101
October 1972
Family: Bromoviridae
Genus: Bromovirus
Species: Broad bean mottle virus
Acronym: BBMV


Broad bean mottle virus

A. J. Gibbs
Australian National University, Canberra, Australia

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 Bawden, Chaudhuri & Kassanis (1951).

A virus with RNA-containing isometric particles about 26 nm in diameter. A member of the bromovirus group. Readily transmitted by inoculation of sap to many legumes. Found in England. Vector not known.

Main Diseases

Causes a mosaic disease of broad beans.

Geographical Distribution

Found in Nottinghamshire, England, in a severely affected broad bean crop, and later in a Cambridge crop (Tinsley, 1957), but in no others despite several surveys (A. J. Cockbain, A. J. Gibbs & G. D. Heathcote, unpublished).

Host Range and Symptomatology

Host range little studied; infects most legumes tested, but only 2 of 16 non-legumes (Bawden et al., 1951; Hollings, 1959a, 1959b; Wetter et al., 1960). Causes chlorotic mosaic and vein-clearing in most hosts.

Diagnostic species

Vicia faba (broad bean). All tested cultivars are susceptible; inoculated leaves are usually symptomless, tip leaves show vein-clearing (Fig.2) and later develop characteristic blotchy mosaic (Fig.1).

Phaseolus vulgaris (French bean). All tested cultivars are susceptible; tip leaves of some, such as Canadian Wonder and Comtesse de Chambord, show bright interveinal mottle (Fig.3).

Pisum sativum (pea). Infects all cultivars, causing lethal systemic wilt.

Nicotiana clevelandii. Mild systemic mottle. N. tabacum (tobacco) is not a host.

Chenopodium amaranticolor. Chlorotic local lesions only.

Propagation species

Vicia faba or Nicotiana clevelandii.

Assay species

No satisfactory local lesion host known.

Strains

None reported.

Transmission by Vectors

None known; four aphid species and the bean weevil (Sitona lineatus) were tested (Bawden et al., 1951).

Transmission through Seed

None found in tests with Vicia faba and Phaseolus vulgaris (Bawden et al., 1951).

Transmission by Dodder

No information.

Serology

Only moderately immunogenic. Gives a granular precipitate in liquid tests, and a single band of precipitate in gel-diffusion tests; tests are best done at pH 5-6.

Relationships

No strains reported. For allied viruses, see Notes.

Stability in Sap

Infectivity of sap from broad bean plants is lost when the sap is heated for 10 min above 95°C, or when kept at 15°C for more than about 20 days, or when diluted more than about 1000-fold (Bawden et al., 1951). Sap kept at -20°C retains infectivity for more than 10 years.

Purification

The virus is easily purified. It is best extracted from fresh or frozen infected tissue by the method of Steere (1956), or by mincing the tissue into a neutral buffer containing 0.1 M of both diethyl dithiocarbamate and ascorbate and clarifying the extract with Celite (Finch, Leberman & Berger, 1967). The extracted virus is most easily purified by differential centrifugation, but can be precipitated chemically by adding ammonium sulphate to 80% saturation (Bawden et al., 1951). Store the virus in 0.1 M pH 5.0 acetate buffer (Hiebert, Bancroft & Wagner, 1968).

Properties of Particles

Sedimentation coefficient (s20, w): (84.8-0.47C) S at pH 7.0, where C is the virus concentration in mg per ml (Yamazaki, Bancroft & Kaesberg, 1961); about 6 S slower at pH 6.0 (Bancroft, 1970a). Over the pH range 5-8 in dilute salt solutions the virus is stable, infective and sediments as a single component.

Molecular weight (daltons): 4.8 x 106 (Finch & Klug, 1967).

Isoelectric point: about pH 5.6 at 0.1 ionic strength.

Electrophoretic mobility: -6.9 x 10-5 cm2 sec-1 volt-1 at pH 7.0 and 0.1 ionic strength (Yamazaki et al., 1961).

Diffusion coefficient (D20, w): 1.38-1.44 x 10-7cm2 sec-1 (Paul, 1961; Yamazaki et al., 1961).

Absorbance at 260 nm (1 mg/ml, 1 cm light path; corrected for light-scattering): 5.40.

A260/A280: 1.7.

Buoyant density: 1.395 g/ml (Yamazaki et al., 1961).

Particle Structure

Particles are isometric (Fig.4) and 26 nm in diameter. The protein shell is icosahedral, and consists of 180 identical polypeptide sub-units clustered in fives and sixes. The shell encloses the RNA but the particle has a hollow centre 10-12 nm in diameter (Finch & Klug, 1967; Finch et al., 1967). Particles dissociate in 1 M NaCl at pH 7.0, and may be re-assembled (Hiebert et al., 1968; Bancroft, 1970a).

Particle Composition

RNA: Each particle contains on average 1.1 x 106 daltons of single-stranded RNA; however, unfractionated purified virus preparations yield RNA molecules of at least three sizes: 1.1, 1.0 and 0.3 million daltons (Fowlks & Young, 1970). Molar percentages of nucleotides: G25; A27; C19; U29. RNA is about 22% of the particle weight.

Protein: Sub-units contain about 193-198 amino acid residues and have a molecular weight around 21,000 daltons (Wittman & Paul, 1961; Yamazaki & Kaesberg, 1963; Miki & Knight, 1965; Gibbs & McIntyre, 1970).

Relations with Cells and Tissues

Cells in chlorotic areas of leaves of infected Vicia faba contain amorphous inclusions (Fig.5); in recently infected cells the inclusions are small and granular, but later vacuolate and enlarge to become several times the size of the nuclei. The inclusions seem to consist mostly of virus particles (Rubio & van Slogteren, 1956).

Notes

This virus is a member of the bromovirus group (Harrison et al., 1971); two other members of this group, brome mosaic and cowpea chlorotic mottle viruses (Bancroft, 1970b, 1971a), seem more similar to each other than either is to broad bean mottle virus, not only in the chemical composition of their particles but also in that they are distantly serologically related to each other but not to broad bean mottle virus (Scott & Slack, 1971). Moreover, in particle re-assembly experiments, mixtures of their protein sub-units formed hybrid particles more readily than did mixtures of either protein with that from broad bean mottle virus (Wagner & Bancroft, 1971).

Particles of brome mosaic and cowpea chlorotic mottle viruses contain RNA molecules of four different sizes (about 1.1, 1.0, 0.7 and 0.3 million daltons); only mixtures containing the three largest are infective (i.e. the viral genome is in three pieces) (Lane & Kaesberg, 1971; Bancroft, 1971b, 1972). Probably the same is true of broad bean mottle virus; this would account for its low specific infectivity (Bawden et al., 1951).

Broad bean mottle virus is easily distinguished from other legume viruses by its characteristic symptoms in broad beans and peas, its inability to infect Nicotiana tabacum, its resistance to heating, and in having isometric particles that sediment as a single component and are degraded in 1 M NaCl or CaCl2 solutions.

References

  1. Bancroft, Adv. Virus Res. 16: 99, 1970a.
  2. Bancroft, CMI/AAB Descriptions of Plant Viruses 3, 3 pp., 1970b.
  3. Bancroft, CMI/AAB Descriptions of Plant Viruses 49, 4 pp., 1971a.
  4. Bancroft, Virology 45: 830, 1971b.
  5. Bancroft, J. gen. Virol. 14: 223, 1972.
  6. Bawden, Chaudhuri & Kassanis, Ann. appl. Biol. 38: 774, 1951.
  7. Finch & KIug, J. molec. Biol. 24: 289, 1967.
  8. Finch, Leberman & Berger, J. molec. Biol. 27: 17, 1967.
  9. Fowlks & Young, Virology 42: 548, 1970.
  10. Gibbs & McIntyre, J. gen. Virol. 9: 51, 1970.
  11. Harrison, Finch, Gibbs, Hollings, Shepherd, Valenta & Wetter, Virology 45: 356, 1971.
  12. Hiebert, Bancroft & Wagner, Virology 34: 492, 1968.
  13. Hollings, Pl. Path. 8: 133, 1959a.
  14. Hollings, Ann. appl. Biol. 47: 98, 1959b.
  15. Lane & Kaesberg, Nature, Lond. 232: 40, 1971.
  16. Miki & Knight, Virology 25: 478, 1965.
  17. Paul, Z. Naturf. B 16: 786, 1961.
  18. Rubio & van Slogteren, Phytopathology 46: 401, 1956.
  19. Scott & Slack, Virology 46: 490, 1971.
  20. Steere, Phytopathology 46: 60, 1956.
  21. Tinsley, Rep. Rothamsted exp. Stn 1956: 98, 1957.
  22. Wagner & Bancroft, Virology 45: 321, 1971.
  23. Wetter, Paul, Brandes & Quantz, Z. Naturf. B 15: 444, 1960.
  24. Wittmann & Paul, Phytopath. Z. 41: 74, 1961.
  25. Yamazaki, Bancroft & Kaesberg, Proc. natn. Acad. Sci. USA 47: 979, 1961.
  26. Yamazaki & Kaesberg, J. molec. Biol. 6: 465, 1963.


Figure 1

Blotchy mosaic in systemically infected leaves of Vicia faba some weeks after infection.

Figure 2

Vein-clearing in tip leaves of recently infected V. faba.

Figure 3

Systemically infected leaf of Phaseolus vulgaris (Canadian Wonder Improved).

Figure 4

Purified virus preparation in uranyl acetate. Bar represents 100 nm.

Figure 5

Amorphous inclusion in epidermal cell of Vicia faba. The inclusion is larger than the adjacent nucleus.