PHYLOGENETIC-RELATIONSHIPS WITHIN THE FAMILY POTYVIRIDAE - WHEAT STREAK MOSAIC-VIRUS AND BROME STREAK MOSAIC-VIRUS ARE NOT MEMBERS OF THE GENUS RYMOVIRUS

The complete nucleotide sequence of wheat streak mosaic virus (WSMV) h as been determined based on complementary DNA clones derived from the 9,384-nucleotide (nt) RNA of the virus. The genome of WSMV has a 130-n t 5' leader and 149-nt 3'-untranslated region and is polyadenylated at the 3' end. WSMV RNA encodes a single polyprotein of 3,035 amino acid residues and has a deduced genome organization typical for a member o f the family Potyviridae (5'-P1/HC-Pro/P3/6K1/Cl/6K2/VPg-NIa/Nlb/CP-3' ). Because WSMV shares with ryegrass mosaic virus (RGMV) the biologica l property of transmission by eriophyid mites, WSMV has been assigned to the genus Rymovirus, of which RGMV is the type species. Phylogeneti c analyses were conducted with complete polyprotein or Nib protein seq uences of 11 members of the family Potyviridae, including viruses of m onocots or dicots and viruses transmitted by aphids, whiteflies, and m ites. WSMV and the monocot-infecting, mite-transmitted brome streak mo saic virus (BrSMV) are sister taxa and share a must recent common ance stor with the whitefly-transmitted sweet potato mild mottle virus, the type species of the proposed genus ''Ipomovirus.'' In contrast, RGMV shares a most recent common ancestor with aphid-transmitted species of the genus Potyvirus. These results indicate that WSMV and BrSMV shoul d be classified within a new genus of the family Potyviridae and shoul d not be considered species of the genus Rymovirus.