Red clover vein mosaic virus

Anupam Varma
Division of Mycology and Plant Pathology, Indian Agricultural Research Institute, New Delhi-12, India

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 Osborn (1937).

Selected synonyms:

Marmor trifolii (Rev. appl. Mycol. 28: 514)

? Pea streak virus 1 (Rev. appl. Mycol. 17: 220)

Trifolium virus 2 (Rev. appl. Mycol. 19: 230)

Wisconsin pea stunt virus (Rev. appl. Mycol. 30: 419 and 31: 98)

An RNA-containing virus with tubular particles about 645 nm long and 12 nm wide. Most of its hosts are legumes. Easily transmissible by sap inoculation and by aphids in the non-persistent manner.

Main Diseases

Causes vein mosaic, mosaic, streaking and stunting in various legumes (Fig.1, Fig.2 and Fig. 4).

Geographical Distribution

Widely distributed in Europe, North America and South Africa.

Host Range and Symptomatology

Host range is restricted to Amaranthaceae, Chenopodiaceae, Leguminosae and Solanaceae.

Diagnostic species

Various species have been used (Gibbs, Varma & Woods, 1966; Sänder, 1959; Stuteville & Hanson, 1965; Varma & Gibbs, 1967).

Chenopodium amaranticolor and C. quinoa. Some isolates give chlorotic lesions; not systemic.

Gomphrena globosa. Purple spreading local lesions (Fig.3); systemic in plants kept in dark for 2 days before inoculation (Wilcoxson & El-Kandelgy, 1966).

Pisum sativum (pea). Plants are stunted, and show vein chlorosis and curling of young leaves (Fig.1 and Fig.4). No symptoms appear in winter.

Trifolium dubium, T. hybridum and Melilotus alba. Systemic vein clearing and mild mottle.

T. pratense (red clover). Vein mosaic and mottle in young leaves of plants in open; mild symptoms in glasshouse (Fig.2).

Vicia faba (broad bean). Chlorotic mottle in tip leaves. Symptomless in winter.

V. sativa (common vetch). Brown necrotic local lesions; sometimes systemic.

Propagation species

Trifolium pratense and T. repens are useful hosts for maintaining cultures; Pisum sativum is a good source of virus for purification.

Assay species

Chenopodium amaranticolor (for some isolates) and Gomphrena globosa can be used as local lesion hosts.

Strains

Only minor variants have been distinguished. Zaumeyer, Goth & Ford (1964) identified a strain P42 differing from the common strain in producing streak in Pisum sativum and Vicia faba var. minor and being latent in Trifolium pratense. Gibbs et al. (1966) distinguished isolates infecting and not infecting Chenopodium amaranticolor.

Transmission by Vectors

Transmitted by the following aphid species: Acyrthosiphon pisum, Therioaphis ononidis, Myzus persicae (Graves & Hagedorn, 1956; Hagedorn, Bos & van der Want, 1959), Cavariella aegopodii and C. theobaldi. It is transmitted in the non-persistent manner, is acquired by the vectors in less than 2 min and inoculated in less than 5 min. Starving the aphids before the acquisition feed aids transmission. Transmission by vectors is not very efficient.

Transmission through Seed

Not common. Seed-borne in Trifolium pratense (Matsulevich, 1957) and Vicia faba (Sänder, 1959).

Serology

The virus is a good immunogen. Tube precipitation tests, in which the virus gives flocculent precipitates, are the most reliable. Chloroplast agglutination can also be used. Virus preparations treated with ultrasonic vibrations give specific bands of precipitate in gel diffusion tests using 0.7% agar-gel buffered with neutral 0.06 M diaminoethane-tetraacetate/borate buffer (Varma, Gibbs & Woods, 1970).

Relationships

Isolates of the virus from England, Germany, the Netherlands and the USA are serologically similar (Varma et al., 1970; Wetter, Quantz & Brandes, 1962). The virus is distantly serologically related to cactus 2, carnation latent, chrysanthemum B, passiflora latent, potato M, and potato S viruses, and closely serologically related to pea streak virus. It is also reported to be serologically related to muskmelon vein necrosis virus (Freitag & Milne, 1970).

Stability in Sap

The virus, in extracts of infected pea, is inactivated when heated for 10 min at between 60°C and 65°C, stored 24 hr at 20°C or diluted beyond 10^-3.

Purification

Several methods are satisfactory. One (Varma et al., 1970) is to triturate fresh or frozen inoculated and systemically infected leaves of peas (harvested 15-25 days after inoculation of the plants) with twice their weight of neutral phosphate-ascorbate buffer. Emulsify with a quarter volume of chloroform. Centrifuge at low speed and collect the aqueous phase. Sediment the virus from this at 76,000 g for 90 min. Resuspend in neutral 0.005 M borate buffer. Purify either by rate zonal centrifugation in sucrose gradients or by restricted diffusion chromatography in agar gel. Purified virus is best stored in 0.005 M borate buffer.

Properties of Particles

Sedimentation coefficient (s_20,w) at infinite dilution: 160 S; no accessory component (Varma et al., 1970).

Isoelectric point: about pH 4.5.

A₂₆₀/A₂₈₀: 1.14.

Ultraviolet radiation inactivates the virus; some of the damage is photoreactivable (Varma et al., 1970).

Particle Structure

Particles are straight or slightly curved tubular filaments about 12 nm wide with a modal length of 645 nm (Fig.5). Phosphotungstate penetrates the particles revealing an axial canal about 3.5 nm wide. Particles stained with uranyl formate show helically arranged subunits; grooves between the subunits and almost parallel to the long axis of the particle are more distinct than those of the basic helix. About 10 subunits per turn of the basic helix of pitch 3.4 nm (Varma et al., 1968; 1970).

Particle Composition

RNA: Single-stranded, about 6.25% of particle weight. Molar percentage of nucleotides G 31; A 24; C 23; U 22 (Varma et al., 1970).

Protein: About 93.75% of particle weight. About 2000 subunits per particle.

Relations with Cells and Tissues

Crystalline and amorphous inclusions are found in pea and in leaf hairs of red clover. X-bodies, bundles of particles and rings of coiled particles are observed in ultrathin sections (Rubio-Huertos, 1964; Sänder, 1959).

Notes

The virus resembles (Wisconsin) pea streak virus but can be distinguished by particle length, serology and reactions in Gomphrena globosa and Vicia sativa; (Wisconsin) pea streak virus has particles c. 620 nm long (Wetter et al., 1962) and produces local lesions in the above hosts more quickly than does red clover vein mosaic virus (Stuteville & Hanson, 1965).

References

1. Freitag & Milne, Phytopathology 60: 166, 1970.
2. Gibbs, Varma & Woods, Ann. appl. Biol. 58: 231, 1966.
3. Graves & Hagedorn, Phytopathology 46: 257, 1956.
4. Hagedorn, Bos & van der Want, Tijdschr. PlZiekt. 65: 13, 1959.
5. Matsulevich, Agrobiology, Moscow 2: 75, 1957.
6. Osborn, Phytopathology 27: 1051, 1937.
7. Rubio-Huertos, Microbiologia esp. 17: 1, 1964.
8. Sänder Phytopathology 49: 748, 1959.
9. Stuteville & Hanson, Phytopathology 55: 336, 1965.
10. Varma, Gibbs, Woods & Finch, J. gen. Virol. 2: 107, 1968.
11. Varma, Gibbs & Woods, J. gen. Virol. 8: 21, 1970.
12. Varma, P. & Gibbs, Ann. appl. Biol. 59: 23, 1967.
13. Wetter, Quantz & Brandes, Phytopath. Z. 44: 151, 1962.
14. Wilcoxson & El-Kandelgy, Phytopathology 56: 364, 1966.
15. Zaumeyer, Goth & Ford, Pl. Dis. Reptr 48: 494, 1964.

Figure 1

Systemic infection in tip leaves of Pisum sativum. cv. Lincoln.

Figure 2

Mild vein mosaic in systematically infected leaf of Trifolium pratense.

Figure 3

Local lesions in inoculated leaf of Gomphrena globosa.

Figure 4

Necrosis and rosetting of systematically infected P. sativum cv. Big Ben.

Figure 5

Virus particles stained with phosphotungstate. Bar represents 200 nm.