First Report of Fenpyrazamine Resistance in Botrytis cinerea from Strawberry Fields in Spain

Botrytis cinerea Pers. is an important fungal pathogen responsible for gray mold, one of the most economically important diseases of strawberry (Fragaria × ananassa) worldwide. The primary disease management strategy involves the application of different classes of fungicides, including the sterol biosynthesis inhibitor class III fungicide fenpyrazamine. In 2014 and 2015, strawberries affected with gray mold symptoms were collected from eight locations in Huelva, where fenhexamid had been used extensively. Twenty-five B. cinerea single-spore isolates were examined to determine EC 50 values and to determine a discriminatory dose to monitor fenpyrazamine resistance in the field in future studies. The in vitro tests divided the isolates into two groups: 15 sensitive (EC 50 from 0.02 to 1.3 μg/ml) and 10 resistant (EC 50 from 50.1 to 172.6 μg/ml), which showed cross-resistance with fenhexamid. Performance of fenpyrazamine in in vivo studies was also carried out. Only the fenpyrazamine-resistant isolates developed gray mold on the fungicide-treated fruit. This is the first report of fenpyrazamine resistance in B. cinerea from strawberry fields in Spain and cross-resistance with fenhexamid.