Characterization of Resistance to Six Chemical Classes of Site-Specific Fungicides Registered for Gray Mold Control on Strawberry in Spain

Botrytis cinerea, causal agent of the gray mold disease, is one of the most economically important fungal pathogens of strawberry worldwide. In Spain, as in other parts of the world, management of gray mold control primarily involves the application of fungicides. To determine the fungicide resistance of the Spanish strawberry field population, 367 B. cinerea isolates were examined from one organic and 13 conventional strawberry fields in Huelva (Spain) in 2014 and 2015. The sensitivities of these isolates to six fungicides used for gray mold management in Spain were examined using a spore germination assay based on previously published discriminatory doses. The frequency of resistance to pyraclostrobin, boscalid, cyprodinil, fenhexamid, iprodione, and fludioxonil was 74.6, 64.8, 37.0, 23.7, 14.7, and 0.8%, respectively. The majority of isolates (35.1%) were resistant to three different fungicides classes. Within these isolates, the most prevalent resistance profile (55.8%) was resistance to pyraclostrobin, boscalid, and cyprodinil, followed by the resistance profile (30.2%) of resistance to pyraclostrobin, boscalid, and fenhexamid. One isolate collected in 2015 was resistant to all six fungicide classes. Resistance to boscalid, fenhexamid, iprodione, and pyraclostrobin was found to be caused by amino acid substitutions on target proteins, including H272R/Y in SdhB, F412I/S/V in Erg27, I365 N/S in Bos1, and G143A in Cytb, respectively. The presence of multifungicide resistance phenotypes in B. cinerea isolates from strawberry fields in Spain must be considered in the development of future resistance management practices.