CucCAP researchers develop genetic tools and diagnostic guide for cucurbit downy mildew

Cucurbit downy mildew (CDM)  is a devastating disease affecting economically important crops such as cantaloupe, cucumber, squash, pumpkin, and watermelon. Plant pathologists from the CucCAP disease management team published two articles focusing on CDM.

In the first article, plant pathologists at North Carolina State University determined that the causal pathogen of Cucurbit downy mildew, Pseudoperonospora cubensis, has two genetically distinct host-adapted clades and also found that wild cucurbits can serve as reservoirs for this pathogen. Clade 1 isolates more frequently infect squash, pumpkin, and watermelon while clade 2 impacts cucumber and cantaloupe. They also found that evidence of recombination in clade 1 isolates but not clade 2 isolates. While previous research had shown evidence of two subpopulations within the pathogen, none were able to identify the main factors underlying those populations due to sampling limitations. Using a population genetics approach, the researchers applied a robust and standardized sampling strategy to investigate P. cubensis populations that infect cucurbit hosts. Moving forward, plant pathologists can provide crop-specific recommendations.

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symptoms on leaf

Cucurbit Downy Mildew on Cucumber. Credit Andres Salcedo, Mary Hausbeck, Stacey Pigg, and Lina M. Quesada-Ocampo

Cucurbit downy mildew is rapid, infectious, and hard-to-diagnose. Accurate and early diagnosis is critical for timely disease management. Plant pathologists from North Carolina State University and Michigan State University developed a guide for beginners and experts with information about the causal agent of cucurbit downy mildew and multiple alternatives for it’s diagnosis and handling. As cucurbit downy mildew is caused by a pathogen that cannot be cultured using standard microbiological methods, this guide provides well-documented written and graphic material to help with diagnosis based on symptoms and the presence of the pathogen in the plant. The guide also covers diagnosis methods based on DNA testing and microscopy as well as methodologies for isolation, damage evaluation, multiplication, and storage under laboratory conditions.

The ability to quickly identify cucurbit downy mildew is crucial for cost-effective chemical or cultural control strategies. To help those who are trying to assess the efficacy of new disease management products, this guide also provides protocols for pathogen handling and evaluation. Parts of the guide are also being used to develop extension training videos to further inform a broader audience about cucurbit downy mildew.

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