Disease Note.

First Report of Stem Rot of Fennel in the United States Caused by Sclerotinia minor. S. T. Koike, University of California Cooperative Extension, Salinas 93901. Plant Dis. 78:754. Accepted for publication 29 March 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0754E.

In 1993, commercial fields of fennel (Foeniculum vulgare Mill.) in the Salinas Valley, California, showed areas of declining plants. Symptoms included chlorosis of stems and leaves, willing and collapse of older foliage, and necrosis of lower stems and crowns. Black sclerotia of Sclerotinia minor Jagger developed profusely on necrotic stem and leaf tissues. Koch's postulates were completed with an isolate from diseased fennel and an isolate from lettuce (Lactuca sativa L.), both from the Salinas Valley. Inoculum of both isolates consisted of 2-mo-old sclerotia produced on sterilized potato pieces incubated in the dark at 25 C (I). Ten-week-old fennel plants were potted into steam-sterilized sand amended with sclerotia of either fennel or lettuce isolates (30 sclerotia/100 cm' of soil). A set of fennel plants was also potted into noninfested sand. Plants were incubated in a greenhouse at 20-22 C. After 6 wk, plants inoculated with either the fennel or lettuce isolate showed chlorosis and collapse of older leaves and necrosis of crown tissue. S. minor was reisolated from symptomatic plants. Noninoculated plants were asymptomatic. This is the first report of 5. minor causing a disease of fennel, which is used as a rotation crop with lettuce in the Salinas Valley.