Developments in plant virus taxonomy since the publication of the 6th ICTV Report
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Virology Division News Arch Virol 144/8 (1999)
1659
Virology Division News
Developments in plant virus taxonomy since the publication of the 6th ICTV Report M. A. Mayo Scottish Crop Research Institute, Invergowrie, Dundee, U.K.
1. Introduction The publication of the 6th ICTV Report [5] marked a significant shift in the way in which plant viruses were classified. Prior to this publication, most plant viruses were placed in one of 33 “Groups”, or in a few instances, into genera in families largely characterised by viruses of vertebrate or invertebrate animals [1]. In the 1995 classification, 41 new genera were recognised, of which 19 were classified into 7 new families. An unusual feature of this classification was that 22 genera were described that were not classified in families. These were unassigned genera, sometimes referred to as “floating” [3]. This shortened classification is now recognised in the International Code of Nomenclature and Taxonomy of Viruses [3] as being an intrinsic, if idiosynchratic, feature of virus classification. There has been substantial taxonomic activity since the publication of Murphy et al. [5] that has been outlined by Pringle [6, 7] and reviewed by Martelli [2] and Mayo and Pringle [4]. There have been four types of activity. The continuation of rapid progress in the molecular characterization of viruses has led to the recognition of 32 more genera. There has been some clustering of genera so as to form families, and in a few instances, genera have been split up so as to form more genera that better represent the diversity within the previous genus. Table 1 lists the current families and genera of plant viruses, the type species for each genus and denotes the taxa created since 1995. The fourth major taxonomic activity has been attention to the delineation of species within genera and the naming of taxa. This is reviewed by Van Regenmortel et al. [8]. In this brief review, the principle changes to genera and families are outlined and the current classification of plant viruses is presented in Table 1. A key by which genera and families of plant viruses may be distinguished can be accessed at the Internet address – http://www.scri.sari.ac.uk/vir/ictvhome.html.
Virology Division News
1660
Table 1. The current classification of families and genera of plant viruses Type of genome
Family
Genus
Type species
ss DNA
Geminiviridae
Mastrevirus a Curtovirus a Begomovirus a
Maize streak virus Beet curly top virus Bean golden mosaic virus
ss DNA
–
Nanovirus a
Subterranean clover stunt virus
Caulimovirus “SbCMV-like”a “CsVMV-like”a “PVCV-like”a Badnavirus “RTBV-like”a
Cauliflower mosaic virus Soybean chlorotic mottle virus Cassava vein mosaic virus Petunia vein clearing virus Commelina yellow mottle virus Rice tungro baciliform virus
Pseudovirus a
Saccharomyces cerevisiae Ty1 virus
Reverse transcribing
Caulimoviridae
Reverse transcribing
Pseudoviridaea
a
a
a
Reverse transcribing
Metaviridae
ds RNA
Reoviridae
Phytoreovirus Fijivirus Oryzavirus
Wound tumor virus
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