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Leaf Spot Disease of Spinach in California Caused by Stemphylium botryosum

February 2001 , Volume 85 , Number  2
Pages  126 - 130

Steven T. Koike and Diana M. Henderson , University of California Cooperative Extension, Salinas 93901 ; and Edward E. Butler , Department of Plant Pathology, University of California, Davis 95616

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Accepted for publication 23 October 2000.

Beginning in 1997, a new disease of spinach was found in the Salinas Valley, Monterey County, CA. Initial symptoms were leaf spots that were 2 to 5 mm in diameter, circular, and gray-green in color. Spots later enlarged, turned tan in color, and became dry and papery in texture, resembling phytotoxicity due to agrichemicals. Although fungal signs were generally absent from the spots, Stemphylium botryosum was consistently isolated and caused identical symptoms when inoculated onto 20 spinach cultivars. Three isolates did not cause disease symptoms when inoculated onto other crop plants representing 16 different genera and a Chenopodium weed species. A fourth isolate showed similar results with the exception of small leaf spots occurring on inoculated fava bean. Isolates produced a Pleospora herbarum teleomorph after 7 months incubation at 5°C. Preliminary experiments with cell-free culture filtrates indicated that phytotoxins apparently were not produced by these isolates. This is the first report of a foliar spinach disease caused by S. botryosum.

Additional keywords: pesticides, phytotoxicity, Spinacia oleracea

© 2001 The American Phytopathological Society