Molecular characterization of field azoxystrobin-resistant isolates of Botrytis cinerea

Sensitivity of 184 Botrytis cinerea field isolates to a Qo inhibitor (QoI) fungicide azoxystrobin was determined in this study. Among the 184 isolates, seven showed resistance to azoxystrobin. All these seven azoxystrobin-resistant (AR) isolates were also resistant to a benzimidazole fungicide carbendazim, and a dicarboximide fungicide iprodione. Negative cross-resistance between azoxystrobin and a carboxamide fungicide boscalid was not observed in AR isolates of B. cinerea. Analysis structure of partial cytochrome b (cyt b) gene from B. cinerea showed that a 1204-bp intron inserted directly after the codon 143 of cyt b gene was detected from 79 out of 184 isolates, and all the isolates having this intron were sensitive to azoxystrobin. This intron was not detected from any AR isolate. Sequence analysis of partial cyt b gene showed that all AR isolates had a point mutation at codon 143, which caused a change of glycine to alanine (G143A) at this codon position. Based on the point mutation, an allele-specific PCR assay was developed for the rapid detection of AR isolates of B. cinerea.