107
October 1972
Family: Tombusviridae
Genus: Panicovirus
Species: Cocksfoot mild mosaic virus
Acronym: CMMV


Cocksfoot mild mosaic virus

W. Huth
Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für landw. Virusforschung, Braunschweig, Germany

H. L. Paul
Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für landw. Virusforschung, Braunschweig, Germany

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 Huth (1968) and Huth, Brandes & Paul (1970).

Synonym

Mildes Mosaik des Knaulgrases (Rev. appl. Mycol. 48: 507)

An RNA-containing virus with isometric particles 25 to 30 nm in diameter. It is readily transmissible by sap inoculation, whereas transmission by the aphid Myzus persicae is poor. It infects species in the Gramineae only, and is widespread in the German Federal Republic.

Main Diseases

Causes mild mosaic in most naturally infected hosts.

Geographical Distribution

Found in the German Federal Republic.

Host Range and Symptomatology

Infected 24 out of 37 species of Gramineae, but none of 8 species of Solanaceae, Chenopodiaceae, or Aizoaceae. The host plant found naturally infected was Dactylis glomerata.

Diagnostic species

Lolium persicum. Initial symptom is chlorotic mottle followed by systemic necrosis and death.

Setaria italica. Diffuse mild mosaic 7 days after inoculation (Fig.2).

Dactylis glomerata. Diffuse mild mosaic or mottle (Fig.1); sometimes strong chlorotic streaking.

Propagation species

Setaria italica is a useful source of virus for purification.

Assay species

No local lesion host found. Systemic assays may be done in Lolium persicum or Setaria italica.

Strains

In addition to the type strain, two other strains have been found in Lolium perenne and Festuca pratensis respectively; these species are immune to the type strain (W. Huth, unpublished).

Transmission by Vectors

The virus is transmitted inefficiently by the aphid Myzus persicae. Possible vectors of other kinds were not tested.

Transmission through Seed

None found.

Transmission by Dodder

Not tested.

Serology

The virus is strongly immunogenic; antisera with titres of 1/1024 in agar gel double diffusion tests are easily obtained.

Relationships

The virus is serologically related to phleum mottle virus and resembles it in some other properties (Paul & Huth, 1970 and unpublished; R. Bercks & G. Querfurth, unpublished). The degree of relatedness is not yet determined. Surprisingly, both viruses show a very distant serological relationship to tobacco mosaic virus and related viruses; furthermore, a very distant relationship was found between cocksfoot mild mosaic virus and viruses of the turnip yellow mosaic virus group (Bercks & Querfurth, 1971 and unpublished).

Stability in Sap

In crude leaf extracts of Setaria italica the thermal inactivation point (10 min) is 80-85°C; the dilution end-point is c. 5 x 10-5; and infectivity is retained at -20°C for up to 5 years.

Purification

The virus is stable and occurs in high concentration in sap of Setaria italica, from which it is easily purified by adding n-butanol to 8% (v/v) allowing the mixture to stand overnight at 4°C and removing the insoluble material. The virus is further purified and concentrated by several cycles of differential centrifugation.

Properties of Particles

Sedimentation coefficient (s20,w) at infinite dilution 105±1 S (determined at both pH 7.2 and 6.6).

Molecular weight (daltons): c. 5.5 x 106.

Diffusion coefficient (D20,w x 10-7 cm2 sec-1): c. 1.5.

Partial specific volume (calculated): 0.69-0.70 ml/g.

Electrophoretic mobility: in 0.002 M Tris, 0.1 M H3BO3, 0.001 M disodium ethylenediamine-tetraacetate, pH 7.8, the virus migrates rapidly as one band towards the anode.

A260/A280: 1.62±0.02, corrected for light-scattering.

Particle Structure

The particles are isometric, 25-30 nm in diameter (Fig.3). Some particles seem to have a hexagonal outline. No empty particles are evident, but penetration by the stain is variable.

Particle Composition

RNA: Molar percentages of bases (±0.3): G26.6; A23.4; C28.4; U21.6. RNA content of particles c. 23.5%.

Protein: the subunits have a M. Wt of 24,900 (H. L. Paul, unpublished).

Relations with Cells and Tissues

No information.

Notes

The only known spherical viruses occurring in cocksfoot are cocksfoot mild mosaic and cocksfoot mottle. These can be distinguished by host plants, serology and some particle properties (Catherall, 1970).

Cocksfoot mild mosaic and phleum mottle viruses are serologically related, but they have distinct host ranges: the type strain of cocksfoot mild mosaic virus does not infect Phleum pratense and phleum mottle virus does not infect Dactylis glomerata.

References

  1. Bercks & Querfurth, Phytopath. Z. 72: 354, 1971.
  2. Catherall, CMI/AAB, Descriptions of Plant Viruses 23, 3 pp., 1970.
  3. Huth, Phytopath. Z. 62: 300, 1968.
  4. Huth, Brandes & Paul, Phytopath. Z. 68: 367, 1970.
  5. Paul & Huth, Phytopath. Z. 69: 1, 1970.

Acknowledgements

Photographs courtesy of Biologische Bundesanstalt, Braunschweig.


Figure 1

Dactylis glomerata: (left) healthy leaf, (centre and right) systemically infected leaves.

Figure 2

Setaria italica: (left) healthy leaf, (centre and right) systemically infected leaves.

Figure 3

Virus particles from a purified preparation, stained with phosphotungstate. Bar represents 100 nm.