Browsing by Author "Bush, Elizabeth Ann"
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- Biological Control Agent Rhizobium vitis, ARK-1 Reduces Incidence and Severity of Grapevine Crown Gall in VirginiaWong, Alexander Thomas (Virginia Tech, 2018-08-06)Crown gall of grapevine (Vitis spp.) is a serious and economically important disease caused by the bacterial pathogen Rhizobium vitis, which transforms healthy plant cell genomes leading to hypertrophic and hyperplastic growth of affected plant cells. Recent studies have documented a strong inhibitory effect against Japanese tumorigenic R. vitis isolates by a newly identified non-tumorigenic strain of R. vitis, ARK-1. We conducted co-inoculation assays in tomato (Solanum lycopersicum) and wine grape cultivars (Vitis vinifera) with four tumorigenic isolates of R. vitis from Virginia. These tumorigenic isolates were co-inoculated with ARK-1 in various ratios and resulting gall incidence and gall size were measured. Analysis was conducted with the generalized linear mixed model (GLIMMIX) in SAS (ver. 9.4). ARK-1 significantly reduced both the mean probability of gall formation and the mean gall size (P < 0.05). ARK-1 efficacy against combinations of two or four tumorigenic isolates and up to twice as many cells of tumorigenic isolates was also significant. However, there was an indication of a loss of efficacy when ARK-1 was challenged with four isolates at four times the cell number of ARK-1. Also, the efficacy of ARK-1 was influenced by both the specific isolate and host plant used in the study. Our results suggest that ARK-1 has promising potential as an effective biological control agent for grapevine crown gall in the United States.
- Control of anthracnose (caused by Colletotrichum gloeosporioides s.l.) on mango in Senegal by fungicides and biofungicidesDiallo, Yaya (Virginia Tech, 2016-06-15)Senegal ranks second for mango production among West African countries and has the potential to competitively produce mangoes for the European market. Colletotrichum gloeosporioides Penz. and Sacc. has historically been considered the causal pathogen of anthracnose of mango and other fruits, but is now known to represent a species complex. Field trials to examine the efficacy of fungicides and biofungicides were conducted in southern and northern production regions of Senegal. In three southern trials, Sonata (Bacillus pumilus strain QST 2808), Serenade Optimum (Bacillus subtilis strain QST 713), and sodium molybdate provided 63%, 67% and 76% control of disease severity, respectively, whereas thiophanate methyl and azoxystrobin provided 77% and 78% control, respectively. Disease severities of all treatments were significantly lower than that of the control. Thiophanate methyl and azoxystrobin produced more disease-free mangoes (64 and 62%, respectively) than Serenade (49%), sodium molybdate (44%), and Sonata (38%). Differences within each trial were not statistically significant, but when all trials were combined, all treatments resulted in significantly more disease-free mangoes than the control. Among treatments, thiophanate methyl and azoxystrobin resulted in significantly more disease-free mangoes than Sonata. No results were obtained in the northern orchards due to an absence of disease development. Sequencing of the ITS gene region of 30 Colletotrichum isolates from mangoes from different regions in Senegal indicated that all belonged to the C. gloeosporioides species complex. Sequencing of the ApMat intergenic region identified all of them as most closely resembling C. siamense.
- Documentation of grapevine leafroll-associated viruses in wine grape varieties and native grape species in Virginia, and examination of the movement of grapevine leafroll disease to develop management strategiesJones, Taylor J. (Virginia Tech, 2012-12-21)Grapevine leafroll-associated virus-2 (GLRaV-2), GLRaV-3, and grapevine fleck virus (GFkV) are widespread in grapes around the world. These viruses can cause significant crop loss and affect wine quality by reducing sugar accumulation and compromising skin color. Mealybugs are vectors of grapevine leafroll-associated viruses (GLRaVs). A statewide survey of commercial and wild grapevines in Virginia was conducted during 2009 through 2011. Also, vector management options were tested in two field studies. GLRaV-2, GLRaV-3, and GFkV were detected in 8%, 25%, and 1%, respectively, of over 1,200 vine samples (41 wine grape varieties) from 77 locations, and 64% of vineyards were positive for at least one of the tested viruses. All 100 wild grapevines tested were free of these three viruses, indicating that they are not alternative hosts. The majority of infected vines from commercial vineyards were planted prior to the 1990\'s; however, some new plantings were also found to be positive, indicating movement of the viruses among vineyards and also potential infection prior to planting. The high frequency of virus-infected vines emphasizes the importance of clean plant materials, as well as management of vector insects. The insecticide trials resulted in promising vector control with dinotefuran and spirotetramat; however, acetamiprid and pryrethroid resulted in an increase in mealybug population. This study is the first to examine multiple grape viruses in VA. It will aid in developing better strategies aimed at controlling mealybugs to restrict the movement of viral diseases.
- Effect of Protective Covers Against Biotic and Abiotic Disorders for Grape Production in VirginiaRedoy, Mahadi Hasan (Virginia Tech, 2024-01-03)Grapes (Vitis spp.), globally cultivated for wine and other grape-based products, are susceptible to various diseases, pests, and disorders. These challenges are particularly pervasive in Virginia and viticultural regions in similar climates. Thus, growers routinely use insecticides and fungicides to protect their fruits. However, frequent or excessive use of these chemicals can pose environmental and human health risks and increase the chances of fungicide resistance. Many crop production systems use physical barriers to shield plant surfaces from biotic and abiotic environmental factors, particularly in Asian countries. This study evaluated the efficacy of paper bags, umbrella-style covers, and fruit-zone shelters in mitigating fungal diseases, insect infestations, and other factors that damage grape clusters. A series of field experiments were conducted at four commercial vineyards in Virginia and one research experiment station at Virginia Tech in five years with eight grape cultivars. Our results highlighted the importance of bag and fruit-zone shelter applications. Especially when these protection measures were applied around bloom, we observed reductions in the level of multiple diseases and insect- and bird-related damages. Fruit bagging resulted in significantly lower (P ≤ 0.05) mean severity and incidence of black rot, sour rot, sooty mold, and grape berry moth damage. Similarly, we found a significantly lower mean incidence of black rot, ripe rot, sour rot, and bird damage with the application of fruit-zone shelters. Thus, fruit bagging and fruit-zone shelter can be an effective cultural method for safeguarding grape clusters from different diseases, potentially reducing pesticide use and offering economic advantages to growers.
- Efficacy of the biological control agent Rhizobium vitis ARK-1 against tumorigenic Rhizobium vitis, the causal agent of grapevine crown gallNahiyan, Md Abdullah Al (Virginia Tech, 2021-06-02)Grapevine crown gall causes significant economic damage in vineyards and nurseries worldwide. Infected vines are not curable due to irreversible genomic transformation by the tumorigenic bacterium Rhizobium vitis. Crown gall results in a gradual decline in yield and vine vigor, then the complete collapse of the vine. R. vitis ARK-1, an antagonistic and non-tumorigenic strain, has been shown to inhibit gall formation when equal cell concentrations of antagonist and tumorigenic strains are co-inoculated in planta. In this study, we tested the efficacy of ARK-1 against higher cell numbers of tumorigenic isolates and evaluated timing and methods of ARK-1 application in in-planta assays in grapevine (Vitis vinifera 'Chardonnay', 'Cabernet Sauvignon', 'Merlot') and tomato (Solanum lycopersicum 'Beefsteak'). ARK-1 significantly (P ≤ 0.01) reduced gall incidence and gall diameter against four times higher tumorigenic bacterial cell numbers. Inoculation of ARK-1 up to 48 hours before or within 6 hours after inoculation with tumorigenic isolates significantly (P ≤ 0.01) reduced gall incidence and gall diameter. Root dipping of grapevine for 24 hours and tomato for 1 hour in the formulated ARK-1 suspension (Kumiai Chemical Industry Co. Ltd., Japan) prior to transplanting in tumorigenic bacteria-infested soil completely inhibited gall formation in the roots. These results are promising and support the development of ARK-1 as a biological control agent to manage grapevine crown gall.
- First Report of Laurel Wilt Disease Caused by Raffaelea lauricola on Sassafras in VirginiaGazis, R.; DeWitt, K. M.; Johnson, L. K.; Chamberlin, L. A.; Kennedy, A. H.; Hansen, Mary Ann; Bush, Elizabeth Ann (American Phytopathological Society, 2022-06)
- Fungicide Resistance of Botrytis Cinerea from Virginia Wine grapes, Strawberry, and Ornamentals CropsAdamo, Noah Robert (Virginia Tech, 2016-07-07)Botrytis cinerea is the principal member of the species complex that causes bunch rot of grapes and gray mold disease on other hosts including fruits and ornamental crops. It has developed resistance to many fungicides, and isolates from eastern US strawberry fields have regularly been identified with resistance to several modes of action. During the 2011-2015 growing seasons, 487 isolates were collected from Virginia wine grapes, strawberries, and ornamental crops and evaluated for sensitivity to eight different fungicides by a germ tube elongation method; for a subset of isolates, a 24-well plate mycelial growth assay was also used, and baseline sensitivity to polyoxin-D was evaluated. Resistance to benzimidazoles and quinone outside inhibitors, and low-level resistance to iprodione were common. Boscalid resistance was common in wine grapes and ornamentals. Resistance to the hydroxyanilide fenhexamid during germ tube elongation was found in only 5% of wine grape isolates, but in 33% of isolates from strawberries and ornamentals. All of the fenhexamid-resistant isolates were identified as B. cinerea carrying various mutations in the erg27 gene. An additional subset of isolates was identified with moderate resistance to fenhexamid during mycelial growth, but not germination and germ tube growth. These were identified as B. cinerea HydR2 isolates, which possess an unknown mechanism of resistance towards fenhexamid in mycelial growth. Moderate resistance to cyprodinil was common, but in grape inoculation tests, moderately resistant isolates were controlled by a field rate of cyprodinil. Diminished sensitivity to fludioxonil and fluopyram was rare. Polyoxin-D controlled most isolates in mycelial growth tests at 100 µg/ml.
- Investigation of Wine Grape Cultivar and Cluster Developmental Stage Susceptibility to Grape Ripe Rot Caused by Two Fungal Species Complexes, Colletotrichum gloeosporioides, and C. acutatum, and the Evaluation of Potential ControlsOliver, Charlotte (Virginia Tech, 2016-04-15)Ripe rot of grape is caused by two fungal species complexes: Colletotrichum gloeosporioides and C. acutatum, both of which cause disease on a variety of crops, such as strawberry and apple. To investigate effect of cultivar and cluster developmental stage on the development of ripe rot, controlled environment and field studies were conducted during 2013-2014. We have identified that a certain level of infection could can take place on most cultivars tested from bloom to the near harvest. In most of the cases, significant cultivar and cluster developmental stage interaction effects were observed (P < 0.05) for the development of disease symptoms in both studies. In general, susceptible cultivar (Cabernet Franc, Cabernet sauvignon, and Chardonnay) demonstrated fluctuations of disease susceptibility among cluster development stages, while resistant cultivars (Merlot) showed consistently low level of the disease throughout the season. To investigate the effect of eleven ten modes of action for control of C. gloeosporioides and C. acutatum, two methods, alamarBlue® assay and inoculation on fungicide-treated detached fruits, were used. Protective fungicides (mancozeb, captan, and copper) as well as some of newer formulations such as azoxystrobin and tetraconazole were identified as excellent products against ripe rot of grape. Four additional materials were identified as good potential candidates to investigate further. The information gained from these studies will help growers to determine the critical period for ripe rot management and chemicals to be applied for management. With better control of cluster rot pathogens, Virginia growers can experience an increase in yield and wine quality.