1Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312, U.S.A.; 2Department of Microbiology, Michigan State University, East Lansing 48824-1101, U.S.A.
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Accepted 27 September 1999.
A cytoplasmically transmissible hypovirulence syndrome has been identified in virus-free strains of the chestnut blight fungus Cryphonectria parasitica isolated from healing cankers on American chestnut trees in southwestern Michigan. The syndrome is associated with symptoms of fungal senescence, including a progressive decline in the growth potential and abundance of conidia, and elevated levels of respiration through the cyanide-insensitive alternative oxidase pathway. Conidia from senescing mycelia exhibited varying degrees of senescence ranging from normal growth to death soon after germination. Cytoplasmic transmission of hypovirulence between mycelia occurred by hyphal contact and coincided with the transfer of a specific restriction fragment length polymorphism from the mitochondrial DNA (mtDNA) of the donor strains into the mtDNA of virulent recipients. The transmission of the senescence phenotype was observed not only among vegetatively compatible strains but also among incompatible strains. Hypovirulence was present in isolates from the same location with different nuclear genotypes as identified by DNA fingerprinting. This study confirms that mitochondrial hypovirulence can occur spontaneously and spread within a natural population of a phytopathogenic fungus.
© 2000 The American Phytopathological Society