Allele-Specific Detection Methods for QoI Fungicide-Resistant in Vineyards.

Grapevine powdery mildew (GPM), caused by the fungus , is a constant threat to worldwide production of grape berries, requiring repeated use of fungicides for management. The frequent fungicide applications have resulted in resistance to commonly used quinone outside inhibitor (QoI) fungicides and the resistance is associated with single-nucleotide polymorphisms (SNPs) in the mitochondrial gene (). In this study, we attempted to detect the most common SNP causing a glycine to alanine substitution at amino acid position 143 (i.e., G143A) in the protein, to track this resistance using allele-specific TaqMan probe and digital-droplet PCR-based assays. Specificity and sensitivity of these assays showed that these two assays could discriminate SNPs and were effective on mixed samples. These diagnostic assays were implemented to survey samples collected from leaf and air samples from California and Oregon grape-growing regions. Sequencing of PCR amplicons and phenotyping of isolates also revealed that these assays accurately detected each allele (100% agreement), and there was an absolute agreement between the presence or absence of the G143A mutation and resistance to QoIs in the sampled. These results indicate that the developed diagnostic tools will help growers make informed decisions about fungicide selections and applications which, in turn, will facilitate GPM disease management and improve grape production systems.