engleski

Molecular characterization of Chryphonectria hypovirus 1 from Slovenia

The pathogenic fungus Cryphonectria parasitica Murrill Barr has been responsible for the decline of European chestnut. This aggressive ascomycete causes chestnut blight, a serious disease that destroys chestnut trees by causing bark cankers that progressively enlarge, girdle and kill branches and trunks of infected trees. This disease in Europe is successfully controlled with naturally-occurring Cryphonectria hypovirus 1 (CHV1), a double-stranded RNA (dsRNA) virus that reduces the virulence, sporulation and pigmentation of fungus and can therefore be used as a biocontrol agent of the chestnut blight. CHV1 was probably introduced together with its fungal host to Europe from Asia and then naturally spread throughout C. parasitica populations. In Slovenia, the disease was first recorded in 1950 and has been reported to date in all investigated chestnut populations. C. parasitica in those chestnut populations has a high diversity of vegetative compatibility (vc) types that can limit the spread of CHV1. It is known that CHV1 easily spreads between C. parasitica strains of the same vc type, but between strains of different vc types it spreads less frequently. Despite a high diversity of vc types, CHV1 is widespread in Slovenian C. parasitica populations. In order to gain a better insight into the genetic diversity of CHV1, we have analysed CHV1 infected C. parasitica isolates from Slovenia. Molecular characterization of CHV1 included hypoviral dsRNA extraction, complementary DNA synthesis, PCR amplification and partial sequencing of CHV1 genome. The obtained nucleotide sequences were assembled and the number of nucleotide differences and genetic distance between them were determined. Phylogenetic analysis grouped CHV1 sequences from Slovenia to the Italian subtype of CHV1, the only subtype found so far in Slovenia. Among sequenced CHV1 isolates a large number of different haplotypes were detected which indicates a high genetic diversity of CHV1 in Slovenia. High genetic diversity is not a consequence of recombination events, but is probably the result of numerous point mutations.

biological control ; chestnut blight ; genetic diversity ; hypovirulence

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