MSB
Research Summary
Impact
of Bt endotoxin-expressing transgenic corn on corn earworm and its
implications to resistance development and areawide suppression
Corn
earworm (or podworm) causes significant damage to soybean in Maryland,
where insecticides are still the mainstay for minimizing losses. Corn
serves as the primary nursery for this pest during the summer, producing
moths that shift to soybean later in the season. Because of this close
association, any measure that significantly reduces the reproductive
output of corn earworm populations in corn may also result in areawide
suppression of podworm injury to soybean.
For
the past two years, we have determined that YieldGard Bt corn hybrids
significantly reduced the larval density (48 percent less) and damage (70
percent less) of corn earworms feeding in the ear. More importantly,
expression of the Bt toxin in silk and kernel tissues delayed larval
development by about two weeks and reduced the number of individuals that
reach pupation age by more than 90 percent. The few moths that did emerge
from Bt corn had fitness advantages, in that they died at a slightly
higher rate and laid 36 percent fewer eggs than moths produced from nonBt
corn. In both years, toxin expression in Bt corn delayed the time of
pupation by 11 to 14 days. Because this delay subjected prepupae to lower
temperatures and shorter day lengths, a greater fraction of the surviving
pupae entered diapause and thus did not emerge as potential colonizers of
soybean. These results clearly show the Bt corn can significantly affect
the temporal alignment of pupation and moth emergence relative to the
attraction of soybean. Since the work done to date involved an atypical
late planting of corn, further field experiments are needed to determine
how many moths survive Bt corn from earlier plantings and contribute to
podworm infestations in soybean. This work will provide insights into the
amount and spatial distribution of Bt corn acreage required to achieve
areawide suppression of podworms in soybean. Galen Dively
Use
of diets containing soy and other plant proteins by tilapia
Although
most tilapia are considered herbivorous (Jauncey and Ross 1982), the feeds
used in their culture are more like those of omnivorous fishes in that
they contain a significant amount of animal protein. Replacement of animal
protein with plant proteins, particularly those derived from soybean,
without a reduction in the efficiency of fish production, would reduce
fish production costs. Recently completed work by our laboratories which
was funded by the Maryland Soybean Board has indicated that the
digestibility by hybrid tilapia of dietary nitrogen and phosphorus are
equal when either fish meal or soybean meal is used as the primary protein
source. These studies have also proven that diets based on 48 percent
protein soybean meal supported excellent growth regardless of the method
of processing (pelleting vs. extrusion). Additional work also has
indicated that it is not supplemental phosphorus, but added calcium which
is required in diets to enhance weight gain for tilapia. This requirement
appears to be related to the very low levels of calcium in the well water
used for fish culture in our laboratory and further research will be
required to determine if the additional calcium will be required at all
locations.
This research confirms the hypothesis that plant proteins, particularly
soybean protein, can support optimal weight gain for hybrid tilapia and
that the use of calcium sources which are less expensive than the
dicalcium (rock) phosphates used in previous studies will further improve
the economy of these feeds. Further improvements in feed economy may be
realized, however, if soy oil could be used as the primary lipid source
rather than fish oil. Steven Hughes
Evaluating
larval parasitoids for biocontrol of corn earworm in soybeans
Cotesia
kazak, an exotic parasite that attacks small corn earworms, was
released at one site in Wicomico County in an attempt to establish this
species in Maryland. More than 2,000 wasps were released in an open
soybean field when the first earworms were detected. Releases were
conducted from Aug. 27 to Sept. 25 by tapping out parasites from plastic
vials directly onto plants at randomly sited locations within the field.
Sweep netting the release areas prior to each release failed to recover
any larvae parasitized by C. kazak. Overall, earworm populations
were low in 1997, which reduced the chances for the parasites to find
enough hosts to attack.
Existing parasites of the corn earwowm in soybeans were surveyed for the
third year in areas which had yielded the most worms in previous years.
Thirteen fields in three counties were sampled every three to 14 days with
standard sweep nets from Aug. 13 to Sept. 25. Lower than average moth
flights and adequate moisture which kept the corn greener for a longer
period resulted in lower collections of earworms. Parasitism was also
lower this year but followed the pattern of previous years of increasing
about 10 percent a week. Again, the most frequently encountered parasites
were Microplites croceipes, followed by Cotesia marginiventris and
Meterous autographae. The incidence of diseases among collected
earworms was also reduced this year with only 10 percent and 1.2 percent
of larvae exhibiting symptoms of the fungus Nomuraea rileye and a
virus, respectively, on Sept. 19.
Experiments investigating the use of diapause in rearing C. kazak
confirmed earlier work that diapause is triggered by short day lengths of
10 hours or less. Currently, work is focusing on the termination of
diapause and how it can be used in a rearing regime to store large numbers
of parasites. Philip W. Tipping
Performance
of a novel SCN bioassay protocol in the greenhouse
A
novel protocol for bioassay of Soybean Cyst Nematode [(SCN) Heterodera
glycines Ichinohe] can be effectively adapted to address a number of
research situations. Having tested successfully in 1996 in controlled
environment chambers, evaluation of the protocol was expanded to
greenhouse and laboratory environments. Adhering to previously published
parameters considered optimum for the SCN infection cycle, and using a
recently developed moisture replacement system (MRS), the protocol allows
for mobility, space and materials conservation, direct seeding practices,
and a controlled moisture supply. The bioassay protocol was evaluated for:
SCN test inoculum production and maintenance; screening for SCN
resistance; and SCN race testing. Trials were conducted in routine
greenhouse and laboratory environments throughout the calendar year. With
minimal modification, the protocol produced results in soybean germination
and growth, and in H. glycines development that were similar to those
reported for chamber testing. Mean numbers of SCN females produced on
Essex soybean were routinely rated at or above 30 percent of the initial
inoculum level. In the greenhouse, systems were seated on benches with
thermostatically controlled propagating mats to prevent soil temperatures
from dropping below the desired optimum. In the laboratory setting,
systems were maintained on an adjustable shelf wire utility rack. Bottom
heat was supplied with propagating mats and overhead light banks were
installed to supplement lighting. The protocol, now used routinely in the
Nematology Laboratory at the University of Maryland at College Park, has
also been successfully incorporated in the Soybean Resistance Screening
Program. In-house SCN race testing is also conducted in association with
Maryland field tested soybean variety evaluations. Sandra Sardinelli
Control
of newly introduced grass species in soybeans
Broadleaf
signalgrass and Texas panicum continue to spread across parts of the
Eastern Shore. These weedy grass species are difficult to control in both
corn and soybeans. Studies have been conducted in 1996 and 1997 to examine
programs for the control of broadleaf signalgrass in soybeans. Sites are
still being evaluated for field plot studies examining control of Texas
panicum in soybeans. In 1996 it was observed that where narrow row,
Roundup-Ready soybeans were planted, one to two applications of Roundup
Ultra provided season-long control of broadleaf signalgrass. Among other
herbicidess evaluated in 1996 and 1997, preemergence control was difficult
to achieve regardless of rainfall patterns. In 1996, we experienced heavy
rainfall, while in 1997, we experienced low rainfall. None of the
preemergence products evaluated provided commercially acceptable
season-long control. In 1996 and 1997, best control of broadleaf
signalgrass in soybeans was provided by postemergence herbicide
applications. Applied early post, both Pursuit and Raptor provided good
control. Applied mid-post, Poast, Select, Assure II and Fusion all
provided good control through mid-season. Differences were noted
late-season in 1996, with Poast and Select providing best control. Ronald
L. Ritter
The
use of genetically engineeted soybeans in Maryland for weed control
A
number of genetically engineered soybeans are in the marketplace and a
number of new ones will soon be there. This includes Roundup-Ready
soybeans, Liberty-Link soybeans and a stacked soybean utilizing STS and
Roundup-Ready traits. Over the past three years, we have been studying
these unique soybean varieties to determine whether or not they have
utility under Maryland conditions.
The Roundup-Ready varieties have sparked a lot of grower interest
statewide. Under conventional, narrow-row soybean systems, one application
of Roundup Ultra may be all that is required. Yet, data have shown that
some weeds may be tolerant to Roundup Ultra applications such as certain
morningglory species, spurred anode and pokeweed to name a few. Under
these circumstances, additional control strategies may be necessary.
Data have also shown that certain Roundup-Ready soybean varieties may be
sensitive to some of the ALS herbicide products that are in the
marketplace. Here, the stacked (RoundupReady + STS) variety of soybean his
proven itself. With the stacked soybean, we have been able to alleviate
associated ALS injury, obtain good to excellent control of weeds that may
escape Roundup Ultra applications, and provide good crop yields as well.
Liberty-Link soybeans should be in the marketplace soon. Liberty herbicide
is a nonselective herbicide that controls both weedy grasses and broadleaf
weeds. A number of management programs have been studied in examining the
utility of these soybeans for Maryland farmers. To date, a preemergence
grass herbicide followed by one application of Liberty herbicide appears
to be the best program. A single application of Liberty will not provide
season-long weed control. Two applications may be necessary, but
unfortunately, may be cost prohibitive. Thus, data have shown that a
preemergence grass herbicide followed by one application of Liberty
provides good season-long control at moderate cost. Ronald L. Ritter
Soybean
variety evaluation and development
The
1997 Maryland Soybean Variety Tests contained 96 entries and were grown in
five environments. The tests included full-season and double-cropped
plantings in no-till and conventionally tilled soil. Row spacings were
7.5, 20, and 30 inches. Rainfall was generally below normal at all
locations where the tests were grown. However, timely rainfall during
August and September at the Wye Research and Education Center in
Queenstown resulted in excellent yields at that location. The highest
overall yields in the full-season tests were obtained at Queenstown where
the yield for all varieties averaged 60 bushels per acre. The highest
average double-crop yields (47 bushels per acre) also occurred at
Queenstown. Complete data for all entries in the 1997 soybean variety
tests are printed in Agronomy Mimeo No. 32 which is available at no cost
from the University of Maryland Cooperative Extension office in each
county.
Two tests containing 45 entries of cyst nemadode-resistant varieties and
breeding lines were grown in Wicomico County in soil infested with the
soybean cyst nematode. Both locations had cyst nematode populations which
were identified as Race 1. The later maturing entries had the highest
yield at both locations. The four released varieties with the highest
average yield over both locations were: Wicomico (28.5 bushels per acre),
Accomac (27.6 bushels per acre), Manokin (25.5 bushels per acre), and
Hartwig (25.1 bushels per acre). Six of the 10 lines in the test with the
highest average yield over the two locations were lines or varieties
developed in Maryland. Complete data for all 45 entries in the 1997 cyst
nematode-resistant variety tests are printed in Agronomy Mimeo No. 43
which is available at no cost from the University of Maryland Cooperative
Extension office in each county. Data are also available for each variety
test and other yield tests on the Cropping System webpage ‹ http://www.agnr.umd.edu/users/nrsl/crops
William Kenworthy
DNA
marker assisted selection for cyst resistance
The
purpose of this project is to identify DNA markers which are linked to
genes for resistance to the soybean cyst nematode. The identification of
DNA markers will greatly facilitate the development of resistant soybean
genotypes. This project has been using SSR DNA markers which have been
found to be widely available in the soybean genome. In previous studies,
over 120 SSR markers have been tested for their association with cyst
nematode resistance. Only 10 SSR markers were found to always appear in a
resistant genotype and, at the same time, not appear in a susceptible
genotype. Of these 10 markers, only three markers were found to have a
weak association with cyst nematode resistance in a set of lines from the
cross of a resistant and susceptible parent. Additional markers were tried
by colleagues at USDA-Beltsville.
In 1997, research at USDA-Beltsville laboratories identified two SSR
markers closely linked to cyst nematode resistance. To complement their
work, our laboratory began looking at other new DNA techniques which have
potential for use in soybean breeding programs. We have had considerable
success with a technique called amplified fragment length polymorphism (AFLP).
One of the important benefits of this procedure is the large number of
informative loci that can be detected by using this technique. This should
increase the chance for identifying useful DNA markers linked to genes of
interest. Our preliminary studies indicate this to be true for cyst
nematode resistance and other traits in our breeding program.
We screened 20 EcoRI and MseI primer pairs for AFLP markers
associated with cyst nematode resistance in a group of cultivars differing
in cyst nematode resistance. Of the hundreds of markers we generated, 17
potential markers always appeared in a resistant genotype and, at the same
time, did not appear in a susceptible genotype. In 1998, these 17
potential markers will be tested against a group of 96 lines from a cross
between a resistant and a susceptible parent to see if any marker can
reliably identify cyst-resistant genotypes. William Kenworthy
Development
of low saturated fat and low linolenic soybean cultivars in maturity
Groups IV and V
Dietary
saturated fatty acids, particularly palmitic acid, have been implicated as
a contributing factor to coronary heart disease. When soybean oil is a
major source of palmitic acid in diets, low palmitic soybean oil would
limit dietary intake of saturated fatty acids without dietary change.
Soybean oil is already lower in saturated fatty acid content compared to
palm oil and other tropical oils. Sunflower and canola, however, have
lower concentrations of palmitic acid (6 percent and 4 percent,
respectively) than soybean oil (11 percent). USDA scientists at North
Carolina State University and Purdue University have developed soybean
lines with palmitic acid concentrations around 4 percent. This project
utilized these soybean lines as parents in crosses with Maryland soybean
lines containing low linolenic acid to develop new cultivars with low
palmitic acid and low linolenic acid which will result in a more desirable
low saturated fat soybean oil.
During 1997, 630 F2 seeds from the cross of Manokin BC2 low palmitic acid
plants and Manokin-crossed low linolenic acid plants were analyzed for
palmitic acid and linolenic acid content and germinated for use as
parents. Two plants were identified with a palmitic acid content of less
than 4.5 percent and also having a linolenic acid content of 3.5 percent.
These two plants were used in crosses to the cultivars Corsica, Enrei,
Manokin, and Stressland. The progeny of these crosses are being grown
during the winter (1997-1998) in the greenhouse. During 1997, more than
200 lines with low palmitic acid were evaluated in field tests and 86
lines were selected for further testing in 1998. Seed yield was determined
on 60 Manokin BC1 low palmitic acid lines at the Wye REC. The average
yield of the 60 lines was 45 bushels per acre with a range of 25 to 57
bushels per acre. The yield of Manokin in the test was 45 bushels per
acre. Several of the low palmitic lines have excellent yields and
acceptable agronomic traits. Additional field testing of the modified oil
soybean lines will be conducted in 1998. William Kenworthy
Effects
of PPFM bacteria on soybean germmation and development
During
the 1997-1998 funding cycle, my lab focused on four areas of research
related to Methylobacterium, a pink-pigmented facultatively
methylotrophic (PPFM) bacterium regularly associated with soybean.
Previous results told us that these bacteria influence seed germination
and seedling growth by producing the plant growth regulator zeatin and
related cytokinins.
The objectives of this year's work were: 1) to extend our knowledge of the
effects of PPFM bacteria on seed germination, working toward a
commercially viable protocol for treating seeds with the bacteria, 2) to
develop protocols for using the PPFM bacteria to rehabilitate aged seed
and seed lots with poor germinability, 3) to optimize the growth of PPFM
bacteria in fermenter culture, and 4) to test the effects of PPFM bacteria
on the growth of soybean cells in tissue culture. The status of these
investigations is as follows.
We have collected considerable data to support the idea that germination
of both fresh and aged seed is enhanced by treatment with PPFMs. We have
also tested a number of options for applying treatments of the bacteria to
seeds. These include use of freeze-dried inocula, vacuum infiltration of
seed, and introduction of the bacteria during seed imbibition. All of
these methods are effective. In the process of applying PPFM bacteria to
seeds and later assaying the bacterial populations, we realized that it
would be necessary to distinguish among naturally occurring and introduced
bacteria. For this reason, we undertook experiments in PPFM
"fingerprinting" using PCR (polymerase chain reaction) to
compare a specific region of the PPFM DNA (16S rRNA genes) among different
bacterial isolates. We demonstrated that the technique can distinguish
among isolates of the bacteria and can be used to differentiate between
native and introduced populations. This work was presented at the American
Society of Plant Physiologists annual meeting last summer. At this stage,
we are talking with two potential industrial partners, a seed priming
company and an agricultural chemical company, about trials involving seed
treatments with the PPFM bacteria on a commercial scale. Other experiments
involving aged seeds showed us that assaying PPFM populations in seed can
be used to predict seed storability. A manuscript describing these
experiments is in preparation. We think that this is an exciting result
since measuring PPFM populations in seed is simple and quickly done, and
also because low populations of the bacteria can be augmented. So far, our
work with fermenter culture of the bacteria has been limited to
characterizing their growth. Culture conditions have not been optimized
for cytokinin production, although one of the students is learning the
analytical techniques necessary to assay cytokinin levels in preparation
for these experiments. Tissue culture experiments are currently in
progress. Mark Holland