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Biosurveillance for precision disease management of Pseudoperonospora cubensis, the cucurbit downy mildew pathogen

Alamgir Rahman: NCSU

<div><em>Pseudoperonospora cubensis</em>, an obligate oomycete pathogen, causes cucurbit downy mildew (CDM) on a broad range of host plants including cucumber, cantaloupe, watermelon, pumpkin, and squash. In 2004, CDM re-emerged in the United States (US) by overcoming host resistance in cucumber and fungicides used for disease control in other cucurbits. Airborne sporangia of <em>P. cubensis,</em> the most important source of inoculum, can survive in no frost areas and travel long distances infecting cucurbits along the eastern US throughout the growing season. Using Next Generation Sequencing (NGS) and bioinformatics, species-specific and host-preference diagnostic markers were identified in the nuclear genome and developed into qPCR assays. Assays were tested for specificity and sensitivity using spore trap sampling rods, and a threshold detection level of <em>P. cubensis</em> sporangia and sporangia-DNA was determined to be 10 spores and 10 pg/μl, respectively. Assays for detection of fungicide resistance are also being developed. Pathogen trap plots and roto-rod spore traps were deployed at two Research Stations in North Carolina for field validation. Our findings will significantly improve <em>P. cubensis</em> biosurveillance efforts and decision tools for growers by monitoring inoculum levels, cucurbit crops at risk of infection, and fungicide resistance occurrence throughout the growing season.</div>