Analysis of mutations in West Australian populations ofBlumeria graminisf. sp.hordei CYP51conferring resistance to DMI fungicides

Summary Powdery mildew caused by Blumeria graminis f. sp. hordei ( Bgh ) is a constant threat to barley production but is generally well controlled through combinations of host genetics and fungicides. An epidemic of barley powdery mildew was observed from 2007 to 2013 in the West Australian wheatbelt (WA). We collected isolates, examined their sensitivity to demethylation inhibitor (DMI) fungicides and sequenced the Cyp51B target gene. Five amino acid substitutions were found of which four were novel. A clear association was established between combinations of mutations and altered levels of resistance to DMIs. The most resistant genotypes increased in prevalence from 0 in 2009 to 16% in 2010 and 90% in 2011. Yeast strains expressing the Bgh Cyp51 genotypes replicated the altered sensitivity to various DMIs and these results were confirmed by in silico protein docking studies.