GENOME STRUCTURE AND VARIABILITY OF FIJIVIRUSES

The Fijiviruses [Fiji disease virus, rice black-streaked dwarf virus ( RBSDV), maize rough dwarf virus (MRDV), and pangola stunt virus (PaSV) , the Mal de Rio Cuarto virus (MRCV) strain of MRDV, and oat sterile d warf virus] are distributed worldwide except for north America, and so me of them cause serious disease. However their genomes have not been extensively studied, and limited molecular data are available only for RBSDV, MRDV, PaSV and MRCV. All Fijiviruses have 10 segments, with an aggregate genome size larger than in other plant reovirus genera. All viruses analysed possess the same terminal conserved sequences, which differ from those of the phytoreoviruses and oryzaviruses. There are also sequence-specific inverted repeats adjacent to the terminal seque nce. With MRDV and RBSDV, at least two of the segments are bicistronic . Homology studies suggest that MRDV and RBSDV, although known as sepa rate viruses, should be considered as geographical races of the same v irus. In contrast, limited data suggest that PaSV and MRCV are less cl ose to each other and to MRDV/RBSDV. Electropherotyping has revealed v ariation among field isolates with RBSDV, MRDV and MRCV.