Baseline sensitivity and resistance analysis of fluopyram against Botrytis cinerea from tomato in Liaoning Province, China

Fluopyram, as a novel succinate dehydrogenase inhibitors (SDHIs) fungicide, was applied for controlling grey mould in China. In order to investigate the possible development of resistance development of Botrytis cinerea to fluopyram, Botrytis cinerea were collected from eight areas in Liaoning Province, and the sensitivities of these isolates were assessed by mycelium growth and the fitness and resistance mechanism of resistant isolates screened. The results showed that the sensitivity baseline of B. cinerea to fluopyram was (4.82 +/- 1.49) mu g/mL, and 5 low resistance isolates to fluopyram were detected. The fitness of resistant isolates showed a downward trend of several variables, such as mycelium growth, mycelium dry weight, sporulation and lesion diameter, which were significantly lower than those of sensitive isolates. Conidia germination did not differ significantly between sensitive and resistant isolates. There was no cross--resistance between fluopyram and fludioxonil/boscalid/pyrimethanil/ procymidone/carbendazim. The succinate dehydrogenase activity of resistant isolates was higher than that of sensitive isolates with fluopyram or not, and the inhibition of fluopyram on succinate dehydrogenase of sensitive isolates was greater than that of resistant isolates. Resistant isolates AS8 and AS14 carried the point mutation (N230I) in subunit B. These results provided that fluopyram belonged to a medium-high resistance risk to B. cinerea. Information for managing resistance suggested that (1) the number of fluopyram applications should be limited to one per season and (2) fluopyram could be a valid alternative to fludioxonil, pyrimethanil, procymidone and carbendazim for the control of grey mould of tomato.