Details of DPV and References

DPV NO: 18 June 1970

Family: Secoviridae

Genus: Nepovirus

Species: Tomato ringspot virus | Acronym: ToRSV

There is a more recent description of this virus: DPV 290

Tomato ringspot virus

R. Stace-Smith Canada Agriculture Research Station, Vancouver, B.C., Canada

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
Satellite
Relations with Cells and Tissues
Ecology and Control
Notes
Acknowledgements
Figures
References

Introduction

Described by Price (1936).
Selected synonyms: Tobacco ringspot virus No. 2 (Rev. appl. Mycol. 15: 831); Nicotiana virus 13 (Rev. appl. Mycol. 36: 303); Annulus zonatus (Rev. appl. Mycol. 28: 514); Peach yellow bud mosaic virus (Rev. appl. Mycol. 24: 65); Grape yellow vein virus (Rev. appl. Mycol. 35: 286)
An RNA-containing virus with isometric particles about 28 nm in diameter. It is readily transmissible by inoculation of sap and has a wide host range, including both woody and herbaceous plants. It is transmitted by the nematode Xiphinema americanum.

Main Diseases

Causes mosaic or ringspot symptoms in tobacco, Pelargonium, Hydrangea, raspberry and blackberry; rasp leaf in cherry; yellow bud mosaic in peach; yellow vein in grapevine; stunt or stub head in Gladiolus; and decline of raspberry.

Geographical Distribution

Field spread restricted to the temperate regions of North America where the nematode vector Xiphinema americanum is prevalent. Endemic in native wild hosts along the California coast (Frazier, Yarwood & Gold, 1961). Has probably been distributed in ornamental crops to other parts of the world although to date there have been no confirmed reports.

Host Range and Symptomatology

Experimental host range is wide; spp. in more than 35 dicotyledonous and monocotyledonous families are susceptible. In nature, the virus occurs mostly in ornamentals and woody or semiwoody plants. Transmissible by sap inoculation, readily to herbaceous hosts but with difficulty to woody hosts.

Diagnostic species: Chenopodium amaranticolor (Fig. 1) and C. quinoa. Small chlorotic local lesions; systemic apical necrosis.; Cucumis sativus (cucumber). Local chlorotic spots; systemic chlorosis and mottle.; Phaseolus vulgaris (bean). Chlorotic local lesions; systemic rugosity and necrosis of tip leaves (Fig. 2).; Nicotiana tabacum (tobacco). Necrotic local spots or rings (Fig. 4); systemic etched ring and line patterns. Leaves produced later are symptomless but contain virus.; Petunia hybrida (Fig. 5). Local necrotic lesions; necrotic collapse of young leaves.; Lycopersicon esculentum (tomato). Local necrotic flecks; systemic mottle and necrosis (Fig. 6).; Vigna sinensis (cowpea; Fig. 7). Chlorotic or necrotic local lesions; most isolates cause systemic tip necrosis.
Propagation species: Nicotiana tabacum or woody plants such as raspberry or currant are suitable for maintaining cultures; Cucumis sativus (cucumber) or Petunia are good sources of virus for purification.
Assay species: Vigna sinensis, Nicotiana tabacum, Chenopodium amaranticolor, and C. quinoa are useful local lesion hosts. Cucumber is useful as a source and bait plant for nematode transmission experiments (Téliz, Grogan & Lownsbery, 1966).

Strains

Variants giving slightly different symptoms in herbaceous hosts have been found. The best known variants, distinguished not by host reactions but on the basis of the field disease attributed to the virus, are as follows:

Tobacco strain = tobacco ringspot virus No. 2 of Price (1936). Occurred spontaneously in tobacco seedlings in a greenhouse. Source Eastern USA.

Peach yellow bud mosaic strain. Occurs naturally in almond, apricot and peach. Herbaceous host reactions similar to those caused by Price’s strain (Karle, 1960) from which it cannot be distinguished serologically (Cadman & Lister, 1961). Source Western USA.

Grape yellow vein strain. Occurs naturally in grape. Herbaceous host reactions similar to above strains but differs in causing no top necrosis in cowpea; also differs somewhat serologically. Source Western USA.

Transmission by Vectors

Transmitted by adults and three larval stages of the nematode Xiphinema americanum. Nematodes can acquire virus within 1 h and can inoculate it into healthy plants within 1 h. Single nematodes can transmit (Téliz et al., 1966). Tobacco ringspot and tomato ringspot viruses can both be transmitted by the same single nematode (Fulton, 1967).

Transmission through Seed

Transmitted occasionally through tobacco and raspberry seed, frequently through soybean (Kahn, 1956) and strawberry (Mellor & Stace-Smith, 1963) seed. Pollen transmission not investigated.

Transmission by Dodder

A virus thought to be tomato ringspot virus was not transmitted by Cuscuta californica, C. subinclusa, or C. campestris (Bennett, 1944).

Serology

The virus is moderately immunogenic; antiserum titres in excess of 1:1000 may be attained. Diagnostic serological reactions can be obtained in ring precipitin, micro precipitin, tube precipitin, gel-diffusion or complement fixation tests. Antisera prepared by intravenous or intramuscular injections give a single band of precipitate in gel-diffusion tests.

Relationships

Tomato ringspot virus is not related serologically to the nematode-borne viruses that occur in Europe (Cadman & Lister, 1961), nor to tobacco ringspot (Tall, Price & Wertman, 1949) or tomato top necrosis (Bancroft, 1968), two similar viruses that occur in North America. Prior to the widespread use of serology, plant protection tests were used to distinguish tomato ringspot and tobacco ringspot viruses; reciprocal tests in recovered tobacco plants (Price, 1936) or petunia plants (Cadman & Lister, 1961) show lack of relationship.

Unilateral protection occurs between tomato ringspot and elm mosaic viruses but serological comparisons, reveal no cross reactions and vector relationships suggest that the two viruses are distinct (Fulton & Fulton, 1970).

The tobacco and peach yellow bud mosaic strains do not differ antigenically but the grape yellow vein strain, although closely related to the others, may be distinguished by the formation of spurs in gel-diffusion tests (Gooding, 1963; Téliz et al., 1966).

Stability in Sap

In tobacco sap, the virus loses infectivity after 10 min at about 58%, 2 days at 20°C, 3 weeks at 4°C, or several months at -20°C. Dilution end-point of sap from inoculated tobacco leaves or cucumber cotyledons is 10^-3; that of sap from systemically infected tobacco is less than 10^-1 (Stace-Smith, 1962).

Purification

The virus is relatively unstable and is destroyed by many routine purification procedures. Two methods seem satisfactory:

1. Gooding (1963). Freeze leaves and stems from infected bean plants and homogenize each 100 g in 50 ml distilled water containing 0.75 g sodium ascorbate. Squeeze through cheesecloth, add n-butanol to 8.5% (v/v) and centrifuge at low speed. Concentrate by four cycles of high- and low-speed centrifugation, resuspending the pellets obtained at high speed in 0.02 M phosphate buffer, pH 7.2. Subject the final product to sucrose density gradient centrifugation.

2. Stace-Smith (1966). Extract each 100 g infected cucumber tissue in 150 ml 0.5 M borate buffer, pH 6.7. Squeeze extract through cheesecloth, freeze overnight, thaw, and centrifuge at low speed. Add granular ammonium sulphate, 15 g/100 ml extract, stir overnight and centrifuge at low speed. Concentrate the supernatant fluid by two cycles of high- and low-speed centrifugation, resuspending the pellets obtained at high speed in 0.01 M versene buffer, pH 7.0. Subject the final product to sucrose density gradient centrifugation. Yield is 10-20 mg/kg of infected leaves.

Properties of Particles

Purified preparations contain two major classes of particles, empty protein shells without RNA (T) and the infective nucleoprotein (B). The two classes of particle are serologically indistinguishable; only the B particles are infective (Stace-Smith, 1966).

Sedimentation coefficients (s_20,w) at infinite dilution (svedbergs): 53 (T), 126-128 (B).

Molecular weights (daltons): About 3.2 x 10⁶ (T), 5.5 x 10⁶ (B).

Isoelectric point: c. pH 5.1.

Electrophoretic mobility: -2.60 x 10^-5 cm² volt^-1 sec^-1 in 0.1 ionic strength phosphate buffer, pH 7.38; or 1.59 x 10^-5 cm² volt^-1 sec^-1 at pH 6.55 (B and T).

A₂₆₀/A₂₈₀: about 1.05 (T), 1.8 (B).

Absorbance at 260 nm (1 mg/ml, 1 cm light path): about 10.0 (B).

Particle Structure

Particles are isometric, about 28 nm in diameter (Fig. 3). They disintegrate somewhat when mounted in phosphotungstate for electron microscopy. They are penetrated by phosphotungstate and contrast poorly.

Particle Composition

RNA: Only the 126 S particle contains RNA. Molecular weight about 2.3 x 10⁶. Molar percentages of nucleotides: G 26; A 23; C 22; U 29. RNA is about 40% of the particle weight (Tremaine & Stace-Smith, 1968).

Protein: About 60% of particle weight. For amino acid composition, see Tremaine & Stace-Smith (1968).

Relations with Cells and Tissues

Particles thought to be those of tomato ringspot virus were observed in low concentration in the cytoplasm and plasmodesmata of infected leaf tissue of Datura stramonium (de Zoeten & Gaard, 1969).

Notes

Tomato ringspot virus is similar in size, shape, physical properties, host reaction and patchy distribution in the field to other nepoviruses but is serologically unrelated to any of them. Serological tests are therefore essential for positive identification of isolates thought to belong to this group of viruses. The geographical distribution, natural host range, and vector relationships of tomato ringspot virus closely parallel those of tobacco ringspot virus. If antisera are not available to distinguish isolates of these viruses, differential host reactions may be useful (McLean, 1962).

The name tomato ringspot has been applied to two apparently unrelated viruses, one isolated from tobacco seedlings by Price (1936) and the other from tomato plants by Samson & Imle (1942). Price’s isolate, or isolates serologically related to it, has been used for physical, chemical, and biological characterization of tomato ringspot virus. The isolate of Samson & Imle was probably related not to Price’s tomato ringspot virus but to tomato top necrosis virus (Bancroft, 1968).