301
September 1985
Family: Secoviridae
Genus: Nepovirus
Species: Olive latent ringspot virus
Acronym: OLRSV


Olive latent ringspot virus

D. Gallitelli
Dipartimento di Patologia Vegetale, UniversitÓ di Bari, 70126 Bari, Italy

G. P. Martelli
Dipartimento di Patologia Vegetale, UniversitÓ di Bari, 70126 Bari, Italy

V. Savino
Dipartimento di Patologia Vegetale, UniversitÓ di Bari, 70126 Bari, Italy

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 Savino et al. (1983).

A virus with isometric particles c. 28 nm in diameter which sediment as three components and contain two functional species of single-stranded RNA. Readily transmitted by inoculation of sap to a narrow range of herbaceous hosts. The natural means of spread is unknown. Reported only from central Italy.

Main Diseases

Natural symptomless infection occurs in olive (Olea europaea).

Geographical Distribution

Reported only in Lazio (central Italy).

Host Range and Symptomatology

Transmitted experimentally by inoculation of sap to a very narrow range of hosts comprising seven species in five dicotyledonous families (Savino et al., 1983).

Diagnostic species
Chenopodium quinoa and C. amaranticolor. Small chlorotic/necrotic local lesions followed by systemic mosaic and, sometimes, apical necrosis.

Gomphrena globosa. Red-rimmed necrotic local lesions (Fig.1), distortion and mottling of upper non-inoculated leaves.

Propagation species
C. quinoa is a good source of virus for purification and is suitable for maintaining cultures.

Assay species
G. globosa is a satisfactory local lesion host.

Strains

None detected.

Transmission by Vectors

No information.

Transmission through Seed

No information.

Serology

The virus is a good immunogen. An antiserum with a titre of 1/512 was obtained by intramuscular and intravenous injections of a rabbit with unfractionated virus preparations. In gel double diffusion tests, this antiserum reacted with the homologous antigen to form a single precipitin band (Savino et al., 1983). Antibody coating of virus particles in electron micrographs can be used for virus identification.

Relationships

Although the virus has no known vector, it is classified as a member of the nepovirus group on the basis of particle size and morphology, physico-chemical properties and intracellular behaviour. It is placed in the tobacco ringspot virus subgroup of Martelli et al. (1978) which corresponds to cluster 1 of Murant & Taylor (1978). However, the virus is serologically unrelated to 26 different viruses with isometric particles including the following 17 definitive or tentative nepoviruses: arabis mosaic, artichoke Italian latent, artichoke yellow ringspot, artichoke vein banding, cherry leaf roll, cherry rasp leaf, chicory yellow mottle, cocoa necrosis, grapevine Bulgarian latent, grapevine chrome mosaic, grapevine fanleaf, myrobalan latent ringspot, raspberry ringspot, strawberry latent ringspot, tobacco ringspot, tomato black ring and tomato ringspot (Savino et al., 1983). The virus particles resemble those of tobacco ringspot virus (Chu & Francki, 1979) and artichoke vein banding virus (Gallitelli et al., 1978, 1984) in yielding a polypeptide of M. Wt 14,300 after exposure to strong denaturing conditions.

Stability in Sap

In expressed sap of C. quinoa, infectivity is lost after dilution to 10-3, heating for 10 min at 60°C or storing for 15 days at 20°C (Savino et al., 1983).

Purification

(Savino et al., 1983). Harvest symptom-bearing C. quinoa leaves 7-10 days after inoculation and homogenize in 2 vol. neutral 0.1 M phosphate buffer containing 0.1% thioglycollic acid. Squeeze the homogenate through cheesecloth and clarify the filtrate by the slow addition, while stirring, of 2.4 g/litre Mg-activated bentonite (Dunn & Hitchborn, 1965). Concentrate the virus by two cycles of alternate low speed (10,000 g for 10 min) and high speed (78,000 g for 2 h) centrifugation and further purify by centrifuging through 10-40% sucrose density gradients at 70,000 g for 3 h. Average yield of virus particles is 1-2 mg/100 g infected tissue.

Properties of Particles

In sucrose density gradients and analytical ultracentrifugation (Fig.2) purified virus preparations separate into three components (T, M and B) sedimenting at different rates. Particles are stable in CsCl.


Sedimentation coefficients, s20,w: 52 S (T), 97 S (M) and 132 S (B) (not extrapolated to infinite dilution).


A260/A280: 1.03 (T), 1.58 (M), 1.80 (B) (not corrected for light-scattering).


Buoyant densities in CsCl at 25°C (g/cm3): 1.29 (T), 1.43 (M), 1.51 (B1), 1.52 (B2) (Fig.3).

Particle Structure

Particles are isometric, c. 28 nm in diameter, and show angular outlines. Details of surface structure are not resolved. T particles are penetrated by negative stain (Fig.4).

Particle Composition

Nucleic acid: Single-stranded RNA, constituting 32% (M), 43% (B1) and 45% (B2) of the particle weight, when calculated according to Reichmann (1965). In polyacrylamide gel electrophoresis under non-denaturing conditions (Loening, 1967), the RNA migrates as two species (RNA-1 and RNA-2) with estimated M. Wt (x 10-6) of 2.65 and 1.4, respectively. Both RNA species are necessary for infectivity. Whereas RNA-1 is extracted from component B only, RNA-2 can be recovered from both M and B components (Savino et al., 1983).

Protein: In SDS-polyacrylamide slab gels in the discontinuous buffer system of Laemmli (1970), a protein preparation made from unfractionated virus particles by dissociation under strong denaturing conditions (Chu & Francki, 1979; Savino et al., 1983) separated into a light (M. Wt 14 300) and three heavier (M. Wt 43,200, 57,600 and 130,000) components (Fig.7) regarded as polymers of the 14 300 monomeric form. The coat protein is not glycosylated (Savino et al., 1983).

Relations with Cells and Tissues

The virus is present in foliar parenchyma tissues. Local lesions induced in G. globosa contain randomly scattered deposits of callose but no other barrier substances (e.g. suberins and lignins) that could account for the confinement of the virus within the lesion. Cytological modifications consist of: (i) vesiculate-vacuolate cytoplasmic inclusions with vesicles containing fine strands of material resembling nucleic acid; (ii) clumping of chloroplasts possibly caused by the adhesion of virus particles to the plastidial surface; (iii) finger-like outgrowths of the cell wall originating at plasmodesmata and containing a row of virus particles within a tubule (Fig.6). Virus particles occur in the cytoplasm, scattered or in discrete paracrystalline or crystalline arrays (Fig.5) or within tubules and in the central vacuole (Di Franco et al., 1983).

Notes

Olive latent ringspot virus is one of many sap-transmissible viruses that infect olive symptomlessly. Three of these other viruses are likewise members of the nepovirus group: arabis mosaic, cherry leaf roll and strawberry latent ringspot viruses (Savino et al., 1979; Savino & Gallitelli, 1981). Two additional viruses with isodiametric particles are cucumber mosaic (Savino & Gallitelli, 1983) and olive latent virus 1 (Gallitelli & Savino, 1985). All the above viruses can be differentiated from olive latent ringspot virus by serology, differences in experimental host range and, in part, by cytopathological features. Olive latent virus 2, another sap-transmissible virus infecting olive, is distinguished by having quasi-spherical to bacilliform particles (Savino et al., 1984).

References

  1. Chu & Francki, Virology 93 : 398, 1979.
  2. Di Franco, Martelli & Russo, J. Submicrosc. Cytol. 15: 539, 1983.
  3. Dunn & Hitchborn, Virology 25: 171, 1965.
  4. Gallitelli & Savino, Ann. appl. Biol. 106: 295, 1985.
  5. Gallitelli, Rana & Di Franco, Phytopath. Mediterranea 17: 1, 1978.
  6. Gallitelli, Martelli & Rana; CMI/AAB Descr. Pl. Viruses 285, 4 pp., 1984.
  7. Laemmli, Nature, Lond. 227: 680, 1970.
  8. Loening, Biochem. J. 102: 251, 1967.
  9. Martelli, Quacquarelli, Gallitelli, Savino & Piazzolla, Phytopath. Mediterranea 17: 145, 1978.
  10. Murant & Taylor, J. gen. Virol. 41: 53, 1978.
  11. Reichmann, Virology 25: 166, 1965.
  12. Savino & Gallitelli, Phytopath. Mediterranea 20: 202, 1981.
  13. Savino & Gallitelli, Phytopath. Mediterranea 22: 76, 1983.
  14. Savino, Barba, Gallitelli & Martelli, Phytopath. Mediterranea 18: 135, 1979.
  15. Savino, Gallitelli & Barba, Ann. appl. Biol. 103: 243, 1983.
  16. Savino, Piazzolla, Di Franco & Martelli, Proc. 6th Congr. Mediterranean Phytopath. Union, Cairo. 1984 : 24, 1984.


Figure 1

Local lesions in Gomphrena globosa.

Figure 2

Schlieren pattern of purified virus preparation after centrifugation for 14 min at 32 000 rev/min at 20°C, showing three virus-specific components (T, M and B). H = host constituents.

Figure 3

Schlieren pattern showing banding at equilibrium in CsCl of bottom component (B1 and B2) after centrifugation for 20 h at 44 000 rev/min at 25°C.

Figure 4

Virus particles from an unfractionated purified preparation mounted in potassium phosphotungstate. Bar represents 100 nm.

Figure 5

A crystalline aggregate of virus particles in the cytoplasm of an infected G. globosa cell. Bar represents 100 nm.

Figure 6

Finger-like protrusions of the cell wall (CW) containing rows of virus particles within tubules. Bar represents 100 nm.

Figure 7

Electrophoresis of coat protein preparations in slab gels of l5% polyacrylamide. Virus preparations were dissociated in 0.125 M tris-HCl buffer, pH 6.8, containing 1% SDS and 2% 2-mercaptoethanol (lane b) or in the same buffer containing in addition 6 M urea (lane a). Lane M contains marker proteins (for details see Savino et al., 1983)