AbstractIsolates ofCryphonectria parasiticafrom chestnut trees in forest stands and commercial orchards were tested for virulence, distribution in vegetative compatibility (v‐c) groups, and capacity of being converted to hypovirulence through acquisition of double‐stranded RNA determinants from five hypovirulent isolates. Even though 77% of the virulent isolates were converted to hypovirulence, the low retrieval of hypovirulent isolates and the relatively high v‐c diversity in our study area warrant further investig