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POSTERS: Pathogen detection, quantification and diagnosis

Development of race-specific diagnostic assays for detection of Podosphaera macularis
Mary Block - Oregon State University. Michele Wiseman- Botany and Plant Pathology, Brian Knaus- USDA ARS, Niklaus Grunwald- USDA ARS, David Gent- US Department of Agriculture, Agricultural Research Service

Hop powdery mildew (Podosphaera macularis) was confirmed in the Pacific Northwest in 1996. Prior to 2012, the most common race of P. macularis was able to infect plants that possessed powdery mildew resistance based on the R-genes Rb, R3, and R5. Post 2012, two additional races of P. macularis were discovered that can overcome the resistance gene R6 and the partial resistance found in the cultivar Cascade. Current methods for race determination for P. macularis involve challenge assays onto differential cultivars and are slow, costly, and labor intensive. We sought to develop a molecular assay to determine race in P. macularis. We sequenced the transcriptomes of 46 isolates of P. macularis to identify loci that differentiate R6-virulent isolates from the other races. Sixteen loci that differentiated R6-virulent isolates from the others were identified. Primers were designed to flank single nucleotide polymorphisms present in the highly differentiated loci and were sequence verified. Locked nucleic acid probes capable of differentiating the races based on the conserved mutations in these loci are in design. Progress towards development, validation, and application of the assays will be presented and discussed.