Managing fungicide resistance: Protecting Western Australia’s barley crops against Blumeria graminis f. sp. hordei

Powdery mildew is a common disease of many monocotyledonous and dicotyledonous plant species. In barley the disease is caused by the obligate Biotrophic fungus Blumeria graminis f. sp. hordei (Bgh). In Western Australia powdery mildew is estimated to be the most economically damaging disease of barley, causing $33m in loses annually. Currently in WA the majority of fungicides registered for control of Bgh belong to the triazole class and numerous reports of resistance towards this chemical class have been reported globally. Instances of reduced efficacy of the in furrow application of fungicides has been noted recently in southern W A. In this study the level of fungicide sensitivity of current WA Bgh isolates was assessed by examining colony inhibition in the presence of both registered and novel fungicides. One strain with reduced sensitivity was genotypically characterized in the target site for triazole fungicides, the Cyp5I gene, and was found to harbor a mutation common in triazole resistant Bgh isolates. This is the first confirmed case of fungicide resistance in Australia.