Occurrence of fenhexamid resistance in Botrytis cinerea from greenhouse strawberries in China

This study assessed the fenhexamid sensitivity of 143 Botrytis cinerea isolates collected from greenhouse strawberries in five regions of China between 2012 and 2013, and identified four isolates with moderate levels of resistance: two from the Xinjiang Uygur Autonomous Region and two from Hebei Province. The baseline fenhexamid sensitivity of B. cinerea exhibited a unimodal distribution with a mean EC₅₀ value of 0.20 ± 0.10 μg/ml (SD). The EC₅₀ values of the fenhexamid‐resistant isolates ranged from 0.05 to 0.40 μg/ml. Molecular analysis of the fenhexamid target gene erg27 revealed that the resistant isolates collected from Xinjiang (163‐6 and 163‐22) contained three mutations that led to amino acid changes (V365A, E368D and A378T) known to be associated with fenhexamid resistance, but that the isolates from Hebei lacked any mutations, indicating that an alternative mechanism could be responsible for their resistance. Most of the biological characteristics of the fenhexamid‐resistant isolates, such as mycelial growth, sclerotia production and pathogenicity, did not significantly differ from those of the sensitive ones (p ≤ .05), but it was noted that some of the resistant isolates exhibited reduced rates of sporulation and spore germination. In addition, the resistant isolates exhibited lower osmotic sensitivity than the sensitive ones. The study found no evidence of cross‐resistance with other fungicides, but that there was negative cross‐resistance with procymidone, iprodione, carbendazim and pyraclostrobin, which indicates that the inclusion of these fungicides within an integrated pest management (IPM) programme could help to minimize the risk of fenhexamid resistance developing in B. cinerea.