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Disease Note

Alternaria tagetica on Marigold in New Jersey. P. J. Cotty, Department of Plant Pathology, University of Arizona, Yuma Agricultural Center, Yuma 85364. Plant Dis. 70:1159. Accepted for publication 31 July 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-1159d.

Leaf spotting of seed-grown marigold plants (Tagetes erecta L. and T. patula L.) was observed during July 1985 at a nursery in Ocean County, New Jersey. Over 60% of the stock was affected. A large-spored, long-beaked Alternaria species was isolated that was indistinguishable morphologically, culturally, and pathogenically from A. tagetica Shome & Mustafee isolates (ATCC 58763 and 58990) from Sinaloa, Mexico. Plants were spray-inoculated to runoff with spore suspensions (700 spores/ml) obtained from cultures grown on 5% V-8 juice, 2% agar under a 12-hr diurnal light cycle of 5,500 lx fluorescent light. Inoculated plants were incubated in a nonilluminated humidity chamber (100% RH) at 25 C for 24 hr and evaluated after 7 days. Tests were replicated three times and repeated twice. The ATCC cultures of A. tagetica and all isolates tested recovered from leaf spots were pathogenic to T. patula ‘Sparky’ and T. erecta ‘Orangeade’ but not to Zinnia elegans Jacq. ‘Cherrytime.’ In 1983, A. tagetica was reported from both Mexico (1) and the United States (South Carolina) (2) for the first time as a pathogen of marigold. This is the first report of this pathogen from the Atlantic northeastern United States and only the second report from the United States.