CHV3-type dsRNAs and the GH2 genotype in a population of Cryphonectria parasitica in Ontario

CCP19, a hypovirulent isolate of Cryphonectria parasitica collected from a site near Bothwell, Ontario, in 1987, has shown potential for use in biological control of chestnut blight. CCP19 contains dsRNA that hybridizes with hypovirus CHV3 from isolate GH2 (CHV3-GH2), a hypovirulent isolate of C. parasitica from Michigan. In 1995, 26 isolates of C. parastica were collected at the Bothwell site, and 22-23 (85-89%) of these 26 isolates had significantly smaller lesion diameters in an apple virulence assay than virulent control isolate EP155. Twenty-two of the 26 isolates (85%) contained dsRNA. Segments of dsRNA in all 22 isolates hybridized with cDNA prepared from CHV3-type dsRNA in CCP19. The CHV3-type dsRNA was present in all three MCGs identified in the population. DNA fingerprint analysis revealed a highly clonal population, Twenty isolates had DNA fingerprint genotypes the same as, or similar to, GH2 and 6 isolates had genotypes similar to CCP19. Similarities, including presence of CHV3-type dsRNA, hig...