| One hundred twenty six isolates of Cryphonectria parasitica were sampled from American chestnut trees in southern Ontario and assessed. Nineteen (15%) isolates had reduced growth on PDA, reduced virulence in apples, and contained dsRNA and, therefore, were considered putative hypovirulent isolates. Double-stranded RNA extractions in combination with Reverse Transcriptase-PCR reactions indicated that 109 (86%) isolates of C. parasitica contained either dsRNAs assumed to be associated with fungal viruses, or a Hypovirus sp. The number and size of dsRNA fragments varied, and the detection of Hypovirus spp. was not always associated with dsRNA detection. Hypovirus species CHV-1, CHV-3, and CHV-4 were identified in 1, 4, and 6 counties, respectively. Comparison of selected isolate, tree, and site characteristics indicated that no relationships existed between tree site and the presence of Hypovirus spp. Significant correlations did exist between the presence of Hypovirus spp. and tree location, canker type, tree size, and reproductive status of the tree. |
