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INVESTIGATOR: Savory, E. A.; Day, R. B.; Buell, C. R.

PERFORMING INSTITUTION:
MICHIGAN STATE UNIV
EAST LANSING, MICHIGAN 48824

AN INTEGRATED LAB TO FIELD APPROACH TOWARDS UNDERSTANDING AND DEVELOPING RESOURCES FOR MANAGEMENT OF CUCURBIT DOWNY MILDEW (PSEUDOPERONOSPOR

NON-TECHNICAL SUMMARY: Cucumber downy mildew is a major limiting factor to production of cucumber and other cucurbit crops in the United States. This disease is caused by the oomycete pathogen, Pseudoperonospora cubensis, which can destroy an entire crop within 2 weeks under optimum conditions. Despite its economic importance, the basic mechanisms underlying the pathogenicity of Ps. cubensis and its interactions with cucumber are not well studied. This project seeks to establish resources to better understand the interaction between Ps. cubensis and cucumber, investigate determinants of the pathogen's virulence and pathogenicity, and to develop materials for an outreach and education program for stakeholders such as cucumber growers and processors. Genes up- or down-regulated during infection of cucumber with Ps. cubensis will be assessed using RNA-Seq, which enables collection of information from both the pathogen and host simultaneously. Differential regulation of genes will be correlated with the pathogen growth stages and symptom development in the host to determine those important in both pathogenicity and virulence as well as host response. Subsequent characterization of upregulated pathogenicity determinants will be performed to determine those essential for disease development. Finally, data gleaned from the first two objectives will be incorporated into an outreach and education program, coupled with information about basic pathogen biology, epidemiology, and control recommendations to better serve our stakeholders.

OBJECTIVES: Cucurbit downy mildew, caused by the oomycete pathogen Pseudoperonospora cubensis, is the major limiting factor in cucumber (Cucumis sativus) production in the United States. In the US, the cucurbit industry occupies approximately 229,000 hectares, with a market value of ~$1.6 billion. As the #1 producer of cucumbers used for processing, with a farm gate value of $30.6 million, Michigan's 38,000 acres of pickling cucumbers generate a finished product valued at $240.7 million. In recent years however, the re-emergence of cucurbit downy mildew as a major disease problem has placed significant strain on the cucurbit industry, not only in Michigan, but also for growers throughout the country. Thus, understanding the molecular-genetic basis for this interaction and the function of virulence determinants of Ps. cubensis is key to the long-term survival of this industry. This project focuses on 1) understanding the interaction between pathogen and host, 2) elucidating genetic components that contribute to virulence and diversity, and 3) disseminating this knowledge in a timely and accessible manner to the appropriate stakeholders (ie., cucumber growers and producers). Completion of these objectives will result in resources that will contribute to development of an effective disease management system for Ps. cubensis as well as establish an effective outreach and education program for our stakeholders.