160
September 1976
Family: Secoviridae
Genus: Nepovirus
Species: Myrobalan latent ringspot virus
Acronym: MLRSV


Myrobalan latent ringspot virus

J. Dunez
Station de Pathologie Végétale, Centre de Recherches de Bordeaux, 33140 Pont-de-la-Maye, France

R. Delbos
Station de Pathologie Végétale, Centre de Recherches de Bordeaux, 33140 Pont-de-la-Maye, France

G. Dupont
Laboratoire de Biologie Cellulaire et Moléculaire, Centre de Recherches de Bordeaux, 33140 Pont-de-la-Maye, France

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 Dunez et al. (1971).

An isometric RNA-containing virus 28 nm in diameter with two sedimenting nucleoprotein components. It is transmissible by inoculation of sap and is serologically related to the nepovirus, tomato black ring. It occurs naturally in some rootstocks of Prunus cerasifera Myrobalan B and in Prunus cultivars grafted on this rootstock. Found in France.

Main Diseases

Latent in myrobalan (Prunus cerasifera). It causes short internodes and rosetting in peach (Prunus persica) and enations on the leaves of sweet cherry (P. avium) cv. Bing (Fig.1).

Geographical Distribution

Found only in south west France.

Host Range and Symptomatology

Many species of Prunus develop no symptoms when infected. However, infected plants of some cultivars of P. avium, especially Bing, develop enations on the underside of the leaves (Fig.1) and peach develops severe rosetting. Additional hosts in the Solanaceae, Chenopodiaceae, Compositae, Cucurbitaceae and Papilionaceae can be infected by inoculation of sap. Inoculum from Prunus should be made by extracting the leaves in 2% nicotine.

Diagnostic species
Chenopodium amaranticolor, C. quinoa. Necrotic local lesions 3 days after inoculation. Systemic necrosis (Fig.2) is followed by partial recovery.

Nicotiana tabacum cv. Xanthi-nc. A few necrotic spots in the inoculated leaves. Systemically infected leaves develop typical ringspot symptoms (Fig.3).

Propagation species
C. quinoa is used as a source of virus for purification. Cultures are maintained in this plant, in Nicotiana clevelandii or in Pisum sativum.

Assay species
Chenopodium quinoa is a satisfactory local lesion host.

Strains

All isolates found are similar in host range and symptomatology and appear serologically identical.

Transmission by Vectors

Nematode transmission suspected but not established.

Transmission through Seed

No information.

Transmission by Dodder

No information.

Serology

The virus is a good immunogen. Dilution end-points of antisera are up to 1/2048. In gel-diffusion tests with crude sap from systemically infected plums or from herbaceous host plants, the virus gives a good reaction with a single line of precipitation. In immunoelectrophoresis in agarose gels there is only one migrating component.

Relationships

The virus is a member of the nepovirus group. A distant serological relationship was detected to beet ringspot and potato bouquet strains of tomato black ring virus (Delbos et al., 1976). Antiserum to myrobalan latent ringspot virus with a homologous titre of 1/1024 reacts only to 1/4 with the heterologous antigens. No relationship was detected to different strains of the following nepoviruses: cherry leaf roll, arabis mosaic, tobacco ringspot, tomato ringspot, strawberry latent ringspot, raspberry ringspot and artichoke Italian latent.

Stability in Sap

Thermal inactivation point is about 72°C; optimum pH is 7.5 but extracts are infective over a wide range of pH from 2 to 10. Dilution end-point is about 10-4. Longevity at 4°C is more than 3 months.

Purification

Dunez et al. (1971) used either Steere’s butanol-chloroform technique or bentonite treatment. Bentonite is prepared by the method of Dunn & Hitchborn (1965). Leaves are blended in the presence of bentonite (10 mg bentonite for 1 g infected leaves). After filtration, the juice is stored 10 min at 4°C and clarified by centrifugation for 10 min at 3000 rev./min. If the supernatant fluid is still green, further treatments with a small amount of bentonite (2.5 mg/g infected leaves) may be performed. The supernatant fluid after bentonite treatment or the aqueous phase from butanol-chloroform clarification are concentrated by ultracentrifugation and purified by sucrose density gradient centrifugation. Yields of 2.5 mg virus, free of host material, are obtained from 100 g infected leaves.

Properties of Particles

Sucrose gradients show that purified virus preparations contain two sedimenting nucleoprotein components, M and B (Fig.4) which are serologically identical. The sedimentation rates (s20) of M and B are 105 and 115 S respectively (concentration 100 µg/ml). The relative concentration of B:M is about 0.6.

Isoelectric focusing shows only one component; the iso-electric point of M and B components is about pH 4.5. Electrophoresis of intact virus in 2.6% polyacrylamide gels in 0.01 M Tris, 0.01 M MgCl2, pH 7.0, gives two components.

A260/A280: 1.65 (M), 1.73 (B).

Buoyant density in CsCl: 1.46 (M), 1.50 (B), (Fig.5).

Particle Structure

Particles are isometric about 28 nm in diameter (using TMV [18 nm diameter] as a size standard) with rather angular outlines. Some particles are not penetrated by sodium phosphotungstate or uranyl acetate (Fig.6).

Particle Composition

Nucleic acid: RNA comprising about 28% (M) or 38% (B) of the particle weight estimated from ultraviolet absorption spectra. Polyacrylamide gel electrophoresis of RNA from sodium dodecyl sulphate-treated particles in 2.5% gel shows two major components: RNA-1 (M. Wt 2.6 x 106) and RNA-2 (M. Wt 1.9 x 106) and a minor one RNA-3 (M. Wt 0.45 x 106). RNA-2 and RNA-3 are present in M particles (Fig.7); all three RNA species are present in B particles (Fig.8).

Protein: In 7% polyacrylamide gels the protein migrates as one component of M. Wt 53,000.

Relations with Cells and Tissues

No information.

Notes

Its host range, symptoms and several other characteristics, such as number of nucleoproteins, RNA content, number of RNA species and molecular weight of the coat protein, are similar to those observed with tomato black ring virus, to which it is distantly serologically related. However some differences exist, especially in the physical properties of nucleoproteins and RNA. The sedimentation constants of M and B components are closer than with strains of tomato black ring virus and, correlated with this, RNA-2 M. Wt is higher.

References

  1. Delbos, Dunez, Barrau & Fisac, Annls Microbiol. A (Institut Pasteur) 127: 101, 1976.
  2. Dunez, Delbos, Desvignes, Marenaud, Kuszala & Vuittenez, Annls Phytopath. Numéro hors série: 117, 1971.
  3. Dunn & Hitchborn, Virology 25: 171, 1965.


Figure 1

Enations on a leaf of Prunus avium cv. Bing.

Figure 2

Top necrosis in Chenopodium quinoa 4 days after inoculation.

Figure 3

Typical ringspot symptom in systemically infected leaves of Nicotiana tabacum cv. Xanthi-nc.

Figure 4

Ultraviolet absorptiometer trace of sucrose density gradient after centrifugation for 2 h at 40,000 rev/min in a Beckman SW40 Rotor.

Figure 5

Isopycnic sedimentation in CsCl solution of initial density 1.480 g/cm3. Microdensitometer trace of an ultraviolet absorption photograph, taken after 24 h at 40,000 rev/mm in the Beckman An-F rotor.

Figure 6

Virus particles stained in uranyl acetate. Bar represents 50 nm.

Figure 7

Polyacrylamide gel electrophoresis of RNA from M component.

Figure 8

Polyacrylamide gel electrophoresis of RNA from B component (5 hours, 8 volts/cm, 8 mA/gel).