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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #403952
Research Project: Disease Management and Improved Detection Systems for Control of Pathogens of Vegetables and Strawberries

Location: Crop Improvement and Protection Research

Title: Seedborne oospores as primary inoculum for spinach downy mildew

Author
item Clark, Kelley
item Anchieta, Amy
item Kandel, Shyam
item Mou, Beiquan
item MCGRATH, MARGARET - Cornell University
item CORRELL, JAMES - University Of Arkansas
item Shishkoff, Nina
item Klosterman, Steven

Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/15/2023
Publication Date: 8/12/2023
Citation: Clark, K.J., Anchieta, A.G., Kandel, S.L., Mou, B., Mcgrath, M.T., Correll, J.C., Shishkoff, N., Klosterman, S.J. 2023. Seedborne oospores as primary inoculum for spinach downy mildew. American Phytopathological Society Annual Meeting, August 12-16, 2023, Denver, Colorado.

Interpretive Summary:

Technical Abstract: Spinach downy mildew, caused by the obligate oomycete Peronospora effusa, is a major challenge to spinach production. The disease is managed with resistant cultivars, but new races of the pathogen continue to appear and overcome resistance. The role of oospores in the disease cycle is not fully understood. Surveys of commercial spinach seed since 2014 revealed oospores in 19% of evaluated lots. To investigate seed transmission by oospores in this study, we used isolated glass chambers to grow out both oospore-infested spinach seed and non-infested seed mixed with oospore-infested crop debris in two independent experiments. Symptomatic spinach plants were observed at 34 and 37 days after planting in the two experiments in chambers that contained one of two oospore-infested seed lots or seeds coated with oospore-infested leaves. Spinach plants in glass chambers initiated from seeds without oospores did not show downy mildew symptoms. Similar findings were obtained using the same seed samples in a third experiment conducted in a growth chamber. Additionally, seed grow outs from an oospore-infested spinach cultivar performed in a collaborating lab revealed characteristic Peronospora sporangiophores growing from spinach seedlings. These findings provide evidence of seed and soilborne transmission of downy mildew via oospores and indicate that oospores can serve as primary inoculum for downy mildew on spinach.