256
July 1982
Family: Tombusviridae
Genus: Carmovirus
Species: Tephrosia symptomless virus
Acronym: TeSV


Tephrosia symptomless virus

K. R. Bock
Overseas Development Administration, Crop Virology Research Project, Kenya Agriculture Research Institute, P.O. Box 30148, Nairobi, Kenya

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 Bock, Guthrie, Figueiredo & Woods (1981).

A virus with c. 33 nm isometric particles that sediment as a single component and resemble those of tombusviruses. It has a very restricted experimental host range and has been isolated only from species of Tephrosia in eastern Kenya. It occurs commonly in the field but its mode of transmission is not known.

Main Diseases

Infection in Tephrosia villosa, a wild leguminous plant, is symptomless, both in the field and in mechanically inoculated plants in the glasshouse. The virus causes no symptoms in any other susceptible species of Tephrosia except T. uncinatum, in which it may cause a mild mottle. It has not been isolated from any economically important legume nor has it been detected in any other wild leguminous plant.

Geographical Distribution

Recorded only in eastern districts of Kenya but possibly occurs throughout the range of its main host, Tephrosia villosa, which extends widely in eastern and southern Africa from sea level to c. 1300 m.

Host Range and Symptomatology

Apparently restricted to the Tephroseae (Tephrosia) and Phaseoleae (Canavalia, Glycine, Phaseolus, Voandzeia) in the Leguminosae. Thirty two other species in the Leguminosae and 28 species in eight other families were not infected (Bock et al., 1981).

Diagnostic species

Glycine max (soybean). Prominent irregular systemic mottle (Fig.2); very susceptible to infection.

Phaseolus vulgaris (French bean). Local chlorotic or necrotic lesions (Fig.1) in many cvs (Canadian Wonder, Long Tom, Premier, Tendercrop, Topcrop); no systemic infection.

Tephrosia villosa. Symptomless systemic infection.

Chenopodium amaranticolor, C. quinoa and Gomphrena globosa are not susceptible.

Propagation and assay species

Glycine max. No satisfactory local lesion host is known.

Strains

No evidence of strain differences among many isolates tested.

Transmission by Vectors

Vector unknown. Aphis craccivora and Apion sp. (Curculionidae) did not transmit (Bock et al., 1981).

Transmission through Seed

Apparently not seed-borne in Tephrosia villosa or Glycine max (Bock et al., 1981).

Serology

Strongly immunogenic in rabbits. An antiserum with a titre of 1/1024 in gel diffusion tests has been prepared.

Relationships

The properties of the virus (M. Wt of the single RNA and single coat protein species, sedimentation coefficient and buoyant density in CsCl) suggest affinities with the tombusvirus group. However, the virus did not react in gel diffusion tests with antisera to any of 44 viruses with isometric particles, including carnation Italian ringspot, carnation mottle, cymbidium ringspot, narcissus tip necrosis, pelargonium leaf curl, saguaro cactus, tomato bushy stunt and turnip crinkle (Bock et al., 1981). In subsequent tests, no relationship was detected to elderberry latent virus (A. T. Jones, unpublished data).

Stability in Sap

In soybean sap, infectivity is lost after dilution 10-5 to 10-6, or after heating for 10 min at 85-90°C, but survives for at least 3 weeks at 18-20°C and for at least 6 months at -12°C.

Purification

(Bock et al., 1981). Homogenize infected soybean leaves in 0.06 M phosphate buffer (2 ml/g tissue) containing 0.001 M sodium ethylenediamine-tetraacetate and 0.1% sodium thioglycollate (pH 7.5). Clarify with an equal volume of a mixture (1:1) of n-butanol and chloroform; concentrate by two or three cycles of differential centrifugation, resuspending pellets in 0.01 M phosphate buffer, pH 7.7. Further purification may be achieved by sucrose density gradient centrifugation.

Properties of Particles

Particles in purified preparations (Fig.4) are isometric, c. 33 nm in diameter when stained in 2% phosphotungstate, pH 6.8.

Single sedimenting component (Fig.3); sedimentation coefficient (s20, w) (svedbergs): c. 127 at infinite dilution.

A260/A280: 1.45-1.50 (not corrected for light-scattering).

Amax(c. 259)/Amin(c. 243): 1.24-1.37 (not corrected for light-scattering).

Buoyant density in CsCl: 1.361 g/cm3.

The virus particles form a single density component in both CsCl and Cs2SO4 isopycnic gradients.

Particle Structure

No information.

Particle Composition

Nucleic acid: RNA, single-stranded, M. Wt c. 1.5-1.6 x 106. About 20% of the particle weight, estimated from the buoyant density in CsCl and A260/A280 ratio.

Protein: Single species, M. Wt c. 42,000, by SDS-polyacrylamide gel electrophoresis.

Relations with Cells and Tissues

No information.

Notes

Although tephrosia symptomless virus is widespread in T. villosa in coastal districts of Kenya, it has not been found in any other wild or cultivated legume: an apparent reflection of a very narrow experimental host range. It shares several characteristics with members of the tombusvirus group but seems not to be serologically related to any of them or to other similar viruses. It is however readily identified by serological tests.

References

  1. Bock, Guthrie, Figueiredo & Woods, Ann. appl. Biol. 97: 277, 1981.


Figure 1

Local lesions induced in Phaseolus vulgaris cv. Canadian Wonder.

Figure 2

Systemic symptoms induced in Glycine max cv. HLS 541.

Figure 3

Schlieren pattern produced after moving boundary sedimentation of purified virus in 0.1 M KCl, pH 7.5.

Figure 4

Virus particles in phosphotungstate. Bar represents l00 nm.