Molecular diversity of chrysoviruses in Korean isolates of a new fungal species, Cryphonectria nitschkei

Genetic diversity of the chrysovirus within the four fungal strains was analyzed by comparing the full-length sequences of cloned chrysoviral genes encoding the RNA-dependent RNA polymerase (RdRp) and capsid protein (CP). Because the morphological characteristics of four chrysovirus-infected Cryphonectria spp. strains were different, strain identification was conducted via sequence comparison of the internal transcribed spacers (ITSs) of the fungal rRNA gene. Phylogenic analysis of the ITS regions revealed that the four strains were closely clustered with the reference strain of Cryphonectria nitschkei, while they were more distantly related to other common Cryphonectria species, indicating that they were likely C. nitschkei. Sequence comparison among chrysoviruses from Korean C. nitschkei strains revealed that similarities of the RdRp and CP genes ranged from 98% to 100% and from 95% to 100%, respectively, at the protein level. Their corresponding nucleotide sequences showed 97% to 100% and 84% to 100% identities, respectively. Compared to RdRp, the CP gene had more divergence, suggesting the presence of genes possessing different evolutionary rates within the chrysovirus genome. Sequence comparisons with other known chrysoviruses showed that the four Korean chrysoviruses were clustered together at the next lineage level. Discovering why two strains (bsl31 and bsl32) containing identical ITS sequences and chrysoviruses display different phenotypes should prove interesting.