Details of DPV and References

DPV NO: 419 November 2007

Family: Tombusviridae

Genus: Carmovirus

Species: Elderberry latent virus | Acronym: ElLV

This is a revised version of DPV 127

Elderberry latent virus

A. T. Jones Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, Scotland.

Contents

Introduction

Described by Jones (1972).

Synonym

Elderberry virus B (Jones & Murant, 1971)

Pelargonium ringspot virus (PelRSV; Stone & Hollings, 1975; 1976; Jones, 1983) is indistinguishable from ElLV in many biological and biophysical properties and is closely related serologically (Jones et al., 2000). This description applies equally to ElLV and PelRSV, except where noted otherwise.

An RNA-containing virus reported as ElLV in American elder (Sambucus canadensis) from eastern USA and as PelRSV in pelargonium worldwide. The infective particles are isometric, about 30 nm in diameter. The virus is readily sap-transmissible to several herbaceous species. Its vector is unknown.

Main Diseases

ElLV causes line-pattern symptoms in American elder (Sambucus canadensis) (Fig. 1, Fig. 2), which develops symptoms following mechanical inoculation only when kept in cool conditions. The virus appears to cause no symptoms in experimentally infected S. nigra (Jones, 1974). PelRSV causes chlorotic ringspots in Pelargonium peltatum and line-pattern symptoms in P. zonale (Jones et al., 2000).

Geographical Distribution

ElLV in Sambucus in Eastern USA and PelRSV in pelargonium worldwide.

Host Range and Symptomatology

ElLV was found in naturally infected Sambucus canadensis cv. Adams No. 2 imported into UK from USA. Probably other cultivars in USA also contain the virus but its presence may be masked by nepoviruses (Jones, 1972). PelRSV is common in pelargonium worldwide inducing chlorotic ringspots and/or line-pattern symptoms (Jones et al., 2000). In limited host range studies, no differences between ElLV and PelRSV were observed. They infected 25 species in the families Amaranthaceae, Chenopodiaceae, Cucurbitaceae and Solanaceae. Almost all plants were infected symptomlessly and many became infected only in inoculated leaves (Jones, 1972; Stone & Hollings, 1975; 1976; Kinard et al., 1999; Jones et al., 2000).

Diagnostic species

Chenopodium quinoa. Large chlorotic local lesions 10-14 days after inoculation, coalescing to produce a general chlorosis of inoculated leaves (Fig. 4); occasionally, systemic chlorotic or necrotic spots develop (Fig. 3).

Symptomless systemic infection occurs in Nicotiana clevelandii, N. tabacum cv. Xanthi-nc and Petunia hybrida.

Propagation species

Chenopodium quinoa.
Nicotiana clevelandii is useful for maintaining cultures.

Assay species

No satisfactory assay species found. Assays can be made by determining the maximum infective dilution of preparations in Chenopodium quinoa.

Strains

For all practical purposes, ElLV and PelRSV may be regarded as strains of a single virus species (Jones et al., 2000). ElLV (Jones, 1972) has historical precedence as the virus name.

Transmission by Vectors

No vector reported. The aphids Macrosiphum euphorbiae and Myzus persicae did not transmit the virus from Chenopodium quinoa to C. quinoa when allowed 5, 30 or 180 min acquisition access periods (Jones, 1972).

Serology

The virus is moderately immunogenic giving antiserum with gel-diffusion titres of 1/512- 1/1024. Reacts well in micro-precipitin tests or in gel-diffusion tests in 1% agar. It produces a single line of precipitation in gel-diffusion tests.

Relationships

ElLV and PelRSV are very similar in their symptomatology and host range in herbaceous plants. They are serologically distinguishable forming a distinct spur in gel double diffusion serological tests (Jones et al., 2000), but they differ by only 1 to 3 SDI units. However, using sequence-based criteria, they are sufficiently different to be regarded as distinct viruses (Kinard & Jordan, 1998).

No serological reaction was obtained with antisera to any of thirty-one distinct isometric viruses and ElLV seems distinct from other similar viruses including Pelargonium flower break, Pelargonium line pattern and Pelargonium ring pattern viruses (Jones, 1972; Jones et al., 2000). Its particle size, physical properties and the sizes of its RNA and protein molecules are similar to those reported for species in the genus Carmovirus but, because its genome expression strategy differs from that of recognised carmoviruses, it may be better placed in a new genus, together with Pelargonium line pattern and Pelargonium chlorotic ring pattern viruses (Kinard & Jordan, 2002).

Stability in Sap

In Chenopodium quinoa sap, the virus lost infectivity after 10 min at 85-90°C, storage at room temperature for 7 days, or dilution to 10^-5 - 10^-6 (Jones, 1972). Most of its infectivity is lost after 10 min at 65°C.

Purification

The virus is easily purified from inoculated Chenopodium quinoa leaves by chloroform clarification of leaf extracts followed by precipitation of the virus at pH 4.8 and differential centrifugation; treatment with butan-1-ol causes much loss of infectivity (Jones, 1972).

Properties of Particles

Purified preparations sediment as a major infective component (B) and a minor non-infective component (T).

Sedimentation coefficients (s°_{20, w}): 48 S (T) and 112 S (B) (Fig. 5).

Molecular weight (daltons): about 7 x 10⁶ (B) (Mayo & Jones, 1973).

Isoelectric point: about pH 4.8.

A₂₆₀/A₂₈₀: 1.62 (B).

Buoyant density: In CsCl solution, purified preparations of an uncloned isolate formed a major band at 1.36 g/cm³ and a minor band at 1.37 g/cm³ (Mayo & Jones, 1973).

Particle Structure

Particles are disrupted in 2% sodium phosphotungstate but in uranyl formate (Fig. 6, Fig. 7) they are isometric with diameters of about 17 nm (T) or 30 nm (B). Particles are not penetrated by the stain (Jones, 1972). Calculations based on the Mol. Wt of the protein and RNA components suggest that the B component may contain 120 protein subunits (Mayo & Jones, 1973).

Particle Composition

Nucleic acid: A single genomic ssRNA species (Jones, 1972) with a Mol. Wt, estimated from polyacrylamide gel electrophoresis after denaturation in glyoxal, of 1.3 x 10⁶ (Mayo & Jones, 1973; Jones et al., 2000). A minor species of Mol. Wt 0.55 x 10⁶ present in purified virus particles is a sub-genomic RNA species (Kinard & Jordan, 1998).

Protein: In polyacrylamide gels the protein from B particles migrated as a single major component with an estimated Mol. Wt of 40,000 (Mayo & Jones, 1973; Jones et al., 2000). However, purified preparations of PelRSV after storage contained an additional species of Mol. Wt 37,000, which is presumably a degradation product of the larger species (Jones et al., 2000). The coat protein sequence deduced from the published gene sequence consists of 338 amino acid residues with a calculated Mol. Wt of 36,678.

Genome Properties

Only coat protein gene sequences are available in public databases: accession numbers AY038066 (ElLV) and AY038068 (PelRSV) (Kinard et al., 1999). These sequences are 65% identical. Other coding regions are reported to have similar levels of identity (Kinard & Jordan, 1998).

DsRNA analysis of infected plants detected up to three dsRNA species (Kinard et al., 1996; Jones et al., 2000; Kinard & Jordan, 2002). The largest, of 3.7 - 4.0 kbp, would correspond to the genomic RNA and the smallest, of about 1.8 kbp, which was not detected consistently (Jones et al., 2000), is presumably the replicative form of the sub-genomic RNA species. The third dsRNA species, of about 2.6 kbp, was detected by Jones et al. (2000) but not by Kinard et al. (1996) or Kinard & Jordan (2002), and is of unknown origin.

Kinard & Jordan (2002) suggest that the genome organisation of ElLV is similar to that of carmoviruses. The two 5'-most ORFs, coding for polymerase and polymerase readthrough proteins, are probably translated from the genomic RNA. However, unlike definitive carmoviruses, only one subgenomic RNA species has been detected for ElLV and all three downstream ORFs, coding for p7, p9 and coat protein, must presumably be translated from this RNA.

Notes

Because the virus caused no symptoms in S. canadensis or S. nigra after 18 months in a heated glasshouse it was called Elderberry latent virus (Jones, 1972). However, in cooler conditions leaves of infected plants of S. canadensis, but not S. nigra, develop line-pattern symptoms.

The virus is distinct from other isometric viruses found in elder: the nepoviruses (arabis mosaic, cherry leaf roll, strawberry latent ringspot, tobacco ringspot and tomato ringspot) induce characteristic symptoms in Chenopodium quinoa and cucumber and have a different sedimentation behaviour; Cucumber mosaic virus and Tobacco necrosis virus do not infect C. quinoa systemically. All are serologically unrelated to ElLV.

ElLV and PelRSV are sufficiently similar to be regarded as strains of a single virus species, except for the reported differences in their nucleotide and aminoacid sequences. However, until the sequences are published, it is difficult to evaluate these differences. Likewise, availability of the sequence data should help in deciding whether the virus(es) should be placed in the genus Carmovirus or in a new genus in the Tombusviridae.

Figures

References list for DPV: Elderberry latent virus (419)

1. Jones, Annals of Applied Biology 70: 49, 1972.
2. Jones, CMI / AAB Descriptions of Plant Viruses 127: 1974.
3. Jones, Report of the Scottish Crop Research Institute, 1982: 195, 1983.
4. Jones & Murant, Report of the Scottish Horticultural Research Institute, 1970: 54, 1971.
5. Jones, McGavin, Brunt & Phillips, Annals of Applied Biology 136: 147, 2000.
6. Kinard & Jordan, Phytopathology 88: S48, 1998.
7. Kinard & Jordan, Acta Horticulturae 568: 17, 2002.
8. Kinard, Jordan & Hurtt, Acta Horticulturae 432: 148, 1996.
9. Kinard, Guaragna & Jordan, Abstracts of the XIth International Congress of Virology, Sydney: 415, 1999.
10. Mayo & Jones, Journal of General Virology 19: 245, 1973.
11. Stone & Hollings, Report of the Glasshouse Crops Research Institute, 1974: 116, 1975.
12. Stone & Hollings, Report of the Glasshouse Crops Research Institute, 1975: 119, 1976.