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Biological control of powdery mildew on cucurbits

Kestrel Mccorkle: AgBiome, Inc.

<div>Cucurbit powdery mildew, caused primarily by the ascomycete <i>Podosphaera xanthii, </i>is an important foliar disease of cucurbits worldwide. Symptoms include early chlorotic spots, necrosis, leaf curling, defoliation, and small and sunburned fruit. An increase in fungicide applications to manage this disease has led to a pathogen population shift towards reduced levels of fungicide sensitivity. In response, industry has pursued the research and development of biological controls that have a broad spectrum of antifungal activity with multiple modes of action. AgBiome, an agriculture biotech company, focuses on microbial-derived crop pest solutions by mining the diversity of its vast collection of over 40,000 fully-sequenced microbes. Isolated microbes are screened for activity in bioassays on multiple foliar pathogens, including <i>P. xanthii, </i><span>using high-throughput detached leaf assays. Utilizing our powdery mildew assay, leaf disks (35 mm diameter circle each) were sprayed with the microbial strain, a day after, they were inoculated with a conidial suspension (10<sup>5</sup></span> conidia/mL and 200µl per leaf disk). Disease severity was rated 5 days post inoculation and percent activity relative to the inoculated control was determined. Strains having greater than 70% activity against <i>P. xanthii</i> were confirmed and progressed through the pipeline for greenhouse bioassays and field testing. In 2017, we identified multiple strains with confirmed activity on <i>P. xanthii </i>which will be sent for field screening in 2018. Strains maintaining a high level of activity will be further characterized by additional field evaluations.</div>