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Toxin Production by Alternaria solani and its Related Phytotoxicity to Tomato Breeding Lines. Marisa Maiero, Department of Horticulture, University of Maryland, College Park 20742, Present address: Department of Agronomy and Horticulture, Box 30003, New Mexico State University, Las Cruces 88003; George A. Bean(2), and Timothy J Ng(3). (2)Department of Botany, University of Maryland, College Park 20742; (3)Department of Horticulture, University of Maryland, College Park 20742. Phytopathology 81:1030-1033. Accepted for publication 5 April 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1030.

The fungus Alternaria solani causes early blight and collar rot diseases on tomatoes. A. solani has been reported to synthesize phytotoxic metabolites, especially alternaric acid and zinniol, in culture. Culture filtrates of several A. solani isolates were tested for their phytotoxicity to tomato genotypes previously evaluated for resistance to early blight and collar rot. Tomato seedlings exposed to culture filtrates for 20 h exhibited marginal and interveinal leaf necrosis and wilting. At a 1:2 dilution, the filtrate was severely phytotoxic to all genotypes tested, but at greater dilutions differences in susceptibility were observed. The collar rot and early blight resistant genotypes (C1943 and NC EBR-2) were tolerant of the filtrate, whereas genotypes that were resistant to early blight but not collar rot (71B2, 87B187, NC EBR-1) had phytotoxic symptoms. The phytotoxic metabolites were not extractable with chloroform, ethyl acetate, or isopropyl alcohol, but were present in the culture filtrate aqueous fraction. Alternaric acid and zinniol could not be detected in any significant quantity.