The nucleotide sequences of genome segments 1 and 3 of Rosellinia anti-rot virus (RArV) from a hypovirulent isolate, W370, of the plant pathogen Rosellinia necatrix were determined. The complete nucleotide sequence of the genome segment 1 encoded a putative RNA-dependent RNA polymerase (RDRP). The deduced amino acid sequence of RDRP of RArV showed 29% identity with RDRPs of Colorado tick fever virus (CTFV) and European Eyach virus (EYAV) in the genus Coltivirus, and identities of 23-21% with members of the genera Fijivirus and Cypovirus. Both RArV and the Coltivirus member might have originated from a common virus ancestor.