Identifying Hypovirulent Isolates ofCryphonectria parasiticawith Broad Conversion Capacity

Kuhlman, E. G., Bhattacharyya, H., Nash, B. L., Double, M. L., and MacDonald, W. L. 1984. Identifying hypovirulent isolates of Cryphonectria parasitica with broad conversion capacity. Phytopathology 74:676-682. When 118 virulent (V) and 27 hypovirulent (H) isolates of Cryphonectria parasitica were paired in culture, 95% of the V isolates were converted to the hypovirulent condition by at least one of the H isolates. The 118V isolates in 54 vegetative compatibility (v-c) groups included representatives from West Virginia, North Carolina, Virginia, Tennessee, and Italy. The average conversion capacity of the 27 H isolates was 15% and ranged from 0 to 41 %. Eight cluster analyses based on different similarity functions were performed to group V isolates according to their susceptibility to conversion. The most useful cluster analysis was based on the square root of the number of sectors converted by individual H isolates and formed nine conversion groups and left only eight isolates ungrouped. Twenty-eight of the 54 v-c groups had more than one V isolate, and isolates in 15 of these v-c groups were also together in conversion groups. Clustering appears useful for determining relatedness among v-c groups. Conidial or mycelial slurries