350
December 1989
Family: Alphaflexiviridae
Genus: Potexvirus
Species: Pepino mosaic virus
Acronym: PepMV


Pepino mosaic virus

Renate Koenig
Institut für Viruskrankheiten der Pflanzen, Biologische Bundesanstalt für Land- und Forstwirtschaft, D-3300 Braunschweig, Germany

D.-E. Lesemann
Institut für Viruskrankheiten der Pflanzen, Biologische Bundesanstalt für Land- und Forstwirtschaft, D-3300 Braunschweig, Germany

R.A.C. Jones
Western Australian Department of Agriculture, Baron Hay Court, South Perth 6151, Western Australia

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 Jones et al. (1980).

A virus with filamentous particles c. 510 x 12.5 nm. It is transmitted by inoculation with sap to solanaceous species and a few in other families. No vector is known but the virus readily spreads through plant contact. The virus has been found so far only in the coastal region of Peru.

Main Diseases

Solanum muricatum (pepino) is the only natural host known. Infected plants show a distinct yellow mosaic (Fig.1).

Geographical Distribution

Reported only from the coastal region of Peru (Jones et al., 1980).

Host Range and Symptomatology

The experimental host range is mainly restricted to solanaceous plants (Jones et al., 1980) but symptomless local infections develop in Tetragonia expansa and Cucumis sativus. Some potato cultivars develop systemic mosaic and/or severe systemic necrosis but others are infected symptomlessly.

Diagnostic species

Datura metel and D. stramonium. Strong systemic mosaic and, in young leaves, systemic necrotic patching, spotting and flecking (Fig.3). Inoculated and lower non-inoculated leaves may later develop irregular expanding necrotic patches resulting in generalized leaf necrosis. Young leaves that develop later are infected symptomlessly.

Nicotiana debneyi. Strong systemic mosaic with some necrotic spots, rings and lines (Fig.4). Expanding necrotic patches and generalized necrosis of inoculated and lower non-inoculated leaves, as with Datura spp., especially under shaded conditions.

N. glutinosa. Distinct yellowish mosaic on tip leaves 4-5 days after inoculation followed both in older leaves and in leaves produced afterwards by generalized milder mosaic symptoms (Fig.2). Generalized necrosis of inoculated and lower non-inoculated leaves, as with Datura spp., especially under shaded conditions.

Propagation species

Nicotiana glutinosa, N. occidentalis.

Assay species

Nicotiana glutinosa. No local lesion host is known.

Strains

None reported.

Transmission by Vectors

No vector known.

Transmission through Seed

No report.

Serology

The virus is a moderately good immunogen. Antisera with titres of 1/512 in slide precipitin tests are readily obtained. Precipitates are floccular.

Relationships

The virus is a typical member of the potexvirus group. Serological relationships were detected with narcissus mosaic and cactus X viruses, but not with eight other potexviruses (Jones et al., 1980).

Stability in Sap

In sap of N. glutinosa, the thermal inactivation point (10 min) was between 60 and 65°C, dilution endpoint 10-4 to 10-5, and infectivity was retained for at least 3 months at 20°C (Jones et al., 1980).

Purification

Mince 100 g infected N. glutinosa or N. occidentalis leaves in 25 ml of a solution at pH 7.8 containing 0.065 M disodium tetraborate, 0.435 M boric acid, 0.2% ascorbic acid and 0.2% sodium sulphite. Filter homogenate through muslin and centrifuge expressed sap at low speed. To 1 vol. of the supernatant fluid add 0.15 vol. 0.4% silver nitrate and leave at room temperature for c. 3 h. Centrifuge at low speed and add 4% (w/v) of polyethylene glycol M. Wt 6000 to the supernatant fluid. Leave at 4°C overnight. Centrifuge at low speed, resuspend the pellets in a solution at pH 7.8 containing 0.065 M disodium tetraborate, 0.435 M boric acid, 0.5 M urea and 0.1% mercaptoethanol. Subject the virus to two cycles of differential centrifugation and resuspend the final pellets in 0.01 M Tris-HCl buffer, pH 8.0.

Properties of Particles

No information.

Particle Structure

The particles (Fig.5) are flexuous filaments measuring mostly c. 510 x 12.5 nm. Cross-banding of particles is not seen as clearly as with potato virus X.

Particle Composition

Nucleic acid: No information.

Protein: In SDS-polyacrylamide gels the coat protein migrates usually as two bands with estimated M. Wt of 26.6 x 103 and 23.2 x 103. The smaller protein is probably a degradation product of the larger one.

Relations with Cells and Tissues

In the cytoplasm of leaf cells of N. glutinosa arrays of the filamentous particles often form inclusions which appear whorled (Fig.6) or banded (Fig.7). Scattered virus particles are rarely seen. Accumulations of proliferated rough endoplasmic reticulum occur in the cytoplasm (Fig.6, lower part) and small vesicles containing dsRNA-like fibrils are produced at the tonoplasts of infected cells (Fig.6, upper part; see also Francki et al., 1985). Mitochondria are sometimes fragmented and have an unusually dense matrix (Fig.8; Jones et al., 1980).

Notes

Pepino may also be naturally infected by at least two other viruses with filamentous particles: a potyvirus which causes a chlorotic mosaic (Jones et al., 1980) and a carlavirus (Jones et al., 1980; Thomas et al., 1980) which provisionally was named pepino latent virus because it infects pepino symptomlessly (Thomas et al., 1980). This carlavirus was later shown to be an isolate of the Andean strain of potato virus S (Dolby & Jones, 1988). The potyvirus was shown be wild potato mosaic virus (C.E. Fribourg, personal communication).

References

  1. Dolby & Jones, Ann. appl. Biol. 112: 231, 1988.
  2. Francki, Milne & Hatta, An Atlas of Plant Viruses, Vol. II, CRC Press, Boca Raton, 248 pp., 1985.
  3. Jones, Koenig & Lesemann, Ann. appl. Biol. 94: 61, 1980.
  4. Thomas, Mohamed & Fry, Ann. appl. Biol. 95: 191, 1980.

Acknowledgements

The senior author’s work was supported by the Deutsche Forschungsgemeinschaft.


Figure 1

Symptoms produced on pepino.

Figure 2

Symptoms produced on Nicotiana glutinosa.

Figure 3

Symptoms produced on Datura stramonium.

Figure 4

Symptoms produced on N. debneyi.

Figure 5

Virus particle from crude extract of N. glutinosa, negatively stained with uranyl acetate. Bar represents 100 nm.

Figure 6

Ultrathin section of infected N. glutinosa leaf parenchyma cells: whorled particle aggregates and accumulations of endoplasmic reticulum in the lower part and small, tonoplast-associated vesicles in the upper part; bar represents 1 µm.

Figure 7

Ultrathin section of infected N. glutinosa leaf parenchyma cells: banded aggregate of particles; bar represents 500 nm.

Figure 8

Ultrathin section of infected N. glutinosa leaf parenchyma cells: fragmented mitochondria with electron dense matrix; bar represents 500 nm.