29
October 1970
Family: Secoviridae
Genus: Comovirus
Species: Broad bean stain virus
Acronym: BBSV


Broad bean stain virus

A. J. Gibbs
John Curtin School of Medical Research, Australian National University, Canberra, Australia

Helen G. Smith
Little Paddock, Kirklington, Newark, Nottinghamshire, England

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 Lloyd, Smith & Jones (1965) and Gibbs, Giussani-Belli & Smith (1968).

Synonym:

Broad bean Evesham stain virus (Rev. appl. Mycol. 44: 3213)

A virus with angular isometric RNA-containing particles, about 25 nm in diameter, which sediment as three components when centrifuged. It is readily transmitted by inoculation of sap and is seed-borne, but no specific vector has been found. It seems to infect only legumes, and occurs in Europe and North Africa.

Main Diseases

Infects broad bean plants (Vicia faba) causing chlorotic mottling and mosaic of the leaves (Fig.1, Fig.2), and necrotic staining of the seed testa (Fig.3).

Geographical Distribution

Europe and North-West Africa.

Host Range and Symptomatology

Hosts restricted to Leguminosae; Gibbs et al. (1968) inoculated 44 species in 19 dicotyledonous families, but the virus infected only 7 species of legume: Crotalaria spectabilis, Lupinus hirsutus, Melilotus alba, Phaseolus vulgaris (French bean), Pisum sativum (pea), Trifolium incarnatum (crimson clover) and Vicia faba (broad bean).

Diagnostic species

Phaseolus vulgaris. Varieties Tendergreen and Canadian Wonder show chlorotic local lesions, and a systemic chlorotic mosaic. The Prince is infected only locally, and Pinto, Idaho Refugee, Blue Lake and Tendercrop not at all.

Pisum sativum. All varieties tested are susceptible, and develop a systemic chlorotic mottle, with stem and leaf necrosis in cool weather.

Chenopodium amaranticolor, Gomphrena globosa, Nicotiana tabacum (tobacco) and N. clevelandii are not susceptible. >

Propagation species

Pisum sativum Onward, Phaseolus vulgaris cv. Tendergreen and Vicia faba.

Assay species

Phaseolus vulgaris cv. Tendergreen, in which the virus gives local lesions, and Vicia faba, which is infected systemically.

Strains

None reported.

Transmission by Vectors

Vector not known, though the virus spreads over large distances within crops (Gibbs et al., 1968).

Transmission through Seed

Common in certain varieties of broad bean, transmitted to up to 10% of the progeny of infected plants.

Transmission by Dodder

Not tested.

Serology

Moderately immunogenic. Gives a single band of precipitate in Ouchterlony gel diffusion tests, and a granular precipitate in tube tests.

Relationships

The physical and chemical properties of the particles of this virus resemble those of cowpea mosaic virus. It is distantly serologically related to red clover mottle virus, F1 virus, and cowpea mosaic virus (Devergne, 1965, 1966; Gibbs et al., 1968; Valenta & Gressnerova, 1966).

Stability in Sap

In broad bean sap the thermal inactivation point (10 min) is between 60° and 65°C. Infectivity survives at least 31 days at 4°C and more than one year at -15°C. The dilution end-point in sap from leaves showing obvious symptoms is somewhat variable but usually around 10-3.

Purification

The virus particles are stable and Steere’s butanol/chloroform method may be used to extract them from plant tissue into a pH 7.0 buffer containing a reducing agent. They may then be sedimented and purified by differential centrifugation (Gibbs et al., 1968).

Properties of Particles

The particles are all the same size but sediment as three components (Fig.4). Sedimentation coefficients (s20,w) are about 60, 100 and 127 S.

Particle Structure

Particles are isometric, about 25 nm in diameter with angular polygonal outlines (Fig.5). The 60 S particles are penetrated by negative stain, and then show a central cavity with a surrounding shell 2.0-2.5 nm thick. The 100 S particles are partially penetrated by stain, and the 127 S particles not at all. The particles show no regularly arranged morphological subunits.

Particle Composition

RNA: Probably single-stranded. Molar percentages of nucleotides: G23.3; A26.5; C18.4; U31.9. Their sedimentation coefficients suggest that the 127 S particles contain about 35% RNA, and the 100 S particles about 25%; the 60 S particles contain none.

Protein. The size and composition of the protein subunits are not yet known.

Relations with Cells and Tissues

No information.

Notes

Readily confused with Echtes Ackerbohnemosaik-Virus, because both viruses cause similar leaf symptoms in broad bean, are seed-borne, and have similar particles. However, Echtes Ackerbohnemosaic-Virus rarely infects Phaseolus vulgaris, is serologically unrelated to broad bean stain virus, and preparations of its particles contain few or no (60 S) RNA-free particles (Fig.5).

References

  1. Devergne, Annls Épiphyt. 16: 41, 1965.
  2. Devergne, Annls Épiphyt. 17: 147, 1966.
  3. Gibbs, Giussani-Belli & Smith, Ann. appl. Biol. 61: 99, 1968.
  4. Lloyd, Smith & Jones, Hort. Res. 5: 13, 1965.
  5. Valenta & Gressnerova, Acta virol., Prague 10: 182, 1966.

Acknowledgements

Photographs: courtesy of Rothamsted Experimental Station, UK.


Figure 1

Broad bean (Vicia faba) plant infected with broad bean stain virus through the seed.

Figure 2

Two systemically infected broad bean leaves.

Figure 3

Seeds of infected broad beans showing the characteristic brown necrosis of the testa around the periphery of the seed.

Figure 4

Sedimentation behaviour of the virus (upper schlieren diagram) compared with that of Echtes Ackerbohnemosaik-Virus (lower diagram); sedimentation is from left to right (note that the menisci of the two diagrams are displaced).

Figure 5

Electron micrograph of a phosphotungstate-stained purified preparation of the virus. Bar represents 100 nm.