Double-stranded RNAs in the dogwood anthracnose fungus, Discula destructiva Redlin

dsRNA banding patterns were determined in 109 isolates of Discula destructiva Redlin collected from South Carolina (SC), Alabama (AL), and Idaho (ID). Molecular similarity existed among dsRNAs of the same size. Previously unreported dsRNA mycoviruses were detected in isolate 247 from SC and isolate 331 from ID and named Discula destructiva virus{09}1{09}(DDV1) and Discula destructiva virus 2 (DDV2), respectively. The complete sequence of the genome of both viruses was determined. DDV1 has properties that indicate that should be a member in the family Partitiviridae . However, the presence of 2 smaller dsRNAs of unknown function prevent its assignment to one of the genera currently contained within the family. The properties of DDV2 suggest that it should be regarded as a distinct species in the genus Partitivirus: Family Partitiviridae .{09}Analysis of the genomes of the two viruses indicated that in both, the dsRNA 1 is of similar size and encodes an RNA-directed, RNA polymerase-RdRp. The two RdRps share 87.5% identity. The dsRNA 2 for both viruses encodes similar viral capsid proteins that share only 64% identity. These values for identity together with hybridization data, and the additional dsRNA 3 and dsRNA 4 support the proposal that DDV1 and DDV2 should be considered distinct viruses that have arisen from a common ancestor. Two short sequence fragments were derived from a 12 kb dsRNA found in SC isolate 272.1. The 800 by fragment contains an RdRP motif located toward the 3′ end of the molecule. In this respect it differs from viruses of the genus Hypovirus which are associated with hypovirulence in fungi, possess genomes of approx. 12 kb, but have no polymerase motif. The sequences of 4 smaller dsRNA bands observed in isolate 272.1 were shown to be identical to the dsRNAs of DDV1. The presence of two possible viruses in isolate 272.1 and other differences in dsRNA banding patterns observed in isolates confirm an earlier hypothesis that the dsRNA found in D. destructiva originates from infection by multiple viruses with dsRNA genomes.