Cocksfoot mottle virus
P. L. Catherall
Welsh Plant Breeding Station, Aberystwyth, Wales
Contents
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 10
6;
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
- Catherall, Rep. Welsh Pl. Breed. Stn, 1967: 120, 1968.
- Huth, Phytopath. Z. 62: 300, 1968.
- Serjeant, Rep. Rothamsted exp. Stn, 1962: 112, 1963.
- Serjeant, Pl. Path. 13: 23, 1964.
- Serjeant, Ann. appl. Biol. 59: 31, 1967.
- Smith, Pl. Path. 1: 118, 1952.
- Upstone, Ann. appl. Biol. 64: 49, 1969.
Acknowledgements
Photographs: courtesy of Rothamsted Experimental Station.
Symptoms in Dactylis glomerata; the leaf on the right shows
the whitening which frequently occurs as the leaves age.
Leaves of Triticum aestivum, (left) healthy, (right) infected.
Virus particles in phosphotungstate. Bar represents 100 nm.
