Mycoviruses related to chrysovirus affect vegetative growth in the rice blast fungus Magnaporthe oryzae

Mycoviruses causing impaired growth and abnormal pigmentation of the host were found in the rice blast fungus, Magnaporthe oryzae Four dsRNAs, dsRNA 1 (3554 bp), dsRNA 2 (3250 bp), dsRNA 3 (3074 bp) and dsRNA 4 (3043 bp), were detected in isolate S-0412-II 1a of M oryzae By picking up single conidia of S-0412-II 1a, cured strains of the fungus were isolated that had completely lost the mycovirus The cured strains had normal mycelial growth and pigmentation, suggesting that this mycovirus modulates host traits The buoyant densities of isometric virus particles (similar to 35 nm diameter) containing these dsRNAs in CsCl ranged from 1 37 to 1 40 g cm(-3) The single ORF (3384 nt) of dsRNA 1 encoded a gene product highly homologous to the viral RNA-dependent RNA polymerase of members of the family Chrysoviridae It is noteworthy that mycovirus S-0412-II la was detected not only in host cells but also in culture supernatant Furthermore, abnormal aggregation of mycelia was observed after adding the mycovirus-containing culture supernatant to an uninfected strain of M oryzae and mycoviral dsRNAs were detectable from the aggregated mycelia This novel dsRNA mycovirus was named Magnaporthe oryzae chrysovirus 1