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Type Species |
(PCV) |
Virions are rod-shaped of about 21 nm in diameter and of two predominant lengths of 190 and 245 nm (Fig. 1). The length distribution of the short particles is broad and in some preparations an additional class of 160 nm is recognizable. Virions have helical symmetry with a pitch of 2.6 nm.
Physicochemical and Physical Properties
Virions sediment as two major components with S20w of 183S and 224S. Buoyant density in CsCl is 1.32 g/cm3. Virion isoelectric point is pH 6.45. Thermal inactivation of infectivity occurs at 64°C. Virions are stable in frozen leaves.
The genome consists of two molecules of linear positive sense ssRNA; RNA-1 consists of about 5900 nts and RNA-2 consists of about 4500 nts. RNAs are thought to have a 5-cap structure but this has not been confirmed. The 3-ends of the RNAs are not polyadenylated.
The virion capsid is constructed from protein subunits of a single capsid protein (CP) of Mr 23 103.
None reported.
None reported.
Genome Organization and Replication
RNA-1 contains two ORFs (Fig. 2). The 5 ORF encodes a protein with Mr 131 103, and suppression of a termination codon results in the synthesis of a readthrough product comprising a protein of Mr 191 103. The 3 ORF encodes a protein of Mr 15 103. The proteins of Mr 131 and 191 103 contain NTP-binding, helicase and RNA polymerase motifs that make a putative replication complex. For Peanut clump virus (PCV), these proteins are respectively 88%, 95% and 75% similar to the products of an isolate of one serotype of Indian peanut clump virus (IPCV). The protein with an Mr 15 103 is translated from a sgRNA. RNA-2 contains 5 ORFs: the ORF near the 5-end encodes the CP, the second ORF which, in PCV RNA-1, overlaps the first ORF by 2 nts encodes a protein with an Mr 39 103. This protein is expressed by leaky scanning and is thought to be involved in the transmission of PCV by its fungus vector. Further downstream, separated by a 135 nts intergenic region, is a triple gene block sequence that codes for proteins of Mr 51, 14 and 17 103 that are thought to be involved in the movement of virus from cell to cell. The proteins are probably expressed via sgRNAs, but these have not been clearly identified. The 3 non-coding regions for PCV are 298 nts for RNA-1 and of 275 nts for RNA-2; the last 96 nts are identical in both RNAs. The non-coding regions differ in size among isolates from the different serotypes of IPCV.
The two RNAs are required for systemic invasion of plants but RNA-1 is able to replicate in absence of RNA-2 in protoplasts. The virus is found in the cells of roots, stems and leaves of systematically infected plants.
The virus is highly immunogenic. There is a great serological variability among isolates of PCV. IPCV isolates fall into one of three very distinct serotypes; IPCV-H, IPCV-L, IPCV-T. All are serologically distinct from PCV.
The natural host first reported was Arachis hypogea (groundnut, Leguminosae). Disease symptoms are stunting-mottle-mosaic-chlorotic ringspot. PCV infects Sorghum arundinaceum, usually symptomlessly. IPCV infects a number of cereal crops and graminaceous weeds, some symptomlessly and others to induce stunting. The experimental host range is wide and includes species of Aizoaceae, Amaranthaceae, Chenopodiaceae, Cucurbitaceae, Graminae, Leguminosae, Scrophulariaceae, and Solanaceae. Nicotiana benthamiana and Phaseolus vulgaris are experimental propagation hosts, Chenopodium amaranticolor, and Chenopodium quinoa are local lesions hosts.
The virus is transmitted naturally by a plasmodiophorid fungus (Polymyxa graminis) or by seed (in groundnuts). It is mechanically transmissible.
PCV spreads in West Africa (Bénin, Burkina Faso, Congo, Côte d’Ivoire, Mali, Niger, Senegal and Pakistan). IPCV is widely distributed in India and Pakistan. A soil type favourable to the vector is a prerequisite for the virus to cause disease.
List of Species Demarcation Criteria in the Genus
The species are distinguished by different reactions with particular antisera (heterologous reactions are weak or undetectable). Also, PCV occurs only in Africa whereas IPCV occurs in the Indian subcontinent. However, isolates of IPCV can be readily assigned to one of three serotypes as protein preparations made from particles of each serotype barely react with heterologous antisera in immunoblotting tests. Isolates of PCV are also heterogeneous in their reactions with a panel of monoclonal antibodies. Moreover, several of the proteins encoded by genes in RNA of the different serotypes of IPCV differ in sequence from corresponding proteins of other IPCV serotypes by about as much as each differs from the corresponding protein of one isolate of PCV.
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:
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Peanut clump virus (235) |
[X78602, L07269] |
(PCV) |
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Indian peanut clump virus |
[X76658, X99149] |
(IPCV) |
Tentative Species in the Genus
None reported.
Phylogenetic Relationships within the Genus
Not available.
There are similarities among the putative replicase proteins of PCV and IPCV with those of Soil-borne wheat mosaic virus (SBWMV), the type species of the genus Furovirus. These proteins are more closely related to those of Barley stripe mosaic virus (BSMV; genus Hordeivirus) than to those of Beet necrotic yellow vein virus (BNYVV: genus Benyvirus, previously classified in the genus Furovirus). The CP sequences are 37% (IPCV) and 36% (PCV) identical to that of the CP of BSMV
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