106 (calculated from the S20w of 115S). The buoyant density of aldehyde-fixed particles in CsCl is 1.37 g/cm3. Particles are readily disrupted in neutral chloride salts and by sodium dodecyl sulphate.
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Type Species |
(RBDV) |
Virions are isometric, about 33 nm in diameter and are not enveloped. They appear flattened in electron micrographs of preparations negatively stained with uranyl salts (Fig. 1).
Physicochemical and Physical Properties
Virion Mr is about 7.5 106 (calculated from the S20w of 115S). The buoyant density of aldehyde-fixed particles in CsCl is 1.37 g/cm3. Particles are readily disrupted in neutral chloride salts and by sodium dodecyl sulphate.
Virion preparations contain three species of linear, positive sense, ssRNA of about 5.5 kb (RNA-1), 2.2 kb (RNA-2) and 1 kb (RNA-3). These RNA molecules are not polyadenylated.
Virions possess one major coat protein species (Mr 
30 103). Sequence data indicate that there are two non-structural proteins with Mr of 188 and 39 103.
None reported.
None reported.
Genome Organization and Replication
The genome is bipartite. RNA-1 has a major ORF encoding a 188 103 protein, and also in a different frame and overlapping the 188 103 protein, a putative small ORF that encodes a 12 103 protein. The 188 103 protein contains sequence motifs characteristic of helicases and polymerases. RNA-2 has two in-frame ORFs: that in the 5
-terminal half encodes a Mr 39 103 protein which has some slight sequence similarities with proteins of other viruses that are thought to have roles in virus transport; that in the 3-terminal half encodes the coat protein. RNA-2 is probably a template for the production of RNA-3 which comprises the 3-most 946 nts of RNA-2 and is a sgRNA for CP. The 3-terminal non-coding 18 nts of RNA-1 and RNA-2 (and hence of RNA-3) are the same and the 3-terminal 70 nts can be arranged in similar extensively base-paired structures. Infected leaves contain dsRNA corresponding in size to double-stranded forms of RNA-1 and RNA-2. In vitro translation yields three major proteins, Mr 190, 44 and 31 103 (CP), which are the translation products, respectively, of RNA-1, RNA-2 and RNA-3 (Fig. 2).
Particles are moderate immunogens.
In nature the host range is confined to Rubus species, all but one in the subgenus Idaeobatus; the experimental host range is fairly wide. The virus occurs in all tissues of the plant, including seed and pollen, and RBDV is transmitted in association with pollen, both vertically to the seed and horizontally to the pollinated plant. This is the only known method of natural spread, but experimentally, the virus can be transmitted by mechanical inoculation. The virus occurs throughout the world wherever raspberry is grown. Infection of raspberry is often symptomless but in some cultivars may be associated with ‘yellows’ or ‘crumbly fruit’. Confusingly, Black raspberry necrosis virus (BRNV) is the main cause of bushy dwarf disease in Lloyd George raspberry. However, because the additional presence of RBDV in plants contributes significantly to the intensity of the disease symptoms usually observed in the field, it can be regarded as an integral component of the disease syndrome.
List of Species Demarcation Criteria in the Genus
Not applicable.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus name, CMI/AAB description number ( ), genome sequence accession numbers [ ], and assigned abbreviation ( ) are:
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Raspberry bushy dwarf virus (165) |
[S51557, S55890, D01052] |
(RBDV) |
Tentative Species in the Genus
None reported.
Phylogenetic Relationships within the Genus
Not available.
RBDV resembles viruses of the genus Ilarvirus, family Bromoviridae, in having easily deformable particles that are transmitted in association with pollen. RNA-2 resembles RNA-3 of viruses in family Bromoviridae in the arrangement and sizes of its encoded gene products, the generation of a 3-terminal sgRNA and in the structured nature of the 3-ends of the molecules. The sequence of the translation product of RBDV RNA-1 resembles, in different parts, sequences in the translation products of viruses in the family Bromoviridae and to a lesser extent the sequence of the helicase + polymerase protein (Mr 183 103) of tobamoviruses. Idaeoviruses, therefore, belong to the ‘Sindbis-like’ supergroup.
Idaeo: from idaeus, specific name of raspberry, Rubus idaeus.
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