Resistance profiles of Botrytis cinerea to fluxapyroxad from strawberry fields in Shanghai, China

Fluxapyroxad, a type of succinate dehydrogenase inhibitor (SDHI) fungicide, has been used to control the growth of gray mold on strawberries for more than five years in China. Selection for resistance to the causal agent Botrytis cinerea has became a threat to the efficacy of fluxapyroxad. A total of 160 B. cinerea isolates collected from Shanghai during 2020 and 2021 were tested for their resistance to fluxapyroxad using mycelial growth inhibition. The results indicated that the curve of baseline sensitivity was unimodal with an approximately normal distribution and a mean EC50 value of 0.18±0.01 µg/ml. A total of 27.78% and 48.57% of isolates were resistant to fluxapyroxad in 2020 and 2021, respectively, where the lowest EC50 value of mycelial growth inhibition was 0.03 µg/mL, and the highest value was 51.3 µg/mL. Resistance mechanism analysis showed that the succinate dehydrogenase subunit B (SdhB) N230I mutation could lead to resistance and P225F mutation could lead to higher resistance. This data suggests that the increase in the frequency of B. cinerea isolate resistance to fluxapyroxad in 2021 compared with 2020, which requires appropriate fungicide rotation strategies to be implemented in order to control gray mold on strawberry in the future.