Xuefei Wang, Elizabeth Kramer, Dean Glawe, David Weller, Timothy Murray, and Patricia Okubara*  
*USDA-ARS & Department of Plant Pathology, 367A Johnson Hall, Washington State University, Pullman, WA 99163 (pokubara@wsu.edu)

Botrytis bunch rot, caused by Botrytis cinerea, can cause significant economic losses to grapes, especially in wet, cool production regions, or during transport and storage. Public and grower concerns about chemical fungicides and the emergence of fungicide resistance can be alleviated in part by biocontrol strategies for B. cinerea and other grape pathogens. Our objectives were to evaluate native yeast strains for their ability to colonize Thompson Seedless berries and to inhibit B. cinerea growth in vitro and suppress rot symptoms on berries in the laboratory. Eleven yeast strains isolated from Washington vineyards were identified as Aureobasidium pullulans var. pullulans, Candida saitoana, Curvibasidium pallidicorallinum, Metschnikowia chrysoperlae, Metschnikowia aff. pulcherrima, Meyerozyma guilliermondii, Saccharomyces cerevisiae, and Wickerhamomyces anomalus. Populations densities of all strains grew from 200 cells to 6.0 to 6.6 log cells/mL after two days in berry tissue. A. pullulans P01A006 showed inhibitory effects against all B. cinerea isolates in vitro, while other yeast species inhibited one to three pathogenic isolates. The most reduction in symptom development in vivo occurred with A. pullulans P01A006, Met. chrysoperlae P34A004, P40A002, Met. pulcherrima P01A016, P01C004, Mey. guilliermondii P34D003, and S. cerevisiae HNN11516. Further studies will be conducted on the population dynamics and the contributions of indigenous yeasts in natural fermentations. Our findings indicate that native yeasts, that can contribute unique flavors to Washington wines, could provide effective in planta biocontrol against B. cinerea. 

Funding Support: Washington State Grape and Wine Research Program 3016-5313, China Scholarship Council, Viticulture and Enology Program at Washington State University, and USDA-ARS CRIS Project No. 5348-22000-013-00D