P-627 - Development of TaqMan qPCR assays for the detection of Podosphaera species

Powdery mildew fungi are specialized plant pathogens characterized by their obligate biotrophic lifestyle and distinct symptomology of circular patches of white to grayish mycelial growth. Within the order Erysiphales, the genus Podosphaera includes species that significantly impact economically important fruit crops in the Rosaceae family, including apple and strawberry, caused by Podosphaera leucotricha (APM) and P.  aphanis (SPM), respectively. Challenges in early detection often lead to frequent fungicide applications, contributing to the emergence of resistant populations. Traditional identification methods, including morphology and analyzing ITS regions, often lack the resolution needed for species-level diagnostics. To address this a species-specific TaqMan qPCR assays targeting the single-copy nuclear gene was developed (i.e. GAPDH) to detect SPM and APM in environmental samples. The assays reliably detected P. aphanis and P. leucotricha at 0.01 ng and 0.005 ng DNA limits, respectively. A diverse panel of powdery mildew specimens, including various genera, was collected from Michigan and Oregon (USA) and sequenced using powdery mildew-specific GAPDH primers for in-silico assay design. Additionally, the P. aphanis assay successfully detected infection 5 days post-inoculation (dpi) during disease progression in Fragaria x ananassa ‘Annapolis’ over a time-course. These assays offer improved taxonomic resolution, enable early pathogen detection, and support more effective pathogen surveillance and management strategies for powdery mildew in fruit crops.