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Fungicide resistance phenotypes in Botrytis cinerea populations from blueberries in California and Washington
S. SAITO (1), T. Michailides (2), C. L. Xiao (3). (1) USDA ARS, Parlier, CA, U.S.A.; (2) University of California-Davis, 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 blueberries grown in the Central Valley of California (CA) and western Washington State (WA). Understanding fungicide resistant phenotypes of <i>B. cinerea</i> is important to the development of preharvest fungicide programs for control of postharvest gray mold. Sensitivities to boscalid, cyprodinil, fenhexamid, fludioxionil, and pyraclostrobin, representing five fungicide classes, were examined on agar media for 251 and 106 <i>B. cinerea</i> isolates recovered from decayed blueberry fruit in CA and WA, respectively. Seven and 17 fungicide resistant phenotypes were detected; 66 and 49% of the isolates were resistant to boscalid; 20 and 29% were moderately resistant to cyprodinil; 29 and 29% were resistant to fenhexamid; and 66 and 55% were resistant to pyraclostrobin in CA and WA, respectively. All isolates from CA were sensitive to fludioxonil, while 70% of the isolates from WA showed reduced sensitivity to fludioxonil. In CA, 26 and 30% of the isolates were resistant to two and three classes of fungicides, respectively. In WA, 31,16, and 9% of the isolates were resistant to two, four, and five classes of fungicides, respectively. Most fungicides failed to control gray mold on detached blueberry fruit inoculated with fungicide resistant phenotypes. Our results suggest that as preharvest treatments, alteration of different classes of fungicides will be needed to control postharvest gray mold in blueberries.

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