Genus Cucumovirus

Type Species	Cucumber mosaic virus	(CMV)

Virion Properties

Morphology

Virions are icosahedral, of uniform size and sedimentation properties, and have electron dense centers by electron microscopy.

Physicochemical and Physical Properties

Purified virions are labile, and are especially susceptible to anionic detergents and high ionic strength buffers that disrupt the RNA-protein interactions required for particle integrity. Most strains are unstable in the presence of Mg²⁺, but at least one strain of Cucumber mosaic virus (CMV) requires Mg²⁺ for stability.

Nucleic Acid

The 3-termini of all RNAs within a species are highly similar and can form tRNA like structures that are aminoacylatable with tyrosine. Within a species, the 5 non-translated regions of RNAs 1 and 2 are also very similar. At least one strain of CMV can form defective RNAs, that are derived from deletions in the 3a ORF of RNA-3. Subgroup II strains of CMV encapsidate the sgRNA for the 2b ORF, called RNA-4a, and an additional small RNA of about 300  nts, called RNA-5, that is co-terminal with the 3-ends of RNAs-3 and 4. In addition, CMV and Peanut stunt virus (PSV) may harbor satellite RNAs of about 330 to 400  nts. The satellite RNAs are more common under experimental conditions than in field conditions, and may dramatically alter the symptoms of the helper virus.

Proteins

Although the CPs are estimated to have an Mr of about 24 10³ by sequence analysis, most migrate on polyacrylamide gels with a slower than predicted mobility.

Genome Organization and Replication

An additional ORF, the 2b ORF is found in all cucumoviruses and has been shown to be active in CMV and Tomato aspermy virus (TAV).

Antigenic Properties

CMV has been divided into two subgroups, based on serology. PSV also has more than one serological group. Sequence analysis has upheld the divisions.

Biological Properties

CMV has an extremely broad host range, infecting 85 distinct plant families, and up to 1000 species experimentally. The other cucumovirus species have narrower host ranges; PSV is largely limited to legumes and solanaceous hosts, and TAV predominantly infects composites and solanaceous plants. All species are transmitted by aphids in a non-persistent manner.

List of Species Demarcation Criteria in the Genus

The criteria demarcating species in the genus are:

	Serological relatedness,
	Compatibility of replicase proteins (1a and 2a proteins), but these distinctions may break down in the case of naturally occurring reassortants,
	Sequence similarity.

Serology and nucleotide sequence similarity is used to distinguish subgroups within a species. Subgroups generally have at least 65% sequence similarity.

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:

Species in the Genus

Cucumber mosaic virus (1, 213)	[D00356, D00355, D10538, X02733, X00985, M21463]	(CMV)
Peanut stunt virus (65, 92) (Robinia mosaic virus)	[U15728, U15729, U15730, D11126, D11127, D00668]	(PSV)
Tomato aspermy virus (79) (Chrysanthemum aspermy virus)	[D10663, D10044, D01015]	(TAV)

Tentative Species in the Genus

None reported.