Biological and molecular characterizations of fluxapyroxad-resistant isolates of Botrytis cinerea

Abstract Gray mold caused by Botrytis cinerea leads to serious losses in various crops. Fluxapyroxad, a succinate dehydrogenase inhibitor (SDHI) fungicide, has been used to control gray mold for several years in China. In this study, we identified six fluxapyroxad-resistant (FluR) isolates from 96 isolates of B. cinerea collected in fields. Phenotypic assays showed that the FluR isolates exhibited defects in mycelial growth, conidiation, sclerotium formation, stress tolerance and virulence. Analysis of nucleotide sequences of succinate dehydrogenase subunit-coding genes revealed that various point mutations, including P225F, N230I, K283N and H272R in BcSdhB, G37S and P80H in BcSdhC, and V9A in BcSdhD, were associated with the resistance to fluxapyroxad in B. cinerea . Sensitivity assays showed that the FluR isolates also exhibited resistance to another SDHI boscalid, but there was no cross-resistance between fluxapyroxad and other fungicides with different modes of action. These results indicate that the resistance of B. cinerea to fluxapyroxad has occurred in fields, and further monitoring and management of the resistance to fluxapyroxad in B. cinerea should be carried out.