Workflows for detecting fungicide resistance in net form and spot form net blotch pathogens

Abstract

AbstractFungicide resistance inPyrenophora teresf.maculataandP. teresf.tereshas become an important disease management issue. Control of the associated barley foliar diseases, spot form and net form net blotch, respectively, relies on three major groups of fungicides, demethylation inhibitors (DMI), succinate dehydrogenase inhibitors (SDHI) and quinone outside inhibitors (QoI). However, resistance has been reported for the DMI and SDHI fungicides in Australia. To enhance detection of different resistance levels, phenotyping and genotyping workflows were designed. The phenotyping workflow generated cultures directly from lesions and compared growth on discriminatory doses of tebuconazole (DMI) and fluxapyroxad (SDHI). Genotyping real-time PCR assays were based on alleles associated with sensitivity or resistance to the DMI and SDHI fungicides. These workflows were applied to a net blotch collection from 2019 consisting predominantly ofP. teresf.teresfrom South Australia andP. teresf.maculatafrom Western Australia. For South Australia theCyp51AL489-3 andSdhC-R134 alleles, associated with resistance to tebuconazole and fluxapyroxad, respectively, were the most prevalent. These alleles were frequently found in single isolates with dual resistance. This study also reports the first detection of a 134 base pair insertion located at position −66 (PtTi-6) in theCyp51Apromoter ofP. teresf.maculatafrom South Australia. For Western Australia, the PtTi-1 insertion was the most common allele associated with resistance to tebuconazole. These workflows will be valuable for screeningP. terespopulations for fungicide resistance, and informing appropriate management strategies.