PROPOSED CLASSIFICATION OF THE BIPARTITE-GENOMED RASPBERRY BUSHY DWARF IDAEOVIRUS, WITH TRIPARTITE-GENOMED VIRUSES IN THE FAMILY BROMOVIRIDAE

Raspberry bushy dwarf virus (RBDV) has an unusual combination of prope rties and has been classified as the sole member of a new plant virus genus, for which the name idaeovirus has been proposed. Particles of R BDV resemble those of ilarviruses (family Bromoviridae) in appearance and in being transmitted in association with pollen. RBDV has two geno mic RNA species, RNA-1 (5 449 nt) and RNA-2 (2 231 nt). The particles also contain RNA-3 (946 nt), a subgenomic monocistronic coat protein m RNA which is derived from the 3' end of the bicistronic RNA-2. The sin gle 190 K protein encoded by RNA-1 contains methyltransferase, helicas e and polymerase domains. Evolutionary distance data obtained from mul tiple alignments of the amino acid sequence of the RBDV 190 K protein and corresponding proteins with replicative function from other plant viruses suggest that the closest affinities of RBDV are with the tripa rtite genomed viruses in the family Bromoviridae. We propose that the genus idaeovirus be included in the family Bromoviridae.