Phenotypic and molecular characterization of fenhexamid resistance in Botrytis cinerea isolates collected from pistachio orchards and grape vineyards in California

Botrytis cinerea causes Botrytis blossom, shoot and fruit blight in pistachio and gray mold in grape. The hydroxyanilide (Hyd) fenhexamid, one of the most frequently used fungicides for Botrytis control, inhibits the 3-ketoreductase (Erg27) of the ergosterol biosynthesis pathway. Due to its site-specific mode of action, this fungicide is at-risk for resistance development. In this study, 74 and 58 B. cinerea isolates, collected from Californian pistachio orchards and grape vineyards, respectively, were evaluated for their in vitro sensitivity toward fenhexamid. Of the 58 grape isolates, 90% were sensitive to fenhexamid (HydS, EC50