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POSTERS: Pathogen detection, quantification and diagnosis

Development of a qPCR Assay for Hop Powdery Mildew Field Specific Differentiation and Late-Season Dispersal Patterns.
Cameron Ross - Oregon State University. Gent David- USDA ARS, Michele Wiseman- Oregon State University

Podosphaera macularis, the causal agent of hop (Humulus lupulus) powdery mildew (HPM), causes severe economic damage annually across the Pacific Northwest through expensive fungicide applications, hop cone degradation, and quality defects. The fungus emerges as flag shoots, focally located, within hop yards in the spring and spreads throughout the season. Determining the late season dispersal patterns of powdery mildew between yards may improve management practices, potentially allowing for detection of the pathogen before disease onset and enabling more strategic use of fungicides. However, conclusive detection of P. macularis within a field through spore trapping has proven difficult because both P. macularis and P. clandestina, powdery mildew of cherry, share a high degree of sequence similarity in the internal transcribed spacer region. The single copy genes ? -tubulin and minichromosome maintenance 7 (MCM7) were investigated for their suitability for developing a quantitative PCR assay (qPCR) capable of detecting and differentiating P. macularis from other fungi. Several single nucleotide polymorphisms have been identified in ? -tubulin and MCM7 which are unique to HPM isolates. Impaction spore traps were deployed near commercial hop yards in western Oregon during 2018 and 2019 to associate airborne inoculum density to disease levels on leaves. Development of the assay and its use as a component of a disease forecasting system for powdery mildew will be discussed.