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Disease Note.

Colletotrichum acutatum Causes Anthracnose of Black Gum (Nyssa sylvatica). . K. O. Britton, USDA Forest Service, 320 Green Street, Athens, GA 30602. R. A. Anderson, USDA Forest Service, P.O. Box 2680, Asheville, NC 28802; and S. C. Redlin, USDA-APHIS, PPQ-BATS, 4700 River Rd., Unit 133, Riverdale, MD 20737-1236. Plant Dis. 79:1187. Accepted for publication 25 August 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1187D.

Necrotic leaf spots, stem lesions, and branch dieback on Nyssa sylvatica Marsh, were first observed in the southern Appalachians in 1989. Isolations repeated over several years consistently yielded Colletotrichum acutatum J. H. Simmonds. Botryosphaeria spp. and a Phomopsis sp. were also occasionally isolated. Field inoculations were conducted in June 1993. Conidial suspensions (100,000 spores/ml) of each possible pathogen were applied to one small branch on each of five replicate mature trees. Control branches were sprayed with sterile water. Inoculated branches and controls were left bagged for 2 weeks. After 3 months, some necrotic leafspots were observed in all treatments. The percent leaf area infected was es(ima(ed visually a( 9% for C. acutatum, 1.8% for (he Phomopsis sp., 1.0% for Discula destructiva Redlin, and 0.8% for (he con(rols. Colletotrichum acutatum was reisolated from 100% of leafspots in the C. acutatum-inoculated branches, 86% of the D. destructiva-inoculated branches, and 33% of the control branches, suggesting the presence of natural inoculum of C. acutatum. Discula destructiva was not reisolated from inoculated branches. The Phomopsis sp. was reisolated from 100% of leafspots on Phomopsis-inoculated branches. In 1994, five potted, healthy black gum seedlings per isolate were inoculated with 10,000 conidia/ml of C. acutatum, D. destructiva, or the Phomopsis sp. Plants were kept in plastic bags and misted frequently to maintain high humidity. On plants inoculated with C. acutatum, 55% of leaves developed necrotic lesions and 27% of shoots developed dieback. Within 3 weeks, all C. acutatum-inoculated plants were dead, and C. acutatum was reisolated from the necrotic tissue. Control plants did not develop any symptoms. Phomopsis-inoculaled plants developed some leafspots, but Phomopsis could not be reisolated. We conclude that C. acutatum is (he main cause of black gum anthracnose.

Reference: (1) P. S. Gunnell and W. D. Gubler. Mycologia 84:157, 1992.