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Disease Note.

First Report of Fusarium Wilt of Basil in Hawaii and Foliar Disease Initiation. J. Y. Uchida, Department of Plant Pathology, University of Hawaii, Honolulu 96822 . R. T Hamasaki, Cooperative Extension Service, 45-260 Waikalua Rd., Kaneohe, HI 96744. Plant Dis. 80:105. Accepted for publication 14 November 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0105B.

In 1991, a disease causing severe losses of mature sweet basil (Ocimum basilicum L.) was observed in commercial fields on the island of Oahu. In January 1995, this disease was present in nearly all commercial fields on Oahu and on the island of Maui. In fields planted to cultivars of Genovese, Italian Large Leaf, and Thai, losses were 50 to 100%. Wilting of entire green plants was a prominent symptom, along with dark vascular necrosis of the crown and lower stem. Long, brown-black external stem lesions, chlorosis, and plant death were other symptoms. During wet weather, stems and petioles of severely diseased plants were covered with white mycelia and spore masses. In addition to root infections from soil inoculum, aerial disease spread was suggested by occurrence of stem lesions in field plantings. Fusarium oxysporum Schlechtend.: Fr. (identification confirmed by Shirley Nash Smith) was consistently isolated on water agar from internal stem tissue. A single-hyphal-tip isolate was used to inoculate healthy 15- to 20-cm-tall potted basil plants. Plants were sprayed to run-off with a spore suspension adjusted to 105 spores/ml. Inoculated plants were kept at 100% relative humidity for 24 h, then returned to the greenhouse for disease development. Black lesions developed at the nodes and progressed into the stems, caused wilting and eventual plant loss in 3 to 8 weeks. Fusarium oxysporum was reisolated from internal stem tissue of inoculated plants only. Uninoculated plants remained symptomless and healthy. This is apparently the first report of foliar disease initiation of this pathogen. This disease was first reported from Massachusetts in 1990 and is now present in at least nine other states (1,2).

References: (1) W. H. Elmer et al. Plant Dis 78:789, 1994. (2) A. P. Keinath. Plant Dis. 78.1211, 1994.