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Baseline Sensitivity to Fluopyram and Fungicide Resistance Phenotypes of Botrytis cinerea Populations from Table Grapes in California
S. SAITO (1), M. J. Themis (2), C. L. Xiao (3). (1) USDA ARS, Parlier, CA, U.S.A.; (2) University of California-Davis, Kearney Agricultural Center, Parlier, CA, U.S.A.; (3) USDA Agricultural Research Service, Parlier, CA, U.S.A.

Gray mold caused by <i>Botrytis cinerea</i> is a major postharvest disease of table grapes grown in the Central Valley of California. Understanding fungicide resistant phenotypes of <i>B. cinerea</i> is important to the development of pre-harvest fungicide programs for control of postharvest gray mold. Baseline sensitivity to fluopyram, and sensitivities to boscalid, cyprodinil, fenhexamid, fludioxonil, and pyraclostrobin were determined on agar media for 80 and 212 <i>B. cinerea</i> isolates collected from vineyards at various locations in the region, respectively. All isolates were sensitive to fluopyram with EC<sub>50</sub> values ranging from 0.001 to 0.054 µg/mL. Seven fungicide-resistant phenotypes were detected; 85.0, 23.1, 13.7, and 94.8% of the isolates were resistant to boscalid, cyprodinil, fenhexamid, and pyraclostrobin, respectively. All isolates were sensitive to fludioxonil. Frequencies of resistance to two, three or four fungicides were 56.1, 23.6, and 6.1%, respectively. Most fungicides failed to control gray mold on detached table grapes inoculated with respective fungicide-resistant phenotypes. Our results suggest that alternation of different classes of fungicides will be needed to control postharvest gray mold and that fluopyram could be an effective fungicide integrated into a pre-harvest fungicide program for control of gray mold in table grapes.

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