A New Alternaria Leaf Blight Disease on Tomato in North Florida. D. O. Chellemi, University of Florida, North Florida Research and Education Center, Quincy, FL 32351. D. Mueller, Glades Crop Care Inc., Jupiter, FL 33458. Plant Dis. 79:426. Accepted for publication 14 March 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0426C.
In June of 1993, small, irregularly shaped leaf lesions with dark brown centers surrounded by yellow margins were observed on Lycopersicon esculentum Mill 'Sunny,' 'Colonial,'and 'Agriset 761' grown in the North Florida tomato production region. Lesions began on the margins of older leaves, lacked any visible signs of concentric rings, and eventually coalesced, resulting in defoliation. An Alternaria species with short-beaked conidia grew from symptomatic leaf pieces plated on water agar. Single-spore isolates grown on dilute potato-carrot agar (1) produced unbranched chains of 7-10 conidia (10-15 ? 50-60 μm) after 5-7 days at 27 C. Pathogenicity was determined by spraying a conidial suspension containing ca. 1 x 06 conidia ml-1 onto 4-wk-old tomato Sunny seedlings and onto both immature and mature green fruit. Detached fruits had been surface sterilized by immersing them in a solution containing 250 μg ml-1 NaCIO, or wounded with carborundum dust, or both surface sterilized and wounded, or left untreated. Inoculated plants and fruit were exposed to artificial dew for 48 hr at 22 C and then maintained in a greenhouse at 29 C (day) and 21 C (night). Seven days after inoculation, disease symptoms developed on inoculated foliage. Morphologically identical Alternaria spp were consistently isolated from necrotic leaf tissue. Lesions did not develop on tomato fruit even after ripening. The causal fungus differs from A. alternata f. sp. lycopersici (2) by its larger conidia formed in unbranched chains and its inability to infect fruit. Although the causal fungus is morphologically distinguishable among known tomato pathogens, E. G. Simmons (personal communication) suggests that it be treated at present as one taxon of a species-complex referred to as "Alternaria sp., in Group I of Simmons" (I) The disease is referred to as "Allernaria leaf blight of tomato." A voucher specimen has been deposited in the Gainesville herbarium (FLAS).Reference: (I) E. G. Simmons, and R. G. Roberts, Mycotaxon 58:109, 1993. (2) R. G. Grogan et al. Phytopathology 65:880. 1975.