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Hypovirulent Isolates of Endothia parasitica Associated with Large American Chestnut Trees. R. A. Jaynes, Horticulturist, Connecticut Agricultural Experiment Station, New Haven 06504. J. E. Elliston, Assistant Plant Pathologist, Connecticut Agricultural Experiment Station, New Haven 06504. Plant Dis. 66:769-772. Accepted for publication 4 December 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-769.

Hypovirulent isolates of E. parasitica were associated with large, chronically infected, American chestnut trees. Normal isolates from such cankers were also commonly obtained. The abnormal isolates varied widely in pathogenicity. Although not all of the hypovirulent isolates had abnormal cultural characteristics, most showed considerable differences in pigmentation, growth rate, mycelial organization, and patterns of segregation of single-conidial isolates compared with normal. Several isolates did not produce perithecia in the field. Segregation of colony types among single-conidial isolates and presence of double-stranded RNA among several isolates suggested that viruslike cytoplasmic agents were responsible for their hypovirulence. The practical value that these isolates might have in the biological control of chestnut blight is still to be determined.

Keyword(s): Castanea dentata, chestnut blight, cytoplasmic hypovirulence.