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Preliminary Evidence for Two Debilitating Cytoplasmic Agents in a Strain of Endothia parasitica from Western Michigan. John E. Elliston, Department of Forestry and Horticulture, the Connecticut Agricultural Experiment Station, P.O. Box 1106, New Haven 06504; Phytopathology 75:170-173. Accepted for publication 24 August 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-170.

Single-conidial isolates (SCI) of EP-60, a highly debilitated, dsRNA-containing strain of Endothia parasitica from western Michigan, segregated into three types. Type A was indistinguishable from EP-60 in cultural characteristics, pathogenicity, and fruiting capacity in American chestnut, and in its pattern of SCI segregation. Type B had cultural characteristics unlike type A or typical E. parasitica, was weakly pathogenic, and produced a few stromata, perithecia, and ascospores typical of E. parasitica in American chestnut. It yielded only type B and C SCI. Type C was indistinguishable from typical E. parasitica. It produced typical perithecia and ascospores in the field and in the laboratory, when mated with a type a mating type tester, and it yielded only type C SCI. When type A, B, and C isolates were paired on agar, type A and B characteristics were rapidly transferred to type C, and type A characteristics were slowly transmitted to type B. These results indicate that EP-60 has a genetic background typical of E. parasitica, with mating type A, and suggest that it contains two debilitating cytoplasmic agents. Type B isolates appear to represent the genetic background of EP-60 when it contains one of the agents and type A this background when it contains both agents. A fourth isolate type, with only the second agent, was not found.

Additional keywords: Castanea dentata, hypovirulence.