Sensitivity of Botrytis cinerea from vineyards to Boscalid, Isofetamid and Pydiflumetofen in Shandong province, China

Abstract

Succinate dehydrogenase inhibitor (SDHI) fungicides are the most commonly and effectively used class of fungicides for controlling gray mold. Among them, only boscalid has been registered in China for controlling grape gray mold, while isofetamid and pydiflumetofen are two new SDHI fungicides that have demonstrated high efficacy against various fungal diseases. However, the sensitivity to these three fungicides against B. cinerea isolates from vineyards in China are currently unknown. In this study, the sensitivity of 55 B. cinerea isolates from vineyards to boscalid, isofetamid and pydiflumetofen were determined, with EC50 values ranging from 1.10 to 393, 0.0300 to 42.0 and 0.0990 to 25.5 μg mL-1, respectively. The resistance frequencies for boscalid, isofetamid and pydiflumetofen were 60.0%, 7.2% and 12.8%, respectively. Three mutations (H272R, H272Y, P225F) were detected in the SdhB subunit, with H272R being the most prevalent (75.7%), followed by H272Y (16.2%) and P225F (8.1%). All three mutations are associated with resistance to boscalid, of which H272R mutants exhibited high resistance. Only P225F and H272Y mutants exhibited resistance to isofetamid and pydiflumetofen, respectively. A weakly positive cross-resistance relationship was observed between boscalid and pydiflumetofen (r = 0.38, P < 0.05). Additionally, the H272R mutants showed no significant fitness costs, whereas the remaining mutants exhibited reduced mycelial growth (P225F) and sporulation (H272Y and P225F). These results suggest that isofetamid and pydiflumetofen are effective fungicides against B. cinerea in vineyards, but appropriate rotation strategies must be implemented to reduce the selection of existing SDHI-resistant isolates.