Diversity of vegetative compatibility types, distribution of mating types and occurrence of hypovirulence of Cryphonectria parasitica in chestnut stands in NW Spain

An extensive survey on chestnut stands in NW Spain was carried out to study the population biology of Cryphonectria parasitica in order to design future biological control programmes of chestnut blight based on the field introduction of native hypovirulent strains. Five hundred and thirty-nine Cryphonectria parasitica isolates, belonging to five populations (A Coruña, Lugo, Ourense, Pontevedra and León), were obtained. The diversity of vegetative compatibility was very low. Six vc types were found, each population showing only from 2 to 4 vc types. Two vc types were the known European testers EU1 and EU66, and the other four were undescribed vc types that were named E1, E2, E3 and E4. E1 was the dominant vc type in Lugo and Ourense populations, and EU1 in Pontevedra and León. Hypovirulent isolates (a total of 15) were only detected in the León population, all but one being compatible with the vc type EU1. Hypovirulent strains belonged to the French subtype F1 of the Cryphonectria hypovirus-1 (CHV1).The study of the sexual compatibility in the León population showed that the idiomorph MAT-1 was present in most isolates (97%). In León, the simple structure of the population (reproduction mainly asexual and very low vc diversity) and the presence of hypovirulent strains compatible with the dominant vc type are factors that favour the application of biological control of chestnut blight in the near future.