Role of the Y134F mutation in cyp51 and overexpression of cyp51 in the sensitivity response of Puccinia triticina to epoxiconazole

A collection of 110 isolates of Puccinia triticina in 2007 from different European wheat-growing regions were examined for their sensitivity to the demethylation inhibiting (DMI) fungicide epoxiconazole and the expression and mutations of the target gene, cyp51. The cyp51 gene was highly conserved across Europe. A mutation at codon 134 (Y134F) was identified in only five isolates. This mutation had a limited impact, if any, on the sensitivity of P. triticina towards epoxiconazole. Over the entire collection of isolates, cyp51 expression and in vitro sensitivity towards epoxiconazole was moderately correlated. A constitutive up-regulation of the cyp51 gene was detected in some of the isolates with higher ED50 values. Such up-regulation was not inducible by exposure to different concentrations of epoxiconazole. Isolates of P. triticina with the highest ED50 values and with the Y134F mutation in the cyp51 gene or with cyp51 overexpression were equally well controlled in vivo by registered field rates of epoxiconazole as compared to an isolate with the lowest ED50 value.