86
June 1972
Family: Potyviridae
Genus: Rymovirus
Species: Ryegrass mosaic virus
Acronym: RGMV


Ryegrass mosaic virus

J. T. Slykhuis
Ottawa Research Station

Y. C. Paliwal
Chemistry and Biology Research Institute, Research Branch, Canada Department of Agriculture, Ottawa, Ontario, Canada

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

First reported by Bruehl, Toko & McKinney (1957).

Synonym

Ryegrass streak mosaic virus (Rev. appl. Mycol. 36: 812). American Type Culture Collection No. PV 96
The Weidelgrasmosaik-Virus (ryegrass mosaic virus) of Ohmann-Kreutzberg (1963), also called ryegrass streak virus (Proll & Schmidt, 1964), is a strain of brome mosaic virus (Proll & Richter, 1965)

A virus with filamentous particles c. 700 nm long and 15 nm in diameter infecting only species of Gramineae. It has been found naturally in Lolium multiflorum, L. perenne and Dactylis glomerata. It is sap-transmissible and has been transmitted by eriophyid mites.

Main Diseases

Causes light green to yellow mosaic on Lolium spp. (Fig.1) and Dactylis glomerata. Some strains of Lolium multiflorum in England were severely damaged by the disease (Slykhuis, 1958).

Geographical Distribution

USA (Bruehl et al., 1957), UK (Slykhuis, Watson & Mulligan, 1957), Canada (Slykhuis, 1964).

A report of ryegrass (streak) mosaic on ryegrass in several countries in northern Europe in 1957 (Slykhuis, 1958) was based only on symptoms, except for the British records, which were based on symptoms, transmission tests and virus properties. In East Germany, mosaic symptoms in ryegrass were later found to be caused by a strain of brome mosaic virus (Ohmann-Kreutzberg, 1963; Proll & Richter, 1965), or by a virus with flexuous particles suspected to be cocksfoot streak virus (Schumann & Brcák, 1963).

Host Range and Symptomatology

Only members of the Gramineae have been reported to be susceptible. Isolates from the USA, UK and Canada are transmissible to Lolium multiflorum, L. perenne, Dactylis glomerata, Avena fatua, A. sativa, Agrostis scabra, Bromus arvensis and Poa annua, usually causing light green mosaic on most hosts. Cynosurus cristatus was infected with isolates from Britain and Canada. In addition, the USA strain was claimed to infect Bromus commutatus, B. mollis, B. racemosus, B. secalinus, B. tectorum, Festuca elatior, Hordeum leporinum, Lolium remotum, L. temulentum and Michigan Amber wheat, but there was no report that the virus was recovered from these species (Bruehl et al., 1957). The British strain was transmitted to and recovered from Alopecurus agrestis, Bromus sterilis, Festuca pratensis, Oryza sativa, Poa pratensis and P. trivialis, but did not infect wheat (Mulligan, 1960). Our attempts to infect several cultivars of wheat and an unidentified cultivar of Oryza sativa with the three virus isolates failed.

Diagnostic species

Systemic mosaic symptoms develop on strains of Lolium multiflorum (Fig.1), L. perenne, Dactylis glomerata and Avena sativa but rarely or never on Triticum aestivum, Hordeum vulgare, Secale cereale and Agropyron repens, which are susceptible to one or more of the other grass viruses with similar particles.

Propagation species

Italian ryegrass (Lolium multiflorum) cv. S22 is suitable for propagating the virus.

Assay species

No local lesion assay host is known. Systemic assays have been done on Italian ryegrass cv. S22.

Strains

Isolates that caused symptoms ranging in severity were obtained in England. All isolates from the USA and Canada are mild. Y. C. Paliwal (unpublished) found that under identical conditions of temperature and light, an English isolate caused more severe mosaic and necrosis on S22 Italian ryegrass than did the USA and Canadian isolates.

Transmission by Vectors

The eriophyid mite Abacarus hystrix (Fig.2) transmitted the virus in England (Mulligan, 1960). The mites acquired the virus when fed for 2 h or longer on infected ryegrass. All instars transmitted but the mites lost infectivity within 24 h after removal from a virus source. Repeated attempts to transmit the Canadian isolate with A. hystrix from Agropyron repens but reared on infected ryegrass or oats have failed (Y. C. Paliwal, unpublished).

Transmission through Seed

None reported.

Transmission by Dodder

No reports.

Serology

An antiserum with a precipitin tube titre of 1/500 was prepared by injecting a rabbit intravenously with a partially purified preparation of an English isolate from S22 Italian ryegrass. Clarified sap from infected S22 Italian ryegrass had a precipitin titre of 1/64, and sap from infected perennial ryegrass a titre of 1/32. No serological reactions were obtained with clarified sap from healthy ryegrass or from infected plants of species with less severe symptoms (Mulligan, 1960). An antiserum prepared by intramuscular injection of rabbits with partially purified preparations of the Canadian isolate had a titre of l/3840 in precipitin tube tests (Y. C. Paliwal, unpublished).

Relationships

Isolates from England, USA and Canada are closely related serologically (Y. C. Paliwal, unpublished). The particles of ryegrass mosaic virus resemble those of agropyron mosaic virus (also transmitted by Abacarus hystrix), wheat streak mosaic virus (transmitted by another eriophyid mite, Aceria tulipae), and hordeum mosaic virus (vector unknown), but no serological relationship to these viruses was detected. Unlike these three viruses, ryegrass mosaic virus does not infect wheat.

Stability in Sap

Thermal inactivation occurred in ryegrass sap after 10 min at 60°C; dilution end-point was about 10-3. The virus lost most of its infectivity during 24 h at 20°C (Mulligan, 1960).

Purification

The Canadian isolate may be partially purified from infected S22 Italian ryegrass by the following procedure: pick the leaves about 14 days after inoculating the plants, grind them and extract the juice. Wash the pulp with distilled water and add the washings to the extract. Heat the total extract for 10 min at 45°C or shake with one-third volume chloroform for 10 min, then clarify by low speed centrifugation. Purify the virus from the extract by three cycles of differential centrifugation (13,000 g for 15 min; 65,000 g for 90 min), resuspending the high-speed pellets in distilled water. Alternatively, precipitate the virus from clarified juice by adding one-third volume saturated (NH4)2SO4, mixing thoroughly and centrifuging immediately at low speed. This is followed by two cycles of differential centrifugation. When phosphate buffer was used either to dilute the juice when extracting from leaves, or to resuspend the virus after precipitation, the yield of virus in the final suspension was decreased (Y. C. Paliwal, unpublished).

Properties of Particles

No reports.

Particle Structure

Particles are flexuous filaments (Fig.3); particles of an isolate from England had a diameter of 15 nm and a normal length of 703 nm (Brandes, 1964). In negatively stained dip preparations, isolates from Canada, USA and England had average dimensions (more than 50 particles of each isolate measured) of 703 x 18, 704 x 17.5 and 675 x 18.5 nm respectively (Y. C. Paliwal, unpublished).

Particle Composition

No reports.

Relations with Cells and Tissues

Pinwheel inclusions, and bundles of virus particles (Fig.4, Fig.5), were found by electron microscopy of sections of ryegrass leaf parenchyma cells (M. James, unpublished).

Notes

In addition to the viruses mentioned under Relationships, several other viruses infect ryegrass naturally or experimentally.

Cocksfoot streak virus is transmissible to S22 Italian ryegrass by manual inoculation and by Myzus persicae, but does not infect Avena sativa. It causes symptoms similar to those produced by ryegrass mosaic virus, but is not transmitted by Abacarus hystrix and does not react with antiserum to ryegrass mosaic virus (Mulligan, 1960). It has flexuous filamentous particles c. 752 x 13 nm (Brandes, 1964). A virus found on Lolium multiflorum and L. perenne in Germany resembles cocksfoot streak virus in particle morphology and means of transmission but has a wider host range (Schumann & Brcák, 1963).

Oat necrotic mottle virus from Manitoba (Gill, 1967), and viruses we obtained from Poa spp. in Alberta and Ontario, also have filamentous particles and infect Lolium multiflorum and Avena sativa, but do not react with antiserum to ryegrass mosaic virus.

Brome mosaic virus, which causes mosaic of ryegrass in Germany (Ohmann-Kreutzberg 1963; Proll & Richter, 1965), is an isometric virus readily transmitted manually to many species of Gramineae that are not hosts of ryegrass mosaic virus (Bancroft, 1970). Seedlings of most cultivars of sweet corn (Zea mays) develop streaks followed rapidly by death. It also causes local lesions on some species of dicotyledonous plants, none of which react to ryegrass mosaic virus.

We have also transmitted barley stripe mosaic virus and poa semi-latent virus to Lolium multiflorum. These viruses have rod-shaped particles c. 133 x 25 nm and 162 x 25 nm respectively. They are readily transmitted to wheat, barley and many other grasses not susceptible to ryegrass mosaic virus, and are not related to it serologically.

References

  1. Bancroft, CMI/AAB Descriptions of Plant Viruses 3, 3 pp., 1970.
  2. Brandes, Mitt. biol. BundAnst. Ld- u. Forstw. 110, 130 pp., 1964.
  3. Bruehl, Toko & McKinney, Phytopathology 47: 517, 1957.
  4. Gill, Phytopathology 57: 302, 1967.
  5. Keifer, Bull. Calif. Insect Surv. 2, 123 pp., 1952.
  6. Mulligan, Ann. appl. Biol. 48: 575, 1960.
  7. Ohmann-Kreutzberg, Phytopath. Z. 47: 1, 1963.
  8. Proll & Richter, Naturwissenschaften 52: 145, 1965.
  9. Proll & Schmidt, Virology 23: 103, 1964.
  10. Schumann & Brcák, Phytopath. Z. 47: 90, 1963.
  11. Slykhuis, Pl. Prot. Bull. F.A.O. 6: 129, 1958.
  12. Slykhuis, Can. Pl. Dis. Surv. 44: 242, 1964.
  13. Slykhuis, Watson & Mulligan, Rep. Rothamsted exp. Stn 1956: 105, 1957.


Figure 1

Leaves of S22 Italian ryegrass infected with a virulent isolate of ryegrass mosaic virus from England. The leaf on the left is healthy.

Figure 2

The mite vector, Abacarus hystrix, dorsal and lateral views. The adult mites are about 250 µm long (Keifer, 1952).

Figure 3

Particles in potassium phosphotungstate. Bar represents 500 nm.

Figure 4

Pinwheel inclusions in sections of a parenchyma cell from a systemically infected leaf of S22 Italian ryegrass. Bar represents 250 nm. (Courtesy Dr Mari James.)

Figure 5

Bundles of virus particles in sections of a parenchyma cell from a systemically infected leaf of S22 Italian ryegrass. Bar represents 250 nm. (Courtesy Dr Mari James.)