231
July 1981
Family: Tombusviridae
Genus: Carmovirus
Species: Bean mild mosaic virus
Acronym: BMMV


Bean mild mosaic virus

H. Waterworth
U.S. Department of Agriculture, Science & Education Administration, Plant Introduction Station, Glenn Dale, Maryland 20769, 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 Waterworth et al. (1977).

A virus with RNA-containing spherical particles sedimenting as a single component. Readily transmitted by inoculation with sap and by beetles. Infects species of Phaseolus and some other leguminous genera, causing mild symptoms. Often occurs in mixed infections with other viruses.

Main Diseases

Reactions of infected French bean (Phaseolus vulgaris) cultivars range from no symptoms to mild mosaic (Fig.1). Plants are not noticeably distorted or stunted. In natural mixed infections bean mild mosaic virus accentuates the symptoms normally incited by the other virus.

Geographical Distribution

El Salvador, Colombia.

Host Range and Symptomatology

Infects all tested cultivars of Phaseolus vulgaris. Incites mild mosaic in a few other leguminous species such as P. acutifolius and Glycine max (soybean), and causes symptomless infection in others. Does not infect species of Arachis, Cicer, Pisum, Vicia, or Vigna radiata, V. unguiculata, Phaseolus coccineus or P. lunatus. Infects few non-leguminous species.

Diagnostic species

Cyamopsis tetragonoloba (guar). Mild systemic mosaic after 10 days (Fig.3).

Dolichos lablab. Distinct systemic mosaic within 10 days followed by stunting (Fig.2).

Phaseolus vulgaris (French bean). Some varieties (27R, Topcrop) develop mild systemic chlorotic vein-banding or mosaic within 10 days (Fig.1); cv. Topcrop shows mild chlorotic local lesions under some conditions.

Propagation species

Most varieties of Phaseolus vulgaris produce large quantities of virus; cvs. Topcrop and Pinto are very susceptible to infection.

Assay species

No good local lesion host is known. The virus may be assayed by recording the proportion of Phaseolus vulgaris plants (cv. Topcrop or Pinto) that become systemically infected

Strains

None reported.

Transmission by Vectors

Transmitted by the Mexican bean beetle, Epilachna varivestis, the spotted cucumber beetle, Diabrotica undecimpunctata howardi (Waterworth et al., 1977), and by the beetles Cerotoma ruficornis, Diabrotica balteata, and Gynandrobrotica variabilis (H. Hobbs, unpublished data). After an acquisition access time of 18 h, spotted cucumber beetles can transmit the virus for at least 30 h after removal from virus-infected plants. The virus is not transmitted by the leaf miner Liriomyza munda, the aphid Myzus persicae (Waterworth et al., 1977), or the whitefly Trialeurodes vaporariorum (Hampton & Hancock, 1981). Tests by Hampton & Hancock (1981) suggested that the virus may spread through the soil more readily than above ground but the mechanism of this spread is unknown.

Transmission through Seed

No information.

Serology

The virus is strongly immunogenic in rabbits; antisera with titres of 1/4096 are readily attainable. Any of several serological tests can be easily performed. The gel double-diffusion system with 0.75% Ionagar and 0.02% sodium azide in water is excellent for detecting the virus in crude sap extracts whether or not the plant has symptoms. A single sharp, curved band can be observed within 8 to 16 h with extracts from most infected plants (Waterworth et al., 1977).

Relationships

The virus is serologically unrelated to 35 other viruses with spherical particles, including 10 viruses usually associated with legumes (Waterworth et al., 1977; Scott & Phatak, 1979) and the following viruses with single sedimenting components: brome mosaic, carnation mottle, carnation ringspot, cucumber mosaic, hibiscus chlorotic ringspot, sowbane mosaic, tobacco necrosis, tomato aspermy, tomato bushy stunt, turnip crinkle, turnip rosette. It is closely related to a virus found in beans in Colombia (F. Morales, unpublished data).

Stability in Sap

In sap from Topcrop bean plants the dilution end-point of infectivity is c. 10-8, the thermal inactivation point (10 min) is c. 84°C, and infectivity is retained for at least 6 weeks at 22°C. For the last two tests the sap was diluted 1/10 in 0.025 M phosphate buffer, pH 7.0 (Waterworth et al., 1977).

Purification

Waterworth et al. (1977): Blend fresh leaves of P. vulgaris in 0.02 M phosphate buffer, pH 7.5. Add chloroform to buffer and tissue so that the final ratio is 0.2:3:1. Centrifuge at 10,000 g for 10 min. Concentrate the virus from the supernatant fluid by centrifuging it at 105,000 g for 1.5 h or by adding polyethylene glycol (M. Wt 6000) to 10% (w/v), without NaCl, followed by centrifugation at 10,000 g. Resuspend the pellets in 0.02 M phosphate buffer and centrifuge at low speed. Further purify by centrifugation in 10 to 40% sucrose gradients. Store the virus in neutral 0.02 M phosphate buffer. Yields of virus are 0.3 to 0.5 mg/g tissue (Waterworth et al., 1977).

Properties of Particles

The particles sediment as a single component (Fig.4) with a sedimentation coefficient (s20, w) of about 127 S.

Absorbance at 260 nm (1 mg/ml; 1 cm light path): 5 (H. Waterworth, unpublished data).

A260/A280: 1.55; Amax(258)/Amin(243): 1.2; both values are uncorrected for light-scattering (Waterworth et al., 1977).

Particle Structure

Particles are isometric, about 28 nm in diameter (Fig.5). Some appear to be penetrated by stain in both leaf-dip and purified preparations stained with 2% phosphotungstate, pH 7 (Waterworth et al., 1977).

Particle Composition

Nucleic acid: RNA, single-stranded, M. Wt about 1.27 x 106, comprising about 20% of the particle weight (H. Waterworth, unpublished data). Molar percentages of nucleotides: G:21.7; A:25.8; C:31.5; U:21.0

Protein: Not studied.

Other components: None reported.

Relations with Cells and Tissues

No data.

Notes

The virus is extremely infectious in legumes and spreads uncontrollably among beans in the greenhouse, often without inciting symptoms. If it is as infective in the field, it may be widespread in Central and South America. It may occur undetected in many bean cultivars in which it incites no obvious symptoms. It often occurs in mixed infections with viruses that themselves cause symptoms, such as bean curly dwarf mosaic virus (Fig.6 ) (Meiners et al., 1977), bean common mosaic virus, and others (Waterworth et al., 1977). Several chrysomelid beetles are prime suspects in spreading the virus because of their widespread distribution. In symptomatology and host range, bean mild mosaic virus could be confused with bean pod mottle virus, but the two can be distinguished by serology and other means.

References

  1. Hampton & Hancock, Phytopathology 71: 223, 1981.
  2. Meiners, Waterworth, Lawson & Smith, Phytopathology 67: 163, 1977.
  3. Waterworth, Meiners, Lawson & Smith, Phytopathology 67: 169, 1977.
  4. Scott & Phatak, Phytopathology 69: 346, 1979.


Figure 1

Systemic mild mosaic symptoms incited in a leaflet of Phaseolus vulgaris cv. 27R.

Figure 2

Systemic mosaic in leaf of Dolichos lablab.

Figure 3

Systemic mild mosaic in leaf of Cyamopsis tetragonoloba.

Figure 4

Schlieren diagrams produced by analytical centrifugation of particles of bean mild mosaic virus (above) and of turnip yellow mosaic virus (below). Sedimentation is from left to right. Photograph taken 16 min after attaining 29,500 rev/min. (Courtesy of J. M. Kaper.)

Figure 5

Particles from a purified preparation in potassium phosphotungstate pH 6.8. Bar represents 100 nm. (Courtesy of R. Lawson.)

Figure 6

Shoot of bean cv. 27R doubly infected with bean curly dwarf mosaic virus (Meiners et al., 1977) and bean mild mosaic virus.