Genetic diversity of the chestnut blight fungus Cryphonectria parasitica and its associated hypovirus CHV-1 in Italy

Chestnut blight, caused by Cryphonectria parasitica, remains a significant threat to sweet chestnut (Castanea sativa) populations in Italy. This study investigated the genetic diversity, the vegetative compatibility (vc) types, the mating type distribution, and the presence of Cryphonectria hypovirus 1 (CHV-1) in 368 isolates from 18 Italian populations. A total of 31 vc types were identified, with vc type EU-02 dominating in central and northern Italy and EU-12 in southern regions. Overall, the southern populations of the pathogen exhibited lower vc diversity. Genetic analysis revealed 85 unique multilocus genotypes, with northern populations showing higher diversity (highest H = 3.04) compared to southern regions (lowest H = 0.20). The presence of CHV-1 in 27.45% of colonies suggests potential for biological control, though the heterogeneous distribution of vc types may limit the spread of the hypovirus. All but one of the isolates infected with CHV-1 belonged to the Italian subtype (I), while one isolate belonged to the French subtype (F1). Our findings highlight the complex population structure of C. parasitica in Italy and emphasize the need for region-specific strategies in CHV-1 deployment to effectively manage chestnut blight.