Leaf spot disease of spinach in California caused by Stemphylium botryosum

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, turn ed tan in color, and became dry and papery in texture, resembling phytotoxi city due to agrichemicals. Although fungal signs were generally absent from the spots, Stemphylium botryosum was consistently isolated-and caused iden tical symptoms when inoculated onto 20 spinach cultivars. Three isolates di d not cause disease symptoms when inoculated onto-other crop plants represe nting 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 aft er 7 months incubation at 5 degreesC. Preliminary experiments with cell-fre e culture filtrates indicated that phytotoxins apparently were not produced by these isolates. This is the first report of a foliar spinach disease ca used by S. botryosum.