Subfamily: Betarhabdovirinae

Genus: Varicosavirus


Distinguishing features

Viruses assigned to the genus Varicosavirus form a monophyletic group based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L sequences. Varicosaviruses infect plants and they have bi-segmented genomes. Lettuce big vein-associated virus (LBVaV; species Varicosavirus lactucae) has non-enveloped, flexuous, rod-shaped virions that, in electron micrographs, resemble nucleocapsids of other rhabdoviruses.



LBVaV vrions are fragile, non-enveloped rods mostly measuring 324–152 nm × approximately18 nm; each has a central canal approximately 3 nm in diameter and an obvious helix with a pitch of about 5 nm (Figure 1.Varicosavirus). The helix of particles, especially those in purified preparations, tends to loosen and particles are then seen as partially uncoiled filaments (Kuwata and Kubo 1981, Kuwata et al., 1983, Vetten et al., 1987).

Figure 1.Varicosavirus. Negative-contrast electron micrograph of virions of an isolate of lettuce big vein-associated virus. The bar represents 100 nm (Courtesy J.A. Walsh and C.M. Clay.)

Physicochemical and physical properties

Virus particles have a density in Cs2SO4 of about 1.27 g cm-3 (Kuwata et al., 1983).

Nucleic acid

LBVaV, Alopecurus myosuroides varicosavirus 1 (AMVV1; species Varicosavirus alopecuri), Allium angulosum virus 1 (AAnV1; species Varicosavirus allii), Brassica rapa virus 1 (BrRV1; species Varicosavirus brassicae), morning glory varicosavirus (MGVV; species Varicosavirus ipomoeae), Lolium perenne virus 1 (LoPV1; species Varicosavirus lolii), Melampyrum roseum virus 1 (MelRoV1; species Varicosavirus melampyri), Pinus flexilis virus 1 (PiFleV1; species Varicosavirus pini), Vitis varicosavirus (VVV; species Varicosavirus vitis), Xinjiang varicosavirus (XVV; species Varicosavirus xinjiangense), Zostera-associated varicosavirus 1 (ZaVV1; species Varicosavirus zosterae) and red clover associated varicosavirus (RCaVV; species Varicosavirus trifolii) genomes consist of negative-sense, single-stranded RNA which is encapsidated by N (previously termed coat protein, CP). The genomes of varicosaviruses (10.4–12.9 kb) occurs as two segments of 6.8 kb (RNA1) and 4.0–6.1 kb (RNA2) (Sasaya et al., 2002, Sasaya et al., 2004, Bejerman et al., 2021, Bejerman et al., 2022). The exception is PiFleV1 in which the genome is unsegmented (Bejerman et al., 2021). The 3′- and 5′-terminal sequences of the two genome segments are similar but do not exhibit inverse complementarities. Compared with orchid fleck virus (OFV; species Dichorhavirus orchidaceae), purified LBVaV virions contain relatively large amounts of anti-genomic RNAs (Sasaya et al., 2001). Conserved motifs in the transcription initiation and termination signals resemble those of viruses in the genus Cytorhabdovirus.


LBVaV RNA2 encodes the 397-aa N with a predicted mass of 44.5 kDa (Mr approximately 48 kDa), as well as protein 2 (36 kDa), protein 3 (32 kDa), protein 4 (19 kDa) and protein 5 (41 kDa) which are of unknown functions but thought to be equivalent to P, P3, M and G of cytorhabdoviruses (Sasaya et al., 2004, Kormelink et al., 2011). LBVaV RNA1 encodes protein 6 (5 kDa), also of unknown function, and the 232 kDa L (Sasaya et al., 2002). N and L share a moderate amount of amino acid sequence identity with their counterparts in other rhabdoviruses.

Genome organisation and replication

PiFleV1 contains five ORFs in the order 5´-N-2-3-4-L-3´ in an unsegmented RNA molecule. All other varicosaviruses have bi-segmented genomes and contain only the L gene in RNA1, except for LBVaV in which RNA1 contains two genes in the order 3′-6-L-5′. LBVaV, VVV and XVV RNA2 contains five genes in the order 3′-N-2-3-4-5-5′, one or two genes more than the other viruses of the genus (Figure 2.Varicosavirus). Although the genome organisation of LBVaV is similar to that of other rhabdoviruses, LBVaV does not have a 3′-non-coding leader sequence. Capped and polyadenylated monocistronic mRNAs are transcribed from individual genes.

 Varicosavirus genome
Figure 2.Varicosavirus. Schematic representation of varicosavirus genomes (RNA1 and RNA2) shown in reverse (positive-sense) polarity. N and L represent ORFs encoding the structural proteins. ORFs numbered 2 to 5 encode putative proteins of unknown function. ORFs that appear to be homologous are shown in the same colour. The genome of Pinus flexilis virus 1 is not segmented.


LBVaV and tobacco stunt virus (TStV; currently unclassified) are transmitted in soil and in hydroponic systems by zoospores of the chytrid fungus Olpidium virulentus (a noncrucifer strain of Olpidium brassicae) (Campbell 1962, Hiruki 1967, Sasaya and Koganezawa 2006, Maccarone et al., 2010b). LBVaV is frequently associated with lettuce big vein disease that is caused by Mirafiori lettuce big-vein virus (MLBVV; species Ophiovirus mirafioriense, family Aspiviridae) (Roggero et al., 2000, Lot et al., 2002). Due to the longevity of infectious LBVaV from stored O. virulentus resting spores, it is assumed that the virus is carried internally by the fungus. The viruses are also transmitted experimentally, sometimes with difficulty, by mechanical inoculation (Huijberts et al., 1990). Neither of the viruses is reported to be seed-transmitted. LBVaV has been reported from Europe, United States, Japan, Saudi Arabia and Australia (Navarro et al., 2005, Maccarone et al., 2010a, Alemzadeh and Izadpanah 2012, Umar et al., 2017).


N does not induce a strong antibody response in laboratory animals. LBVaV is closely related serologically to TStV, which is currently unclassified but may be considered to be a strain of LBVaV (Kuwata and Kubo 1986, Sasaya et al., 2005).

Species demarcation criteria

Viruses assigned to different species within the genus Varicosavirus have several of the following characteristics: A) the nucleotide sequence identity of complete genomes is lower than 75%; B) they occupy different ecological niches as evidenced by differences in hosts and/or chytrid vectors; and C) they can be clearly distinguished in serological tests or by nucleic acid hybridisation.

Virus nameAccession numberVirus abbreviation
Aconitum virus 1BK061734; BK061735AcoV1
Apera virus 1BK061737; BK061738ApeV1
Aponogeton virus 1BK061739; BK061740ApoV1
Arceuthobium virus 8BK061732; BK061733ArcV8
Artemisia virus 1BK061741; BK061742ArtV1
Asclepias syriaca virus 3BK061743; BK061744AscSyV3
Brassica virus 2BK061747; BK061748BrV2
Caladenia virus 1BK061755; BK061756CalV1
Centaurea virus 1BK061757; BK061758CenV1
Cucumis virus 1BK061761; BK061762CucV1
Didymochlaena virus 1BK061764; BK061765DidV1
Erysimum virus 1BK061766; BK061767EryV1
Frullania virus 1BK061768; BK061769FruV1
Guizotia virus 1BK061770; BK061771GuiV1
Holcus virus 1BK061772; BK061773HolV1
Leucanthemum virus 1BK061774; BK061775LeuV1
Luffa virus 1BK061780; BK061781LufV1
Melilotus virus 1BK061784; BK061785MelV1
Monoclea gottschei varicosa-like virusOX380363; OX380364MgVV
Pennisetum virus 1BK061790; BK061791PenV1
Primula virus 1BK061795; BK061796PriV1
Ranunculus virus 1BK061797; BK061798RanV1
Raphanus virus 1BK061799; BK061800RapV1
Ribes virus 1BK061801; BK061802RibV1
Silene virus 1BK061807; BK061808SilV1
Streptoglossa virus 1BK061813; BK061814StrV1
Tanacetum virus 1BK061815; BK061816TanV1
tobacco stunt virusAB190521*TStV
tree fern varicosa-like virusOW528630; OW528632TfVV
Treubia virus 1BK061819; BK061820TreV1
Triticum virus 1BK061821; BK061822TriV1
Vicetoxicum virus 1BK061823; BK061824VinV1
Zea virus 1BK061825; BK061826ZeaV1

Virus names and virus abbreviations are not official ICTV designations.

* Coding region sequence incomplete