GENOMIC HETEROGENEITY OF RICE DWARF PHYTOREOVIRUS FIELD ISOLATES AND NUCLEOTIDE-SEQUENCES OF VARIANTS OF GENOME SEGMENT-12

Electrophoretic profiles of the dsRNAs of field isolates of rice dwarf virus (RDV) were compared with those of an isolate maintained at Hokk aido University (RDV-H). Unexpectedly, the genomic dsRNAs of most of t he field isolates showed distinct electrophoretic mobility profiles. T his was the case even among isolates from the same region. Genome segm ent 12 (S12) from some variants migrated faster than S12 from RDV-H. T hese RNAs were converted to full-length cDNAs and sequenced. S12 from all the variants had the same length of 1066 nucleotides with nucleoti de sequence identities of 96 to 99%. Three open reading frames previou sly reported were present in ah the variants, and the sequence identit ies were 95 to 99% for P12, 98 to 100% for P120Pa, and nearly 100% for P120Pb. A comparison of the nucleotide and amino acid sequences of th e variants with sequences of the RDV-H and Akita isolate showed that t here are two genomic types, one represented by RDV-H and the other by the Akita isolate.