105
October 1972
Family: Tymoviridae
Genus: Tymovirus
Species: Wild cucumber mosaic virus
Acronym: WCMV


Wild cucumber mosaic virus

M. H. V. van Regenmortel
Laboratoire des Virus des Plantes, 8, rue Goethe, 67-Strasbourg, France

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 Freitag (1952) and Lindberg, Hall & Walker (1956).

An RNA-containing virus with isometric particles about 28 nm in diameter which sediment as two components in the ultracentrifuge. It is found only in the USA, has a host range largely restricted to the Cucurbitaceae and is transmitted mechanically and by flea beetles. It is distantly serologically related to turnip yellow mosaic and cacao yellow mosaic viruses.

Main Diseases

Causes mosaic in Marah macrocarpus (wild cucumber) in California (Milne, Grogan & Kimble, 1969) and in Marah oreganus in Oregon (Allen & Fernald, 1971).

Geographical Distribution

USA.

Host Range and Symptomatology

Largely restricted to the Cucurbitaceae (Lindberg et al., 1956); however, an Oregon isolate also symptomlessly infects Vinca rosea.

Diagnostic species

The Californian isolate produces vein-clearing, green blisters and a bright yellow mottle in Cucurbita pepo (pumpkin) (Fig.1, Fig.2) and does not infect Cucumis sativus (cucumber). The Oregon isolate infects Cucumis sativus and produces vein-clearing, star mottle, wilting and necrosis in Cucurbita pepo and Citrullus lanatus (watermelon) (Allen & Fernald, 1971).

Propagation species

Cucurbita pepo (pumpkin).

Assay species

Some isolates produce local lesions on the cotyledons of Citrullus vulgaris (watermelon) (Lindberg et al., 1956) and Cucumis melo (cantaloupe) (Milne et al., 1969).

Strains

Isolates from California (Milne et al., 1969) can be distinguished from those of Oregon (Allen & Fernald, 1971) by host range and symptoms. Two serologically distinguishable strains have been reported from California (Grogan, Taylor & Kimble, 1964).

Transmission by Vectors

Transmitted by the striped cucumber beetle, Acalymma trivittata (Freitag, 1941; Walters, 1969).

Transmission through Seed

Not tested.

Transmission by Dodder

Not tested.

Serology

The virus is strongly immunogenic. After prolonged immunization, antisera prepared against the virus also react with the depolymerized protein subunits of the virus in gel-diffusion tests (Bekker, 1967).

Relationships

Distantly serologically related to turnip yellow mosaic virus (MacLeod & Markham, 1963; van Regenmortel, 1966) and cacao yellow mosaic virus (Brunt et al., 1965). The nucleic acid resembles that of turnip yellow mosaic virus in its large cytidylic acid content (Symons et al., 1963).

Stability in Sap

In Cucurbita pepo sap, the virus is inactivated when heated at 70°C for 10 min; sap of infected plants retains its infectivity at room temperature for 28 days. The dilution end-point is 10-4 (Lindberg et al., 1956).

Purification

Sap from infected pumpkin plants may be clarified by adding ethanol to 20% (v/v) (Symons et al., 1963), by acidification to pH 4.9 (Grogan et al., 1964), or by adding bentonite (Dunn & Hitchborn, 1965). The virus can be precipitated with ammonium sulphate and concentrated by differential centrifugation. Pellets should be resuspended in a buffer because the virus precipitates in the absence of salt.

Properties of Particles

Two major classes of particles occur in purified preparations, ‘empty’ protein shells (top component, T) and infective nucleoprotein (bottom component, B) (Sinclair, Geil & Kaesberg, 1957; Anderegg et al., 1961). Intermediate components have also been reported (Yamazaki & Kaesberg, 1961b; Markham, 1962, 1967; MacLeod & Markham, 1963). The top component is more readily adsorbed by bentonite than is the bottom component; a marked differential in adsorption is observed in 10-3 M MgSO4, 10-2 M phosphate, pH 7.3. Under these conditions the electrophoretic mobility of the two components is also different (Hitchborn & Dunn, 1965).

Sedimentation coefficients (s20, w) at infinite dilution (svedbergs): 119 (B), 53 (T) (Yamazaki & Kaesberg, 1961a).

Diffusion coefficient (D20, w): 1.27 x 10-7 cm2 sec-1 (T and B).

Isoelectric point: pH 6.6 in 0.1 M Na phosphate buffer (T and B).

Electrophoretic R Ø value in zone electrophoresis: 0.14 (van Regenmortel, 1968).

Partial specific volume (calculated): 0.740 (T) and 0.670 (B) (Yamazaki & Kaesberg, 196la).

Particle Structure

The particles are isometric, c. 28 nm in diameter (Fig.3). The ‘empty’ shells are penetrated by negative stains used in electron microscopy whereas the ‘full’ particles are not. In crude preparations outer shells of 41 nm diameter have been found, associated preferentially with ‘empty’ particles (Hitchborn & Hills, 1965).

Particle Composition

RNA: 35% of particle by weight. Molar percentage of nucleotides: G16.4, A17.0, C41.0, U25.6 (Symons et al., 1963).

Protein: 65% of particle by weight. 190 amino acid residues per subunit of Mol. Wt 20,200 (Symons et al., 1963).

Relations with Cells and Tissues

Distinctive vesicles, similar to those induced by turnip yellow mosaic virus (Ushiyama & Matthews, 1970), develop in the chloroplasts (Allen, 1972).

Notes

There are numerous similarities between this virus and turnip yellow mosaic virus, although they have totally different host ranges. Points of similarity include: size and shape, RNA composition, size of protein subunit, common antigenic determinants, beetle vector and induction of chloroplast abnormalities.

Squash mosaic virus is also found in wild cucumber (Lindberg et al., 1956) but can be distinguished by serology.

References

  1. Allen, Virology 47: 467, 1972.
  2. Allen & Fernald, Pl. Dis. Reptr 55: 546, 1971.
  3. Anderegg, Geil, Beeman & Kaesberg, Biophys. J. 1: 657, 1961.
  4. Bekker, M. Sc. Thesis, University of Stellenbosch, 75 pp., 1967.
  5. Brunt, Kenten, Gibbs & Nixon, J. gen. Microbiol. 33: 81, 1965.
  6. Dunn & Hitchborn, Virology 25: 171, 1965.
  7. Freitag, Phytopathology 31: 8, 1941.
  8. Freitag, Phytopathology 42: 8, 1952.
  9. Grogan, Taylor & Kimble, Phytopathology 54: 163, 1964.
  10. Hitchborn & Dunn, Virology 26: 441, 1965.
  11. Hitchborn & Hills, Virology 26: 756, 1965.
  12. Lindberg, Hall & Walker, Phytopathology 46: 489, 1956.
  13. MacLeod & Markham, Virology 19: 190, 1963.
  14. Markham, Adv. Virus Res. 9: 241, 1962.
  15. Markham, In Methods in Virology 2: 1, ed. K. Maramorosch & H. Koprowski, Academic Press, New York and London, 1967.
  16. Milne, Grogan & Kimble, Phytopathology 59: 819, 1969.
  17. Sinclair, Geil & Kaesberg, Phytopathology 47: 372, 1957.
  18. Symons, Rees, Short & Markham, J. molec. Biol. 6: 1, 1963.
  19. Ushiyama & Matthews, Virology 42: 293, 1970.
  20. Van Regenmortel, Proc. internat. Conf Plant Viruses, Wageningen, 1965: 213, 1966.
  21. Van Regenmortel, S. Afr. med. J. 42: 118, 1968.
  22. Walters, Adv. Virus Res. 15: 339, 1969.
  23. Yamazaki & Kaesberg, Biochim. biophys. Acta 51: 9, 1961a.
  24. Yamazaki & Kaesberg, Biochim. biophys. Acta 53: 173, 1961b.

Acknowledgements

Photographs courtesy of J. S. Hahn and M. B. von Wechmar.


Figure 1

Cucurbita pepo: (left) healthy leaf, (right) infected leaf of same age showing vein-clearing and star mottle.

Figure 2

(Left to right) raised green blisters, vein-banding and mosaic in C. pepo.

Figure 3

Virus particles in phosphotungstate. Bar represents 100 nm.