Disease Note.

First Report of Pseudomonas viridiflava Causing a Leaf Necrosis on Basil. E. L. Little, Department of Plant Pathology, University of California, Davis 95616. R. L. Gilbertson, Department of Plant Pathology, University of California, Davis 95616, and S. T. Koike, University of California Cooperative Extension, Salinas 93901. Plant Dis. 78:831. Accepted for publication 5 May 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0831D.

Basil (Ocimum basilicum L.) transplants produced in commercial greenhouses in San Luis Obispo County, California, were afflicted with leaf necrosis. Initially, water-soaked, dark brown to black lesions developed on cotyledons and leaves. These lesions became necrotic and progressed inward from the margins, resulting in leaf death and plant dieback. A fluorescent, gram-negative bacterium was consistently isolated from diseased tissues onto King's B medium. Representative strains were oxidase, arginine dihydrolase, and levan negative: they utilized glucose, erythritol, D-sorbitol, and DL-lactate, but not sucrose, as sole carbon sources. The isolates induced a hypersensitive response in tobacco (Nicotiana tabacum L. cv. 'Havana') and rotted potato slices. These results strongly suggest that this bacterium is Pseudomonas viridiflava (Burkholder) Dowson. Thirty-day-old basil plants were gently rub-inoculated with bacterial suspensions (108 cfu/ml) of the P. viridiflava strains from basil or with nutrient broth, and inoculated plants were maintained in a growth chamber at 24 C. After 5-7 days, inoculated plants developed water-soaked lesions that became dark brown and necrotic. P. viridiflava was reisolated from these lesions. No disease symptoms developed on plants rubbed with broth alone. These experiments were repealed three times. We conclude that P. viridiflava is the causal agent of the leaf necrosis of basil. P. viridiflava is widely distributed on plant surfaces and can be an opportunistic pathogen, causing necrosis on the leaves, stems, and fruit of a wide variety of herbaceous dicotyledonous plants. However, this is the first time that P. viridiflava has been reported to cause a disease of basil.