In a commercial greenhouse in upstate New York, dark brown, angular lesions were first observed in April on lower, older leaves of 4-month-old tomato plants (Lycopersicon esculentum Mill. ‘Jumbo’). Chlorosis frequently developed around the lesions. Removal of the infected leaves reduced the rate of epidemic development. However, by July, lesions were present throughout the plant canopy, up to 2 m. The irregularly shaped lesions varied in size from 1 to 5 mm, frequently with tan-colored centers initially. Conidia developed in the center of the lesions, primarily on the outer, or adaxial side of the leaf, but were infrequent on the abax-ial surface. This contrasts with Cladosporium leaf mold caused by Fulvia fulva, in which the conidia develop as a velvety brown patch in lesions on the abaxial, or underside of the leaf, accompanied by chlorosis on the upper side of the leaf (1). The conidia ranged in shape from oval or li-moniform (5 to 6 μm in diameter) to cylindrical (5 to 6 μm wide, 7 to 20 μm long). The fungus was identified as Cladosporium oxysporum Berk. & M. A. Curtis (3) by C. J. K. Wang and J. M. McKemy of the State University of New York College of Environmental Science and Forestry in Syracuse, NY. Koch's postulates were fulfilled with a tuft of mycelium and conidia grown on potato dextrose agar as inoculum on fully expanded leaves of 5-week-old tomato plants, cv. Jumbo. Two weeks later, characteristic sporulating lesions developed on inoculated plants, about 1 cm from the inoculation site. Within 3 weeks, in the research greenhouse, the disease spread to healthy tomato plants in the vicinity, confirming the highly infectious nature observed in the commercial greenhouse. The fungus was reisolated from inoculated leaves and also from the adjacent naturally infected plants. C. oxysporum was previously reported as the causal agent of a leaf spot disease of pepper (2) and also a storage disease of ripe tomato fruit (4). To the best of our knowledge this is the first report of C. oxysporum causing disease on tomato foliage.
References: (1) E. E. Chamberlain. N.Z. J. Agric. 45:136, 1932. (2) A. M. Hammouda. Plant Dis. 76:536, 1992. (3) J. M. McKemy and G. Morgan-Jones. Mycotaxon 41:397, 1991. (4) S. Singh et al. Indian J. Microbiol. 23:133, 1983.
