Details of DPV and References

DPV NO: 25 October 1970

Family: Luteoviridae

Genus: Enamovirus

Species: Pea enation mosaic virus | Acronym: PEMV

RNA1 is now PEMV-1 (Genus Enamovirus); RNA2 is PEMV-2 (Genus Umbravirus);
there is a more recent description of this virus: DPV 257

Pea enation mosaic virus

R. J. Shepherd Department of Plant Pathology, University of California, Davis, California, USA

Contents

Introduction

Described by Osborn (1935).

Selected synonyms

Enation pea mosaic virus (Stubbs, 1935)

Pea virus 1 (Rev. appl. Mycol. 15: 418)

Pisum virus 1 (Smith, 1937)

An RNA-containing virus with isometric particles about 30 nm in diameter. The virus has a restricted host range, is easily transmissible by mechanical means, and by aphids in a persistent manner. It is widely distributed in temperate regions.

Main Diseases

Causes common diseases of broad bean, garden pea and sweet pea. Infected plants develop mosaic, translucent spots, and enations.

Geographical Distribution

Widely distributed in northern temperate regions.

Host Range and Symptomatology

Host range of the virus is narrow. Though it infects many legumes (Hagedorn, Layne & Ruppel, 1964; McEwan & Schroeder, 1956), few species in other families are susceptible. It infects Nicotiana clevelandii systemically and induces local lesions in Chenopodium album, C. amaranticolor and C. quinoa.

Diagnostic species

Pisum sativum (garden pea), Trifolium incarnatum (crimson clover), and Vicia faba (broad bean). Systemically infected leaves show conspicuous, hyaline, translucent spots (‘windows’), mosaic patterns, and, frequently, small necrotic flecks and streaks (Fig. 1, Fig. 2). Chronically infected plants generally develop enations associated with the veins on undersides of leaves (Hagedorn et al., 1964; Quantz, 1952) (Fig. 3).

Propagation species

Garden peas contain the highest virus concentration 10-12 days after mechanical inoculation when plants are grown at 18-22°C (Izadpanah & Shepherd, 1966).

Assay species

The chenopodiaceous species that give local lesions can be used for assay, though not all seed stock of these species gives suitable local lesions.

Strains

Isolates from different geographical areas differ in host range, symptomatology, and properties in vitro (Ruppel & Hagedorn, 1963; McWhorter & Cook, 1958). Strains commonly differ in ease of mechanical transmission. Divergent types arise when isolates are transmitted solely by aphids or by mechanical inoculation (Osborn, 1938).

Transmission by Vectors

Transmissible by 5 of more than 20 species of aphids tested (Kennedy, Day & Eastop, 1962), including Acyrthosiphon pisum and Myzus persicae. All instars transmit, nymphs more efficiently than adults. Nymphs can acquire virus in 15 min, adults in 1-2 h; all exhibit a temperature-dependent latent period of 4-70 h (Osborn, 1935; Sylvester, 1965; Sylvester & Richardson, 1966). After the latent period, insects can inoculate plants in 1-2 min (Nault, Gyrisco & Rochow, 1964). The virus can be retained by moulting individuals up to 30 days but most cease to transmit within a few days. Not transmitted to progeny. Multiplication in insects uncertain.

Transmission through Seed

Not known to be seed-borne.

Serology

The virus is not strongly immunogenic in rabbits. It diffuses well through agar gels and two specific precipitin bands may be obtained. Sap from recently infected plants contains a rapidly diffusing virus protein which may precipitate in double-diffusion tests. Chronically infected plants may contain too little virus for positive reactions in agar gels. Specific precipitates in liquid are of the granular (somatic) type.

Relationships

No serologically related viruses have been reported.

Stability in Sap

In sap of Vicia faba the thermal inactivation temperature (10 min) is about 65°C, dilution end-point 10^-4 and longevity at 20°C 4 days (Osborn, 1938).

Purification

Inoculate young pea plants with a highly infectious extract and collect material 10-12 days after inoculation to insure that sufficient virus is present to make purification practical. Chronically infected plants contain very little virus. The following method for purification (Izadpanah & Shepherd, 1966; Shepherd, Wakeman & Ghabrial, 1968) frequently yields 0.1-0.3 mg virus per g infected material:

Blend pea tissue in 0.2 M acetate buffer (pH 6.0). To clarify, adjust the homogenate to pH 5.2 and after 30 min adjust back to pH 6.0 and centrifuge at slow speed. The partially clarified supernatant is given 2-3 cycles of differential centrifugation using 0.1 M acetate, pH 6.0, as suspending fluid. The virus may be further purified by sucrose density-gradient centrifugation or further incubation of the extracts at pH 5.2 followed by additional differential cycles. Exposure to strong salt solutions (e.g. 1 M CaCl₂) degrades the virus.

Properties of Particles

Purified preparations contain two sedimenting components. It is not clear whether one or both of these is associated with infectivity (Bozarth & Chow, 1966; Gibbs, Harrison & Woods, 1966, Izadpanah & Shepherd, 1966).

Sedimentation coefficients (s_20,w): c. 100 and 120 S.

Diffusion coefficient (D_20,w): c. 1.89 x 10^-7 cm²/sec (Bozarth & Chow, 1966).

Absorbance at 260 nm (1 mg/ml, 1 cm light path): 7.5.

Buoyant density (in CsCl)= 1.42 g/cm³.

Particle Structure

Purified virus preparations appear to contain particles of two types. Though both types are isometric and about 30 nm in diameter when mounted in neutral phosphotungstate, one type appears irregular and distorted unless previously treated with 1% formaldehyde; the other type exhibits a more regular appearance (Gibbs et al., 1966). When shadowed, the two types of particle are not differentiated and both appear somewhat larger in diameter (36 nm) (Izadpanah & Shepherd, 1966). Fig. 4 shows particles mounted in uranyl acetate.

Particle Composition

Contains 2.48% phosphorus.

RNA: Single-stranded; 28% by weight of particle. Molar percentages of nucleotides G26; A24; C24; U26. (Shepherd et al., 1968). Top component estimated to contain 18% RNA (Bozarth & Chow, 1966).

Protein: 72% of particle by weight. In the particle there is a single type of protein which has a relatively large content of basic amino acids. The protein contains about 199 amino acid residues, and has a molecular weight of 21,800 (Shepherd et al., 1968).

Other components: No polyamine detected.

Relations with Cells and Tissues

In plants, large accumulations of virus occur in cell nuclei and the virus may multiply there; less virus is found in the cytoplasm and vacuoles. Virus-like particles have been observed in the cytoplasm of fat body cells of an aphid vector, Acyrthosiphon pisum (Shikata, Maramorosch & Granados, 1966; Shikata & Maramorosch, 1966).

Notes

The virus is readily distinguished from all others by its characteristic symptoms, mechanical transmissibility and persistence in its aphid vector.

Figures

References list for DPV: Pea enation mosaic virus (25)

1. Bozarth & Chow, Contr. Boyce Thompson Inst. Pl. Res. 23: 301, 1966.
2. Gibbs, Harrison & Woods, Virology 29: 348, 1966.
3. Hagedorn, Layne & Ruppel, Phytopathology 54: 843, 1964.
4. Izadpanah & Shepherd, Virology 28: 463, 1966.
5. Kennedy, Day & Eastop, A conspectus of aphids as vectors of plant viruses, London, Commonwealth Institute of Entomology, 1962.
6. McEwan & Schroeder, Pl. Dis. Reptr 40: 11, 1956.
7. McWhorter & Cook, Pl. Dis. Reptr 42: 51, 1958.
8. Nault, Gyrisco & Rochow, Phytopathology 54: 1269, 1964.
9. Osborn, Phytopathology 25: 160, 1935.
10. Osborn, Phytopathology 28: 923, 1938.
11. Quantz, NachrBl. dt. PflSchutzdienst (Braunschw.), Stuttg. 4: 24, 1952.
12. Ruppel & Hagedorn, Phytopathology 53: 813, 1963.
13. Shepherd, Wakeman & Ghabrial, Virology 35: 255, 1968.
14. Shikata, Maramorosch & Granados, Virology 29: 426, 1966.
15. Shikata & Maramorosch, Virology 30: 439, 1966.
16. Smith, Textbook of Plant Virus Diseases, London, Churchill, 1937.
17. Stubbs, Viruses of the garden pea (Pisum sativum), Ph.D. thesis, Univ. Wisc., 1935.
18. Sylvester, Virology 25: 62, 1965.
19. Sylvester & Richardson, J. econ. Ent. 59: 255, 1966.