A New Canker Disease of Apple Caused by Leucostoma cincta and Other Fungi Associated with Cankers on Apple in Michigan. T. J. Proffer, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824-1312. A. L. Jones, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824-1312. Plant Dis. 73:508-514. Accepted for publication 23 January 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0508.

Leucostoma cincta was found to be the cause of a newly recognized disease of apple in North America. The fungus was isolated from margins of cankers on trunks and branches of diseased trees and from spores taken from perithecia embedded in cankers. Key identifying characters were a perithecial stromata with a black delimiting conceptacle and a central pycnidium. The optimum temperature for growth of the fungus in culture was 20 C. Vegetative compatibility groups were demonstrated by pairing isolates on a modified cornmeal agar. A total of 21 vegetative compatibility groups were identified among 75 isolates from 48 trees. The vegetative compatibility groups did not segregate during conidiogenesis or ascosporogenesis. Other fungi associated with cankers on apple were Valsa malicola, Botryosphaeria stevensii, B. obtusa, Nectria galligena, N. cinnabarina, Neofabraea malicorticis, Fusicoccum sp., Coniothyrium sp., Phomopsis sp., and Fusarium sp. L. cincta, but not V. malicola, was pathogenic in inoculation trials conducted on cultivars Redchief and Empire apple trees and on cultivar Newhaven peach trees. In separate pathogenicity trials, B. stevensii caused greater canker formation on apple than B. obtusa, implicating this species for the first time in the canker complex on apple trees in Michigan.

Keyword(s): Cytospora, Malus pumila.