142
October 1975
Family: Secoviridae
Genus: Nepovirus
Species: Mulberry ringspot virus
Acronym: MRSV


Mulberry ringspot virus

T. Tsuchizaki
Institute for Plant Virus Research, Chiba, Japan

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 Tsuchizaki, Hibino & Saito (1971).

An RNA-containing virus with isometric particles 22-25 nm in diameter spreading naturally in Japan. It is readily sap-transmissible, has a moderate host range and is transmitted by the nematode, Longidorus martini.

Main Diseases

Found naturally only in mulberry, in which it usually causes mosaic and ringspot symptoms (Fig.1). Some isolates are associated with leaf enations.

Geographical Distribution

Japan.

Host Range and Symptomatology

Restricted in nature to mulberry. In limited host range studies, it infected 10 species in 5 dicotyledonous families.

Diagnostic species
Morus alba (mulberry). Systemically infected leaves develop mosaic, ringspots (Fig.1) or enations

Vigna sinensis cv. Black Eye (cowpea). Necrotic spots or ringspots in inoculated leaves (Fig.2), followed by mosaic or necrosis of leaves and necrosis of stems.

Glycine max (soybean). Systemically infected leaves develop mosaic or chlorotic spots.

Pisum sativum (pea). Chlorotic spotting or mosaic of systemically infected leaves (Fig.3).

Chenopodium quinoa. Indistinct chlorotic local lesions may form; systemically infected leaves show mosaic.

Propagation species
Vigna sinensis cv. Black Eye is a suitable host for maintaining cultures.

Assay species
Vigna sinensis cv. Black Eye, although not always satisfactory, can be used for local lesion assays.

Strains

No strains reported.

Transmission by Vectors

Transmitted by the nematode, Longidorus martini, but not by a species of Xiphinema (Yagita & Komuro, 1972). Infested soil containing L. martini was still infective after storage, in the absence of plants, for 14-17 months at room temperature or for more than 30 months at 0-9°C (H. Yagita, unpublished).

Transmission through Seed

About 10% of progeny seedlings of Glycine max cv. Mikawashima are infected (Tsuchizaki et al., 1971).

Transmission by Dodder

Not reported.

Serology

Moderately antigenic, giving antisera with titres up to 1/320. In gel-diffusion tests it reacts with antisera to produce a distinct single band of precipitate.

Relationships

Mulberry ringspot virus did not react with antisera to arabis mosaic, cherry leaf roll (type and golden elderberry strains), grapevine fanleaf, grapevine chrome mosaic, raspberry ringspot, strawberry latent ringspot, tobacco ringspot, tomato black ring or tomato ringspot viruses (B. D. Harrison, unpublished results).

Stability in Sap

In sap of Glycine max, the virus lost infectivity after 10 min at 50-60°C, storage at room temperature for 3-5 days, or dilution to 10-3-10-4 (Tsuchizaki et al., 1971).

Purification

Harvest cowpea plants about 2 weeks after inoculation, then homogenize at 4°C in two volumes of 0.5 M citrate buffer (pH 7.0) containing 0.1% thioglycollic acid. Express juice through cheesecloth, and add 20 ml carbon tetrachloride to every 100 ml extract. Shake the extract for 15 min, and clarify by low-speed centrifugation. Concentrate the virus by three cycles of differential centrifugation. Resuspend the pellets from high speed centrifugation in 0.01 M citrate buffer. Purify further by sucrose density-gradient centrifugation (Tsuchizaki et al., 1971).

Properties of Particles

The particles are all the same size but sediment as three components, apparently empty protein shells (T) and two kinds of nucleoprotein (M and B) (Tsuchizaki et al., 1971).

Sedimentation coeflicients (s20,w) (svedbergs): 50 (T), 96 (M), 126 (B) (T. Tsuchizaki, unpublished data).

Other physical properties are unknown.

Particle Structure

Particles are isometric, 22-25 nm in diameter. Electron micrographs show some particles completely, some partially and some not penetrated by negative stain (Fig.4).

Particle Composition

No quantitative information, but the particles contain RNA (T. Tsuchizaki, unpublished data).

Relations with Cells and Tissues

In infected cowpea and mulberry leaves, electron microscopy revealed tubules containing a single row of spherical virus-like particles (Fig.5), and characteristic vesicular inclusion bodies (Tsuchizaki et al., 1971).

Notes

Similarity of properties and transmissibility by a nematode place mulberry ringspot virus in the nepovirus group, although its particles are perhaps smaller than those of other viruses in the group. Symptoms in experimental hosts may be confused with those caused by other nepoviruses. Identification should be made by serology. An elongated virus is frequently found in mulberries naturally infected with this virus. The two viruses differ in their infectivities for cowpea or soybean.

References

  1. Tsuchizaki, Hibino & Saito, Ann. phytopath. Soc. Japan 37: 266, 1971.
  2. Yagita & Komuro, Ann. phytopath. Soc. Japan 38: 275, 1972.


Figure 1

Systemic ringspot symptoms in Morus alba.

Figure 2

Local lesions in Vigna sinensis cv. Black Eye.

Figure 3

Systemic symptoms in Pisum sativum.

Figure 4

Virus particles from purified preparation in phosphotungstate. Bar represents 100 nm.

Figure 5

Tubule with virus particles in a leaf cell of systemically infected Vigna sinensis cv. Black Eye. Bar represents 100 nm.