that it is the only parasitic plant family with
species displaying the full range of parasitic
abilities plus a free-living basal lineage, Lindenbergia, that is sister to the parasitic
Orobanchaceae. This makes for an ideal comparative framework to understand the evolution of parasitism and the processes central to
the parasitic lifestyle. Additionally, the parasitic Orobanchaceae are the most destructive
parasitic weeds, causing $US billions of damage each year to agricultural crops in Africa
and the Mediterranean4. Previous efforts to
control parasitic Oroban-chaceae have been
focused upon developing resistant hosts
through mostly traditional breeding programs. These efforts have been met with
limited success, so the search for new control
strategies became part of the impetus to focus
“Parasitic plants, especially living examples that challenge standard
botanical teachings of what parts and processes comprise a plant,
are also extremely interesting to students of any age.”
Questions like this drive scientific inquiry into parasitic plants, and the emerging
answers have far reaching implications for
plant biology. Parasitic plants, especially living examples that challenge standard botanical teachings of what parts and processes
comprise a plant, are also extremely interesting to students of any age. This article will
highlight cultivation methods for parasites
from three plant families (Orobanchaceae,
Convolvulaceae and Loranthaceae) that are
on the parasites. The National Science Foundation’s Plant Genome Research Program
funded the Parasitic Plant Genome Project
(PPGP)5 and continues to support parasitic
plant research in the lab of Dr. Claude dePamphilis and collaborators, including John
Yoder (University of California), James
Westwood (Virginia Tech), and Michael
Timko (University of Virginia).
One of the focal species of the PPGP is
Triphysaria versicolor (yellowbeak owl’s
Page 4
clover). This facultative, generalist parasitic
plant has a long history of botanical interest
and has been developed as an experimental
model for parasitic plant research. It is one of
four plants that are the focus in the current
phase of the PPGP. The others are Lindenbergia philippensis, Striga hermonthica (an obligate hemiparasite), and Phelipanche
aegyptiaca (an obligate holoparasite). An ongoing series of experiments is underway to
explore host dependent growth patterns in
Triphysaria. This work presents additional
challenges of parasite-host co-culture since
the experiments are designed to uncover parasite phenotypes that are correlated with exposure to different hosts across its broad host
range (which spans flowering plants). At
Penn State, Triphysaria is grown with Solanum, Medicago, Arabidopsis, Oryza, Zea,
and Juncus.
The parasite seeds are collected from
native grass stands near Napa, CA. Cultivation of Triphysaria begins with scarification
using concentrated sulfuric acid, surface sterilization using concentrated bleach, stratification, and finally germination on sterile
petri-plates with a minimal-nutrient, low-sugar medium. At the same time that hosts are
transplanted, the Triphysaria seedlings are
moved to pots (when the first true leaves
begin to emerge). To facilitate establishment
of the parasites, pots are frequently misted
during the first week (Figure 1). The soil
mixture is, by weight, mostly sand and the
other media component is primarily peat.
This nutrient poor, high drainage media is
supplemented with slow release fertilizer to
support healthy plant growth over the course
of experiments that can last 8 weeks or more.
With helpful advice from greenhouse manager Scott DiLoreto, an automated, multi-channel watering system was designed with parts
from the hardware store. One version of the
system was used to water 145 pots in 5 randomized blocks, each containing pots representing 7 treatments for a total of 16
independent channels (4 channels served the
controls), and only cost $600 (Figure 1). The
system was calibrated to deliver a small volume of water to each pot 2-3 times per day.
AERGC Newsletter
FINAL DRAFT
Volume 27, No.1, Spring 2015
Figure 1.
Clockwise from top left;
Triphysaria co-cultured with Tomato
(Solanum lycopersicum) ~2 days after
transplant; Triphysaria ~2 weeks after
transplant; the automated watering system
made with parts from local hardware store;
and Triphysaria ~6 weeks after transplant
with inflorescences.
Figure 2.
Orobanche californica growing on roots
of host plant Grindelia integrifolia.
Clockwise from top left:
Orobanche plus Grindelia in 5” pot;
removed from pot, showing three
flowering Orobanche and smaller plants
of various stages; close-up of small
parasite seedlings attached to Grindelia
roots.
This kept soil moisture high, supporting
healthy Triphysaria, but drained sufficiently
to prevent waterlogging of host roots.
The experiments are planned during
spring and fall in central Pennsylvania to
avoid excessive temperatures, and receive
supplemental lighting as necessary. Diloreto
has biological control methods at the ready
and prefers to avoid spraying whenever possible. This conservative pest control ap-
proach allows tight control of experiments
leading to cleaner data. These experiments
have revealed host dependent phenotypes
that are being explored in axenic growth
conditions that favor experimental molecular
approaches. It is hoped that understanding
host-dependent phenotypes will shed light on
host selection/preference mechanisms and
parasitic plant-host plant communication.
Page 5
Another Orobanchaceae species that has
been cultivated at Penn State is Orobanche
californica. This North American native holoparasite is grown on the perennial host
Grindelia integrifolia (Figure 2) and has
been used frequently in teaching demonstrations at Penn State. As a holoparasite that
lacks photosynthetic activity, it has been
routinely included in our examinations of
parasite growth and next generation sequenc-
AERGC Newsletter
ing experiments. The transcriptome of O.
californica was recently deeply sequenced to
provide additional evidence for comparisons
of several Orobanche species in the context
of ongoing PPGP studies. Originally collected from the field by Dr. Alison Colwell (now
a botanist with the National Park Service),
these species have been co-cultivated continuously for more than 20 years. Native to
Pacific Northwest coastal headlands, this pair
grows well in a soil mix of 1 part metro 360:
1 part sand with supplemental light as needed. Orobanche plants will grow and flower
almost year ‘round under greenhouse conditions, spending the early part of their life
underground and pure white, then emerging
energetically from the soil as an inflorescence of purple flowers. Flowers will set seed
without hand pollination, and will self-sow to
maintain an active parasite-host culture for
years. From time to time, the Grindelia
plants need to be transferred to larger pots or
propagated from cuttings with the addition of
fresh Orobanche seeds to the soil mix.
Several other parasitic Orobanchaceae
have also been grown successfully in our
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greenhouses, including Schwalbea americana, Buchnera americana, and multiple
species of Castilleja and Agalinis. For all of
these hemiparasites, slow-growing host
plants worked well, especially native grasses
like Blue Gramma (Bouteloua gracilis) that
could be trimmed back/mowed/grazed to allow light to reach the young parasites. More
importantly, all of those species require light
for germination. The seedlings are so tiny
that it's usually helpful to let them get a few
sets of true leaves before starting the host or
creating a 'host-free' area of the pot in which
they can get established without being shaded out.
A long-term goal of studying parasitic
Orobanchaceae is to leverage understanding
of parasite biology in the fight against parasitic plants. Knowing more about the parasitic plant lifestyle will aid in the development
of novel control strategies for the pernicious,
weedy Orobanchaceae. The dePamphilis
group publishes parasitic plant research regularly; check http://cwd.huck.psu.edu/ for
more information about our current research
efforts and publications.
Volume 27, No.1, Spring 2015
Loranthaceae (Santalales)
Contributed by
Marcos Caraballo-Ortiz
This family is one of several in the order
Santalales that contains species displaying
the so-called mistletoe habit. It appears that
within the order, multiple lineages of hemiparasitic stem parasites evolved the mistletoe
habit independently6. In Loranthaceae,
which consists of ~1000 species, most are
mistletoes. Of particular interest in this family are Dendropemon mistletoes, which are
restricted to the Caribbean Islands, and present a unique opportunity to understand plant
evolution on insular ecosystems from the
perspective of a parasite.
These hemiparasitic plants depend on
woody hosts to obtain water and mineral
nutrients. Although they are photosynthetic
plants, Loranthaceae and other mistleoes are
slow growers; they can take many months to
fully establish and will only occupy a small
space in the greenhouse for years. Because of
their slow growth rates, these can be thought
of as the “tortoises” of the parasite world.
Seeds of mistletoes are short lived, and ger-
Figure 3. Clockwise from top left: Dendropemon mistletoe seed with the fruit flesh removed showing strands of sticky viscin; seed planted on
Citharexylum spinosum (Verbenaceae); seedling producing first pair of leaves on Thespesia populnea (Malvaceae); seedling
established on Thespesia; seedling developing epicortical roots on Thespesia; seedling arrested in growth at the cotyledon stage on
Tabebuia heterophylla (Bignoniaceae).
Page 6
AERGC Newsletter
mination is initiated as soon as the fruit is
removed from the plant. Thus, mistletoe
seeds are planted on branches of host trees
shortly after being removed from the plant.
To preserve freshness of fruits, they are collected while still attached to the infructescences (even better if collected with stems),
placed in brown paper bags, and maintained
in cool temperature (~4°C) for no more than
three days. After three days, there is a high
probability that the sticky substance surrounding the seeds (viscin) will degrade,
decreasing the likelihood that seeds will anchor on host stems. The fruits are peeled to
completely expose the seeds because the
fruit flesh can interfere with seed germination and promote growth of pathogens (Figure 3). In the wild, the fruit flesh is removed
and degraded in the digestive tract of birds
before deposition on tree stems. Some mistletoe species have most of their viscin concentrated into a ‘disk’ at the top of the fruit
that can be detached easily if fruits are peeled
FINAL DRAFT
incorrectly or if the fruits are not ripe
enough. After peeling, seeds are pinched
between two fingers to remove some viscin
for application directly on the host branch. It
is recommended to leave the viscin drying
for one or two days before exposure to water,
and hosts should be watered in such a way to
avoid dislodging seeds from host branches.
Although mistletoe germination is often
very high, not all seeds germinate and sometimes seedlings will fail to make haustorial
connections to host branches. In addition,
mistletoes (especially tropical ones) are sensitive to overdrying by low humidity during
germination, which can cause incomplete
cotyledon emergence. Water quality can be
an additional factor to take into consideration in greenhouses, as hard water can accumulate mineral deposits on young tissues.
Last, selection of host trees is crucial for
successful establishment of mistletoes, as
not all mistletoes can be established on all
tree species. Finding a suitable host will
Figure 4.
Clockwise from top left:
Cuscuta seed germination on filter
paper after scarification; initial
seedling attachment to host; mature
vines in flower; newly transplanted
seedlings.
Page 7
Volume 27, No.1, Spring 2015
depend largely on the species of mistletoe to
be planted. In the greenhouse we have planted seeds of tropical mistletoes from the Loranthaceae family (Dendropemon spp.) on a
variety of hosts including known hosts for
each species. Mistletoes established better
and growth faster on their known hosts while
seeds planted on hosts not known for the
species either grow slowly, remain arrested
in growth (at cotyledon stage) for an indefinite period of time, or die.
The work underway uses traditional taxonomy and modern molecular techniques to
build high-resolution molecular phylogenies.
This will clarify the taxonomy of the group
and advance our understanding of the factors
that might be involved in species diversification such as host choice, environmental conditions, and geography. The long-term goals
include understanding how long-term interactions between parasites and hosts can promote speciation and host specialization in
island ecosystems.
AERGC Newsletter
Convolvulaceae
Contributed by
Joel McNeal
Cuscuta is the only parasitic genus in this
family and contains about 200 species. Also
called dodder, this obligate stem parasite has a
broad host range including many flowering
plants, but not grasses. In contrast to the mistletoes, Cuscuta plants have the ability to grow
at a surprisingly fast rate and die soon after
seed production; Cuscuta represents the jackrabbit in our ‘tortoise and hare’ comparison of
parasitic plant growth rates. Some species are
mild to moderate agricultural pests, and they
have recently made news because they seem to
trade large amounts of RNA with their hosts6.
This represents the first such observation and
may provide insights into how parasitic plants
communicate with their hosts. Cuscuta species
have been grown at Penn State for systematics,
chloroplast genome studies and volatile sensing studies and are currently grown at Kennesaw State University for studies on evolution
of nuclear photosynthetic genes, haustorial
development, and host specificity. Their fast
life cycle, broad host range, and above-ground
haustoria make them an excellent model for
studying the evolution of parasites.
Cuscuta seeds can either be collected as
soon as capsules are swollen or well after
maturity. If they are still soft, the seed capsules
can be left to dry in low humidity conditions
until the seed coat has hardened. When stored
at dry conditions either at room temperature or
refrigerated, seeds can be viable for decades
provided they aren’t exposed to high heat;
40-year old seeds have even been successfully
germinated from herbarium specimens that
weren’t placed in a heated dryer. Like their
Morning Glory relatives, they have an extremely tough outer seed coat that must be
scarified in order to allow water permeability
and germination. The most effective means for
achieving synchronized germination is to use
concentrated sulfuric acid as the scarifying
agent8. Porcelain Gooch Crucibles with a pore
size small enough that the seeds won’t fall
through or become lodged in the pores are
useful in transferring seeds between beakers to
avoid contact with the acid. Thirty minutes to
one hour in acid is usually sufficient to allow
permeability for most Cuscuta species, and
periodic agitation during that time can increase
evenness of germination. The acid should be
rinsed off thoroughly with water and the seeds
briefly transferred to a weak bleach solution to
sterilize the seed surface. After a final rinse,
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the seeds can be placed on wet filter paper in
a petri dish and sealed.
Seeds will frequently swell within 24-48
hours and germinate shortly thereafter, although germination may sporadically occur
over weeks or even months if the seeds were
insufficiently scarified. A swollen, root-like
hypocotyl emerges first, and the seedling
gradually sheds the seed coat as the stem
uncoils. Seedlings are best transplanted as
soon as they have shed their seed coat. The
hypocotyl doesn’t absorb nutrients but
should be kept wet and can be immersed in a
small microcentrifuge tube filled with water
as long as the yellow shoot sticks out from
the tube (Figure 4). Most of the tube’s opening can be covered with parafilm to prevent
the water in the tube from evaporating until
the seedling is established. The seedlings are
very fragile to bruising or folding at this
stage, and they usually will not survive if the
stem is folded during transplanting. While
almost any non-grass host can be used for
mature plants, a host with a thin, vertical
shoot should be used during initial seedling
establishment, and the microcentrifuge tube
can be placed in the soil next to the host
(Figure 4). The host plants should be watered
carefully to prevent damaging or dislodging
the Cuscuta seedling until it has formed its
first tight coil around the host stem. Cuscuta
will not attach successfully if strictly grown
under artificial light as the searching motions
of the seedlings are coordinated by natural
sunlight cues.
After a few days, the parasite stem will
swell and commence rapid growth, after
which it can be placed near other larger
hosts. Each stem tip from the branching
vines can grow inches per day, and most
species will quickly cover an entire greenhouse bench if allowed to grow unabated.
Any other greenhouse plants that you don’t
want parasitized should be kept well away
from the growing Cuscuta vines, and the
Cuscuta stems can be trimmed back liberally
without killing the parasite. Growth will
slow considerably once they commence
flowering, and most species die after they
have produced hundreds or thousands of
seeds. New plants will have to be started
every few months to maintain them in a
greenhouse collection long term. The most
common greenhouse pests on Cuscuta are
aphids. Maintaining low greenhouse thrip
levels at the time of planting is essential as
they find Cuscuta seedlings particularly at-
Page 8
Volume 27, No.1, Spring 2015
tractive and can kill the fragile seedlings with
a single bite.
Conclusion
The cultivation of parasitic plants, while
challenging, is a rewarding endeavor. Seeing
the extreme adaptations firsthand can have a
lasting effect on the observer and frequently
generates enthusiasm among students of all
ages. The few examples reported here represent years of careful experiments and observations that led to reliable methods for parasitic
plant growth. Indeed challenges exist for
many parasitic plants that have not been overcome, especially for the endophytic parasites,
such that they have not been successfully
cultivated. Pressing research questions and
curiosity will continue to drive exploration of
parasitic plant biology at all levels study. If
you have questions or comments regarding
how to grow parasitic plants, especially about
the cultivation of parasites for teaching collections or outreach, we encourage the reader to
reach out to the authors.
1. Barkman T. J., Lim S. H., Salleh K. M., Nais J.
Mitochondrial DNA suggests at least 11 origins
of parasitism in angiosperms and reveals genomic chimerism in parasitic plants. BMC Evolutionary Biology. 7 (2007)
2. Wickett N. J., Honaas L. A., Wafula E. K., Das
M., Wu B., Landherr L., Timko M. P., Yoder J. I.,
Westwood J. H., dePamphilis C. W. Transcriptomes of the Parasitic Plant Family
Orobanchaceae Reveal Surprising Conservation
of Chlorophyll Synthesis. Current biology. 21,
2098-2104 (2011)
3. Nickrent D. The Parasitic Plant Connection,
http://www.parasiticplants.siu.edu/
4. Parker C. Parasitic Weeds: A World Challenge.
Weed Science. 60, 269-276 (2012)
5. The Parasitic Plant Genome Project,
http://ppgp.huck.psu.edu/
6. Vidal-Russell R. & Nickrent D. L. The first mistletoes: Origins of aerial parasitism in Santalales.
Molecular Phylogenetics and Evolution. 47, 523537 (2008).
7. Kim G., LeBlanc M. L., Wafula E. K., Depamphilis C. W. & Westwood J. H. Genomic-scale exchange of mRNA between a parasitic plant and
its hosts. Science. 345, 808-811 (2014)
8. Gaertner E. E. Studies of seed germination,
seed identification, and host relationships in dodders, Cuscuta spp. Memoirs of the Cornell University Agricultural Experiment Station. 3–56,
294. (1950)
Acknowledgements:
Thanks to Anthony Omeis, Scott DiLoreto and L.
Shawn Burghard, greenhouse managers at Penn
State, for their help and suggestions for parasitic
plant cultivation.
Photographic Credits:
Loren Honaas, Sam Jones, Huiting Zhang (Triphysaria); Paula Ralph (Orobanche); Marcos Caraballo-Ortiz (Dendropemon); Joel McNeal (Cuscuta).
FINAL DRAFT
AERGC Newsletter
Volume 27, No.1, Spring 2015
IPM
How Do Plants Affect
the Performance of Natural Enemies?
Raymond Cloyd
Kansas State University
Biological control is a plant protection
strategy that involves using natural enemies
(=biological control agents) such as parasitoids and predators to suppress or regulate
insect and/or mite pest populations at levels
that results in minimal noticeable plant damage. The success of any biological control
program depends on a number of factors
including quality of natural enemies, timing
of release, environmental conditions (e.g.,
temperature and light intensity), and release
rates. However, what is usually not taken
into consideration is how plants may impact
the performance of natural enemies.
In general, natural enemies may benefit
plants by reducing the number of plant-feeding insects or mites (herbivores), and plants
may subsequently help by increasing the
susceptibility of herbivores to natural enemies. In addition, lower quality plants
based on nutritional content—may suppress
or delay the growth and development of herbivores, which consequently increases susceptibility to natural enemies for an extended
period of time. This then prolongs feeding,
which increases exposure to natural enemies.
However, certain toxic compounds produced
by plants such as alkaloids, cardiac glycosides, tomatine, and other allelochemicals
may be sequestered by herbivores for defensive purposes against natural enemies.
Plants produce two types of defenses:
extrinsic and intrinsic. Extrinsic defenses are
affiliated specifically with natural enemies
by means of plants producing volatile compounds (e.g., terpenoids) in order to attract
natural enemies that will attack herbivores
feeding on plants. Plants may respond to
insect or mite feeding by releasing volatiles
from damaged areas. These volatiles may
then help natural enemies in locating specific
prey on areas of the plant. For example, lima
bean (Phaseolus spp.) plants will emit volatiles from leaves damaged by the two-spotted
spider mite (Tetranychus urticae) so as to
attract predatory mites. This makes is easier
for the predatory mite to locate prey on damaged plants instead of randomly searching.
Furthermore, these volatile compounds may
assist certain parasitoids searching for small
prey that are difficult to locate because they
are well camouflaged (e.g., mealybugs or
scales) or they are feeding on leaf undersides
(e.g., whiteflies). Volatile compounds emitted from plant leaves in response to insect or
mite damage allows parasitoids and even
some predators to determine the difference
between infested and non-infested plants;
thus making it easier for natural enemies to
locate prey. The concentration of volatiles
emitted depends on plant type, herbivore
species, and environmental conditions including light intensity and day-length. Furthermore, cultural factors such as water
-stress may impact the release of volatiles
from plant leaves.
Intrinsic or physical defenses are those
exclusively produced by plants; either chemically via toxins or digestibility reducers that
slow development thus increasing exposure
to natural enemies or by physical means such
as plant architecture, leaf toughness, cuticle
thickness, leaf waxiness, and trichomes (leaf
hairs), or combinations of any one of these.
Physical defenses may prolong the development time of larvae/nymphs thus increasing
their susceptibility to natural enemies. For
example, tough leaves or thick cuticles may
diminish the feeding rate and consequently
prolong the development time of each larval
instar. This, in turn, increases exposure to
natural enemies. However, some natural enemies including ladybird beetle adults may
fall off of plants with leaves having waxy
cuticles; thus allowing aphids to escape attack.
Foliar pubescence, which is associated
with trichomes or leaf hairs, may negatively
impact the performance of both parasitoids
and predators by hindering movement or
mobility, influencing walking speed, and
changing walking patterns. This may be related to length, alignment, and/or density of
trichomes. Trichomes may be angled downward forming a physical barrier; may be
hooked, thus entangling natural enemies; or
glandular, which may entrap natural enemies
by means of adhesive extractions or they
Page 9
Raymond Cloyd
may be directly killed via contact with toxic
fluids. In addition, trichomes may affect the
foraging behavior such as the searching ability or efficiency of parasitoids and predators,
and thus their effectiveness in suppressing or
regulating pest populations. Trichomes
like a jungle—can impede the ability of certain natural enemies to locate hosts on plants.
Leaves with a dense layer of trichomes make
it more difficult for natural enemies to move
around. Moreover, natural enemies may turn
more frequently on leaves with trichomes;
thus leading to searching on areas of the leaf
that were previously visited.
Trichome density may lead to a decrease
in encounter rate, which would compromise
the success of a biological control program.
For example, larvae of the aphid predator,
Coleomegilla maculata fall off cucumber
(Cucumis sativus) leaves that contain many
trichomes thus reducing their ability to find
aphids on plants. Leaves with a high
trichome density may also decrease the
walking speed of the predatory mite, Amblyseius swirskii thus influencing the predators’
ability to suppress or regulate pest populations. Honeydew, which is a clear, sticky
substance excreted by phloem-feeding insect
pests such as aphids and whiteflies, may be
retained or accumulate more on leaves with
many trichomes than on smooth leaves
(without trichomes). This can lead to parasitoids and even predators encountering droplets of honeydew, thus causing them to spend
an
exorbitant
amount
of
time
preening/grooming themselves. This results
in natural enemies spending less time searching for prey, or they may even drown in the
honeydew.
Certain varieties of cucumbers may contain trichomes that interfere with the searching efficiency (and thus parasitism rates) of
the parasitoid, Encarsia formosa against the
FINAL DRAFT
AERGC Newsletter
greenhouse whitefly (Trialeurodes vaporariorum). The parasitoid has difficulty finding
and thus parasitizing greenhouse whitefly
larvae on cucumber varieties with dense
trichomes because the trichomes interfere
with searching efficiency, by means of affecting walking speed and pattern. Therefore, a reduction in leaf trichomes may
increase the performance of E. formosa. In
fact, the parasitoid tends to walk faster on
leaves with fewer trichomes and has a greater
searching efficiency on cucumber varieties
that do not contain trichomes compared to
those with trichomes. Thus, E. formosa can
parasitize more greenhouse whitefly larvae
on cucumbers with fewer trichomes than
cucumbers with a higher density of
trichomes.
It has been suggested that breeding programs should focus on developing plant cultivars that may allow natural enemies to be
more effective. Plants with fewer trichomes
may lead to an increase in the searching
efficiency of certain parasitoids such as E.
formosa. Trichomes on the leaves of trans-
Volume 27, No.1, Spring 2015
vaal daisy (Gerbera jamesonii) may impede
the effectiveness of both E. formosa (for
greenhouse whitefly) and the predatory mite,
Phytoseiulus persimilis (for two-spotted spider mite). However, it should be noted that
E. formosa may not be effective on smooth
leaves (no trichomes) because they walk so
fast that they fail to notice greenhouse whitefly larvae, resulting in reduced parasitism
and a decrease in their ability to suppress or
regulate whitefly populations.
Glandular trichomes such as those found
on tomato (Lycopersicon Lycopersicum)
may entangle or entrap natural enemies in a
sticky exudate or the exudate may accumulate on their bodies thus impairing movement. This may also cause natural enemies to
spend considerable time grooming themselves instead of searching for prey. Whitefly
parasitoids parasitiods such as Eretmocerus
eremicus may become entrapped within the
exudate of glandular trichomes of certain
plant types, which inhibits their ability to
locate prey, or they may be killed outright.
The glandular trichomes associated with the
Help Wanted
We need your input for the AERGC Newsletter. The Newsletter is
produced by an all-volunteer staff who enjoy putting together each issue
of the Newsletter. But, it’s your input that makes it an interesting and
valuable publication.
Please contribute a facility profile, description of special collections,
articles about your favorite plant or growing technique, an IPM success
story, equipment selection guides, research tips, etc.
Submissions can be a simple text file,or MS Word Doc. Include pictures
or graphics (any format, the higher the resolution the better, and please
include the captions.) The length of the article can be small (part of a
page), medium (2 or 3 pages) or large (anything above 3 pages).
Please send your submissions to Michael Mucci, mmucci@uoguelph.ca
plant, Nicotiana glutinosa, have been reported to ensnare E. formosa. Potatoes, with a
higher number of glandular trichomes, are
less susceptible (=more resistant) to aphids;
however, this negatively affects the natural
enemies of aphids because the natural enemies may become entrapped in the exudates
produced by the trichomes.
In conclusion, the success of a biological
control program is contingent on a number of
factors including natural enemy quality, timing of releases, environmental conditions,
and release rates. However, it is also important to understand how plants may directly or
indirectly impact the performance of natural
enemies via the presence of physical impediments such as hairs or trichomes.
Raymond Cloyd is a Professor and Extension
Specialist in Horticultural Entomology/Plant
Protection at Kansas State University Department of Entomology. Contact Ray via e-mail at
rcloyd@ksu.edu
The AERGC Foum
The AERGC Forum is a convenient and popular
way to communicate with your colleagues across
the continent. The Forum, an e-mail discussion
group, is a service provided for AERGC members.
Non-members can join the discussion by signing
up for a free 3 Month Trial Membership.
Subscribing is easy and the Forum is automatic
once you subscribe. To subscribe to the AERGC
Forum, please visit:
www.aergc.org
You are encouraged to subscribe and participate in
the Forum by posting items of interest to your
greenhouse colleagues and by replying to messages from other subscribers. This may include information, questions, answers and discussions on
greenhouse systems, growth chambers, pest control, biological controls and greenhouse IPM,
equipment, supplemental lighting, management
policies, greenhouse environmental control systems, operating tips, current events, greenhouse
design, job openings, plant culture, plant and seed
exchanges, etc.
For questions regarding your AERGC membership status, please contact:
The Secrest Arboretum on the campus of the
Ohio Agricultural Research and Development Center (OARDC)
in Wooster, Ohio.
Page 10
Joan Leonard
leonard.4@osu.edu
FINAL DRAFT
AERGC Newsletter
Volume 27, No.1, Spring 2015
Plant Cultivation Systems
Simulating Winter
in a Mediterranean Climate
Danica Taber
University of California, Santa Barbara
Thinking Outside the Greenhouse
A general truth faced by “plant people”
is that we don’t always live near what we
enjoy—or, in many cases, study. Often,
though, we’re able to close that distance
through creative and cooperative effort.
Topping your breakfast cereal with fresh
strawberries in the middle of a New England
winter, or baking South American bananas
into Midwestern bread, are both examples
of what the freight industry can achieve.
However, one such problem that a shipping
business can’t address is of great interest to
plant researchers at the University of California Santa Barbara: How do you grow
cold-dependent mountain and alpine plants
in Southern California? You can ship a fruit,
but can you ship cold weather?
When the University of Santa Barbara
received a NSF grant* to expand its plant
research facilities (made possible by a generous seed donation from Professor Emeritus
Dr. A.H. “Barry” Schuyler and Mrs. Jeanne
Schuyler), finding a solution to this question—how does one grow cold-weather
plants in a warm climate?—was a top priority for faculty in the Department of Ecology,
Evolution, and Marine Biology. The ultimate solution: A 713 square-foot “alpine”
greenhouse.
short, anyway. Why not just chill the air
around the plants? This is how UCSB’s
Alpine Greenhouse came to resemble the
meat section of a Costco.
Danica Tabor
The Original Design and Intent
The Alpine Greenhouse is a 31’x23’
ssquare foot, aluminum-framed glass house
that is equipped with a centrally programmable, four-stage cooling/two-stage heating
system to maintain the interior environment
for conventional greenhouse use. Supplementary LED grow lights are used in place of
HPS units to limit the amount of heat that is
imported into the greenhouse. (This substitution was made possible by grants from the
NSF* and UCSB’s The Green Initiative
Fund, a student-supported fund for reducing
energy consumption and waste on campus.)
The “alpine” capability arises from four
rows of grocery-style cooling benches that
chill a total area of 322 square feet to a height
of one foot. (Figure 1 )Each row of benches
is comprised of two or more “plant compartments” that are chilled by equipment specific
to each compartment. This allows multiple
growing temperatures to be maintained in
one row.
The open-air design of the chilling bench
allows the plants to be exposed to maximum
available light. The plants are kept cool with
the air curtain that is created 12” above the
compartment floor. The bench walls rise to
18” (6” above the air curtain) to protect the
air curtain from disruption. The current minimum growing temperature is 40oF/4.4oC,
and is regulated by a direct digital command
(DDC) controller and other components as
described below. Fluctuations in plant compartment temperature are tracked with portable sensor/logger units that are easily
interchanged among compartments (and researcher computers, for data retrieval).
The plant compartments are kept cold by
two industrial glycol-water chillers. These
chillers are housed outside the greenhouse
and alternate in operation for redundancy
and to minimize wear and tear. The temperature of the glycol-water solution can be programmed at the chillers. Copper piping
carries the solution from an industrial chiller
The Original Design and Intent
According to engineers, cooling such a
greenhouse to near-freezing temperatures
would entail 40 tons of cooling equipment
and a considerable demand on the campus
electrical grid (46,488 kWh). David Davis,
who serves as the Building Manager for
UCSB’s Division of Mathematical, Life and
Physical Sciences (College of Letters and
Science), was involved with this project
from the start. He wondered how the efficiency of the original design could be improved. Then, one day when David was in
the frozen meats section of a grocery store,
he had an idea. Forget about chilling the
entire house; many cold-weather plants are
Figure 1. A Chilled Grocery-Style Chilling Bench split into 2 compartments.
Page 11
FINAL DRAFT
AERGC Newsletter
Volume 27, No.1, Spring 2015
to a bench interior, where an aftermarket
actuator moderates the flow of solution to
cooling coils according to cues from the
DDC controller. The cooling coils chill the
surrounding air before fans blow it into a
plant compartment. The glycol-water solution is then transported back to the industrial
chiller for re-cooling.
Due to their common use in various industries, all components of this system are
commercially available. Additionally, the
system is low-maintenance and serviceable
by in-house HVAC technicians.
A
B
C
1. Copper pipes carry chilled glycolwater solution to coil (2).
2. Coil chills air in plenum.
3. Fan blows air from plenum into
plant compartment (4).
4. Plant Compartment fills with
chilled air to the load limit line
5. Chilled air curtain forms at load
limit line.
Issues Encountered
(See Our Solutions Below)
1.
2.
3.
4.
Frozen cooling coils inside the benches result from attempting growing temperatures below 40oF. Frozen coils
reduce heat transfer, thus causing the
growing temperature to increase rapidly
in the warmer greenhouse environment
and requiring the implementation of corrective measures.
The first model of aftermarket actuator
that was implemented was rated to
function in <95% humidity, but the condensation of moisture in the cold installation environment exposed the
actuator components to water and ice.
This resulted in electrical failure of the
actuators.
Regular first-person inspection was
required to identify high temperatures
and frozen coils caused by #1 and #2
above. This represented a wide margin
for temperature error and a draw on
staffing hours.
The plant compartments consisted of
black panels that retain solar energy.
5.
The chilling benches shipped with interior fans that lack the power to move
chilled air at a rate that would maintain
the desired temperatures when ambient
temperatures are higher than 70oF (presumably the average temperature of a
grocery store).
6.
The greenhouse cooling pads and
fans are positioned on the walls above
the benches and blow air laterally over
the plant compartments. This turbulence disrupts the chilled air curtain and
interferes with maintenance of a constant temperature in the plant compartments.
lem is remedied via insulation of exposed copper pipes and sealed
electrical components.
3.
2.
To prevent frozen cooling coils: The
current minimum temperature asked of
the system is 40°F.
To prevent actuator failure due to
condensation: The condensation prob-
To reduce staff time spent checking
for chilling equipment failure: A remote temperature alarm alerts university staff to frozen coils and permits timely
responses.
4.
To minimize retention of solar energy
in the plant compartments: The floor
panels are painted white to reduce heat
absorption around the plants.
5.
To account for a warmer ambient operating temperature: The interior fans
are upgraded to a higher CFM (cubic
feet per minute) model. These fans form
a stronger air curtain over the plants.
6.
To minimize disruption of the air curtain by ambient cooling equipment:
Hoods or shields of various materials
are placed over chilling bench edges as
needed to direct the warmer airflow
from cooling pads and fans over the
chilled air curtain. Also, see #5 above.
Possible Refinements
●
A temperature-initiated defrost mechanism for the cooling coils could allow a
controlled "freeze-thaw" cycle, decreasing the time in which the plant compartment temperatures could rise before the
issue is (automatically) remediated.
This defrost capability could allow temperatures colder than 40°F/4.4°C to be
achieved and maintained with minimal
staff attention.
●
Replacement of the glycol cooling system with direct-expansion coils could
enable the reliable production of sub40°F temperatures.
Our Solutions
1.
Discharge Air
Rear Baffle
Return Air
Page 12
●
"Centralized programmable controls for
defrost operation, day/night temperature
scheduling, and industrial chiller operation sequencing could simplify the current control schematic.
●
Re-designing the greenhouse cooling
system to avoid use of a horizontallydirected airflow from cooling pads could
prevent interference with the chilled air
curtain over the plant compartments. A
vertical airflow could be achieved by
positioning the cooling pads at floor-level and using
Conclusion
At first glance, the “deli” approach might
seem bizarre for a greenhouse operation.
However, when compared to the astronomical cost—in electricity and in greenbacks—
of chilling an entire greenhouse, the savings
and flexibility of use that accompany this
“outside-the-greenhouse” strategy make a lot
of sense for a research facility. Indeed, as I
write this article, at around 4:30 PM on an
early February day in Southern California,
clumps of the Alaskan sedge Eriophorum
vaginatum sit in a chilling bench at 42°F. All
other benches are drawing minimal electricity. The air inside the greenhouse is 83°F.
What other possible greenhouse hacks and
advances might be lurking in our daily lives?
Danica Taber is the Greenhouse Manager for
the The Department of Ecology, Evolution, and
Marine Biology (EEMB) at the University of California, Santa Barbara. Contact Danica via Email
at danica.taber@lifesci.ucsb.edu