Abstract
European chestnut (Castanea sativa) is threatened by the invasive fungus Cryphonectria parasitica, which causes chestnut blight. The virulence of the fungus can be reduced by a group of mycoviruses that can spread among vegetatively compatible strains through hyphal anastomosis. Hypovirulent isolates are used as biocontrol agents, but their efficiency can be diminished by restricted hyphal anastomosis if the variability of vegetative compatibility (vc) types in a population is high. Sexual reproduction could increase the vc type diversity and further complicate biocontrol in a region. Therefore, knowledge of genetic diversity of C. parasitica is important to assess the effectiveness of a biological control program. The present study was performed in the Autonomous Province of Bozen-Bolzano (South Tyrol) in northern Italy, where chestnut cultivation provides an additional income to farmers. The genetic characterization of C. parasitica isolates from 35 chestnut stands and one forest population in different districts of South Tyrol was performed based on the analysis of vegetative incompatibility loci, the mating type locus, and the internal transcribed spacer (ITS) region. In this study, a total of 23 different vc types were found all over South Tyrol with a Shannon diversity index of 1.86. EU-2, EU-1, and EU-13 were the most widespread vc types comprising 51%, 13%, and 9% of the fungal isolates, respectively. Both mating types were present in the region with a ratio close to 1:1. Three different haplotypes were identified based on ITS sequence analysis, which pointed to two introduction events of the fungus to the region and allowed placing C. parasitica from South Tyrol into a larger phylogeographic context.
Highlights
European or sweet chestnut (Castanea sativa) covers an estimated area of 2.5 million hectares in several European countries, including Italy, Spain, France, Greece, and Portugal (EU Science Hub, 2019)
Twenty-three different vc types of C. parasitica were found in South Tyrol (Fig. 2) with a mean of 9.17 per district (Supplementary Fig. 2)
Genetic diversity of C. parasitica was investigated in different European regions, but so far, no such study was performed in South Tyrol, even though it could considerably support the implementation of disease management strategies
Summary
European or sweet chestnut (Castanea sativa) covers an estimated area of 2.5 million hectares in several European countries, including Italy, Spain, France, Greece, and Portugal (EU Science Hub, 2019). Bozen-Bolzano (South Tyrol), chestnut stands occur on an area of approximately 123 hectares that are managed by 262 farms, in addition to the forest trees (ASTAT, 2016). Chestnut stands in this region show a fragmented distribution in mid-mountain locations, with an average of 23 trees per owner, while the overall annual production of chestnuts amounts to around 400 tons (Bender, 2002). Chestnut trees represent an essential element of the local landscape and forests, and provide additional income to farmers. Chestnut stands provide valuable ecosystem services and enhance recreational and touristic activities in the region
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