126
July 1974
Family: Secoviridae
Genus: Unassigned Secoviridae
Species: Strawberry latent ringspot virus
Acronym: SLRSV


Strawberry latent ringspot virus

A. F. Murant
Scottish Horticultural Research Institute, Invergowrie, Dundee, Scotland

Contents

Introduction
Main Diseases
Geographical Distribution
Host Range and Symptomatology
Strains
Transmission by Vectors
Transmission through Seed
Transmission by Grafting
Transmission by Dodder
Serology
Nucleic Acid Hybridization
Relationships
Stability in Sap
Purification
Properties of Particles
Particle Structure
Particle Composition
Properties of Infective Nucleic Acid
Molecular Structure
Genome Properties
Satellites
Relations with Cells and Tissues
Ecology and Control
Notes
References
Acknowledgements
Figures

Introduction

Described by Lister (1964).

Synonym
Rhubarb virus 5 (Rev. appl. Mycol. 45, 2647)

An RNA-containing virus with isometric particles c. 30 nm in diameter spreading naturally in Europe and found once in Canada. It is readily sap-transmissible, has a wide host range, infects the seed of several host plants and is transmitted by nematodes (Xiphinema spp.).

Main Diseases

Infects strawberry and raspberry (Fig.2) (Lister, 1964; Taylor & Thomas, 1968) causing various degrees of mottle and decline depending on the cultivar. Causes strap-leaf of celery (Walkey & Mitchell, 1969), mosaic of Robinia pseudoacacia and, possibly, yellow mottle of Euonymus europaeus and line-pattern of Aesculus carnea (Schmelzer, 1969); in rose, it was associated with chlorotic ringspotting and stunting (Cammack, 1966; Harrison, 1967); it has also been found in asparagus, blackberry, blackcurrant, redcurrant, cherry, elderberry, grapevine, plum, peach, rose, rhubarb and narcissus.

Geographical Distribution

Occurs throughout western Europe. Found once in Canada (Allen, Davidson & Briscoe, 1970), but not known to spread there naturally.

Host Range and Symptomatology

Occurs naturally in many species of wild and cultivated plants, and infects (often symptomlessly) a wide range of commonly used herbaceous test plants. Out of 167 species of dicotyledonous plants inoculated mechanically, the virus infected 126, belonging to 27 families (Schmelzer, 1969); most were infected systemically without showing symptoms. Isolates differ in virulence.

Diagnostic species
Chenopodium amaranticolor, C. murale, C. quinoa. Chlorotic or necrotic local lesions (Fig.1, Fig.4); systemic chlorosis and distortion (Fig.3) or, sometimes, necrosis or faint chlorotic mottle.

Cucumis sativus (cucumber). Chlorotic local lesions or none; systemic interveinal chlorosis or necrosis (Fig.5). In summer, subsequent leaves are symptomless but contain virus; in winter, symptoms may persist. Some isolates induce formation of enations in some cultivars (Tomlinson & Walkey, 1967).

Nicotiana rustica, N. tabacum and Petunia hybrida. Symptomless systemic infection.

Propagation species
Cucumis sativus.

Assay species
Chenopodium murale (Fig.1) seems the most reliable local lesion host, but is less susceptible than C. amaranticolor.

Strains

The Hampshire strawberry isolate (Lister, 1964) is the type strain. Apart from differences in virulence, other strains from the UK, Europe and Canada seem to resemble each other closely in physical properties and serological behaviour. Isolates from Euonymus, Robinia and Aesculus in eastern Europe (Schmelzer, 1969) were serologically indistinguishable from the Hampshire isolate.

Transmission by Vectors

Transmitted by the nematodes Xiphinema diversicaudatum (Lister, 1964) and X. coxi (Putz & Stocky, 1970). Adults and larvae both transmit (Harrison, 1967; Taylor & Thomas, 1968; Putz & Stocky, 1970). The virus was retained for up to 84 days in X. diversicaudatum kept without plants (Taylor & Thomas, 1968). Virus-like particles were associated with the cuticular linings of the lumina of the odontophore (stylet extension) and the oesophagus of X. diversicaudatum that had fed on plants infected with strawberry latent ringspot virus (W. M. Robertson, unpublished data).

Transmission through Seed

Seed-borne in Mentha arvensis (Taylor & Thomas, 1968), Lamium amplexicaule, Rubus idaeus and Stellaria media (Murant & Goold, 1969), Chenopodium quinoa (Schmelzer, 1969; Allen et al., 1970) and celery (Walkey & Whittingham-Jones, 1970). The amount of seed-transmission often exceeds 70%.

Transmission by Dodder

Not transmitted by Cuscuta californica or C. subinclusa but one strain was recovered from dodder after it had grown on infected plants (Schmelzer, 1969).

Serology

Antisera with precipitin titres of 1/2048 are readily obtained. Tube-precipitin or gel-diffusion tests give satisfactory results. The virus gives one line of precipitate in gel-diffusion tests.

Relationships

All isolates studied seem to be serologically identical. Strawberry latent ringspot virus resembles the nepoviruses in many of its properties but is unrelated to any of them serologically and differs in the composition of its protein coat. The significance of this for classification of the virus is not clear, but it suggests possible affinities to comoviruses (Wu & Bruening, 1971; Geelen, Van Kammen & Verduin, 1972) or to broad bean wilt virus (Doel, 1973). However, no relationship was detected to cowpea mosaic (yellow or severe strains), bean pod mottle, broad bean stain, Echtes Ackerbohnenmosaik, radish mosaic, squash mosaic or broad bean wilt viruses in gel-diffusion serological tests (Mayo et al., 1974).

Stability in Sap

In Chenopodium quinoa sap the isolates studied by Lister (1964) lost infectivity after 10 min at 52-58°C, or after dilution to 10-3-10-5, but were still infective after 50 days at room temperature. Isolates studied by Schmelzer (1969) had similar properties, but those obtained from rhubarb by Tomlinson & Walkey (1967) and from peach by Richter & Kegler (1967) survived only up to 7 days at room temperature.

Purification

Lister (1964) and Richter & Proll (1970) found that a modification of Steere's butanol/chloroform method gave preparations freer of plant protein than did the n-butanol method of Tomlinson, Shepherd & Walker or the ether/carbon tetrachloride method of Wetter. Allen et al. (1970) used a procedure based on chloroform clarification followed by treatment with ammonium sulphate to separate the virus from contaminating plant proteins. Further purification can be achieved by sucrose density gradient centrifugation. Yields are of the order of 1 mg/100g leaf.

The virus tends to aggregate when highly purified preparations are concentrated by ultracentrifugation; aggregation can be avoided by adding bovine serum albumin to 0.2% before ultracentrifugation or by using Sephadex G-200 instead of ultracentrifugation to concentrate the virus preparations (Richter & Proll, 1970).

Properties of Particles

Preparations contain a major component (B) sedimenting at 126 S (Mayo et al., 1974), 128-130 S (Brunt, 1964), 130 S (Richter & Proll, 1970) or 134 S (Allen et al., 1970). Sometimes a component (T) sedimenting at about 50 S (Richter & Proll, 1970) or 58 S (Mayo et al., 1974) is present. Particles of B component aggregated in caesium chloride and formed a band of buoyant density 1.46 g/cm3 (Mayo et al., 1974).

Particle Structure

Isometric, c. 30 nm in diameter, usually with obvious hexagonal outlines (Fig.6). Electron micrographs show some particles penetrated by stain and others not, presumably corresponding to the B and T components respectively.

Particle Composition

Nucleic acid: RNA, single-stranded. Some particles of B component contain one RNA molecule of M.Wt c. 2.6 x 106, others contain two molecules of M. Wt c. l.6 x 106. The average RNA content of B particles is 38% (Mayo et al., 1974).

Protein: Particles contain two kinds of polypeptide molecule, of M. Wt 44,000 and 29,000 (Mayo et al., 1974). In protein composition, strawberry latent ringspot virus differs from other nepoviruses studied, which have only one kind of polypeptide of about 55,000 M. Wt (Mayo, Murant & Harrison, 1971).

Relations with Cells and Tissues

In systemically infected Chenopodium amaranticolor leaves, inclusion bodies form adjacent to cell nuclei (Roberts & Harrison, 1970; Walkey & Webb, 1970). They contain membranous material and tubular structures enclosing rows of virus particles (Fig.7). They also contain material thought to be shells of virus protein (Roberts & Harrison, 1970).

Notes

Diseases caused by this virus typically show a patchy distribution because of the slow lateral migration in soils of its nematode vectors (Xiphinema spp.). The virus sometimes occurs in soils together with arabis mosaic virus, which also is transmitted by X. diversicaudatum. The two viruses are serologically unrelated but some strains of each give similar reactions in host plants. Serological tests provide the only reliable means of identification.

References

  1. Allen, Davidson & Briscoe, Phytopathology 60: 1262, 1970.
  2. Brunt, Rep. Glasshouse Crops Res. Inst. 1963: 92, 1964.
  3. Cammack, Pl. Path. 15: 47, 1966.
  4. Doel, Ph.D. Thesis, University of East Anglia, 1973.
  5. Geelen, Van Kammen & Verduin, Virology 49: 205, 1972.
  6. Harrison, Ann. appl. Biol. 60: 405, 1967.
  7. Lister, Ann. appl. Biol. 54: 167, 1964.
  8. Mayo, Murant & Harrison, J. gen. Virol. 12: 175, 1971.
  9. Mayo, Murant, Harrison & Goold, J. gen. Virol. 24: 29, 1974.
  10. Murant & Goold, Rep. Scott. hort. Res. Inst. 1968: 48, 1969.
  11. Putz & Stocky, Annls Phytopath. 2: 329, 1970.
  12. Richter & Kegler, Phytopath. Z. 58: 298, 1967.
  13. Richter & Proll, Acta phytopath. Acad. Sci. hung. 5: 151, 1970.
  14. Roberts & Harrison, J. gen. Virol. 7: 47, 1970.
  15. Schmelzer, Phytopath. Z. 66: 1, 1969.
  16. Taylor & Thomas, Ann. appl. Biol. 62: 147, 1968.
  17. Tomlinson & Walkey, Ann. appl. Biol. 59: 415, 1967.
  18. Walkey & Mitchell, Pl. Path. 18: 167, 1969.
  19. Walkey & Webb, J. gen. Virol. 7: 159, 1970.
  20. Walkey & Whittingham-Jones, Pl. Dis. Reptr 54: 802, 1970.
  21. Wu & Bruening, Virology 46: 596, 1971.


Figure 1

Local lesions in Chenopodium murale (photograph: Scottish Horticultural Research Institute) .

Figure 2

Symptoms in naturally infected raspberry (Rubus idaeus) cv. Malling Jewel (photograph: Scottish Horticultural Research Institute).

Figure 3

Systemic necrosis and distortion in Chenopodium amaranticolor (photograph: Scottish Horticultural Research Institute).

Figure 4

Local lesions in C. amaranticolor (photograph: Scottish Horticultural Research Institute).

Figure 5

Systemic interveinal chlorosis in Cucumis sativus (photograph: Scottish Horticultural Research Institute).

Figure 6

Virus particles in phosphotungstate. Bar represents 50 nm. (Photograph: Scottish Horticultural Research Institute.)

Figure 7

Ultrathin section of systemically infected leaf of C. amaranticolor, showing part of an inclusion body adjacent to nucleus (N). Note membranous structures (M) and tubules (T) in longitudinal and oblique section, enclosing rows of virus particles. (Photograph: Scottish Horticultural Research Institute.)