A novel mycovirus closely related to hypoviruses that infects the plant pathogenic fungus Sclerotinia sclerotiorum

Three dsRNA segments, two similarly sized at 9.5 kbp and a third one of approximately 3.6 kbp, were extracted from a hypovirulent strain SZ-150 of Sclerotinia sclerotiorum. The complete cDNA sequence of one of the two large dsRNA segment (10398 bp, excluding the poly (A) tail) reveals a single ORF that encodes a polyprotein with conserved domains of putative papain-like protease, UDP glucose/sterol glycosyltransferase, RNA-dependent RNA polymerase and viral RNA Helicase. This virus is closely related to Cryphonectria hypovirus (CHV) 3/GH2 and CHV4/SR2 in the family Hypoviridae and designated as Sclerotinia sclerotiorum hypovirus 1 (SsHV1/SZ-150). The satellite-like 3.6 kbp dsRNA segment (S-dsRNA) shares high sequence identity with the 5'-UTR of SsHV1/SZ-150. SsHV1/SZ-150 alone is not the primary causal agent for hypovirulence of strain SZ-150 since strains without the S-dsRNA show normal phenotype. This is the first report of a naturally occurring hypovirus that infects a fungus other than Cryphonectria parasitica. (C) 2011 Elsevier Inc. All rights reserved.