This volume of the series The Plant Viruses is devoted to viruses with
rod-shaped particles belonging to the following four groups: the toba-
moviruses (named after tobacco mosaic virus), the tobraviruses (after
to- bacco rattle), the hordeiviruses (after the latin hordeum in honor
of the type member barley stripe mosaic virus), and the not yet
officially rec- ognized furoviruses (fungus-transmitted rod-shaped
viruses, Shirako and Brakke, 1984). At present these clusters of plant
viruses are called groups instead of genera or families as is customary
in other areas of virology. This pe- culiarity of plant viral taxonomy
(Matthews, 1982) is due to the fact that the current Plant Virus
Subcommittee of the International Committee of Taxonomy of Viruses is
deeply split on what to call the categories or ranks used in virus
classification. Some plant virologists believe that the species concept
cannot be applied to viruses because this concept, according to them,
necessarily involves sexual reproduction and genetic isolation (Milne,
1984; Murant, 1985). This belief no doubt stems from the fact that these
authors restrict the use of the term species to biological species.
According to them, a collection of similar viral isolates and strains
does constitute an individ- ual virus, i. e., it is a taxonomy entity
separate from other individual viruses.
