Baseline sensitivity and resistance analysis of Botrytis cinerea to pydiflumetofen in Liaoning Province, China

Pydiflumetofen is a new succinate dehydrogenase inhibitor fungicide, registered in China in 2021 for the control of tomato gray mold. In order to characterize and decipher the sensitivity of tomato B. cinerea to pydiflumetofen, the sensitivity to pydiflumetofen was determined in 103 B. cinerea isolates collected from diseased tomato fruits and leaves from greenhouses in eight districts of Liaoning province in China during 2020–2022. The results indicated that for the 76 tested isolates, the EC₅₀ values of pydiflumetofen conformed to a normal distribution. The mean EC₅₀ value was determined to be 1.0641 ± 0.5820 (SD) μg/mL and was considered as the baseline sensitivity. Thirty-two resistant isolates were detected, corresponding to a resistance frequency of 31.07%. Differences were observed in mycelium growth rate and dry weight, spore production, and spore germination rate among isolates, which were not associated with resistance to pydiflumetofen. However, the resistant isolates had lower pathogenicity compared to the sensitive isolates. No cross-resistance was observed between pydiflumetofen and fludioxonil, pyrimethanil procymidone, and iprodione. Some resistant isolates had mutations in the SdhB subunit gene (N230I, H272R). These results indicated a moderate to high risk of pydiflumetofen resistance development in B. cinerea. Therefore, pydiflumetofen should be used in an alternating or mixed application with fungicides with no cross-resistance and not more than twice per season to delay resistance development.