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Title: Field response of cucurbit hosts to Pseudoperonospora cubensis in Michigan

item CESPEDES-SANCHEZ, M - Michigan State University
item NAEGELE, R - Michigan State University
item Kousik, Chandrasekar - Shaker
item HAUSBECK, M - Michigan State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2014
Publication Date: 5/1/2015
Citation: Cespedes-Sanchez, M.C., Naegele, R.P., Kousik, C.S., Hausbeck, M.H. 2015. Field response of cucurbit hosts to Pseudoperonospora cubensis in Michigan. Plant Disease. 99:676-682.

Interpretive Summary: Melon (cantaloupe) is an important cucurbit crop and belongs to the same family as cucumbers and watermelon. It is grown throughout the United States for its nutritious fruit. Many different pests and diseases attack melon and other cucurbit crops causing extensive damage. In recent years, downy mildew, a disease caused by a fungus, has overcome previously resistant cucumber plants and caused severe losses throughout the United States. The fungus that causes downy mildew on cucumber can also affect melon plants and hence a study was undertaken in Michigan to determine if commercial melon varieties and other cucurbit crops (squash, pumpkin, watermelon, bottle gourd, and Luffa) were also susceptible to downy mildew. Several melon varieties with resistance were identified and these can be used by commercial producers for whom downy mildew is a serious problem. Use of downy mildew resistant varieties by growers can also help them reduce pesticide applications where the disease occurs regularly.

Technical Abstract: Downy mildew, caused by Pseudoperonospora cubensis, is a severe foliar disease of many cucurbit crops worldwide. Forty-one cucurbit cultigens (commercial cultivars and plant introductions) from five genera (Cucumis, Citrullus, Cucurbita, Lagenaria, and Luffa) were assessed for susceptibility to Ps. cubensis in a Michigan research field exposed to natural inoculum. Eight cultigens from a differential set for pathotype determination were included within the 41 cultigens to provide information regarding the Ps. cubensis pathotypes present in Michigan. No pathotype differences were found between 2010 and 2011 in this study. Cucumis melo cultigen, MR-1, was less susceptible to Michigan Ps. cubensis populations than other C. melo cultigens. No symptoms or signs of infection were detected on cultigens of Cucurbita moschata and C. pepo. Disease onset was later in 2011 than 2010; greater than 90% disease severity in pickling cucumber ‘Vlaspik’ was observed in both years. This study confirmed that Cucumis is the most susceptible cucurbit genus, while Citrullus and Cucurbita cultigens were the least susceptible genera to Michigan Ps. cubensis populations. Disease progress was relatively slow on all Citrullus cultigens and sporulation was not detected. Michigan producers could benefit from a reduced fungicide program in less susceptible Cucumis melo cultivars Edisto 47, Primo, Athena, Strike, Ananas, Banana, and Tam-Dew. Many of the melons were selected on the basis of their stated resistance to DM, yet showed signs of infection to Michigan DM populations. Evaluating downy mildew resistance to local pathogen populations will be important for determining effective resistance.