Disease Note.

First Report of Radicchio as a Host of Sclerotinia minor . S. T. Koike, University of California Cooperative Extension, Salinas 93901 . K. V. Subbarao, Department of Plant Pathology, University of California, Davis and located at U.S. Agricultural Research Station, Salinas 93905. Plant Dis. 79:966. Accepted for publication 10 July 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0966C.

During June and July of 1994 in Monterey County, Calif., commercial plantings of radicchio (Cichorium intybus L.) were affected by a previously undescribed disease. Plants nearing maturity wilted and collapsed. Crown tissues became necrotic, and white mycelium and small (0.5 to 3.0 mm) black sclerotia formed on these tissues. On the basis of sclerotia size, the fungus was identified as Sclerotinia minor Jagger and was consistently isolated from these plants. To test pathogenicity, 4-week-old radicchio (cv. Rossana Rogers) and lettuce (Lactuca sativa L. cv. Alpha) transplants were potted into sterilized sand. Sclerotia of the radicchio isolate of 5. minor were produced on sterilized potato pieces (1) and inserted into the sand at a depth of 0.5 cm and 0.5 cm from test plants. Control radicchio and lettuce plants did not receive sclerotia. All test plants were incubated in a greenhouse at 21 to 23°C. After 3 weeks, inoculated radicchio and lettuce plants wilted and collapsed and 5. minor was reisolated from necrotic crown and stem tissues. Uninoculated plants were asymptomatic. The experiment was repeated and results were similar to the first inoculations. In addition, radicchio (cv. Chioggia) was included in experimental field plots designed to evaluate lettuce drop resistance. One week after thinning, all plants in the field were inoculated with an isolate of S. minor from lettuce. Near crop maturity, radicchio plants became diseased and S. minor was again isolated. This is the first report of radicchio as a host of 5. minor. Radicchio plantings may contribute to inoculum levels and lettuce drop incidence for the extensive lettuce crop in the Salinas Valley.