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Disease Note.

Damping-off of Flowering Dogwood Seedlings Caused by Colletotrichum acutatum and Fusarium oxysporum . K. O. Britton, USDA Forest Service, 320 Green Street, Athens, GA 30602. S. C. Redlin, USDA-APHIS, PPQ-BATS, 4700 River Rd., Unit 133, Riverdale, MD 20737-1236. Plant Dis. 79:1188. Accepted for publication 15 September 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1188D.

Colletotrichum acutatum J. H. Simmonds is known to cause leaf necrosis and limb dieback (1) as well as lesions on fruit (2) of flowering dogwood, Cornus florida L. Seedlots collected for a provenance study were cold-stratified in moist sand. As seedlings emerged, many developed large, watersoaked tan lesions on radicles, hypocotyls, and cotyledons. Colletotrichum acutatum and Fusarium oxysporum Schlechtend.:Fr. were isolated from 82 and 29%, respectively, of 113 lesions. Most seedlots were primarily infected with C. acutatum, but diseased seedlings from one seedlot were 100% infected with F. oxysporum. Inoculation tests showed that both fungi completely inhibited seed germination when conidial suspensions were atomized onto emerging seedlings in sterile potting mix. In greenhouse inoculation tests, C. acutatum and F. oxysporum caused lesions similar to those originally observed, and reduced seedling survival 95 and 93%, respectively, compared with noninoculated controls. Both fungi were reisolated from diseased tissue. This is the first report that these fungi cause damping-off of flowering dogwood. They may also be responsible for poor seed germination.

References: (1) D. O. Chellemi and G. Knox. Plant Dis. 77:100, 1993; (2) V. L. Smith. Plant Dis. 77:536, 1993.