Low genetic diversity but frequent sexual reproduction of the chestnut blight fungus Cryphonectria parasitica in Azerbaijan

Chestnut blight was first recorded in Azerbaijan on the native European chestnut (Castanea sativa) in 2004, and since then, the disease is expanding in the country. In this study, chestnut blight was detected in seven of eight forest districts that were inspected. To characterize the local population structure of the chestnut blight fungus, 199 Cryphonectria parasitica isolates were collected and assessed for vc type, mating type and microsatellite genotype. Among these isolates, one dominant vc type was detected comprising 93% of the isolates. Six additional vc types were identified among the other isolates. The microsatellite analysis revealed a very similar pattern with 96.5% of the isolates belonging to the same multilocus genotype. Both mating types of C. parasitica were present in all seven districts with a mating type ratio not different from 1:1 in five districts. In accordance with the occurrence of both mating types, sexual fruiting bodies (perithecia) of C. parasitica were found in all districts with an overall prevalence on 20.6% of the cankers. The dominant vc type and microsatellite genotype in Azerbaijan do not occur in Europe, but have previously been found to be widespread in neighbouring Georgia. Our study reveals that sexual reproduction in the invasive C. parasitica population in Azerbaijan is frequent, although the population shows a low genetic diversity. This could favour the biological control of chestnut blight using hypovirulence, which so far does not seem to be present in Azerbaijan.