Details of DPV and References

DPV NO: 139 July 1974

Family: Bromoviridae

Genus: Ilarvirus

Species: Elm mottle virus | Acronym: EMoV

There is a more recent description of this virus: DPV 404

Elm mottle virus

A. T. Jones Scottish Horticultural Research Institute, Invergowrie, Dundee, Scotland

Contents

Introduction

Described by Schmelzer, Schmidt & Schmidt (1966) and Schmelzer (1969).

Synonym

Lilac white mosaic virus (Rev. appl. Mycol. 47: 1587)

An RNA-containing virus with spherical or oval particles c. 30 nm in diameter, which sediment as three nucleoprotein components. Readily sap-transmissible to many herbaceous hosts. Seed-borne in elm. Vector unknown. Found in Europe.

Main Diseases

Induces a systemic white mosaic or chlorotic ringspots in mechanically inoculated Forsythia intermedia and Syringa vulgaris (Fig. 3) (Schmelzer, 1969). It is associated with ringspot and line-pattern leaf symptoms in elm (Fig. 1, Fig. 2) (Schmelzer, 1969; Jones & Mayo, 1973), but mechanically inoculated elm seedlings did not develop leaf symptoms when kept in a heated glasshouse (Jones & Mayo, 1973).

Geographical Distribution

Detected in Syringa vulgaris and Ulmus carpinifolia in Germany (Schmelzer, 1969) and in Ulmus glabra in Germany and Scotland (Schmelzer, 1969; Jones & Mayo, 1973). On the basis of leaf symptoms in elm it possibly also occurs in Bulgaria, Czechoslovakia, England and the USSR (Schmelzer et al., 1966).

Host Range and Symptomatology

Found naturally infecting Ulmus carpinifolia, U. glabra and Syringa vulgaris (Schmelzer, 1969; Jones & Mayo, 1973). A German isolate infected 66 species from 22 families by mechanical inoculation. These included many members of the Chenopodiaceae, Solanaceae and Leguminoseae. Many developed symptoms and most were infected systemically.

Diagnostic species

Chenopodium quinoa. Faint chlorotic local lesions; mottle or mosaic in systemically infected leaves in 7-10 days (Fig. 5).

Phaseolus vulgaris (French bean) and Vigna sinensis (cowpea). Necrotic local lesions and small rings in 4-5 days (Fig. 4). Not systemic.

Nicotiana megalosiphon. Necrotic local lesions in 5 days (Fig. 6). Systemic necrotic or chlorotic spots.

Propagation species

Chenopodium quinoa and Nicotiana tabacum (tobacco) have been used. Petunia hybrida is useful for maintaining cultures.

Assay species

Chenopodium quinoa appears the most sensitive indicator for detecting the virus from natural hosts. Phaseolus vulgaris and Vigna sinensis are excellent local lesion hosts.

Strains

Schmelzer (1969) distinguished isolates from Syringa vulgaris and Ulmus glabra by minor differences in host range and by antiserum titres. The Scottish isolate differs from the German isolates in being symptomless in Nicotiana clevelandii and Petunia hybrida (Jones & Mayo, 1973). The Scottish and German isolates are serologically related but it is not known whether they are serologically distinguishable (Jones & Mayo, 1973).

Transmission by Vectors

No vector reported. The aphids Aphis craccivora and Myzus persicae did not transmit the virus to herbaceous test plants after 15-30 min access periods on infected herbaceous plants (Schmelzer, 1969).

Transmission through Seed

Seed-borne in Ulmus glabra (Jones & Mayo, 1973) and detected in the pollen of infected Syringa vulgaris (Schmelzer, 1969).

Transmission by Dodder

Not transmitted by Cuscuta californica or C. subinclusa (Schmelzer, 1969).

Serology

The virus is weakly immunogenic, giving antiserum titres with precipitin end-points of 1/32-1/64. It reacts well and produces a single line of precipitation in gel-diffusion tests.

Relationships

Serologically unrelated to other well-characterized viruses (Schmelzer, 1969: Jones & Mayo, 1973). However, it resembles tobacco streak virus (Jones & Mayo, 1973) in its particle morphology, multicomponent nature and sedimentation behaviour, in the size of its coat protein subunit and in the number and sizes of its RNA components.

Stability in Sap

All described isolates have similar properties (Schmelzer, 1969; Jones & Mayo, 1973). In C. quinoa sap, the Scottish isolate lost infectivity after 10 min at 55-60°C, storage at room temperature for 9 days or dilution in 0.006 M phosphate buffer (pH 7.0) to 10^-3-10^-4. Sap kept at 4°C or -15°C was infective after 32 days, and C. quinoa leaves freeze-dried by vacuum sub-limation gave infective extracts after 2 years, the longest period tested (Jones & Mayo, 1973).

Purification

Using the Scottish isolate, Jones & Mayo (1973) obtained good yields of virus relatively free from host plant material by the following procedure. Extract inoculated and systemically infected leaves of C. quinoa in 0.05 M citrate buffer (pH 7.0). Squeeze the extract through muslin, clarify by adding n-butanol (to 8.5% v/v) and stir for 30-60 min. Concentrate the virus by differential centrifugation. Resuspend the pellets from high speed centrifugation in 0.005 M citrate buffer (pH 7.0).

Properties of Particles

Purified preparations contain at least three nucleoprotein components distinguishable by their sedimentation rates (Fig. 7). Most of the infectivity is associated with the fastest sedimenting component (component 3), but it is enhanced by adding either or both of the two slower sedimenting components (components 1 and 2) (Jones & Mayo, 1973). No nucleic acid-free particles have been observed.

Sedimentation coefficients (s°_{20, w}): 83 S (1), 88 S (2), 101 S (3) (Jones & Mayo, 1973).

A₂₆₀/A₂₈₀ of unfractionated virus: 1.3 (Jones & Mayo, 1973).

Buoyant density: when centrifuged to equilibrium in CsCl solution, unfractionated virus formed two bands of density c. 1.27 and c. 1.35 g/cm³. Only the band of greater buoyant density was infective but both bands contained virus-like particles. However, whereas most of the particles in the infective band were c. 28 nm in diameter, most of those in the non-infective band were 15-22 nm in diameter (Jones & Mayo, 1973).

Particle Structure

Particles are disrupted in 2% sodium phosphotungstate but in uranyl formate they are quasi-spherical and not penetrated by the stain (Fig. 8) (Jones & Mayo, 1973). The mean diameter of particles is 28 nm but particles have a broad distribution in the size range 25-30 nm suggesting heterogeneity in size. This was also suggested by the partial resolution of purified virus into three bands by electrophoresis in acrylamide gels (Jones & Mayo, 1973).

Particle Composition

Nucleic acid: RNA, single-stranded (Jones & Mayo, 1973). About 20% of particle weight on the basis of buoyant density in CsCl solution. In polyacrylamide gels, RNA preparations from unfractionated virus were resolved into 3 major species with estimated M. Wt of 1.30, 1.15 and 0.82 x 10⁶ and two minor species with M. Wt of 0.39 and 0.30 x 10⁶. Component 1 contains 0.82 x 10⁶ Mol. Wt RNA and component 3 contains 1.30 x 10⁶ M. Wt RNA (Jones & Mayo, 1973).

Protein: In polyacrylamide gels, protein preparations from unfractionated virus migrated as a single major component of estimated M. Wt 25,000 (Jones & Mayo, 1973).

Relations with Cells and Tissues

No information.

Notes

This virus differs from elm mosaic virus from North America. The two viruses are not serologically related and do not protect against one another in cross-protection tests (Schmelzer, 1969). They also differ in symptomatology in herbaceous test plants such as Chenopodium quinoa and Nicotiana tabacum (Schmelzer, 1969; Jones & Murant, 1971; Jones & Mayo, 1973).

Acknowledgements

(Photographs: Scottish Horticultural Research Institute, except Fig. 3 which is by courtesy of Dr K. Schmelzer.)

Figures

References list for DPV: Elm mottle virus (139)

1. Jones & Murant, Ann. appl. Biol. 69: 11, 1971.
2. Jones & Mayo, Ann. appl. Biol. 75: 347, 1973.
3. Schmelzer, Schmidt & Schmidt, Arch. Forstws. 15: 107, 1966.
4. Schmelzer, Phytopath. Z. 64: 39, 1969.