23
October 1970
Family: Unallocated ssRNA+ viruses
Genus: Sobemovirus
Species: Cocksfoot mottle virus
Acronym: CoMV


Cocksfoot mottle virus

P. L. Catherall
Welsh Plant Breeding Station, Aberystwyth, Wales

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 Serjeant (1963).

An RNA-containing virus with isometric particles about 30 nm in diameter, infecting only a few species of Gramineae. It is transmitted by at least two species of beetle in the semi-persistent manner and by inoculation of sap, and occurs in central and southern England.

Main Diseases

Causes severe mottling and ‘dying-out’ of cocksfoot seed- and forage-crops: has been found in one wheat crop (Serjeant, 1964).

Geographical Distribution

Has been found only in central and southern England. Common in crops of pure cocksfoot and in cocksfoot/legume mixtures (Serjeant, 1964). Incidence is greater in cut than in grazed crops (Upstone, 1969).

Host Range and Symptomatology

Host range is narrow, being restricted to a few species in the family Gramineae (Serjeant, 1967). Transmissible by inoculation of sap to the following:

Diagnostic species

Dactylis glomerata (cocksfoot) and other Dactylis spp. Conspicuous yellow streaking and mottling, becoming white or necrotic as the leaves age (Fig.1). Infected plants are flattened and stunted, produce few tillers and usually die without flowering.

Triticum aestivum (wheat). Conspicuous yellow mottling and stunting (Fig.2). Plants infected as seedlings die within 6-8 weeks.

Avena sativa (oat). Mild yellow-green mottle with necrotic brown streaks and stripes.

Hordeum vulgare (barley). Very mild mottle with necrotic spots.

Propagation species

Cocksfoot and wheat are suitable for maintaining cultures; wheat is a good source of virus for purification.

Assay species

No known local-lesion hosts.

Strains

No variants have been distinguished.

Transmission by Vectors

Transmitted by at least two species of Chrysomelid beetles: Lema melanopa and L. lichenis (Serjeant, 1967; Catherall, 1968). Adults and larvae transmit, but adults are the more efficient. The virus is sometimes acquired in less than 5 min and is sometimes inoculated in less than 5 min, but transmission increases with increasing length of acquisition and inoculation feeds up to 3 days. No latent period. The virus is occasionally retained for only a few minutes, but sometimes for up to 2 weeks.

Transmission through Seed

Not apparently seed-transmitted.

Transmission by Dodder

Not tested.

Serology

The virus is weakly immunogenic. It forms only one band of precipitate in agar gel-diffusion tests using 1% agar and antisera prepared by intravenous injection. Precipitates of the virus in serological tests in liquids are granular (somatic).

Relationships

Serological tests failed to show any relationship between cocksfoot mottle and a number of other viruses with particles of similar size and shape, including some with beetle vectors (Serjeant, 1967).

Stability in Sap

In wheat sap, the thermal inactivation point (10 min) is about 65°C, dilution end-point about 10-3, and infectivity is retained at 20°C for 4-6 days. Addition of 0.1 M phosphate buffer extends the infectivity of plant extracts to 12 days (Serjeant, 1967).

Purification

The virus is comparatively stable in vitro and can be purified by several methods (Serjeant, 1967).

1. For serology, extract tissue in water and acidify to pH 5 with glacial acetic acid. After 12 h, centrifuge at 8000 g for 10 min, discard the pellet and centrifuge the supernatant fluid at 100,000 g for 2 h.

Resuspend the pellet in water and centrifuge at 8000 g for 10 min.

2. To study chemical and physical properties extract tissue in 0.2 M borate buffer enough to form a homogeneous slurry, add an equal volume of chloroform and blend.

Squeeze through muslin, centrifuge at 8000 g for 15 min and retain aqueous phase. Concentrate the virus by differential centrifugation, resuspending the pellets in borate buffer (pH 7) or distilled water. Further purify by rate zonal centrifugation in sucrose density-gradients.

Properties of Particles

Sedimentation coefficient (s20,w) at infinite dilution: c. 118 S. No accessory viral components are found by analytical ultracentrifugation.

Electrophoretic mobility: -7.6 x 10-5 cm2 sec-1 volt-1 at pH 7 in 0.07 M phosphate buffer.

A260/A280: 1.60.

Particle Structure

Particles are isometric, about 30 nm in diameter (Fig.3). They have no obvious surface structure in phosphotungstate negative stain, but appear slightly angular in shadow-cast preparations. Many particles are penetrated by phosphotungstate, but fewer are if the preparation is fixed for 10 min in 0.04% formaldehyde (Serjeant, 1967).

Particle Composition

RNA: Single stranded, molecular weight about 1 x 106; constitutes about 25% of particle weight.

Protein: about 75% of particle weight.

Relations with Cells and Tissues

No information.

Notes

Cocksfoot streak virus (Smith, 1952) produces symptoms in cocksfoot indistinguishable from those caused by cocksfoot mottle virus, and both viruses sometimes occur in the same plant. Unlike cocksfoot mottle virus, however, cocksfoot streak virus has flexuous filamentous particles, is transmitted by aphids and does not infect wheat, oats or barley.

Cocksfoot mild mosaic virus (Huth, 1968), which occurs in association with cocksfoot streak virus in Germany, has isometric particles similar to those of cocksfoot mottle virus, but is transmissible by aphids to Setaria italica.

References

  1. Catherall, Rep. Welsh Pl. Breed. Stn, 1967: 120, 1968.
  2. Huth, Phytopath. Z. 62: 300, 1968.
  3. Serjeant, Rep. Rothamsted exp. Stn, 1962: 112, 1963.
  4. Serjeant, Pl. Path. 13: 23, 1964.
  5. Serjeant, Ann. appl. Biol. 59: 31, 1967.
  6. Smith, Pl. Path. 1: 118, 1952.
  7. Upstone, Ann. appl. Biol. 64: 49, 1969.

Acknowledgements

Photographs: courtesy of Rothamsted Experimental Station.


Figure 1

Symptoms in Dactylis glomerata; the leaf on the right shows the whitening which frequently occurs as the leaves age.

Figure 2

Leaves of Triticum aestivum, (left) healthy, (right) infected.

Figure 3

Virus particles in phosphotungstate. Bar represents 100 nm.