115
July 1973
Family: Rhabdoviridae
Genus: Nucleorhabdovirus
Species: Eggplant mottled dwarf virus
Acronym: EMDV


Eggplant mottled dwarf virus

G. P. Martelli
Istituto di Patologia Vegetale, Università di Bari, 70126 Bari, Italy

M. Russo
Istituto di Patologia Vegetale, Università 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 Martelli (1969) and Martelli & Cirulli (1969).

An enveloped virus with bacilliform particles c. 220 x 66 nm in plant tissue sections or c. 225 x 90 nm in partially purified preparations. It causes a severe disease of eggplant in Italy. Transmitted by grafting and by inoculation of sap.

Main Diseases

Causes severe stunting of eggplant (Solanum melongena) accompanied by pronounced mottling and crinkling of the leaves (Fig.1) and general unfruitfulness. The low incidence in the field (only 1-2% of the plants are infected) limits the economic importance of the disease.

Geographical Distribution

Reported from southern Italy.

Host Range and Symptomatology

Eggplant is the only known natural host. Many varieties can be infected by grafting (Martelli & Cirulli, 1969) or mechanical inoculation (Martelli & Rana, 1970). Experimental host range is rather narrow, comprising species from four dicotyledonous families (Martelli & Rana, 1970). Readily transmitted by inoculation of sap to some species of Solanaceae (eggplant, Nicotiana species). Attempts to infect lettuce were unsuccessful.

Diagnostic species

Solanum melongena (eggplant). Small chlorotic local lesions after 2-3 weeks followed after another week by systemic mottle, severe vein-clearing, leaf deformation and crinkling (Fig.1).

Nicotiana glutinosa. Chlorotic local lesions appear in inoculated leaves after 10-15 days. Systemic invasion is characterised by vein-yellowing (Fig.2), flecking of the leaves and stunting. Basal leaves wither and dry out.

N. tabacum. Cvs. Samsun, White Burley and Xanthi-nc react like N. glutinosa but exhibit more obvious chlorotic local lesions (Fig.3).

Propagation species

S. melongena, N. glutinosa and N. tabacum are suitable for maintaining cultures, and are good sources of virus for purification.

Assay species

N. tabacum, and to a lesser extent N. glutinosa, can be used for local lesion assays.

Strains

No information.

Transmission by Vectors

The vector (probably aerial) is not known. Experimental transmission tests with aphids (Myzus persicae, Macrosiphum euphorbiae) and leafhoppers (Laodelphax striatellus) were unsuccessful (M. Conti, pers. comm.).

Transmission through Seed

No seed-transmission was found in N. glutinosa.

Transmission by Dodder

Not tested.

Serology

No information.

Relationships

In particle shape eggplant mottled dwarf virus resembles several other plant-infecting rhabdoviruses (sensu Howatson, 1970) but differs from all of them in one or more of the following characters: mode and site of particle development, particle size, transmissibility by inoculation of sap, symptom type and host range. It resembles lettuce necrotic yellows virus in the symptoms produced in some experimental hosts but differs in the mode of multiplication of the particles and in their intracellular localization (Wolanski & Chambers, 1971).

Stability in Sap

In sap of N. glutinosa or N. tabacum the thermal inactivation point (10 min) is about 54°C, dilution end-point is between 10-3 and 10-4 and infectivity is retained for 30-44 hr at 4°C (Martelli & Rana, 1970). The virus does not withstand desiccation or freezing in infected leaves. It is sensitive to organic solvents (n-butanol, chloroform, ether).

Purification

Clean virus preparations are obtained by grinding infected tissues in 0.2 M Na2HPO4 (pH 8.5) followed by filtration of expressed sap through Celite and differential centrifugation. However, the infectivity is lost during the early stages of purification (Russo & Martelli, 1973).

Properties of Particles

No information.

Particle Structure

Bacilliform particles 220-230 x 90 nm are seen in partially purified preparations fixed in glutaraldehyde before negative staining with phosphotungstate. In unfixed samples and leaf dips mounted in phosphotungstate the particles are mostly bullet-shaped (Fig.7) and measure 60-190 x 90 nm. Unfixed particles mounted in uranyl formate are mostly bacilliform. The virus particles exhibit surface projections c. 6 nm long and a helically arranged internal filament with a pitch of c. 4.5 nm (Fig.6) which is thought to be the nucleocapsid. In cross section (Fig.5) the particles show an outer envelope 10-12 nm thick which, depending on the fixing and staining procedure, may appear single- or double-layered. An electron-lucent region 5 nm across separates this external structure from an underlying ring c. 5.5 nm thick. The latter is, in turn, separated by an electron-lucent zone 4-4.5 nm wide from a central core, c. 18 nm in diameter, which itself has an electron-clear centre (Russo & Martelli, 1973). In tissue sections, ‘immature’ particles, i.e. those still connected to the nuclear envelope (Fig.4), are bullet-shaped whereas the ‘mature’ particles are bacilliform and measure 220 x 66 nm (Martelli, 1969; Martelli & Castellano, 1970).

Particle Composition

No quantitative data available. Circumstantial evidence based upon the reaction of particles to differential electron microscope staining techniques suggests the presence of lipids in the outer envelope (Martelli & Castellano, 1970; Russo & Martelli, 1973). Pepsin-sensitive material constitutes the bulk of the particles (Russo & Martelli, 1973).

Relations with Cells and Tissues

The general structure of infected cells is fairly well preserved even when the plants show severe symptoms. The nuclei are the only organelles seriously affected, showing depletion of chromatinic material and uniformly granular nucleoplasm. Chloroplasts and mitochondria suffer minor structural modifications. Virus particles are present in leaf parenchyma tissue, in all parts of the flower except stamens, and in the fruit pericarp. They are also found in phloem parenchyma cells but not in mature sieve and tracheary elements. The particles develop by ‘budding’ at the nuclear envelope, with the nucleocapsid either oriented perpendicularly to the nucleus (Fig.4) or, more rarely, parallel to the nuclear membrane. Virus particles accumulate in the perinuclear space. They can also be present in the ground cytoplasm within an extended network of membranous cisternae connected to the nuclear membrane (Martelli, 1969; Martelli & Castellano, 1970; Russo & Martelli, 1972).

Notes

Eggplant mottled dwarf virus is easily distinguished from other viruses infecting eggplant by the distinctive symptoms induced in the natural host and by the reaction of Nicotiana species to mechanical inoculation.

References

  1. Howatson, Adv. Virus Res. 16: 195, 1970.
  2. Martelli, J. gen. Virol. 5: 319, 1969.
  3. Martelli & Castellano, Phytopath. medit. 9: 39, 1970.
  4. Martelli & Cirulli, Annls Phytopath. Numéro hors série: 393, 1969.
  5. Martelli & Rana, Phytopath. medit. 9: 187, 1970.
  6. Russo & Martelli, Phytopath. medit. 11: 136, 1972.
  7. Russo & Martelli, Virology 52: 39, 1973.
  8. Wolanski & Chambers, Virology 44: 582, 1971.


Figure 1

Systemic mottling and deformation in a leaf of naturally infected Solanum melongena.

Figure 2

Severe vein-yellowing in Nicotiana glutinosa.

Figure 3

Chlorotic local lesions in Nicotiana tabacum.

Figure 4

Cross section of the periphery of a nucleus (N) showing virus particles budding at the nuclear envelope into the spaces between the inner (il) and outer (ol) lamella of the membrane. Note the nuclear pore (np). Bar represents 200 nm.

Figure 5

A group of virus particles in cross section. Bar represents 150 nm.

Figure 6

Virus particles from a purified preparation mounted in phosphotungstate. Surface projections and transverse striations of the nucleocapsid are visible. Bar represents 200 nm.

Figure 7

A group of virus particles from a leaf dip preparation contained within an enveloping membrane. All the particles are bullet-shaped and the axial canal is partially penetrated by phosphotungstate. Bar represents 200 nm.