66
October 1971
Family: Pospiviroidae
Genus: Pospiviroid
Species: Potato spindle tuber viroid
Acronym: PSTVd


Potato spindle tuber 'virus'

T. O. Diener
Plant Virology Laboratory, Plant Science Research Division, Agricultural Research Service, USDA, Beltsville, Maryland 20705, USA

W. B. Raymer
Campbell Institute for Agricultural Research, Cinnaminson, New Jersey 08077, USA

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 Martin (1922) and Schultz & Folsom (1923).

Selected synonyms

Potato ‘Gothic’ virus (in part - Rev. appl. Mycol. 45: 1478)
Tomato bunchy top virus (Rev. appl. Mycol. 11: 481)

An agent which appears to exist in the plant as free RNA; no protein-containing particles have been reported. The RNA occurs in several states of aggregation; the smallest infective molecule has a M. Wt of c. 50,000 daltons. It has a restricted host range, mostly among the Solanaceae, and is transmitted in nature mainly by foliage contact and by machinery. Widespread in temperate regions of North America, and also occurs in the USSR and S. Africa.

Main Diseases

Causes spindle tuber of potato and bunchy top of tomato (Benson et al., 1965).

Geographical Distribution

Common in the potato-growing regions of northern and northeastern USA and Canada and to an unknown extent in the USSR and South Africa. It has not been reported from Western Europe.

Host Range and Symptomatology

The known hosts are mostly solanaceous species of the genera Capsicum, Datura, Lycopersicon, Nicandra, Nicotiana, Petunia, Physalis and Solanum. The agent has also been transmitted with difficulty to Gomphrena globosa (Amaranthaceae). It is easily transmitted by inoculation of sap (O’Brien & Raymer, 1964), though resistance to sap inoculation was found in certain potato seedlings (Manzer, Akeley & Merriam, 1964).

Diagnostic species

Solanum tuberosum (potato). Foliage symptoms are often obscure; the plant may be severely stunted or not at all (Fig.1); stems are erect and leaves form acute angles with them, the small leaflets often overlapping; from late spring to mid-summer, foliage turns slate grey with dull leaf surface; tubers are elongated with prominent bud scales (‘eyebrows’) and may have severe growth cracks (Fig.3).

Lycopersicon esculentum (tomato) cv. Rutgers or Sheyenne. Symptoms show first in 10-14 days when plants are inoculated at the 2-4 leaf stage and kept at 25-35°C (Fig.4). There is epinasty and rugosity of the new leaves with stunting, followed by yellowing and necrosis of the midribs and lateral veins of rugose leaflets, and stunting, rugosity, and ‘bunchiness’ of the apical leaves (Raymer & O’Brien, 1962) (Fig.5).

Propagation species

Solanum tuberosum cv. Saco or Lycopersicon esculentum cv. Rutgers.

Assay species

No local lesion host is known but preparations may be assayed by inoculating various dilutions to Lycopersicon esculentum cv. Rutgers or Sheyenne plants and determining the proportion systemically infected.

Strains

Type strain of Schultz & Folsom (1923).

Unmottled curly dwarf strain of Schultz & Folsom (1923). Causes the same symptoms as the type strain in tomato plants but more severe growth cracking of potato tubers (Fig.3).

Mild strains (Fernow, 1967; Singh, Finnie & Bagnall, 1970). Cause less severe stunting, rugosity, and necrosis of tomato plants than does the type strain. Produce few or no symptoms in infected tomato plants grown in low light intensities during winter months.

Transmission by Vectors

Reported to be transmitted by two species of aphids (Schultz & Folsom, 1925), and by grasshoppers, flea beetles, tarnished plant bug, leaf beetle, and Colorado potato beetle (Goss, 1931). New studies of vector transmission are needed to confirm these reports now that it is known how easily this agent is spread by foliage contact and by machinery (Bonde & Merriam, 1951; Manzer & Merriam, 1961).

Transmission through Seed

McClean (1948) reported transmission through seed of Physalis peruvianum and one species of Solanum. Singh (1966; 1970), Hunter, Darling & Beale (1969), and Fernow, Peterson & Plaisted (1970) found that potato progeny can be infected either through the pollen or the ovule, and that 0-100% of the seed may be infected. This is the only virus infecting potato known to be seed-transmitted. Seed-transmission in tomato has also been reported (Singh, 1966; 1970).

Serology

Allington, Ball & Galvez (1964) and Ball, Allington & Galvez (1964) reported that one strain of potato spindle tuber ‘virus’ reacted with antiserum to potato virus X. However, these reports have not been confirmed, and it now seems possible that the plants used for these experiments contained potato virus X as a contaminant. Singh & Bagnall (1968) reported a suspected viral antigen in tomato and potato plants infected with potato spindle tuber ‘virus’ was a plant component. There is no confirmed report of an antiserum to the potato spindle tuber ‘virus’ alone.

Relationships

This ‘virus’ has not been shown to be related to any other virus, though the causal agents of citrus exocortis and chrysanthemum stunt diseases have some similar properties (Semancik & Weathers, 1968; Lawson, 1968).

Stability in Sap

In extracts from potato leaves in 0.2 M NaCl, the thermal inactivation point (10 min) is between 75 and 80°C, dilution end-point between 10-2 and 10-3. In phenol-treated preparations, the thermal inactivation point (10 min) is between 90 and 100°C, dilution end-point between 10-3 and 10-4 (Singh & Bagnall, 1968).

Purification

Infective material is most efficiently extracted by grinding infected tissue in 0.1-0.5 M potassium phosphate buffers at pH 7.5-9.0. The extracts are clarified by shaking with a mixture of chloroform and n-butanol (Raymer & Diener, 1969), and fractionated by centrifuging through density gradients to give infective material, some sedimenting very slowly (8-12 S) and smaller amounts sedimenting more rapidly (20-200 S) (Fig.2) (Diener & Raymer, 1967, 1969). Before fractionation the preparation may be treated with phenol, when the infectivity is unaffected (Raymer & Diener, 1969) or enhanced (Singh & Bagnall, 1968). Phenol treatment does not affect the sedimentation properties of the infective agent (Diener & Raymer, 1967).

The RNA can be further purified by treatment with DNase, followed by chromatography on columns of methylated serum albumin, CF-cellulose (Diener & Raymer, 1969), or hydroxyapatite (Diener, 1970a); but such preparations still consist predominantly of host RNA (Diener, 1970a, 1970b).

Properties of Infective Nucleic Acid

Although infective material that sediments at the same rates as the nucleoproteins of viruses is present in extracts from infected tissue, several lines of evidence indicate that this material is free RNA (Diener, 1971a). No virus-like particles have been seen in thin sections of infected tissue (R. H. Lawson, pers. comm.); and analyses of proteins in infected and healthy plants gave no evidence for the production of coat proteins (Zaitlin & Hariharasubramanian, 1970).

The infective agent is sensitive to treatment with RNase, but not with DNase (Diener & Raymer, 1967, 1969; Singh & Bagnall, 1968). Elution from hydroxyapatite columns indicates that the infective RNA is single-stranded. It is resistant to attack by exonucleases (either snake venom or bovine spleen phosphodiesterases) alone or in conjunction with alkaline phosphatase (Diener, 1970b). These properties and electron microscopy (Diener & Koller, unpublished) indicate that the molecule may be circular. Polyacrylamide gel electrophoresis indicates a M. Wt of c. 50,000 daltons for the smallest infective molecule (Diener, 1971b). Preparations of the infective agent have extremely high specific infectivity.

Relations with Cells and Tissues

In tissue extracts the infective RNA is exclusively associated with nuclei (and/or nucleoli) of infected cells (Diener & Raymer, 1969; Diener, 1971a). All tissues appear to be infected, but the greatest infectivity is extracted from young, actively growing tissues.

Notes

In certain potato cultivars, high soil temperatures induce tuber symptoms that can be confused with those of potato spindle tuber ‘virus’ (Goss & Peltier, 1925); and some potato cultivars infected with potato spindle tuber ‘virus’ develop vascular necrosis of the stems and leaf petioles similar to that induced by potato virus Y (Raymer, unpublished).

References

  1. Allington, Ball & Galvez, Pl. Dis. Reptr 48: 597, 1964.
  2. Ball, Allington & Galvez, Phytopathology 54: 887, 1964.
  3. Benson, Raymer, Smith, Jones & Munro, Potato Handb. 10: 32, 1965.
  4. Bonde & Merriam, Am. Potato J. 28: 558, 1951.
  5. Diener, Phytopathology 60: 1014, 1970a.
  6. Diener, Phytopathology 60: 1289, 1970b.
  7. Diener, Virology 43: 75, 1971a.
  8. Diener, Virology 45: 411, 1971b.
  9. Diener & Raymer, Science, N.Y. 158: 378, 1967.
  10. Diener & Raymer, Virology 37: 351, 1969.
  11. Fernow, Phytopathology 57: 1347, 1967.
  12. Fernow, Peterson & Plaisted, Am. Potato J. 47: 75, 1970.
  13. Goss, Agric. Res. Bull. Neb. agric. Exp. Stn 53: 36 pp., 1931.
  14. Goss & Peltier, Agric. Res. Bull. Neb. agric. Exp. Stn 29: 32 pp., 1925.
  15. Hunter, Darling & Beale, Am. Potato J. 46: 247, 1969.
  16. Lawson, Phytopathology 58: 885, 1968.
  17. Manzer & Merriam, Am. Potato J. 38: 346, 1961.
  18. Manzer, Akeley & Merriam, Am. Potato J. 41: 411, 1964.
  19. Martin, Hints to Potato Growers, New Jers. St. Potato Assoc. 3: 8, 1922.
  20. McClean, Sci. Bull. Dep. Agric. S. Afr. 256: 28 pp., 1948.
  21. O'Brien & Raymer, Phytopathology 54: 1045, 1964.
  22. Raymer & O'Brien, Am. Potato J. 39: 401, 1962.
  23. Raymer & Diener, Virology 37: 343, 1969.
  24. Schultz & Folsom, J. agric. Res. 25: 43, 1923.
  25. Schultz & Folsom, J. agric. Res. 30: 493, 1925.
  26. Semancik & Weathers, Virology 36: 326, 1968.
  27. Singh, Ph.D. Thesis, N. Dak. St. Univ., 1966.
  28. Singh, Am. Potato J. 47: 225, 1970.
  29. Singh & Bagnall, Phytopathology 58: 696, 1968.
  30. Singh, Finnie & Bagnall, Am. Potato J. 47: 289, 1970.
  31. Zaitlin & Hariharasubramanian, Phytopathology 60: 1537, 1970.

Acknowledgements

Photographs: Courtesy of US Department of Agriculture.


Figure 1

Foliage symptoms in Solanum tuberosum cv. Irish Cobbler. Healthy plant at left.

Figure 2

Distribution of UV absorbance and infectivity in centrifuged density gradient columns containing extracts from (a) healthy and (b) infected tissue. Gradients were linear, 0.2-0.8 M sucrose in 0.02 M phosphate buffer, pH 7.0, and were centrifuged for 16 h at 50,000 g.

Figure 3

Tuber symptoms in Solanum tuberosum. (Upper row) cv. Saco; (lower row) cv. Kennebec. (Left) healthy; (centre) infected with the type strain; (right) infected with the unmottled curly dwarf strain.

Figure 4

Symptoms in Lycopersicon esculentum cv. Rutgers, 14 days after inoculation.

Figure 5

Symptoms in Lycopersicon esculentum cv. Rutgers, 30 days after inoculation.