Fungus-Transmitted and Similar Labile Rod-Shaped Viruses

Abstract

At least 12 viruses (Table I) are known to have rod-shaped particles which, although superficially similar to those of authentic tobamoviruses (Matthews, 1982; Gibbs, 1977), differ in that they occur within plants in low concentration, are relatively unstable in vitro, and have particles of two or more modal lengths which are purified and separated with difficulty; moreover, unlike tobamoviruses, most are transmitted by plasmodiophoromycete fungi (Table II), and three are reported to have bipartite genomes (Shirako and Brakke, 1984a; Richards et al., 1985; Mayo and Reddy, 1985). Three of these labile viruses [broad bean necrosis (BBNV), potato mop-top (PMTV), and soilborne wheat mosaic viruses (SBWMV)] are reported to be serologically related to one or more tobamoviruses (Kassanis et al., 1972; Powell, 1976; Nakasone and Inouye, 1978) and, since 1976, have been recognized as possible members of the tobamovirus group (Fenner, 1976). It has been suggested, however, that SBWMV and similar viruses should now be included in a new group for which the name furovirus (fungus-transmitted rod-shaped viruses) group has been proposed (Shirako and Brakke, 1984a). Although evidence is accumulating to support the formation of a new group, the taxonomic status of the fragile tobamo-like viruses is still uncertain and will be considered further (see Section VI).