237
July 1981
Family: Tombusviridae
Genus: Carmovirus
Species: Blackgram mottle virus
Acronym: BMoV


Blackgram mottle virus

H. A. Scott
Department of Plant Pathology, University of Arkansas, Fayetteville, AR 72701, USA

J. W. Hoy
Department of Plant Pathology, University of California, Davis, CA 95616, USA

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 Phatak (1974) and Scott & Phatak (1979).

A seed-borne virus with RNA-containing, isometric particles c. 28 nm in diameter. It is transmitted by beetles, is readily sap-transmissible and is restricted to legumes.

Main Diseases

Causes mottling and stunting in blackgram (Vigna mungo) (Phatak, 1974).

Geographical Distribution

India (Phatak, 1974) and Thailand (Y. Honda, personal communication).

Host Range and Symptomatology

The known hosts are all members of the Leguminosae. Transmitted readily to 11 species by inoculation with sap.

Diagnostic species

Cyamopsis tetragonoloba. Necrotic local lesions in inoculated cotyledons (Fig.1). No systemic infection.

Phaseolus aureus. Necrosis in inoculated primary leaves (Fig.3) and mottling in systemically infected secondary leaves.

P. vulgaris cv. Black Valentine. Systemic mosaic and distortion in trifoliolate leaves (Fig.2).

P. vulgaris cv. Pinto. Small, necrotic local lesions in inoculated primary leaves (Fig.4). No systemic infection.

Propagation species

Phaseolus vulgaris cv. Black Valentine is a good source for virus purification and for maintaining cultures.

Assay species

Phaseolus vulgaris cv. Pinto gives satisfactory local lesions (Fig.4); cv. Black Valentine has been used for tests of transmission by vectors.

Strains

None reported.

Transmission by Vectors

The bean leaf beetle, Cerotoma trifurcata (Chrysomelidae), transmitted the virus for up to 4 days after acquisition and the Mexican bean beetle, Epilachna varivestis (Coccinellidae), for up to 1 day after acquisition (Scott & Phatak, 1979). Aphis craccivora, A. fabae and Myzus persicae failed to transmit the virus (Phatak, 1974).

Transmission through Seed

Transmitted through 8% of seed of Vigna mungo (Phatak, 1974).

Serology

The virus is strongly immunogenic. A rabbit injected subcutaneously over a period of several weeks with a total of 7 mg virus emulsified with Freund’s incomplete adjuvant yielded antiserum with a titre of 1/1024. A single band of precipitate is formed in gel diffusion tests. Good reactions are obtained with crude sap.

Relationships

The virus was reported to be serologically related to broad bean mottle virus (Phatak, 1974) but more extensive tests showed the viruses to be unrelated (Scott & Phatak, 1979). Reciprocal serological tests showed no relationship with the cowpea strain of southern bean mosaic virus, or with cowpea mosaic, cowpea severe mosaic, bean pod mottle, cowpea chlorotic mottle or quail pea mosaic viruses (Scott & Phatak, 1979). The virus resembles several others that have small, stable, isometric particles and infect legumes, such as southern bean mosaic (Shepherd, 1971), bean mild mosaic (Waterworth et al., 1977), and cowpea mottle viruses (Bozarth & Shoyinka, 1979) in having a single sedimenting component and in containing a single species of RNA of M. Wt about 1.4 x 106. However, it differs from these viruses in the M. Wt of its coat protein and is serologically unrelated to them. Its affinities are therefore not certain.

Stability in Sap

In sap from infected blackgram assayed on Cyamopsis tetragonoloba, the virus loses infectivity after 10 min at 90-92°C, after dilution to 10-5 and after 45 days at 20°C (Phatak, 1974).

Purification

Scott & Phatak (1979). The virus is easily purified by a modification of Steere’s butanol-chloroform method. Harvest Black Valentine bean plants 10-14 days after inoculation and homogenize each 1 g tissue in 1.0-1.5 ml of 0.2 M sodium phosphate, 0.1 M ascorbic acid, pH 7.2, and 1 ml of a 1:1 mixture of butanol and chloroform. Keep the extract overnight at room temperature, centrifuge at 5000 g for 10 min, and subject the aqueous phase to three cycles of differential centrifugation (80,000 g for 1 h; 9000 g for 10 min). Resuspend the high speed pellets in 0.01 M sodium phosphate buffer, pH 7.2. Virus yields range from 75-125 mg/kg tissue.

Properties of Particles

(Scott & Phatak, 1979). Purified preparations contain a single sedimenting component (Fig.5).

Sedimentation coefficient: 122 S (at virus concentration of 2 mg/ml).

Absorbance at 260 nm (1 mg/ml, 1 cm light path): 5.0.

A260/A280: 1.62.

Buoyant density in CsCl: 1.364 g/cm3.

In immunoelectrophoresis, using Tris-sodium barbital buffer, pH 8.8, the virus particles migrate toward the anode as a single component.

Particle Structure

Particles are isometric, c. 28 nm in diameter (Fig.6).

Particle Composition

Nucleic acid: RNA, single-stranded, 20% of the particle weight (calculated according to Sehgal et al., 1970). M. Wt c. 1.4 x 106, estimated by electrophoresis in polyacrylamide gel under non-denaturing conditions. Molar percentages of nucleotides: G 24.9, A 25.9, C 25.2, U 24.0. Isolated RNA is infective (Scott & Phatak, 1979).

Protein: Single species, of M. Wt c. 38,200, estimated by polyacrylamide gel electrophoresis.

Relations with Cells and Tissues

Virus particles occur in the cytoplasm of epidermal and mesophyll cells (Fig.7) and in the lumen of xylem elements (Fig.8). Particles are distributed throughout the cytoplasm, in clusters along the perimeter of the cytoplasm bounded by the tonoplast, and are scattered through the central vacuole. Crystalline arrays of virus particles are rare, but those observed occur in necrotic cells and mature tracheary elements (Fig.8). Proliferation of cell membrane systems is the characteristic response to virus infection. Reticulate membrane systems are formed in close association with dictyosomes and endoplasmic reticulum; dictyosomes show increased activity resulting in the accumulation of Golgi vesicles in the cytoplasm, and paramural bodies are common along the plasmalemma (Hoy, 1979).

Notes

Blackgram is grown extensively in India as a pulse crop (Phatak, 1974). The only virus other than blackgram mottle reported in blackgram is bean common mosaic (Shahare & Raychaudhuri, 1963), which is a potyvirus (Bos, 1971). The two viruses can be easily distinguished by particle morphology and serology. Also, bean common mosaic virus is transmitted by aphids and has a much lower thermal inactivation point (c. 60°C) than blackgram mottle virus (90-92°C).

References

  1. Bos, CMI/AAB Descriptions of Plant Viruses 73, 4 pp., 1971.
  2. Bozarth & Shoyinka, CMI/AAB Descriptions of Plant Viruses 212, 3 pp., 1979.
  3. Hoy, M. S. Dissertation, University of Arkansas, 1979.
  4. Phatak, Seed Sci. Technol. 2: 3, 1974.
  5. Scott & Phatak, Phytopathology 69: 346, 1979.
  6. Sehgal, Jean, Bhalla, Soong & Krause, Phytopathology 60: 1778, 1970.
  7. Shahare & Raychaudhuri, Indian Phytopath. 16: 316, 1963.
  8. Shepherd, CMI/AAB Descriptions of Plant Viruses 57, 4 pp., 1971.
  9. Waterworth, Meiners, Lawson & Smith, Phytopathology 67: 169, 1977.


Figure 1

Local lesions in inoculated cotyledons of guar, Cyamopsis tetragonoloba.

Figure 2

Systemic symptoms in trifoliolate leaf of Phaseolus vulgaris cv. Black Valentine.

Figure 3

Necrosis in inoculated primary leaf of mung bean, P. aureus.

Figure 4

Local lesions in inoculated primary half-leaf of P. vulgaris cv. Pinto.

Figure 5

Schlieren pattern obtained by analytical ultracentrifugation of purified virus preparation. Sedimentation is from left to right.

Figure 6

Virus particles stained with sodium phosphotungstate, pH 6.8. Bar represents 100 nm.

Figure 7

Electron micrograph of a large aggregate of virus particles in the cytoplasm of a palisade mesophyll cell. Bar represents 500 nm.

Figure 8

Electron micrograph of crystalline array of virus particles near secondary cell wall thickening of a xylem tracheary element. Bar represents 500 nm.