Genus Nepovirus
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Type Species |
Tobacco ringspot virus |
(TRSV) |
Distinguishing Features
Capsids of TRSV are composed of a single polypeptide species (Mr 
52-60 
103), whereas the capsids of most tentative nepoviruses yield two or three smaller polypeptides (Mr 21-44 103). Genome organization and expression are similar to those of comoviruses, except that RNA-2 specifies a single primary translation product (Mr 105-207 103) (Fig. 5). Definitive nepoviruses can be divided in three subgroups. Subgroup a has an RNA-2 with Mr 1.3-1.5 106, that is present in both M and B components. Subgroup b has an RNA-2 with Mr 1.4-1.6 106, that is present in M components only. Subgroup c has an RNA-2 with Mr 1.9-2.2 106, that is present in M components that sometimes are barely separable from B components. Sequence analysis so far suggests that the typical types of polyprotein cleavage sites and the occurrence of nucleotide sequence identity at the RNA termini support this subdivision. Sequence analysis of RNA-2 of Strawberry latent ringspot virus (SLRSV) and of RNA-1 of Satsuma dwarf virus (SDV) suggest that these two tentative nepoviruses are clearly distinct from the above described subgroups. Linear or circular satellite RNAs, which sometimes modulate symptoms, are found associated with several viruses. The linear satellite RNAs (1100-1800 nts) have a VPg linked to their 5
-end, are polyadenylated and code for a protein of Mr 36-48 103, the circular satellite RNAs (300-460 nts) are non-coding and replicate through a rolling circle mechanism. Nepoviruses are widely distributed in temperate regions. Natural host ranges vary from wide to restricted to a single plant species, depending on the virus. Ringspot symptoms are characteristic, but mottling and spotting are equally frequent. Twelve species are acquired and transmitted persistently by longidorid nematodes (Xiphinema or Longidorus spp), three are transmitted by pollen, one is transmitted by mites Blackcurrant reversion associated virus (BRAV) and the others have no known vector.
List of Species Demarcation Criteria in the Genus
The criteria demarcating species in the genus are:
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Coat protein amino acid sequence less than 80% identical, |
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Polymerase amino acid sequence less than 80% identical, |
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No pseudo-recombination between components possible, |
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Differences in antigenic reactions, |
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Different vector species. |
Using polyclonal rabbit antisera in agar gel diffusion tests Grapevine chrome mosaic virus (GCMV) and Grapevine fanleaf virus (GFLV) differ by more than 10 two-fold dilution steps. Their CP sequences have less than 25% identity and 32% homology between the aligned nucleic and amino acid sequences respectively. Their Pol protein sequences have less than 40% identity and 51% homology between the aligned nucleic and amino acid sequences respectively. No reassortment has been demonstrated between these viruses. GFLV is vectored by Xiphinema index nematodes, the vector of GCMV is not known (but is not Xiphinema index).
List of Species in the Genus
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, CMI/AAB description numbers ( ), genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
Three clusters of species in the genus names “Sugroup a, b and c” are based on length and packaging of RNA-2, and serological relationships (Murant, 1981).
Species in the Genus
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Subgroup a: |
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Arabis mosaic virus (16) |
[X81814/5] |
(ArMV) |
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Arracacha virus A (216) |
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(AVA) |
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Artichoke Aegean ringspot virus |
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(AARSV) |
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Cassava American latent virus |
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(CsALV) |
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Grapevine fanleaf virus (28) |
[X16907, D00915] |
(GFLV) |
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Potato black ringspot virus (206) |
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(PBRSV) |
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Raspberry ringspot virus (6, 198) |
[S46011] |
(RpRSV) |
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Tobacco ringspot virus (17, 309) |
[U50869] |
(TRSV) |
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Subgroup b: |
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Artichoke Italian latent virus (176) |
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(AILV) |
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Beet ringspot virus (138) |
[D00322, X04062] |
(BRSV) |
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Cocoa necrosis virus (173) |
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(CoNV) |
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Crimson clover latent virus |
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(CCLV) |
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Cycas necrotic stunt virus |
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(CNSV) |
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Grapevine chrome mosaic virus (103) |
[X15346, X15163] |
(GCMV) |
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Mulberry ringspot virus (142) |
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(MRSV) |
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Olive latent ringspot virus (301) |
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(OLRSV) |
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Tomato black ring virus (138) |
[X80831, X96485] |
(TBRV) |
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Subgroup c: |
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Artichoke yellow ringspot virus (271) |
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(AYRSV) |
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Blackcurrant reversion associated virus |
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(BRAV) |
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Blueberry leaf mottle virus (267) |
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(BLMoV) |
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Cassava green mottle virus |
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(CsGMV) |
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Cherry leaf roll virus (80, 306) |
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(CLRV) |
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Chicory yellow mottle virus (132) |
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(ChYMV) |
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Grapevine Bulgarian latent virus (186) |
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(GBLV) |
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Grapevine Tunisian ringspot virus |
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(GTRSV) |
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Hibiscus latent ringspot virus (233) |
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(HLRSV) |
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Lucerne Australian latent virus (225) |
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(LALV) |
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Myrobalan latent ringspot virus (160) |
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(MLRSV) |
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Peach rosette mosaic virus (150) |
[AF016626] |
(PRMV) |
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Potato virus U |
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(PVU) |
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Tomato ringspot virus (18, 290) |
[L19655, D12477] |
(ToRSV) |
Tentative Species in the Genus
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Arracacha virus B (270) |
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(AVB) |
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Artichoke vein banding virus (285) |
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(AVBV) |
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Cherry rasp leaf virus (159) |
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(CRLV) |
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Cherry rosette virus |
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(CRV) |
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Lucerne Australian symptomless virus |
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(LASV) |
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Rubus Chinese seed-borne virus |
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(RCSV) |
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Satsuma dwarf virus (208) |
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(SDV) |
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Strawberry latent ringspot virus (126) |
[X77466] |
(SLRSV) |
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Tomato top necrosis virus |
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(ToTNV) |
List of Unassigned Viruses in the Family
None reported.
Phylogenetic Relationships within the Family
See Fig. 6.
Similarity with Other Taxa
Comoviruses and nepoviruses have properties similar to members of the families Potyviridae and Picornaviridae; e.g., genome organization, VPg at 5-end and poly(A) tract at 3-end of genomes, post-translational processing of polyproteins and sequence similarities among nonstructural proteins. Moreover, comoviruses, nepoviruses and picornaviruses have very similar capsid morphology.
Derivation of Names
Como: sigla from cowpea mosaic.
Faba: Latin Faba, bean; also Vicia faba, broad bean.
Nepo: sigla from nematode, polyhedral particles to distinguish these viruses from the tobraviruses.
