Occurrence of Cercosporidium punctum on Fennel in California. S. T. Koike, University of California Cooperative Extension, Salinas 93901. E. E. Butler, and A. S. Greathead. Department of Plant Pathology, University of California, Davis 95616; and Salinas, CA 93908. Plant Dis. 76:539. Accepted for publication 11 February 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0539C.
In August 1991, commercial plantings of fennel (Foeniculum vulgare Mill.) in Monterey County, California, were affected by a new disease. Symptoms consisted of withering and drying up of older foliage. Affected leaf tips and stems turned brown. The stems and threadlike leaves were extensively covered with discrete brown pustules that became white when the fungus sporulated. Microscopic examination showed that the pustules consisted of erumpent fascicles of conidiophores and conidia. The conidiophores were brown, unbranched, geniculate, dark at the conidial attachment scars, and mostly aseptate above the basal septum. The conidia were hyaline, smooth, cylindric, and usually one septate and measured 28-51 (av. 34-45) X 6-9 µm. The fungus was identified as Cercosporidium punctum Deighton (1). Pathogenicity was tested by spraying a conidial suspension (3 X 105 conidia per milliliter) onto 15 2-mo-old plants in a greenhouse; four control plants were sprayed with distilled water. After 21 days the erumpent fascicles of C. punctum were observed on all of the test plants; foliage later withered. None of the control plants showed symptoms. Although C. punctum has been reported on fennel from France, Italy, Ethiopia, India, Jamaica, and the Canary Islands (1), this is the first report on this host from the United States. This fennel pathogen has also been observed in Santa Barbara and Santa Cruz counties. Voucher specimens have been deposited at the University of California herbarium at Berkeley.