Chase Straw
Crop and Soil Sciences
Tolerance of perennial ryegrass (Lolium Perenne L.) overseeding to residual activity of Tribute Total.
Research was conducted from August to December 2011 on a common bermudagrass [Cynodon
dactylon (L.) Pers.] fairway at Reese Golf Course (Lubbock, TX) and a 'Tifway 419' hybrid bermudagrass
(Cynodon dactylon x. C. transvaalensis Burtt-Davy) fairway at the Rawls Golf Course (Lubbock, TX). Plots
were arranged in a 2 x 4 factorial within a randomized complete block design with four replications. The
main factor was herbicide rate and the sub-factor was application timing [weeks before overseeding
(WBO)]. Treatments included thiencarbazone + foramsulfuron + halosulfuron (Tribute Total) at 136 and
271 g ai ha-1 + MSO at 0.5% v/v applied on August 15, 2011 (8 WBO), August 29, 2011 (6 WBO),
September 12, 2011 (4 WBO), and September 26, 2011 (2 WBO). Treatments were applied to 1.5 x 1.5 m
plots with a CO2 powered boom sprayer equipped with XR8004VS nozzle tips calibrated to deliver 375 L
ha-1 at 221 kPa. The entire experimental area was overseeded with perennial ryegrass (Lolium perenne
L.) at 392 kg ha-1 on October 10, 2011. Perennial ryegrass cover was evaluated bi-monthly through
December 2011 using digital image analysis. As Tribute Total rate increased and applications were made
closer to overseeding, perennial ryegrass establishment decreased. Untreated check plots exhibited 80%
perennial ryegrass cover on December 14, 2011. Similar ryegrass cover (75% to 76%) was observed on
December 14, 2011 in plots sprayed with Tribute Total at 136 g ai ha-1 applied 6 and 8 WBO,
respectively. Ryegrass cover in response to Tribute Total at 136 g ai ha-1 applied 4 and 2 WBO was 45
and 36%, respectively. No Tribute Total treatment at the 271 g ai ha-1 rate exhibited similar ryegrass
cover to the untreated check, regardless of application timing. Ryegrass cover in response to Tribute
Total at 271 g ai ha-1 applied 8, 6, 4, and 2 WBO was 54%, 40%, 43%, and 16%, respectively. Applications
of Tribute Total may be limited to rates of 136 g ai ha-1 made 6 WBO when utilized in overseeded
bermudagrass turf in order to avoid reductions in perennial ryegrass establishment.
Additional Authors: Gerald Henry
Diego Barcellos
Crop & Soil Sciences
Assessment of Phytoremediation of Soils Contaminated with Chlorobenzene & Benzene at a Site in
Southern Brazil
Phytoremediation is a remediation strategy defined as the use of plants and their associated
microorganisms to achieve contaminate degradation, stabilization or attenuation. This technology is an
emerging, cost-effective alternative to the traditional remediation methods. A site located in southern
Brazil is contaminated by benzene and chlorobenzene. The site is a former pesticide manufacturing
facility, placed in a terrace, and chemical oxidation was the first remediation method adopted. Given the
environmental and waste characteristics of the site, we proposed phytoremediation as a component to
clean up the pollutants on this site. We conducted three greenhouse studies at The University of
Georgia (Athens, GA, USA). As our first experiment, we exposure Pinus taeda under a range of
contaminant concentrations (similar to the field), and no mortality was notice, even on the higher
concentrations. On the second experiment, we exposure Eucalyptus urograndis under three
concentrations of sodium persulfate (0 %, 1 %, and 10%), and there was plant mortality only at the
higher concentration. Then, we conducted a greenhouse experiment using Eucalyptus, Pinus, and a nonplanted control (4 replications) placed on pot containing washed sand. A solution containing benzene
and chlorobenzene were added to each pot. Leachate were collected daily from the bottom (through a
valve), and nominal contaminant level was maintained. Aqueous solution was extract on organic phase
(using hexane), and analyzed on GC/MS (Gas chromatography – mass spectrometry) equipment. Results
suggest that the presence of plants increase loss of contaminant on the environment. Thus, with these
results, we proceed to use Eucalyptus trees on the field Site in Brazil.
Additional Authors: Lawrence Morris, Aaron Thompson
Jasmine VanExel
Department: Crop and Soil Scences
A climatological study of wave-modified turbulence fluxes using wavelet analysis
Turbulence, which at times has an unknown or elusive origin, can be caused by pervasive mechanisms
that disrupt and change the atmospheric stability. The instability that results is the underlying factor in
the very irregular and chaotic motions that often define turbulence. Calculating turbulent fluxes within
the atmosphere can be done using eddy covariance. The eddy-covariance technique measures fluxes of
momentum and scalars under well mixed convective boundary layer conditions. The method is accurate,
direct, and secure; it relies on direct and fast measurements of actual gas transport. However, the
inability to measure net ecosystem exchange accurately in the stable nocturnal boundary layer (NBL) has
been reported. There are many potential hazards when attempting to measure fluxes in the stable NBL
and little work has explored the potential problems and uncertainties of calculating turbulence statistics
and fluxes in the presence of wave activity. The purpose of my research is to present a climatological
study of wave frequency and periods and their impact on wave-modified turbulence fluxes above a
forest canopy. This research will examine the characteristics of NBL turbulence influenced by gravity
waves. A wavelet analysis will be performed on the detected signals to identify the time, period, and
duration of the wave event after differentiating the turbulence and the wave event. As a climatological
study, the diurnal variations and long term averages/trends of these wave events will be considered. In
particular, wave events will be selected from dates in different seasons across a year's span to evaluate
the wave enhancement of turbulence in contrasting seasons. Variation of the wave signal and impacts
on turbulent parameters and fluxes will be evaluated using different averaging times at measurement
heights of 33.5, 68, and 329m on a tall tower. It is hypothesized that the presence of waves will modify
the calculation of turbulent parameters for averaging times longer than the wave period; this impact will
vary with height, and by removing 30-60 minute period gravity waves from the turbulence, for averaging
times shorter than such periods, the turbulence statistics will show significant inflation.
Allen, Charles
Horticulture
Smoke Point Testing of Camellia oleifera Extract and Common Cooking Oils
Camellia oleifera is an oilseed crop native to the southern provinces of China where, for thousands of
years, its extract has been traditionally used a cooking oil. In the region it is commonly referred to as the
“eastern olive oil” and has been found to exhibit many of its health benefits. Camellia has recently been
developed to suit the climate of the southeastern United States. The purpose of this experiment was to
evaluate the smoke point of Camellia oil to other common cooking oils. The smoke point of cooking oil is
defined as the temperature in which a continuous stream of smoke is emitted from a heated sample. It
is thought that at this temperature the oil degrades and starts to produce free radicals. There is very
little literature on experimentation with Camellia in the United States and virtually none on its smoke
point. Seventeen oils were tested, five replications each, using American Oil Chemists Society (AOCS)
official method Cc 9a-48 with slight modifications. Out of the oils tested, Hollywood Enriched Gold
Peanut Oil had the highest smoke point, and crude Camellia oil had the lowest smoke point. Commercial
extra virgin Camellia oil smoked higher than both pure olive and extra virgin olive oil by 11.2% and
13.7% respectively. This data gives a more accurate representation of common cooking oil smoke points
which can help consumers make more informed decisions on which oils are healthier for their specific
cooking purposes.
Lisa Baxter
Crop and Soil Science
Bermudagrass Stem Maggot: An Exotic Pest in the Southeastern USA
Since first discovered in southern Georgia in July 2010, the bermudagrass stem maggot (BSM;
Atherigona reversura Villeneuve) has infested and damaged bermudagrass (Cynodon dactylon) hayfields
throughout the southeastern United States but there is a paucity of information about the biology and
management of this new invasive pest. Our objectives are to compare the severity of damage among
selected cultivars, determine if there are phenotypic differences in the cultivars that are preferred by
the BSM, and assess the fecundity of the BSM on the different varieties. Eight Cynodon cultivars were
used in this study. Flies collected from infested bermudagrass fields were introduced six times
throughout the 4-wk growing period to the cultivars, which were grown in the greenhouse and
contained in acetate and mesh enclosures. Every four weeks the forage was harvested and
morphological characteristics analyzed. Preliminary results show that some varieties have more and a
higher percentage of shoots damaged by the BSM than others. There was a trend for the more heavily
damaged varieties to have finer stems. In addition, damaged plants tended to have darker leaves and a
thicker stem, possibly due to a reallocation of nutrients. In this study, fly damage did not result in a
significant yield reduction yet a difference in BSM fecundity among cultivars was found. Additional
research is underway to better understand the lifecycle of this species; confirm and quantify the degree
of preference A. reversura has for bermudagrass cultivars; and quantify the severity of damage in yield,
quality, and aesthetics.
Additional Authors: Dennis Hancock, Will Hudson
Clinton Steketee
Institute of Plant Breeding, Genetics, and Genomics
Genotype-Isolate Interaction for Dollar Spot Resistance in Seashore Paspalum
Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is a major fungal disease that affects
seashore paspalum (Paspalum vaginatum Swartz) and other turfgrass species. Current management of
this disease relies heavily on frequent fungicide applications, which has led to cases of fungicide
resistance. An alternate management strategy is host plant resistance, but more needs to be known
about the pathogen and host interaction to incorporate this resistance into elite genotypes. Five
genotypes of seashore paspalum with dollar spot resistance differences were artificially inoculated with
five isolates of S. homoeocarpa from three warm-season and one cool-season turfgrass species, and
visually evaluated for disease expression (0-100%). Significant differences among isolate treatments
were found indicating varying levels of isolate virulence, irrespective of seashore paspalum
genotype. The general paspalum isolate (P1) was the most virulent isolate used in this study based on
area under the disease progress curve (AUDPC) values. A lack of race-specific interactions was indicated
by no significance (p=0.3042) in genotype by isolate treatments. Using this information, breeders
should be able to use one or a few highly virulent dollar spot isolates to select for host plant resistance
in seashore paspalum.
Additional Authors: Alfredo Martinez-Espinoza, Paul Raymer
Susan Hawkins
Department: Horticulture
Interspecific and Intergeneric Hybrids in Two Genera of Fabaceae, Baptisia and Thermopsis
Interspecific and intergeneric crosses are often made in an attempt to produce hybrids with the best
qualities of both parents. Baptisia and Thermopsis are two closely related genera in the Fabaceae family.
Both are used in the ornamental horticulture industry, although Thermopsis is much less well known
than Baptisia. No hybrids between the genera Baptisia and Thermopsis are known to exist. Interspecific
and intergeneric crosses were performed between species in the genera Baptisia and Thermopsis.
Interspecific crosses produced a higher number of seeds per fertile cross and higher percentage of
fertile crosses than intergeneric crosses. Germination rate was not different between interspecific and
intergeneric crosses. Since seedlings could be obtained from both interspecific and intergeneric crosses,
production of a Baptisia-Thermopsis hybrid is possible. Steps to increase the percentage of fertile
crosses and number of seedlings include use of bridge parents, new species as parents, and embryo
rescue for further breeding efforts.
Additional Authors: John M. Ruter, Carol Robacker
Chris Johnston
Crop and Soil Science
Effect of the Presence of Native Indiangrass (Sorghum nutans) on Johnsongrass (Sorghum halepense)
Establishment
Johnsongrass is one of the most aggressive weeds in the southeast United States, and control is often
challenging due to its competitive nature. One possible alternative method of control is restoring land
invaded by Johnsongrass with a native, non-invasive grass species. Greenhouse studies were conducted
in Griffin, GA to evaluate the ability of Georgia-native indiangrass (Sorghastrum nutans) to compete with
and/or displace Johnsongrass. The two grasses were planted by seed and thinned to the density of four
plants per 6.35 cm pot in five different ratios from 100% Johnsongrass to 100% indiangrass in 25%
increments. Root and shoot biomass harvests were done at 30 and 60 days after seeding both species.
Once the 60 day harvests were completed, all plants were mowed to a typical roadside height of six
inches to determine if any shifts in biomass production occurred. Shoot biomass harvests were then
conducted 15 and 30 days after mowing. Initial data suggests that Johnsongrass produces four times as
much biomass in mixture relative to its biomass in monoculture (relative yield) than Indiangrass. This
trend did not appear to change significantly after mowing, although 15 days after mowing a reduction in
total relative yield (yield of each species divided by its yield in monoculture added on to the yield of the
competing species divided by its yield in monoculture) suggests that once the Johnsongrass to
indiangrass ratio reached 50:50, respectively, Johnsongrass’s biomass production may have been
inhibited.
Amanda Bayer
Horticulture
Reduced fertilizer applications and irrigation volume effects on plant growth and leachate volume of
Gardenia jasminoides
Best management practices have helped nursery growers better manage irrigation and fertilization;
however, over-irrigation is still common in plant production. Over-irrigation is a problem for many
reasons, including poor water distribution uniformity and efficiency of irrigation systems, the belief that
it is necessary to maintain the substrate near container capacity to maximize growth, and a lack of
knowledge about how much water is actually needed to support growth. Soilless substrates, which are
lightweight mixtures of shredded tree bark and peat moss, are a challenge because of variable water
holding capacities. Along with excessive irrigation, fertilizers are often leached and enter local
ecosystems. More efficient irrigation can reduce the leaching of water and fertilizers, potentially
reducing fertilizer requirements. Our objective was to determine the effect of fertilizer rate and
irrigation volume on plant growth and leachate volume. Gardenia jasminoides Heaven Scent® were
grown with a soil moisture sensor controlled, automated irrigation system in Watkinsville, GA.
Controlled release fertilizer was incorporated into the substrate at 100, 50, or 25% of the recommended
rate and irrigation was applied for 2, 3, 4, or 5 minutes. Irrigation occurred when the volumetric
substrate water content of the control plants (2 minute irrigation duration, 100% fertilizer treatment)
dropped below 35%. At this time the entire block was irrigated, but different treatments were irrigated
for different durations (2, 3, 4, or 5 minutes). Irrigation events and rainfall were recorded
daily. Leachate volume was measured biweekly. The 25% fertilizer rate resulted in significantly lower
shoot dry weight (18.7 g/plant) than the 50 and 100% rates (25.3, and 27.3 g/plant respectively),
suggesting that a moderate fertilizer rate (50%) can be used. Irrigation duration did not affect shoot dry
weight. There were no treatment effects on plant height. Leachate volume varied greatly over the
growing season due to rainfall. In the final leachate collection, in which there was no rainfall
contribution, irrigation duration and the interaction between irrigation duration and fertilizer rate
affected leachate volume. The results of this study suggest that reduced fertilizer rates and more
efficient irrigation can be used to produce salable plants with reduced leaching.
Additional Authors: John, Ruter, Marc, van Iersel
Josh Clevenger
Institute of Plant Breeding, Genetics, and Genomics
Homeolog-specific transcriptome assembly in cultivated peanut
Gene expression analysis of distinct tissues and developmental stages can be utilized to create a global
atlas of gene expression dynamics. Cultivated Peanut is an allotetraploid (AABB), resulting from a
probable interspecies hybridization and spontaneous chromosome duplication. Accurate profiling of
gene expression requires a highly sensitive transcript assembly that minimizes the presence of
“chimeric” contigs; transcripts that are composed of a consensus sequence of two homeologous
genes. RNA sequencing of the genotype 'Tifrunner' has been done on seedling leaves; leaves on main
and lateral shoots when plants begin to flower; vegetative shoots from the main stem and reproductive
shoots from laterals at the stage of first flowering; flowers; roots at ten days post-emergence and
nodules formed on inoculated roots (25 days post-emergence). We used a subgenome-specific
transcript assembly method that first parsed reads into A and B-genome-specific sets and then
assembling transcripts from each set separately using Trinity. We compared our method to un-parsed
read set assembly using Trinity, SoapDenovo-Trans, and CLC Bio. The homeolog-specific assembly was
able to align 66% of reads with zero SNPs; compared to 40% for Trinity, 36% for SoapDenovo-Trans, and
33% for CLC Bio. Further, blasting our tetraploid assembly to diploid progenitor transcript assemblies
provided evidence that our “A” and “B” transcripts are properly assigned. Our method has highly
increased the accuracy of homeolog-specific transcript assembly and will provide an important resource
for studying gene expression and transcriptome dominance in cultivated peanut.
Additional Authors: Peggy Ozias-Akins, Scott Jackson
Kate Cassity-Duffey
Crop and Soil Sciences
Modeling Ammonia Volatilization From Surface-Applied Broiler Litter
Broiler litter is a valuable source of plant available nitrogen for pastures and crops. However, large
losses of N (nitrogen) to the atmosphere through ammonia volatilization can lead to low crop yields and
environmental contamination. Ammonia volatilization is dependent on many factors: manure
management, soil characteristics, and environmental conditions. Environmental conditions may be most
influential for surface application of broiler litter to pastures. The objective of this study was to model
ammonia volatilization from surface applied litter dependent on environmental variables. Ammonia loss
was measured with an integrated horizontal flux method during 11 28-day studies between the months
of April and November in 2011 and 2012. Litter was applied at a rate of 120 kg total N ha-1 for each
study (four replications per study). Ammonia was trapped and measured biweekly. Relative humidity,
temperature, rainfall, vapor pressure, dew point, leaf wetness, air temperature and soil water content
were measured onsite at 5 minute intervals. Ammonia loss ranged from 1.1 to 9.9% of the N
applied. Cumulative ammonia loss was related to both average vapor pressure and the initial
ammonium concentrations of the litter applied. Increased vapor pressure may lead to increased litter
water and increased mineralization on the pasture surface, subsequently, increasing ammonia loss.
Additional Authors: Miguel Cabrera,
Hao-Xi Li
Plant Pathology
Understanding the epidemiology of gummy stem blight in the southeastern US by assessing the
population structure of the causal pathogen, Didymella bryoniae
A complete understanding of sources of inoculum for epidemics is essential for effective management of
devastating plant diseases. Gummy stem blight, caused by the fungus Didymella bryoniae, is the one of
the most destructive foliar disease on watermelon and other cucurbits in the southeastern U.S. where
over half of the annual watermelon yield in the United States is produced. D. bryoniae has a wide host
range in the cucurbit family, but no specialization among species within the family has been detected.
The inoculum source of gummy stem blight epidemics is not clear; however, seed, transplant seedlings,
and spores from plant debris in the field are all potential sources. The aim of this study was to use a
population genetics approach to identify major sources of inoculum and mechanisms of dispersal by
determining gene flow and within and among field genetic diversity. We collected 206 isolates of D.
bryoniae from four watermelon fields in the southeastern US during the 2012 epidemic. The field
locations were Tift County, GA; Cook County, GA; Suwannee County, FL; and Colleton County, SC. All
isolates were genotyped using 20 microsatellite loci. Multiple analyses were conducted to determine if
the four field populations were differentiated. Principal coordinates analysis (PCoA) showed overlap
among isolates from different locations; however, populations were distinct based on significant
differences among populations for each coordinate. Discriminate analysis also supported distinct
populations for the four fields. Additional evidence of differentiation was based on analysis of
molecular variance (AMOVA), which showed that all field populations were significantly different from
each other. There was trend of increasing genetic difference with increasing geographic distance, but
this was not significant. These results indicate that dispersal is limited and, therefore, local sources of
inoculum contribute more to the epidemics than other factors, such as seed. Current studies on
populations from the same field locations collected during 2013 epidemics are ongoing. If populations
show no differentiation over time, this will further support local sources of inoculum as a major
contributor to epidemics.
Additional Authors: Marin Talbot Brewer
Geoffrey Meru
Horticulture
Watermelon seed oil, anyone? Exploring the genetic factors associated with seed oil percentage and
fatty acid composition in watermelon
Seed oil percentage (SOP) and fatty acid composition are important traits for people who consume
watermelon seed kernel as part of their daily diet. Oil yields from watermelon seed exceed 50% (w/w)
and are high in unsaturated fatty acids and low in saturated fatty acids, a profile comparable to that of
sunflower and soybean oil. To improve the nutritive value of watermelon seed and establish
watermelon as a potential oil crop, it is critical to understand the genetic factors associated with SOP
and fatty acid composition. The egusi watermelon (Citrullus lanatus subsp. mucosospermus var. egusi)
which has a unique fleshy-pericarp is particularly of interest to breeders because it's high in SOP.
Genetic mapping studies have established that the variation in SOP between the egusi watermelon and
normal non-egusi watermelon can be explained by the egusi (eg) locus, which is also associated with the
unique seed phenotype. However, variation in SOP also occurs within egusi and normal non-egusi seed
types suggesting contribution by additional genetic factors towards SOP. The current study sought to
determine additional factors associated with SOP and identify genomic regions associated with fatty
acid composition in watermelon seed oil. Kernel percentage (KP) showed a significant (α = 0.05) positive
correlation with SOP in both egusi and normal seed types while seed size traits showed significant
negative correlations with SOP. QTL associated with KP and seed size traits in normal seed were colocalized with a previously mapped locus for SOP on linkage group (LG) 2 (Chr. 6), but in egusi seed, a
QTL explaining 33% of phenotypic variation in KP was localized on LG 7 (Chr. 1). Linoleic acid (C: 18) and
oleic acid (C: 16) were the major unsaturated fatty acids constituting >80% of the total fatty acids while
palmitic acid and stearic acid were the main saturated fatty acids constituting <20% of the total fatty
acids. A single QTL explaining 23% of phenotypic variation in palmitic acid was localized on LG 11B (Chr.
3), but no QTL were detected for the other fatty acids. These results will facilitate breeding for SOP and
palmitic acid in watermelon.
Additional Authors: Cecilia McGregor
Sarah Doydora
Crop and Soil Sciences
Alum effects on ionophore antibiotics in runoff from surface-applied broiler litter
Georgia is the top broiler-producing state in the USA with a production of 1.3 billion broilers in 2012 and
generation of about 1.5 million Mg of broiler litter, most of which is surface applied to grasslands.
Surface application of broiler litter leaves it exposed to surface runoff, which may result in surface water
contamination with veterinary antibiotics. This study was conducted to evaluate 1) the effect of alum
added to surface-applied broiler litter and 2) the effect of time prior to raining on losses of ionophore
antibiotics, monensin and salinomycin, in surface runoff from grassed plots in the summer and winter
seasons, In the summer season, litter+alum significantly reduced the total monensin (p-value 0.0010),
total salinomycin (p-value 0.0025), monensin concentration (p-value 0.0262), and salinomycin
concentration (p-value 0.0247) compared to unamended litter across all weeks of rainfall simulation. In
the winter season, litter+alum did not significantly reduce total monensin (p-value 0.7274), total
salinomycin (p-value 0.5466), monensin concentration (p-value 0.9167), and salinomycin concentration
(p-value 0.1214) from the litter across all weeks. No significant reduction on ionophore amounts or
concentration was observed as a function of time for each treatment in either season. At this point, the
reason for ineffectiveness of alum in reducing the amounts and concentrations of ionophores in runoff
during the winter season could not be ascertained.
Additional Authors: Miguel Cabrera, Aaron Thompson
Suchitra Chavan
Plant Pathology
Expression profiling and evolution of pathogenesis related genes in maize and teosinte in response to
Ustilago maydis.
Ustilago maydis (U. maydis), the causal agent of corn smut, is an important agricultural pathogen and is
responsible for significant yield losses of approximately $1.5 billion annually in the United States. Several
methods are currently used to control corn smut. However, host resistance is the only practical method
for managing smut. To identify genes controlling resistance to corn smut, transcriptome profiling was
conducted in maize genotypes showing high levels of resistance and susceptibility against U. maydis.
Maize, teosinte and 40 maize teosinte near Isogenic lines (NILs) were inoculated with a strain of U.
maydis. Two teosinte lines (Zea diploperennis and Zea luxurians) and three NILs demonstrated a high
level of resistance and a phenotypic response similar to maize. Among the 17,555 genes analyzed with
the Affymetrix GeneChip Maize Genome Array, 5,639 genes demonstrated significant differential
expression between inoculated (U. maydis) and uninoculated maize lines. From this data set, 529 genes
were up-regulated (≥ 1.5 fold change), whereas 5,110 were down-regulated (≤ 1.5 fold change) in
inoculated resistant and susceptible maize plants, respectively. The 529 differentially expressed genes
were grouped into 8 functional categories including biotic stress, enzyme families, oxidation and
receptor like kinase. The 5,110 down regulated genes were grouped into 8 functional categories
including photosynthesis, metabolism, transcription and glycolysis. These findings were confirmed with
real-time PCR (qRT-PCR). This work represents the first report of new potential sources of resistance to
U. maydis from the wild progenitor (teosinte) and provides novel insight into the complexity of biotropic
interactions.
Additional Authors: Dr. Shavannor M. Smith
Benjamin, Stewart-Brown
Institute of Plant Breeding, Genetics, and Genomics
Yield QTL Mapping in Soybean
Soybean [Glycine max (L.) Merr.] is an important crop globally as a source of both protein and oil.
Breeding to increase yield is a primary goal for soybean breeders. Selection for beneficial alleles while
breeding for quantitative traits, such as yield, is a difficult task. Molecular markers have offered a great
opportunity to allow for the identification and selection of QTL for yield. Single nucleotide
polymorphisms (SNPs) are commonly used today due to many advantages over previous marker
systems. Soybean Infinium Chips, consisting of 50k SNPs, are a useful tool for QTL discovery for
advanced molecular breeding. Not only is identification and selection of QTL for yield difficult, but so is
finding new unique alleles to incorporate into elite cultivars. Most current elite soybean varieties share
similar pedigrees due to very few ancestor lines accounting for 95% of the diversity between a majority
of today's elite cultivars. This issue has lead soybean breeders to look to wild germplasm in order to find
more unique alleles that can help boost soybean yields. Woodruff, a high yielding soybean cultivar
developed at UGA, was derived from PI 416937, which is a successful example to develop high yielding
cultivars from a Japanese landrace. Using the Infinium Chip fingerprinting data, we have identified
haplotypes inherited from PI416937 to Woodruff, which likely contribute to an increase in yield. From
these haplotypes, we have converted “tag SNPs” into KASP markers for confirmation and selection of
yield QTL alleles. In this presentation, I will also discuss the allele frequency in soybean ancestral lines
and how incorporating unique yield alleles from wild germplasm can contribute to the increased rate of
soybean genetic gain.
Additional Authors: Zenglu, Li,
Tripti Vashisth
Horticulture
Changes in cell wall composition and wall-related gene expression during blueberry fruit abscission
The spatial and temporal changes in the cell wall composition and metabolism within the abscission
zone (AZ) during organ separation are not completely understood. In blueberry, fruit abscission occurs
at the pedicel-peduncle junction (PPJ). The objective of this study was to obtain a comprehensive
understanding of changes in the cell wall during blueberry fruit abscission. Ethephon (1000 mg L-1) and
Methyl Jasmonate (MJ; 20 mM) were used to induce abscission. Around 60% of the fruit abscised in
response to Ethephon and MJ treatments. The PPJ tissue was collected at 24 h after treatment and cell
wall glycan composition was monitored by glycome profiling using ~150 glycan-directed monoclonal
antibodies. More Xyloglucan (XG) epitopes were released in MJ treated PPJ tissues, suggesting that
loosening of XG is a PPJ-specific phenomenon induced by MJ mediated mechanisms. Also, the relative
abundance of hemicellulosic epitopes (Xylan and XG) released in the chlorite extracts of walls from
treated plants were reduced during abscission induction by Ethephon and MJ, potentially as a result of
reduced lignin-hemicellulose association within the cell walls of the active AZ. Next generation
sequencing of the AZ transcriptome was performed to identify genes expressed within this
region. Twenty eight cell wall carbohydrate metabolism-related genes were identified and changes in
their expression in response to treatment with Ethephon and MJ were studied. Expression of
POLYGALACTURONASE increased by 4-fold in response to MJ and ethephon treatments, while PECTATE
LYASE, BETA-GLUCANASE, and BETA-GALACTOSIDASE increased by more than 8 to10-fold at 48 h after
treatment. Expression of PECTIN METHYLESTERASE and INVERTASE PECTIN METHYLESTERASE
INHIBITOR POLYGALCTURONASE ISOZYME was down-regulated by 2- to 7-fold in response to these
treatments. Also, the expression of CELLULOSE SYNTHASE decreased in response to these
treatments. Together, these data suggests that blueberry fruit abscission is mediated by specific
changes in cell wall synthesis and metabolism at the PPJ.
Thomas, Baldwin
Plant Pathology
Seedling Blight of Maize by Fusarium verticillioides Causes Accumulation of Fumonisin B1 in Upper
Leaves apart from Colonization of the Leaves
Fusarium verticillioides is the primary fungus associated with maize and is a producer of the mycotoxin
fumonisin. Seedling blight of maize attributed to F. verticillioides infection has been shown to require
the production of fumonisins to result in the full spectrum of disease symptoms in maize including
stunted root development, leaf lesions, and leaf atrophy. Previous studies on the phytotoxic effects of
fumonisins on the susceptible maize cultivar Silver Queen during seedling blight development showed
accumulation of fumonisin B1 (FB1) mainly in the roots with limited accumulation in the
leaves. Conversely, studies watering Silver Queen with FB1 in the absence of the pathogen resulted in
accumulation of FB1 in only the roots. To date, the role of fumonisin in F. verticillioides colonization of
maize from the roots to the aerial tissue is not well understood. We hypothesized that fumonisin
accumulation in maize host leaf tissue is dependent upon localized F. verticillioides colonization of the
leaves. Alternatively, fumonisin accumulation in the maize host leaf tissues may require infection by F.
verticillioides, but doesn't require localized colonization of the leaf tissues. To resolve this discrepancy
and investigate colonization, seedlings of the cultivar Silver Queen were inoculated with fumonisinproducing and fumonisin non-producing strains of F. verticillioides and utilized previously characterized
strains that lack the ability to produce conidia. A holistic approach was taken to sample the soil, roots,
mesocotyl, stem, and leaves for fumonisin accumulation and colonization by F. verticillioides. FB1 was
detected in the first and second leaves with no detected colonization of the aerial tissues of seedlings
grown from seed inoculated with fumonisin-producing aconidial strain AEG 3-A3-5. In comparison,
wildtype F. verticillioides colonized the leaves and accumulated FB1. Along with FB1, Fumonisin B2 and
B3 were detected in the soil and seedling roots, but were not detected in the leaves of any
treatment. Our data suggest infection by F. verticillioides is necessary for discriminant accumulation of
FB1 in leaves, but utilizes a mechanism for accumulation apart from direct colonization of the leaf.
Additional Authors: Nicholas, Zitomer, Anthony, Glenn
Lisa Woodruff
Crop and Soil Sciences
Soil and Plant Nitrogen Dynamics under Organic or Conventional Sweet Corn Production Systems
Improved understanding of nitrogen (N) cycling in agro-ecosystems is essential for increasing N use
efficiency and enhancing the sustainability of food production. Many factors influence N cycling and
availability to plants in cropping systems, including how the soil is managed. In this study we examined
the impacts of managing the soil under organic or conventional N management systems on corn yield,
plant uptake of N and soil inorganic N pools. As the demand for organic produce increases, the impact of
organic farming on crop productivity and on the ability of the soil to supply nutrients and maintain its
functionality needs to be studied. Sweet corn was grown in plots receiving four treatments: Control (no
N), ammonium sulfate at 112 (AS100) or 224 (AS200) kg N per ha and poultry litter (PL) at 112 kg per ha.
Cornstalk N (%) was highest in the conventional plots, which received N in the form of AS. The greatest
difference (p<0.0001) was observed between the AS200 and the Control group with means of 1.75% and
0.79%, respectively. Post-season NO3-N pools in the soil were highest for the AS200 and AS100
treatments with means of 30 and 12 kg N per ha, respectively, with no differences between the Organic
(N from PL) and Control. No differences were observed in terms of crop yield and plant height. This,
along with the fact that significantly larger N pools remained in the soil post-harvest in the ammoniumsulfate-treated plots, indicates that there is room for improvement in terms of N use efficiency in the
conventionally managed plots.
Additional Authors: Mussie Habteselassie, Jeanette Norton