Virginia Agricultural Experiment Station

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https://hdl.handle.net/10919/24235
The Virginia Agricultural Experiment Station conducts research on food and fiber systems, their impact on the environment, and their relation to the future needs of Virginia, the nation, and the world.

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Browsing Virginia Agricultural Experiment Station by Subject "0703 Crop and Pasture Production"

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    Conidial production and viability of Calonectria pseudonaviculata on infected boxwood leaves as affected by temperature, wetness, and dryness periods
    Avenot, Herve F.; Baudoin, Antonius B.; Hong, Chuanxue (Wiley, 2021-10-31)
    Calonectria pseudonaviculata causes lesions on boxwood leaves and twigs. Controlled-environment experiments were conducted to determine the effects of temperature and leaf wetness period on C. pseudonaviculata sporulation on diseased (cv. Suffruticosa) leaves and of dryness periods and high temperature on conidial survival. Infected leaves were incubated in moist chambers and subjected to six temperatures (9, 13, 17, 21, 25, and 29°C) and six leaf wetness periods (0, 12, 24, 40, 48, and 72 h). Spore production was influenced significantly by wetness period, temperature, and their interaction. Increasing duration of leaf wetness and increasing temperature generally increased sporulation, with no sporulation occurring at 29°C or 9 and 13°C, except at 72 h of wetness exposure, while it was optimal at 21°C. Detached leaves with profuse conidia were subjected to a range of drying (relative humidity at 65%) times (0, 2, 4, 6, and 8 h) at two temperatures of 21 and 29°C. Conidia were then harvested and plated on water agar. Germinating conidia were counted to measure the spore viability. Spore mortality increased with increasing dryness duration at both temperatures but occurred more quickly and severely at 29 than 21°C. Overall, this study extended biological knowledge of conditions required for crucial stages of the C. pseudonaviculata disease cycle and the obtained results will be vital for developing boxwood blight forecasting and management tools.
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    Herbicide options for effective weed management in dry direct-seeded rice under scented rice-wheat rotation of western Indo-Gangetic Plains
    Singh, Vijay; Jat, Mangi L.; Ganie, Zahoor A.; Chauhan, Bhagirath S.; Gupta, Raj K. (Elsevier, 2016-03-01)
    Farmers' participatory field trials were conducted at Madhuban, and Taraori, the two participatory experimental sites/locations of the Cereal Systems Initiative for South Asia (CSISA), a collaborative project of IRRI and CIMMYT in Karnal district of Haryana, India, during Kharif (wet season) 2010 and 2011. This research aimed to evaluate preemergence (PRE) and postemergence (POST) herbicides for providing feasible and economically viable weed management options to farmers for predominant scented rice varieties. Treatments with pendimethalin PRE fb bispyribac-sodium + azimsulfuron POST had lower weed biomass at 45 days after sowing (DAS). At Madhuban, highest grain yield of scented basmati rice (3.43 t ha(-1)) was recorded with the sequential application of pendimethalin PRE fb bispyribac-sodium + azimsulfuron POST. However, at Taraori, yields were similar with pendimethalin or oxadiargyl PRE fb bispyribac-sodium and/or azimsulfuron POST. Applying oxadiargyl by mixing with sand onto flooded field was less effective than spray applications in non-flooded field. The benefit-cost ratio of rice crop was higher with herbicide treatments at both sites as compared with the non-treated weed-free check except single PRE and POST applications and sequential application of oxadiargyl PRE fb oxadiargyl PRE. In a separate experiment conducted at Nagla and Taraori sites, scented rice cultivars' ('CSR 30' and 'Pusa 1121') tolerance to three rates of azimsulfuron (15, 25, and 35 g ai ha(-1)) was evaluated over two years (2010 and 2011). CSR 30 (superfine, scented) was more sensitive to higher rates (35 g ai ha(-1)) of azimsulfuron as compared to Pusa 1121 (fine, scented). Crop injuries were 8 and 28% in case of CSR 30; 5 and 15% in Pusa 1121 when applied with azimsulfuron 25 and 35 g ai ha(-1), respectively. Azimsulfuron applied at 35 g ai ha(-1) reduced yield in both cultivars but in CSR 30 yield reduction was twofold (11.5%) as that of Pusa 1121 (5.2%).
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    Influence of landscape factors and abiotic conditions on dispersal behavior and overwintering site selection by Halyomorpha halys (Hemiptera: Pentatomidae)
    Cullum, John; Nixon, Laura J.; Morrison, Wiilliam; Shrewsbury, Paula M.; Venugopal, V.; Martinson, Holly; Bergh, J. Christopher; Leskey, Tracy C. (2020-08-01)
    Since the initial detection of the invasive Halyomorpha halys (Stål) in the United States in the late 1990s, this insect has emerged as a severe agricultural and nuisance pest. Nuisance problems are due to adult dispersal to overwintering sites in the fall at which time they alight onto and eventually settle within humanmade structures in addition to natural harborage. This study examined how three factors, elevation, light, and moisture affected overwintering site selection by H. halys in the mid-Atlantic. Observational counts performed along elevational transects revealed elevation was significant predictor of H. halys abundance during both years of the study in 2014 and 2015 with more adults observed at higher elevations. Choice tests examining effects of moisture and light on settling behavior demonstrated H. halys settled within overwintering shelter boxes in significantly greater numbers when shelters were dry compared with those having moist conditions, and in darkened shelters compared with those augmented with LED lights. Our findings indicate that H. halys use cues at both landscape and very localized levels when seeking and selecting overwintering sites.
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    Morphophysiological diversity and its association with herbicide resistance in Echinochloa ecotypes
    Liu, Rui; Singh, Vijay; Abugho, Seth; Lin, Hao-Sheng; Zhou, Xin-Gen; Bagavathiannan, Muthukumar V. (Cambridge University Press, 2021-10-01)
    The genus Echinochloa constitutes some of the most prominent weed species found in rice (Oryza sativa L.) production worldwide. The taxonomy of Echinochloa is complex due to its morphological variations. The morphophysiological diversity and taxonomic characteristics of Echinochloa ecotypes infesting rice fields in Texas are unknown. A total of 54 Echinochloa ecotypes collected during late-season field surveys in 2015 and 2016 were characterized in a common garden in 2017. Plants were characterized for 14 morphophysiological traits, including stem angle; stem color; plant height; leaf color; leaf texture; flag leaf length, width, and angle; days to flowering; panicle length; plant biomass; seed shattering; seed yield; and seed dormancy. Principal component analysis indicated that 4 (plant height, flag leaf length, seed shattering, and seed germination) of the 14 phenological traits characterized here had significantly contributed to the overall morphological diversity of Echinochloa spp. Results showed wide interpopulation diversity for the measured traits among the E. colona ecotypes, as well as diverse intrapopulation variability in all three Echinochloa species studied, including barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], junglerice [Echinochloa colona (L.) Link], and rough barnyardgrass [Echinochloa muricata (P. Beauv.) Fernald]. Taxonomical classification revealed that the collection consisted of three Echinochloa species, with E. colona being the most dominant (96%), followed by E. crus-galli (2%), and E. muricata (2%). Correlation analysis of morphophysiological traits and resistance status to commonly used preemergence (clomazone, quinclorac) and postemergence herbicides (propanil, quinclorac, imazethapyr, and fenoxaprop-ethyl) failed to show any significant association. Findings from this study provided novel insights into the morphophysiological characteristics of Echinochloa ecotypes in rice production in Texas. The morphological diversity currently present in Echinochloa ecotypes could contribute to their adaptation to selection pressure imposed by different management tools, emphasizing the need for a diversified management approach to effectively control this weed species.
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    Proof of Concept for Shoot Blight and Fire Blight Canker Management with Postinfection Spray Applications of Prohexadione-Calcium and Acibenzolar-S-Methyl in Apple
    Aćimović, Srđan G.; Meredith, Christopher L.; Santander, Ricardo Delgado; Khodadadi, Fatemeh (Scientific Societies, 2021-12-03)
    To reduce the severity of shoot blight and prevent the resulting development of cankers on perennial apple wood, we evaluated eight fire blight postinfection spray programs of prohexadione-calcium (PCA) alone or with acibenzolar-S-methyl (ASM) over 2 years. On mature trees of cultivar Royal Court, a single application of the high PCA rate (247 mg/liter) at 2 to 3 days after inoculation resulted in 89.5 and 69.5% reduction of shoot blight severity after inoculation. Two applications of PCA 247 mg/liter 12 or 14 days apart, with the first one applied 2 to 3 days after inoculation, resulted in 78.8 and 74.5% reduction of shoot blight severity in both years. A 100% control of canker incidence on perennial wood from infected shoots in both years was achieved with a single application of PCA (247 mg/liter) applied at 2 or 3 days after the inoculation, and three applications of PCA (125 mg/liter) + ASM (25 mg/liter) 12 to 16 days apart reduced canker incidence by 83.5 and 69% in the 2 years. The other programs with lower PCA rates and frequencies of application reduced shoot blight severity 50.8 and 51.8% (PCA) and 62.6 to 72% and 59.3% (PCA + ASM) over 2 years, respectively. Reduction of canker incidence on wood by the other programs was 66.5% and 69 to 90.4% in the two years, respectively. As fire blight cankers lead to death of dwarf apple trees and serve as primary sources of inoculum, our effective PCA and PCA + ASM programs could serve as viable postinfection management options. These treatments can reduce or prevent canker development and thus significantly abate tree losses in high-density apple orchards after fire blight epidemics occur.
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    Strain-level identification of bacterial tomato pathogens directly from metagenomic sequences
    Mechan Llontop, Marco Enrique; Sharma, Parul; Aguilera Flores, Marcela; Yang, Shu; Pollock, Jill; Tian, Long; Huang, Chengjie; Rideout, Steven L.; Heath, Lenwood S.; Li, Song; Vinatzer, Boris A. (Scientific Societies, 2019-12-12)
    Routine strain-level identification of plant pathogens directly from symptomatic tissue could significantly improve plant disease control and prevention. Here we tested the Oxford Nanopore Technologies (ONT) MinIONTM sequencer for metagenomic sequencing of tomato plants either artificially inoculated with a known strain of the bacterial speck pathogen Pseudomonas syringae pv. tomato (Pto), or collected in the field and showing bacterial spot symptoms caused by either one of four Xanthomonas species. After species-level identification using ONT's WIMP software and the third party tools Sourmash and MetaMaps, we used Sourmash and MetaMaps with a custom database of representative genomes of bacterial tomato pathogens to attempt strain-level identification. In parallel, each metagenome was assembled and the longest contigs were used as query with the genome-based microbial identification Web service LINbase. Both the read-based and assembly-based approaches correctly identified Pto strain T1 in the artificially inoculated samples. The pathogen strain in most field samples was identified as a member of Xanthomonas perforans group 2. This result was confirmed by whole genome sequencing of colonies isolated from one of the samples. Although in our case, metagenome-based pathogen identification at the strain-level was achieved, caution still needs to be exerted when interpreting strain-level results because of the challenges inherent to assigning reads to specific strains and the error rate of nanopore sequencing.
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    Sweet Corn Sentinel Monitoring for Lepidopteran Field-Evolved Resistance to Bt Toxins
    Dively, G. P.; Kuhar, Thomas P.; Taylor, Sally V.; Doughty, H. B.; Holmstrom, K.; Gilrein, D.; Nault, B. A.; Ingerson-Mahar, J.; Whalen, J.; Reisig, D.; Frank, Daniel L.; Fleischer, S. J.; Owens, David; Welty, C.; Reay-Jones, F. P. F.; Porter, P.; Smith, J. L.; Saguez, J.; Murray, S.; Wallingford, A.; Byker, H.; Jensen, B.; Burkness, E.; Hutchison, W. D.; Hamby, K. A. (Oxford University Press, 2021-02-01)
    As part of an insect resistance management plan to preserve Bt transgenic technology, annual monitoring of target pests is mandated to detect susceptibility changes to Bt toxins. Currently Helicoverpa zea (Boddie) monitoring involves investigating unexpected injury in Bt crop fields and collecting larvae from non-Bt host plants for laboratory diet bioassays to determine mortality responses to diagnostic concentrations of Bt toxins. To date, this monitoring approach has not detected any significant change from the known range of baseline susceptibility to Bt toxins, yet practical field-evolved resistance in H. zea populations and numerous occurrences of unexpected injury occur in Bt crops. In this study, we implemented a network of 73 sentinel sweet corn trials, spanning 16 U.S. states and 4 Canadian provinces, for monitoring changes in H. zea susceptibility to Cry and Vip3A toxins by measuring differences in ear damage and larval infestations between isogenic pairs of non-Bt and Bt hybrids over three years. This approach can monitor susceptibility changes and regional differences in other ear-feeding lepidopteran pests. Temporal changes in the field efficacy of each toxin were evidenced by comparing our current results with earlier published studies, including baseline data for each Bt trait when first commercialized. Changes in amount of ear damage showed significant increases in H. zea resistance to Cry toxins and possibly lower susceptibility to Vip3a. Our findings demonstrate that the sentinel plot approach as an in-field screen can effectively monitor phenotypic resistance and document field-evolved resistance in target pest populations, improving resistance monitoring for Bt crops.