20
June 1970
Family: Secoviridae
Genus: Comovirus
Species: Broad bean true mosaic virus
Acronym: BBTMV


Echtes Ackerbohnemosaik virus

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

H. L. Paul
Institut für Landwirtschaftliche Virusforschung, Braunschweig, Germany

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 Quantz (1953).

Synonyms:

Broad bean true mosaic virus (Rev. appl. Mycol. 33: 461)
Vicia virus 1 (Rev. appl. Mycol. 33: 461)
Viciavirus varians (Rev. appl. Mycol. 33: 461)

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

Main Diseases

Common in crops of broad bean (Vicia faba), causing mosaic symptoms. There seem to be no varieties of broad bean or pea that escape infection with the virus in the field (Quantz, 1953).

Geographical Distribution

Europe and North-west Africa.

Host Range and Symptomatology

Only hosts known are legumes; Quantz (1953) obtained symptoms in 24 of 31 species of legume inoculated, but none of 7 species belonging to 5 non-legume genera. However, none were tested for symptomless infection by inoculating sap to test plants.

Diagnostic species

Vicia faba (broad bean). Characteristic systemic mottling and mosaic (Fig.1), evanescent in hot weather, severe, often with shoot necrosis in cool weather. Severity of symptoms and virus concentration in the youngest leaves vary cyclically (Fig.1) throughout the growth of the plant (Paul & Quantz, 1959).

Pisum sativum (pea). Severe systemic chlorotic mosaic, occasionally necrotic. Plant stunted, and leaf lamina deformed.

Phaseolus vulgaris (bean). Some varieties are occasionally infected by some strains of the virus, giving chlorotic flecking.

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

Propagation and assay species

Pisum sativum or Vicia faba. No local lesion host known.

Strains

Minor variants, differing in the severity of the symptoms they cause, are readily obtained (Quantz, 1953).

Transmission by Vectors

Vectors not yet known, though the virus spreads over large distances within broad bean crops (Quantz, 1953; Gibbs, Giussani-Belli & Smith, 1968).

Transmission through Seed

Common. Up to 15% of the progeny of infected plants may be infected.

Transmission by Dodder

Not tested.

Serology

Moderately immunogenic. Gives a single band of precipitate in Ouchterlony gel diffusion tests, and a granular precipitate in mixed-liquid serological tests.

Relationships

The physical and chemical properties of the particles of this virus are typical of viruses in the cowpea mosaic virus group, except that, like radish mosaic virus (another member of the group), preparations contain few or no RNA-free particles. No serological relationships to other viruses in the cowpea mosaic virus group has been established (Gibbs et al., 1968).

Stability in Sap

In pea sap, four strains of the virus lost infectivity after heating for 10 min at between 65° and 75°C, dilution to about 10-4, or storage at room temperature for 6-7 days (Quantz, 1953). In bean sap the virus was infective after 3 years at -20°C.

Purification

The particles of the virus are stable, and Steere’s chloroform/butanol method is convenient for extracting the virus from plant tissue, into pH 7.0 buffer containing a reducing agent; the latter is not needed to stabilize the virus particles, but prevents darkening of sap. The virus particles are then purified and concentrated by differential centrifugation (Paul, 1963; Gibbs et al., 1968).

Properties of Particles

The particles are all of one size but sediment as two components (Fig.2).

Sedimentation coefficients (s20,w) at infinite dilution: 98 and 119 S.

Molecular weights (daltons): about 6.1 x 106 and 7.5 x 106.

Diffusion coefficient (D20,w x 10-7 cm2 sec-1): 1.26.

Absorbance at 260 nm (1 mg/ml, 1 cm light path): about 7.7 (normal mixture of 98 and 119 S particles) (Paul, 1962).

A260/A280: 1.76 (98 S particles), 1.81 (119 S particles).

Particle Structure

The particles are isometric, about 25 nm in diameter with angular polygonal outlines (Fig.3). The central parts of the 98 S particles are penetrated by negative stain but those of the 119 S particles are not. The particles show no regularly arranged morphological subunits.

Particle Composition

RNA: Molecular weight of nucleic acid in 98 S particles 1.7 x 106, in 119 S particles 2.8 x 106 (calculated from the molecular weights of the particles and their nucleic acid contents). Probably single-stranded. Molar percentage of nucleotides of unfractionated preparations: G22.8; A26.5; C18.4; U32.3. RNA is about 26% of weight of 98 S particles and about 35% of weight of 119 S particles (Paul, 1962; 1963).

Protein: Amino acid composition has been reported by Wittmann & Paul (1961). The size of the chemical subunits is uncertain.

Notes

Echtes Ackerbohnemosaik-Virus (EAMV) is readily confused with broad bean stain virus, because both cause similar leaf symptoms in V. faba plants, are seed-borne, and have similar particles. However, broad bean stain virus, unlike EAMV, infects P. vulgaris varieties Tendergreen and Canadian Wonder, causes chlorosis and necrosis but no distortion of infected pea plants, produces many RNA-free 60 S particles (Fig.2), and is serologically unrelated to EAMV. Broad bean mottle virus also gives symptoms in V. faba that could be confused with those caused by EAMV, and these viruses were thought to be the same until Wetter et al. (1960) showed that they are distinct. Broad bean mottle virus has a thermal inactivation point 20°C higher than that of EAMV, causes tiny chlorotic lesions in C. amaranticolor leaves 5 days after inoculation (Hollings, 1957), and has particles that differ in composition from those of EAMV and sediment as a single component when centrifuged.

References

  1. Gibbs, Giussani-Belli & Smith, Ann. appl. Biol. 61: 99, 1968.
  2. Hollings, Pl. Path. 6: 133, 1957.
  3. Paul, Phytopath. Z. 43: 315, 1962.
  4. Paul, Phytopath. Z. 49: 161, 1963.
  5. Paul & Quantz, Arch. Mikrobiol. 32: 312, 1959.
  6. Quantz, Phytopath. Z. 20: 421, 1953.
  7. Wetter, Paul, Brandes & Quantz, Z. Naturf. 158: 444, 1960.
  8. Wittmann & Paul, Phytopath. Z. 41: 74, 1961.

Acknowledgements

Photographs: courtesy of Rothamsted Experimental Station, UK and Institut für Landwirtschaftliche Virusforschung, Braunschweig, Germany.


Figure 1

Shoot of a Vicia faba plant infected with Echtes Ackerbohnemosaik-Virus; the severity of symptoms (and virus concentration) differs in different leaves and varies cyclically throughout the growth of the plant.

Figure 2

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

Figure 3

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