Hypovirulence, Vegetative Incompatibility, and the Growth of Cankers of Chestnut Blight

Abstract

American chestnut trees were inoculated with pairs of strains of Endothia parasitica, and the rate (b) of the expansion of the area of cankers was measured. Hypovirulence (H) agents in 1 strain of the pair decreased b markedly if both strains were in the same vegetative compatibility (v-c) group. With increasing numbers of v-c alleles different between the pair, the decrease in b became less and less until the decrease became insignificant when different alleles at 5 v-c genes separated the pair of strains. Although various strains in different v-c groups were used, the results were consistent. French and Italian H agents had similar effects on b.