Cryphonectria parasitica in Portugal:: diversity of vegetative compatibility types, mating types, and occurrence of hypovirulence

Cryphonectria parasitica, the causal agent of chestnut blight, has been responsible for the decline in chestnut in Portugal for the last two decades. In order to improve understanding of C. parasitica diversity, a total of 617 isolates from all affected chestnut-growing areas in continental Portugal, Madeira and the Azores archipelagos were studied. Nine vegetative compatibility (vc) types were identified among the isolates. EU-11 was the most widespread vc type comprising 80.2% of the isolates, followed by EU-12 (7.1%) and EU-66 (6.6%). Two of the Portuguese vc types could not be assigned to a known European vc type. The diversity of vc types was low in the Portuguese populations of C. parasitica, but comparable with other areas where C. parasitica was introduced recently. The frequent occurrence of perithecia and both mating types of C. parasitica indicates that sexual reproduction of the chestnut blight fungus is common in Portugal. One C. parasitica isolate from Tras-os-Montes showed a white culture morphology and contained dsRNA, indicating the presence of hypovirulence in this area.