190
August 1978
Family: Potyviridae
Genus: Potyvirus
Species: Guinea grass mosaic virus
Acronym: GGMV


Guinea grass mosaic virus

J.-C. Thouvenel
Laboratoire de Virologie, ORSTOM-Adiopodoumé, B.P. V51-Abidjan, Côte d'Ivoire

C. Fauquet
Laboratoire de Virologie, ORSTOM-Adiopodoumé, B.P. V51-Abidjan, Côte d'Ivoire

D. Lamy
Laboratoire de Virologie, ORSTOM-Adiopodoumé, B.P. V51-Abidjan, Côte d'Ivoire

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 Thouvenel, Givord & Pfeiffer (1976).

A virus with flexuous, filamentous particles c. 815 nm long. It is readily transmitted by inoculation of sap to plants in a few tribes of Gramineae. It is probably restricted to tropical areas in Africa. No vector is known.

Main Diseases

Causes dwarfing and light-green mosaic in Panicum maximum (Guinea grass) (Fig.1) cultivated as a forage crop.

Geographical Distribution

Widespread wherever Guinea grass is grown in Ivory Coast.

Host Range and Symptomatology

Host range restricted to the Paniceae, Maydeae and Bromeae tribes of the family Gramineae. Mechanically transmissible to the following:

Diagnostic species
Panicum maximum (Guinea grass). General dwarfing and light green mosaic. On some cultivars e.g. K189, light green eyespots are the first systemic symptom; later, they anastomose to form a striped mosaic (Fig.2). Other cultivars e.g. K187 seem to be tolerant.

Setaria italica (Italian ryegrass). Systemic chlorotic elongated spots one week after inoculation, followed by mottle.

Zea mays (maize). Dwarfing; light green mosaic appearing on the new leaves.

Propagation species
S. italica is a useful host for maintaining cultures.

P. maximum cv. K189 is a good source of virus for purification.

Assay species
S. italica is a good systemic assay host. No local lesion host is known.

Strains

A strain from maize differs somewhat from Guinea grass strains in host range and is serologically distinguishable (D. Lamy, unpublished data).

Transmission by Vectors

Aphid transmission suspected but not established. No transmission to Panicum maximum, Setaria italica or Zea mays was obtained using Rhopalosiphum maidis, Hysteroneura setariae, Aphis spiricola or A. gossypii.

Transmission through Seed

Not seed-borne in P. maximum or S. italica.

Transmission by Dodder

Dodder (Cuscuta subinclusa) did not parasitize Guinea grass.

Serology

The virus is moderately immunogenic. Rabbit antisera with titres of 1/2048 were obtained after six intramuscular injections of purified virus emulsified with Freund’s incomplete adjuvant. Microprecipitin tests were used, because intact virus particles do not diffuse in agar gel.

Relationships

Serologically moderately closely related to pepper veinal mottle virus (Ivory Coast and Ghana strains), to dioscorea mosaic virus (Thouvenel & Fauquet, 1977 and unpublished results) and a tobacco virus from Kenya (E. J. Guthrie, personal comm.). Not related to sugarcane mosaic virus.

Stability in Sap

Infectivity in Guinea grass sap is lost after 10 min at 50°C; dilution end-point is 10-3. Sap stored at 24°C lost infectivity within a few h; it remained infective at 4°C for 24 h. Frozen diseased leaves of Guinea grass remained infective for 2 weeks.

Purification

A combination of the methods described by Damirdagh & Shepherd (1970) and Van Oosten (1972) is useful. Grind Guinea grass leaves in phosphate buffer (pH 7.5) containing 1 M urea and 1% sodium bisulphite and clarify by treating with 5% Triton X-100 for 30 min.

Purified virus is obtained after one cycle of high and low speed centrifugation, followed by ultracentrifugation through 8 ml of 20% sucrose. Finally resuspend the pellet in 0.05 M borate buffer (pH 8.2). Preparations can be further purified by centrifuging in 10-40% sucrose density gradients in which the virus forms a single light-scattering zone. Infected P. maximum leaves yield c. 25 mg virus per kg.

Properties of Particles

Isoelectric point: about pH 4.7; the virus is precipitated at this point (unpublished data).


A260/A280: 1.22 ± 0.02 (not corrected for light-scattering).


Amax(260)/Amin(247): 1.10 ± 0.02.

Particle Structure

Particles are flexuous filaments about 815 nm long and 15 nm in diameter (Fig.3). After exposure to 0.05 M MgCl2 the particles become straighter (Fig.4), a feature characteristic of several viruses in the potyvirus group (Govier & Woods, 1971).

Particle Composition

Nucleic acid: comprises c. 6% of particle weight (estimated spectrophotometrically).

Protein: A major protein of M. Wt 35,000, estimated by SDS-polyacrylamide gel electrophoresis, with a minor component of M. Wt 32,000 (unpublished results). Probably the second component is a degradation product as observed for other potyviruses (Huttinga, 1975).

Relations with Cells and Tissues

No information.

Notes

Although no aphid vector has been found, Guinea grass mosaic virus has been classified in the potyvirus group on the basis of the size and morphology of its particles and its serological relationship to pepper veinal mottle virus and other members of the potyvirus group.

References

  1. Damirdagh & Shepherd, Phytopathology 60: 132, 1970.
  2. Govier & Woods, J. gen. Virol. 13: 127, 1971.
  3. Huttinga, Neth. J. Pl. Path. 81: 58, 1975.
  4. Thouvenel & Fauquet, C.r. hebd. Séanc. Acad. Sci., Paris 284: 1947, 1977.
  5. Thouvenel, Givord & Pfeiffer, Phytopathology 66: 954, 1976.
  6. Van Oosten, Neth. J. Pl. Path. 78: 33, 1972.


Figure 1

Naturally infected Guinea grass (Panicum maximum) cv. K 189.

Figure 2

(Left) Infected leaf of Guinea grass cv. K 189 showing the characteristic mosaic. (Right) Healthy leaf.

Figure 3

Particles from a purified preparation, negatively stained with 1% uranyl acetate. Bar represents 200 nm.

Figure 4

Particles in 0.05 M MgCl2, stained with 1% uranyl acetate. Bar represents 200 nm.