48
June 1971
Family: Potyviridae
Genus: Tritimovirus
Species: Wheat streak mosaic virus
Acronym: WSMV


Wheat streak mosaic virus

M. K. Brakke
Agricultural Research Service, US Department of Agriculture, Plant Pathology Department, University of Nebraska, Lincoln, Nebraska, 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 McKinney (1937).

Selected synonyms

Wheat viruses 6 and 7 (McKinney, 1937)
Marmor virgatum (Rev. appl. Mycol. 24: 136)
American Type Culture Collection Numbers AC29, AC85, PV57 and PV91

A mite-transmitted cereal virus with filamentous particles c. 700 nm long and 15 nm in diameter, containing RNA. Readily sap-transmissible and gives symptoms at all temperatures above 10°C at which wheat grows.

Main Diseases

Causes a severe mosaic of winter wheat and certain millets, and a mild mosaic in some varieties of maize. The disease causes serious losses in wheat infected in the autumn, producing severe stunting (Fig.1), varying degrees of necrosis and death of tillers, and reduced seed set and seed weight (McKinney, 1967).

Geographical Distribution

USA, Canada, Jordan, Rumania, Yugoslavia and Russia (Slykhuis, 1967).

Host Range and Symptomatology

Infects most or all varieties of wheat (Triticum aestivum), oats (Avena sativa), barley (Hordeum vulgare), and rye (Secale cereale), and some varieties of maize (Zea mays) and millets (Panicum, Setaria, and Echinochloa spp.). Infects many wild grasses, including species of Aegilops, Bromus, Digitaria, Echinochloa, Eragrostis, Haynaldia, Hordeum, Lolium, Panicum, Phalaris, Setaria, Cenchrus, Agropyron, Bouteloua, Elymus, Oryzopsis, Poa and Stipa. No dicotyledons have been infected (Sill & Agusioba, 1953; Sill & Conin, 1953). Readily sap-transmissible.

Diagnostic species

Gives systemic mosaic symptoms, often accompanied by stunting, at both warm and cool temperatures in almost all varieties of wheat (Fig.2), oats and barley, and some varieties of maize. Does not systemically infect Agropyron repens, Bromus inermis, Saccharum officinarum (sugar cane), Sorghum bicolor (sorghum) or Hordeum jubatum.

Propagation species

Wheat. Mildew-resistant varieties such as Michigan Amber and Kent are frequently used.

Assay species

No satisfactory local-lesion assay host known. Systemic assays may be done with wheat. Vector transmission tests should be done with wheat, which is the best host for the mite.

Strains

Many variants can be selected on the basis of symptom severity, but few studies have been done on such strains. McKinney (1956) selected a mild strain (AC85, Catalogue of Plant Viruses, 1958, American Type Culture Collection; No. PV91 in current ATCC collection) for use in interference or blocking tests.

Transmission by Vectors

Transmitted by adult and all nymphal stages of the eriophyid mite, Aceria tulipae (Fig.3), but can only be acquired from plants by nymphs. They acquire the virus in feeding periods of 15 min or more. The virus persists for at least 9 days in infective mites kept on virus-immune plants. The virus does not pass from the adult mite to its progeny through the egg (Slykhuis, 1955; Staples & Allington, 1956).

Transmission through Seed

Not reported.

Serology

The virus is a good antigen: antisera with microprecipitin titres of 1/256-1/1024 have been prepared by injecting rabbits with about 5 mg purified virus. The precipitin test is not always reliable with unconcentrated plant sap because the virus concentration is low, but it is reliable when the virus is first concentrated by centrifugation. Gel-diffusion tests work better when the virus is disrupted, e.g. by treatment with a detergent (Brakke & Ball, 1968). The leaf-dip serological method works well (Ball & Brakke, 1968).

Relationships

Its particles resemble those of agropyron mosaic, ryegrass mosaic and hordeum mosaic viruses; the first two viruses are transmitted by another eriophyid mite, Abacarus hystrix. However, using the available antisera, which are comparatively low-titred, no serological relationship has been found between these viruses. Agropyron mosaic virus systemically infects Agropyron repens, and hordeum mosaic virus infects Hordeum jubatum, but neither of these species is infected systemically by wheat streak mosaic virus.

Stability in Sap

Thermal inactivation point in wheat sap (10 min) is 54°C; dilution end-point is 10-3-10-4. Survives for 4 days but not 8 days in wheat sap at 20°C, and for 1 month, but not 2 months, at 2°C. Can be kept at least 16 years in desiccated leaves over CaCl2 at 2°C (McKinney et al., 1965).

Purification

As with other viruses of similar morphology, the results of attempted purification are often erratic, but the following procedure gives consistent results (Brakke & Ball, 1968). The two youngest leaves of infected wheat are harvested about 10 days after inoculation and ground with 2 ml of 0.01 M K2HPO4 per g leaf. The homogenate is adjusted to pH 6.0-6.1, kept for 1 h at 40°C, clarified by low speed centrifugation, adjusted to pH 8.0 and, after adding citrate to a concentration of 0.01 M, centrifuged for 2.25 h at 68,000 g. The pellet is suspended in 0.01 M sodium citrate, pH 8.0, and the virus further purified by centrifugation first through a gradient column of 100-400 mg of sucrose per ml dissolved in 0.01 M sodium citrate, pH 8.0, and then through a gradient column of 200-600 mg of sucrose per ml dissolved in pH 6.5, 0.1 M Tris(hydroxy-methyl)aminomethane, 0.032 M citric acid, 0.1 mM bis(3-aminopropyl)amine, and 1/500 normal rabbit serum. The virus zones are collected, freed of sucrose by dialysis against the pH 6.5 buffer without serum, and the virus concentrated by ultracentrifugation. The average yield is about 1.2 A254 units (approximately 0.4 mg) from 100 g leaf, i.e. about half the virus detectable in clarified sap.

The virus has also been purified by differential centrifugation from pH 5.0 clarified sap of leaves previously frozen for 1 day (Slykhuis & Bell, 1965).

Properties of Particles

Sedimentation coefficient (s20, w) about 165 S at small concentrations in sucrose gradients.

A260/A280: 1.37; A230/A260: 2.7; A260/A320: 16 (Brakke & Van Pelt, 1968).

Particle Structure

Infective particles are 700 nm long (Fig.4). Shorter particles of differing lengths are usually present, but there is no indication that these are infective.

Particle Composition

RNA: May be prepared by treating virus at 2°C with 1% sodium dodecyl sulphate in pH 9.0, 0.1 M ammonium carbonate, 0.001 M EDTA, containing 100-500 µg/ml bentonite, followed by density gradient centrifugation. Phenol and salt methods have not been successful. The particle contains a single molecule of RNA with a sedimentation coefficient (s20, w) in 0.15 M NaCl, 0.015 M sodium citrate, pH 7.0, of 40 S (measured at 14°C in sucrose gradients). The M. Wt of the RNA is 2.8 x 106, calculated from its sedimentation coefficient after formaldehyde treatment. Susceptibility to RNase at high salt concentration and reactivity with formaldehyde suggests that the RNA is single-stranded.

Protein: No information.

Relations with Cells and Tissues

Inclusion bodies containing virus particles are visible by electron microscopy but not by light microscopy. They are found in all the different types of cells in the leaf. ‘Pinwheel’ inclusions are also found, but these probably do not contain virus. When normal components of some cells are disrupted during fixation and embedding, pinwheels may still be present, but not the virus-containing inclusion bodies (Shepard & Carroll, 1967; W. G. Langenberg, unpublished).

Notes

An experienced observer can identify plants infected with wheat streak mosaic virus in the field by the general pattern of their distribution in the crop, together with their symptoms and the presence of mites, but symptoms on individual plants are not reliable for identification. Other viruses giving similar mosaics differ from wheat streak mosaic virus in the following ways: the soil-borne wheat mosaic viruses do not give symptoms at 25°C and above; the leafhopper-transmitted viruses are not sap-transmissible; brome mosaic virus kills ‘Golden Giant’ sweet corn and infects Bromus inermis; and both brome mosaic and barley stripe mosaic viruses have higher thermal inactivation points. None of the above viruses have long flexuous particles and they can be easily distinguished from wheat streak mosaic virus by leaf-dip electron microscopy. Other viruses in wheat that have long, flexuous particles and are mite-transmitted may be distinguished from wheat streak mosaic virus by host range (see Relationships).

References

  1. Ball & Brakke, Virology 36: 152, 1968.
  2. Brakke & Ball, Phytopathology 58: 963, 1968.
  3. Brakke & Van Pelt, Analyt. Biochem. 26: 242, 1968.
  4. McKinney, Circ. U.S. Dep. Agric. 442, 23 pp., 1937.
  5. McKinney, J. Wash. Acad. Sci. 34: 322, 1944.
  6. McKinney, Pl. Dis. Reptr 40: 898, 1956.
  7. McKinney, in Wheat and Wheat Improvement, ed. K. S. Quisenberry & L. P. Reitz, Am. Soc. of Agronomy, Madison, Wisconsin, USA., pp. 355-374, 1967.
  8. McKinney, Silber & Greeley, Phytopathology 55: 1043, 1965.
  9. Shepard & Carroll, J. Ultrastruct. Res. 21: 145, 1967.
  10. Sill & Agusioba, Pl. Dis. Reptr 39: 633, 1953.
  11. Sill & Conin, Trans. Kans. Acad. Sci. 56: 411, 1953.
  12. Slykhuis, Phytopathology 45: 116, 1955.
  13. Slykhuis, Rev. appl. Mycol. 46: 401, 1967.
  14. Slykhuis & Bell, Can. J. Bot. 44: 1191, 1965.
  15. Staples & Allington, Res. Bull. Neb. agric. Exp. Stn 178, 40 pp., 1956.


Figure 1

A much stunted infected wheat plant in the field.

Figure 2

Wheat leaves; (left) healthy; (centre and right) two leaves showing symptoms of infection.

Figure 3

Wheat leaf infested with the mite vector, Aceria tulipae. Bar represents 0.5 mm.

Figure 4

Virus particle in a mixture of potassium phosphotungstate and potassium vanadatomolybdate. Bar represents 100 nm.