`2015 Southern Division Meeting Abstracts
`
`Abstracts presented at the APS Southern Division meeting in Atlanta, Georgia, February 1–2, 2015. The abstracts are arranged alphabetically by the
`first author’s name. Recommended format for citing division meeting abstracts, using the first abstract below as an example, is as follows: Appel, D. N., and
`Ong, K. L. 2015. The results of survey for citrus greening on the Upper Gulf Coast of Texas. (Abstr.) Phytopathology 105(Suppl. 2):S2.1. http://
`dx.doi.org/10.1094/PHYTO-105-4-S2.1
`
`
`The results of survey for citrus greening on the Upper Gulf Coast of
`Texas
`D. N. APPEL (1), K. L. Ong (1)
`(1) Texas A&M AgriLife Extension Service, College Station, TX, U.S.A.
`Phytopathology 105(Suppl. 2):S2.1
`Annual citrus surveys have been conducted for Diophorina citri, the Asian
`Citrus Psyllid (ACP) and citrus greening disease, along the Texas Upper Gulf
`Coast since 2010. The objective is to determine whether any ACPs carry the
`citrus greening pathogen, Candidatus Liberibacter asiaticus. The focus is
`largely on dooryard citrus throughout 8 counties in Southeast Texas. Through
`2013, 1839 samples were collected, consisting of adults (n = 657), nymphs
`(367), eggs (4), and citrus foliage (811). No samples were positive for the
`pathogen, as tested with a multiplex, quantitative real-time PCR assay by the
`Texas Plant Disease Diagnostic Laboratory (TPDDL) in College Station, TX.
`Two Potential Actionable Suspect Samples (PASS) were forwarded to the
`USDA-APHIS-PPQ-CPHST Laboratory in Beltsville, MD. The 2012 sample
`tested inconclusive and the 2013 sample confirmed negative. Although the
`surveys were not conducted to investigate population dynamics of the ACP,
`some seasonal trends in psyllid numbers were observed. In contrast,
`contaminated ACPs and diseased trees have been detected by others in the
`commercial citrus growing region in the Rio Grande Valley (RGV) of South
`Texas. Contaminated nursery stock from the RGV was suspected to have been
`delivered to nurseries within the survey area. As of November, 2014, the
`TPDDL has confirmed the presence of infected nursery stock in 10 nurseries
`in 3 counties. Quarantines and other regulatory actions are in place to contain
`the disease. These events reinforce the need for continuing survey for
`pathogen encroachment into the Upper Gulf Coast landscape.
`
`The effect of oscillating temperatures on the growth rate of Sclerotium
`rolfsii
`R. L. BAROCCO (1), N. S. Dufault (1)
`(1) University of Florida, Gainesville, FL, U.S.A.
`Phytopathology 105(Suppl. 2):S2.1
`Sclerotium rolfsii is a soil-borne fungal pathogen that causes significant
`diseases on a wide variety of crop hosts. Weather-based models for site-
`specific management of plant diseases typically use microbial growth curves
`based on studies with constant mean temperatures. However, daily changes in
`temperatures under natural conditions fluctuate over time with variable
`minimum to maximum ranges. For this study, the growth rates of 23 Florida S.
`rolfsii isolates from peanut, tomato, and pepper were measured under 15, 20,
`25, 30, and 35°C mean temperatures that oscillate along a sine wave curve
`
`The abstracts are published as submitted. They were formatted but not
`edited at the APS headquarters office.
`
`http://dx.doi.org/10.1094 / PHYTO-105-4-S2.1
`© 2015 The American Phytopathological Society
`
`with a 24-hour cycle and amplitudes of 0, 4, or 8°C. Plugs of hyphae were
`plated on 2.5% acidified potato dextrose agar, and growth was measured
`every 12 hours for a duration of 48 hours. Mycelial growth decreased with
`increasing amplitudes for the mean temperatures of 25, 30, and 35°C. When
`the amplitudes were 0 or 4°C, optimum mycelial growth rates for all isolates
`were observed at the 30°C mean temperature. However, optimal mean
`temperatures for mycelial growth differed among isolates when the amplitude
`was 8°C. At this amplitude some isolates grew optimally at a mean of 25°C
`and others at a mean of 30°C. This study indicates that the growth response of
`S. rolfsii to temperature will vary depending on the isolate and range of
`temperatures which the pathogen is exposed to during a day. The information
`from this study can be used to improve risk models for diseases caused by this
`devastating pathogen.
`
`In furrow applications of azoxystrobin for peaut seed and seedling
`disease management
`T. BRENNEMAN (1), R. Kemerait (1), A. Culbreath (1)
`(1) UGA, Tifton, GA, U.S.A.
`Phytopathology 105(Suppl. 2):S2.1
`Azoxystrobin (Abound 2.08F) was evaluated as an in furrow (IF) spray at
`three different rates with peanut (Cv. Tifguard) seed either nontreated or
`treated with Dynasty PD (250 g/kg of seed). Two tests were conducted in
`2014, each with 5 replications in a split plot design, with seed treatment as
`whole plots and IF sprays a sub plots. When Dynasty PD was used, the IF
`sprays had no effect on plant stands, growth, diseases or yield in either test.
`With no seed treatment applied, all three rates of azoxystrobin (0.5, 0.11 and
`0.22 kg/ha) IF more than doubled final plant stand in both tests, and also
`increased plant growth. These treatments had no effect on stem rot
`(Sclerotium rolfsii) at harvest, but pod yield was increased significantly by all
`IF treatments in both trials by an average of 1383 and 1783 kg/ha,
`respectively. There were few differences among the three rates of IF sprays.
`While seed treatments alone are usually adquate for a good plant stand and
`pod yield, an IF spray of azoxystrobin at 0.05–0.11 kg/ha can help protect
`young plants under more severe disease pressure.
`
`Evaluation of systemic fungicides in pecans and implications for disease
`management
`K. A. BROWN (1), T. B. Brenneman (1)
`(1) University of Georgia, Tifton, GA, U.S.A.
`Phytopathology 105(Suppl. 2):S2.1
`Scab (Fusicladium effusum) is a common disease of pecans, especially during
`wet years, and frequent fungicide sprays are needed to prevent serious losses.
`Some fungicides used on pecans are known to move systemically in other
`crops, but little is known about this phenomenon in pecan tissues. The
`movement of tebuconazole (TEB = Orius 3.6), azoxystrobin (AZO = Abound
`2.08), a phosphite (PHO = Rampart), and TPTH (Super Tin 4L), a protectant,
`was studied by treating lower leaves on a terminal, then sampling nontreated
`leaves above those on the same stem. Samples were taken 1, 3, 5 and 7 days
`after fungicide application and bioassayed with Sclerotium rolfsii. TEB, AZO
`
`Vol. 105 (Supplement 2), No. 4, 2015 S2.1
`
`SYNGENTA EXHIBIT 1008
`Syngenta v. UPL, PGR2023-00017
`
`

`

`and PHO all reduced the diseased area versus the protectant (Super Tin). AZO
`showed the best control 1 day after spray application, whereas PHO had better
`control at 7 days. AZO and PHO exhibited faster movement and better
`residual control 7 days after application than other treatments. Results indicate
`that systemic fungicides can help protect foliage that was not uniformly
`sprayed, or that developed after the previous application.
`
`Influence of application technology on foliar fungicide efficacy in
`Cercospora sojina infected soybeans
`S. A. BUTLER (1), H. Young-Kelly (1), G. Kruger (2)
`(1) University of Tennessee, Jackson, TN, U.S.A.; (2) University of Nebraska,
`North Platte, NE, U.S.A.
`Phytopathology 105(Suppl. 2):S2.2
`Use of new herbicide tolerant crops will require growers to use drift-reducing
`nozzle
`technology
`that produces very-coarse
`to ultra-coarse droplets.
`Pesticides that have contact or locally systemic activity are typically not as
`effective when applied with large spray droplets. Due to the frequency of
`tank-mixed pesticide applications and the cost associated with utilizing drift-
`reduction technology, these changes will also affect other foliar pesticides.
`Soybean crops infected with Cercospora sojina, the causal agent of frogeye
`leaf spot (FLS) in soybean, could be negatively impacted by reductions in
`spray coverage. Field experiments were conducted in Jackson and Milan,
`Tennessee in 2014 to evaluate the influence of application technology on
`foliar fungicide efficacy in soybean infected with FLS. Quadris Top
`(azoxystrobin and difenoconazole) was applied
`through 9 nozzle
`arrangements. Nozzle treatments included 3 angles of 0°, 30°, and a
`combination of 10° and 50°, 2 fan arrangements of single and twin, and 3
`droplet size ranges of >medium (200–250 microns), >ultra-coarse (400–850
`microns), and a combination of medium and ultra-coarse (575 microns).
`Disease index ratings were taken at 14 and 28 days after application (DAA).
`Leaf samples were collected 0, 2, 4, 7, and 14 DAA for dosage quantification
`to be analyzed using high-performance
`liquid chromatography/mass
`spectrometry In 2014 between 2 locations, no significant differences have
`been found between treatments of spray angle, fan arrangement, or droplet
`size based on disease control and yield comparisons. Results suggest that
`drift-reduction nozzle technology may not negatively affect fungicide efficacy
`on FLS in soybean.
`
`Effects of an experimental seed treatment supplement and potash
`fertilization on seedling diseases of snap bean and soybean and on crop
`yield
`C. CANADAY (1), S. D. Stewart (1), A. McClure (1)
`(1) University of Tennessee, Jackson, TN, U.S.A.
`Phytopathology 105(Suppl. 2):S2.2
`Seedling diseases cause damping-off, root rot, stunting, and yield loss on
`many crops. Losses can be exacerbated with application of muriate of potash
`(KCl). The effect of experimental seed treatment supplements on seedling
`diseases of snap bean and soybean, with and without potash fertilization, were
`evaluated in a series of field experiments in 2013 and 2014. A split-plot
`design was used in all tests with potash rates as whole plots and seed
`treatment supplements as subplots. In 2013, adding an experimental seed
`treatment supplement (Supplement A) to the standard snap bean seed
`treatment increased snap bean emergence, reduced seedling disease incidence,
`increased the stand of healthy plants, and increased yield by over 65%. Potash
`applied 3 days after planting (and after 1.3 inch of rain) had no effect on any
`variable. In 2014, twelve soybean seed treatment supplements were evaluated.
`None of the supplements had an effect on seedling emergence or disease
`incidence. Adding Supplement A to the standard seed treatment increased
`soybean yield by over 6.0 bu/A. Soybean yield with no potash was nearly
`identical to an application of 50 lb K2O/A applied 11 days before planting.
`Application of muriate of potash at 100 and 150 lb K2O/A reduced soybean
`yield by 5.8 and 9.9 bu/A, respectively, compared to the 50 lb K2O/A rate.
`The disease control benefits of Supplement A appear to vary with the crop. A
`yield increase with Supplement A appears more consistent.
`
`Fungal colonization and cercosporin and flavonoid concentrations for
`two different symptoms of Cercospora leaf blight in soybean
`E. CHAGAS FERREIRA DA SILVA (1), T. G. Garcia Aroca (1), A. V.
`Lygin (2), A. K. Chanda (3), C. L. Robertson (1), B. M. Ward (1), R. W.
`Schneider (1)
`(1) Louisiana State University AgCenter, Baton Rouge, LA, U.S.A.; (2)
`University of Illinois, Urbana, IL, U.S.A.; (3) University of Minnesota,
`Crookston, MN, U.S.A.
`Phytopathology 105(Suppl. 2):S2.2
`Cercospora leaf blight (CLB), caused by Cercospora kikuchii, is the most
`important soybean disease in Louisiana. Two different symptoms are
`
`S2.2 PHYTOPATHOLOGY
`
`associated with CLB: purple leaves (believed to be due to cercosporin
`accumulation) and blight. Previous publications suggested that CLB starts
`with leaf purpling and leaves become blighted as the disease progresses. Our
`findings showed that there was not a significant correlation between these two
`symptoms, which suggests that they may be a result of two diseases caused by
`the same pathogen. We investigated the possibility that the purple symptom is
`a plant reaction, and the blight is the actual disease. The objectives of this
`work were: 1) to determine the relationships among fungal biomass in leaves,
`cercosporin concentration and the two symptoms, and 2) to determine the
`concentrations of flavonoids in symptomatic leaves. Four soybean cultivars
`were planted at two locations. Leaves showing different severities of the two
`symptoms were collected for quantification of anthocyanins, flavonoids and
`cercosporin, using HPLC, and fungal colonization, using qPCR. In general, C.
`kikuchii was detected in all leaves (including symptomless); however, blighted
`leaves had higher fungal biomass
`than purple
`leaves. Cercosporin
`concentrations also were higher in blighted leaves. No anthocyanins were
`found in any leaves. Coefficients of determination ranged from 0.09 to 0.24
`for glyceollin and other variables.
`
`Complete genome sequences of nine isolates of Canna yellow streak virus
`reveal its relationship to Sugarcane mosaic virus subgroup of potyviruses,
`intraspecies genetic diversity and expands the natural host range of
`SCMV subgroup of potyviruses
`R. P. CHAUHAN (1), P. Rajakaruna (1), J. Verchot (1)
`(1) Department of Entomology and Plant Pathology, Oklahoma State
`University, Stillwater, OK, U.S.A.
`Phytopathology 105(Suppl. 2):S2.2
`Canna yellow streak virus (CaYSV) was first reported in Europe and the full
`genome sequence was reported in 2010 from UK. CaYSV has been recently
`reported in USA but there is no information about the genetic variation or
`possible origin of CaYSV in the country. Given the popularity and global
`trade of cannas a clear picture of disease incidence and genetic diversity of
`CaYSV is critical to disease management. In this project, eight RT-PCR
`reactions were carried out to amplify the entire genome of one CaYSV-OK,
`three CaYSV-BZ and five CaYSV-NC isolates which were obtained locally in
`Oklahoma. These PCR products were either cloned or directly sequenced.
`Contigs were prepared and assembled using CAP3 DNA sequence assembly
`program. The maximum likelihood tree using MUSCLE algorithm with 1000
`bootstrap replications determined that CaYSV belongs to Sugarcane mosaic
`virus (SCMV) subgroup of potyviruses. It was intriguing to see that the BZ
`isolates clustered with the European and Israeli isolates and OK isolate
`clustered with the Thai isolates reported in GenBank. Multiple sequence
`alignment of amino acid sequences among CaYSV isolates showed greatest
`sequence diversity in N-terminal region of the coat protein suggests that this
`might be the most suitable region for discriminating CaYSV isolates. Further
`biological characterization identified N. benthamiana, C. quinoa and P.
`vulgaris as experimental hosts that support systemic infection. Studying the
`molecular variability, genetic structure and biological characters of CaYSV
`will provide new insight into molecular history, dispersion and emergence of
`these viruses which is critical to disease management.
`
`Impact of outer membrane protein MopB on the biofilm formation of
`Xylella fastidiosa
`H. CHEN (1), P. P. Kandel (1), J. Parker (1), L. Cruz (1), L. De La Fuente (1)
`(1) Auburn University, Auburn, AL, U.S.A.
`Phytopathology 105(Suppl. 2):S2.2
`Xylella fastidiosa is the causal agent of many economically important plant
`diseases. This bacterium is limited to surviving inside the xylem vessels of
`host plants, where mineral nutrients are transported from roots to leaves. The
`virulence of this pathogen is significantly correlated with the available
`concentrations of mineral elements. Previous research showed that Ca2+
`increases the virulence traits of this bacterium, including twitching motility
`and biofilm formation. The mechanisms of these effects are not well
`understood. In this work, we focus on the role of the outer membrane protein
`MopB in the biofilm formation of Xylella fastidiosa. A mopB gene knockout
`the effects of Ca2+
`mutant was constructed. Experiments
`to assess
`supplementation on biofilm formation showed that the mopB mutant has
`decreased biofilm formation compared to the wild-type strain. Furthermore,
`the mopB mutant shows no increase in biofilm formation in response to Ca2+
`supplementation, in contrast to the wild-type strain. In addition, two different
`calcium-binding motifs were identified based on the analysis of the amino
`acid sequence of MopB. Currently the virulence of this mutant is being
`assessed in greenhouse experiments. We hypothesize that MopB is im-
`portant for the biofilm formation inside xylem vessels of the host plant, and
`in particular this protein has a role in the increased virulence mediated by
`Ca2+.
`
`

`

`Frogeye leaf spot response to solo and combination fungicides
`A. M. COCHRAN (1), H. M. Kelly (2), K. Lamour (1), W. J. Jordan (2), B. P.
`Vega (2)
`(1) The University of Tennessee, Knoxville, TN, U.S.A.; (2) The University
`of Tennessee, Jackson, TN, U.S.A.
`Phytopathology 105(Suppl. 2):S2.3
`In 2010 frogeye leaf spot (FLS) demonstrated resistance to the quinone
`outside inhibitor (QoI) fungicides. In an effort to understand the efficacy of
`different fungicides in light of QoI fungicide resistance, field trials were
`conducted in a randomized complete block design in five locations in
`Tennessee and one in Illinois during the 2013–2014 soybean growing seasons.
`A minimum of six foliar fungicides with different solo or combination modes
`of actions were evaluated on Asgrow 4832 soybean using an R3 application
`time. FLS disease severity and yield were obtained from the center two rows
`of each plot. C. sojina spores from test plots were evaluated for QoI resistance
`by plating on fungicide amended and unamended media. The negative
`correlation between yield (bu/a) and increasing FLS disease severity (%) was
`demonstrated during both growing seasons. The three-way combination
`treatment (Priaxor+Domark) was the highest yielding in half of the 2014
`trials. Dual combination treatments were generally within the top three highest
`yielding of each trial, while the lowest yielding were the solo QoI and DMI
`treatments which were ranked similarly to the untreated controls. FLS severity
`did not differ significantly between the untreated and the solo strobilurin
`treatment. Future research will focus on analyzing FLS lesion DNA to assess
`the pressure exerted by the various fungicides on selection for G143A
`mutation conferring QoI-fungicide resistance using qPCR and to evaluate the
`overall population diversity of C. sojina using 48 designed SNP markers.
`
`Experiences with fungicide resistance in Florida citrus
`M. M. DEWDNEY (1)
`(1) University of Florida, Lake Alfred, FL, U.S.A.
`Phytopathology 105(Suppl. 2):S2.3
`Foliar fungal diseases of citrus are historically production limiting for fresh
`fruit and processing cultivars in Florida because of cosmetic defects,
`defoliation, and premature abscission. Few fungicide classes have been
`registered for use in citrus limiting rotation options. The primary fungicide
`class used for the last decade, aside from copper, are the quinone-outside
`inhibitors (QoI) but recently 57.6% of the Alternaria alternata isolates, causal
`agent of Alternaria brown spot, were found to be resistant to QoI fungicides in
`a statewide survey of tangerine blocks. The proportion of resistant isolates
`differed significantly (P < 0.0001) with cultivar susceptibility and application
`frequency. All resistant isolates carried the G143A point mutation in the
`cytochrome b gene (cytb). The resistance was stable and isolate fitness was
`not affected by the resistance trait. Since QoIs are fundamental to the control
`of the emerging disease citrus black spot, a baseline study was done on the
`Florida population of Guignardia citricarpa. All isolates were found to be
`sensitive to QoIs and an intron was found in cytb immediately post G143
`potentially blocking resistance conferring mutations. In addition, the G.
`citricarpa population was screened for sensitivity to five demethylation
`inhibitor (DMI) fungicides to be potentially field tested. All isolates were
`sensitive and difenoconazole and fenbuconazole had greater efficacy than the
`other tested DMI’s (P < 0.0001).
`
`Screening winter canola for seedling resistance to black leg
`C. I. DIAZ (1), J. Damicone (1)
`(1) Oklahoma State University, Stillwater, OK, U.S.A.
`Phytopathology 105(Suppl. 2):S2.3
`Black leg disease, caused by the fungus Leptosphaeria maculans, is a
`common disease of winter canola (Brassica napus) in Oklahoma. Major
`resistance genes (Rlm) are expressed in seedlings and interact with avirulence
`genes in L. maculans (AvrLm). The presence of avirulence alleles in the local
`pathogen population was determined by inoculating differential cultivars
`harboring Rlm1 and Rlm2,3 and PCR amplification of avirulence alleles
`AvrLm1, AvrLm4-7, AvrLm6. Avirulence alleles AvrLm6 (90%) and AvrLm4-7
`(96%) were prevalent in the local population (n = 94), whereas AvrLm1 and
`AvrLm2-3 presence was only 27% and 10%, respectively. Five races (AvrLm6,
`AvrLm4-7, AvrLm6,4-7, AvrLm1,6,4-7 and avrLm1,2,3,6,4-7) were identified
`and used to characterize seedling resistance in 25 commercial cultivars and
`breeding lines. Most (64%) commercial cultivars and breeding lines were
`susceptible to all five races and lack specific resistance genes. Some entries
`(12%) presented race non-specific resistance, while other (24%) had
`heterogeneous resistance to one, more than one, or all races. The study
`showed that commercial Roundup-Ready cultivars currently grown in the
`region generally lacked seedling resistance genes, except for DKW46-15
`which seemed to be resistant to AvrLm4. Most conventional cultivars and
`hybrids appeared to have heterogeneous resistance to one or more races with
`
`in pepper
`
`is affected by cation
`
`the exception of Dimension, Visby and Rossini which were resistant to all
`races. Several breeding lines had heterogeneous resistance to all races, except
`for KSUR21 which was susceptible to all races.
`
`leaf spot
`Severity of bacterial
`concentrations in pepper tissues
`B. DUTTA (1), D. Langston (2), H. Sanders (1), S. Smith (1), R. Gitaitis (1)
`(1) University of Georgia, Tifton, GA, U.S.A.; (2) Tidewater Agricultural
`Research and Extension Center, Suffolk, VA, U.S.A.
`Phytopathology 105(Suppl. 2):S2.3
`Regression models based on cation concentrations in plant tissues were
`developed for predicting bacterial leaf spot (BLS) severity in pepper
`(Capsicum annuum L.) caused by Xanthomonas euvesicatoria. Models from
`two consecutive years of field study (2012–2013) consisted mainly of
`combinations of Cu2+, Fe2+, Zn2+ and Mn2+. Among other roles, these cations
`act as co-factors for superoxide-dismutase (SOD) enzymes, namely Cu-
`ZnSOD, FeSOD, and MnSOD. SODs detoxify reactive oxygen species
`forming salicylic acid (SA, a component of systemic acquired resistance
`(SAR)). The BLS-cation model was also a good fit for relative expression of
`the genes Cu-ZnSOD (P = 0.05; adj.R2 = 0.92) and MnSOD (P = 0.009; adj.R2
`= 0.98). Relative expression of the NPR1 gene (non-expresser pathogenesis-
`related protein, another component of SAR) fit a model consisting of Cu-
`ZnSOD, FeSOD, and MnSOD values (P ≤ 0.0001; adj.R2 = 0.93). In addition,
`SA levels and MnSOD expression were related to BLS severity in two
`commercial pepper fields. Learning how cation concentrations and their
`relative ratios affect SODs, SA and SAR could lead to improved disease risk
`predictions and prescribed fertilization practices using precision agricultural
`techniques.
`
`Management of daylily rust with different fungicide combinations and
`spray intervals
`R. S. EMMITT (1), K. L. Stevenson (2), T. B. Brenneman (2), J. W. Buck (1)
`(1) University of Georgia, Griffin, GA, U.S.A.; (2) University of Georgia,
`Tifton, GA, U.S.A.
`Phytopathology 105(Suppl. 2):S2.3
`Daylily (Hemerocallis spp.) is an herbaceous perennial that is used
`extensively in the American landscape. Daylilies remained relatively pest-free
`until the introduction of daylily rust caused by the fungus Puccinia
`hemerocallidis, in 2000. Fungicides across several chemical classes are
`currently registered for daylily rust and growers rely heavily on these for the
`management of this disease. The objectives of this study were to determine
`the most cost effective fungicide combinations and application intervals for
`managing daylily rust in the field. Foliar spray combinations and spray
`intervals were evaluated in field experiments, under high disease pressure, in
`Griffin, GA
`in 2014. Foliar spray combinations of azoxystrobin +
`propiconazole, azoxystrobin + chlorothalonil, and azoxystrobin alone at 21
`days provided comparable protection to azoxystrobin alone at 14 days. The
`combinations of propiconazole + chlorothalonil and thiophanate-methyl +
`chlorothalonil at 21 or 28 days did not differ from the untreated control.
`Elimination of less efficacious active ingredients and unnecessary applications
`from spray regimes can help growers maximize profitability by reducing
`expenses and simplifying inventory and storage.
`
`Aflatoxin production and oxidative stress in Aspergillus flavus
`J. C. FOUNTAIN (1), L. Yang (1), P. Khera (2), R. C. Kemerait (1), R. D.
`Lee (1), B. T. Scully (3), R. K. Varshney (2), B. Guo (4)
`(1) University of Georgia, Tifton, GA, U.S.A.; (2) International Crops
`Research Institute for the Semi-Arid Tropics, Hyderabad, India; (3) USDA-
`ARS, Fort Pierce, FL, U.S.A.; (4) USDA-ARS, Tifton, GA, U.S.A.
`Phytopathology 105(Suppl. 2):S2.3
`The colonization of crops by Aspergillus flavus results in the production of
`aflatoxins. Aflatoxin production is also exacerbated by abiotic stresses in the
`field. Here, we investigated the role of reactive oxygen species (ROS), which
`accumulate in plant tissues in response to drought and heat stress, and
`aflatoxin production in different isolates of A. flavus and A. parasiticus. Ten
`isolates were used, including nine A. flavus toxigenic (+) and atoxigenic (-)
`isolates: NRRL3357(+), A9(+), AF13(+), Tox4(+), A1(-), K49(-), K54(-),
`AF36(-), and Aflaguard(-), and one A. parasiticus isolate, NRRL2999(+). The
`isolates were cultured in toxin-conducive yeast extract-sucrose (YES) media
`supplemented with hydrogen peroxide (H2O2) with a concentration gradient
`from 0 to 45mM in 5mM increments for 7 days at 32°C. The different isolates
`responded to the H2O2 gradient differently in terms of biomass and
`survivability. Aflatoxin production was also found to be enhanced by
`increasing [H2O2]. However, growth in the toxin-inconducive media, yeast
`extract-peptone (YEP), all isolates survived at a higher [H2O2]. Therefore,
`additional studies will seek to understand why different isolates behave
`
`Vol. 105 (Supplement 2), No. 4, 2015 S2.3
`
`

`

`differently in YES and YEP media in response to H2O2 stress in order to
`examine the potential functional roles of aflatoxin production and ROS in
`Aspergillus spp. The activity levels of antioxidant enzymes and the expression
`of stress responsive genes will also be examined.
`
`Nematodes associated with edamame, Glycine max L. (Merr.), and their
`effect on yield and quality in Arkansas
`J. E. FULTZ (1), T. Kirkpatrick (2)
`(1) University of Arkansas, Fayetteville, AR, U.S.A.; (2) University of
`Arkansas, Hope, AR, U.S.A.
`Phytopathology 105(Suppl. 2):S2.4
`Edamame, also known as vegetable soybean, Glycine max, has been growing
`in popularity in the US as a high-fiber, low-sugar snack in recent years. In
`2012, American Vegetable Soybean and Edamame, Inc. established the first
`commercial processing plant in the United States near Mulberry, Arkansas.
`Since edamame is harvested as an immature bean, management practices vary
`from those used for conventional soybean. Plant-parasitic nematodes,
`particularly Meloidogyne incognita (root-knot) and Heterodera glycines
`(soybean cyst) known to be wide-spread in Arkansas, are pests of concern.
`The objective of this study was to 1) determine the nematodes associated with
`edamame in Arkansas edamame fields 2) evaluate new breeding lines for
`resistance to M. incognita and H. glycines 3) determine the effect of root-knot
`and soybean cyst nematode infection on edamame quality and yield.
`Production fields were surveyed in 2013 and 2014 immediately following
`harvest to determine the presence, identity, and relative population density of
`parasitic nematodes. Edamame lines developed by the Arkansas soybean
`breeding program were evaluated for host suitability to M. incognita and H.
`glycines in greenhouse trials. Moderate resistance to root-knot was identified
`in one studied line. Yield was notably reduced by both Heterodera and
`Meloidogyne. However, quality analysis of infected crops did not show
`significant alteration of components of lipid, starch, protein, and sugar. This
`work will aid producers and crop advisors in developing nematode
`management strategies for edamame production and provide insight on the
`potential risk of root-knot and soybean cyst nematodes to this emerging crop.
`
`An evaluation of Cercospora arachidicola epidemic subprocesses as
`confirmation of field observations
`L. GONG (1), K. Bowen (1)
`(1) Auburn University, Auburn, AL, U.S.A.
`Phytopathology 105(Suppl. 2):S2.4
`Cultivated peanut (Arachis hypogaea L.) is an economically important crop
`that is produced in the United States and throughout the world. Cercospora
`arachidicola (Ca) causes early leaf spot on cultivated peanut and can
`contribute to yield losses of up to 50%. Recently released peanut cultivars,
`such as Georgia-06G, Georgia-09B, and Georgia-12Y, have shown varying
`levels of resistance to Ca in field observations. This study examines
`incubation period, number and size of lesions, and proportion of sporulating
`lesions of these three cultivars using whole peanut plants in a growth
`chamber. Lesions were evaluated on five leaves of each plant; cultivars were
`replicated three times. Incubation periods for GA-09B, GA-06G, and GA-12Y
`were 9.06, 20.50, and 26.00 days, respectively. At 17 days after inoculation
`(DAI), lesion counts for GA-09B, GA-06G, and GA-12Y were 10.20, 5.55,
`and 0.33, respectively. At 42 DAI, GA-09B had the largest lesions at 5.03 mm
`diameter, while GA-06B and GA-12Y had 3.36 and 2.53 mm diameter
`lesions, respectively. At 42 DAI, the proportion of lesions with conidia were
`22.79%, 10.99%, and 7.67% on GA-09B, GA-06G, and GA-12Y,
`respectively. GA-12Y has a longer incubation period, lower lesion count,
`smaller lesion size, and lower proportion of sporulating lesions than other
`cultivars, which suggests this is the most resistant cultivar of these three.
`Conversely, GA-09B has a shorter incubation period, higher lesion count,
`larger lesion size, and higher proportion of sporulating lesions than other
`cultivars, which suggests greater susceptibility.
`
`Effect of fungicides on chlorophyll content, yield, and test weight of
`winter wheat in the absence of foliar disease
`N. GRAF GRACHET (1), R. M. Hunger (1), M. E. Payton (1), J. T. Edwards
`(1)
`(1) Oklahoma State University, Stillwater, OK, U.S.A.
`Phytopathology 105(Suppl. 2):S2.4
`Fungicides can alleviate losses caused by diseases in susceptible cultivars of
`wheat. Some of these fungicides are labeled as plant health promoters with
`associated claims of increased greenness, improved drought tolerance, and
`increased yield. This study measured changes in chlorophyll content, yield
`and test weight associated with fungicide application in hard red winter wheat
`in the absence of foliar disease. Near Stillwater, OK, two field trials (a dryland
`
`S2.4 PHYTOPATHOLOGY
`
`and an irrigated trial) were planted with ‘Duster’ (resistant to most foliar
`diseases) and ‘OK Bullet’ (susceptible) cultivars. At Feekes 10.3, the
`commercial fungicides Headline (pyraclostrobin), Caramba (metconazole),
`and Twinline (pyraclostrobin plus metconazole) (BASF Corporation, Florham
`Park, NJ) were applied at labeled rates. Chlorophyll content of leaves was
`determined using a SPAD (Soil and Plant Analyzer Development) 502 Plus
`Chlorophyll Meter (Spectrum Technologies, Inc., Aurora, IL) before and after
`fungicide application. Disease incidence in both experiments was absent due
`to an extended dry winter and spring. None of the fungicides increased
`chlorophyll content, yield or test weight in either trial compared to the not
`sprayed control. Hence, these results do not support claims of plant health
`benefits afforded by application of fungicide in the absence of disease.
`
`Relationship between target spot intensity and seed cot