125
July 1973
Family: Unallocated ssRNA+ viruses
Genus: Sobemovirus
Species: Turnip rosette virus
Acronym: TRoV


Turnip rosette virus

M. Hollings
Glasshouse Crops Research Institute, Littlehampton, Sussex, England

Olwen M. Stone
Glasshouse Crops Research Institute, Littlehampton, Sussex, England

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 Blencowe & Broadbent (1957) and Broadbent & Heathcote (1958).

A virus with isometric particles about 28 nm in diameter. Found rarely in turnip (Brassica rapa) and swede (B. napus) crops in Scotland and transmitted by inoculation of sap and possibly by flea-beetles. It infects very few hosts outside the Cruciferae.

Main Diseases

In turnip the virus induces necrosis of petioles and veins, with severe dwarfing, leaf twisting and rosetting. In swede it causes vein-banding, rosetting and stunting (Broadbent & Heathcote, 1958).

Geographical Distribution

Recorded only twice, both times in Scotland.

Host Range and Symptomatology

Known hosts are restricted to 20 species in the Cruciferae, Compositae, Resedaceae and Solanaceae.

Diagnostic species

Brassica pekinensis (Pe-tsai, Chinese cabbage). Local necrotic and occasional chlorotic spots in 6-10 days (Fig.1). The rarity of systemic infection (veinal necrosis, leaf distortion and crinkle; Fig.2) is of diagnostic value.

B. napus (swede). Local chlorotic spots; systemic vein-clearing, followed by necrosis of the petioles and leaf veins, with leaf twisting and severe rosetting. Infected plants are commonly killed at c. 20°C, but show milder symptoms at c. 10°C.

B. rapa (turnip). Local chlorotic or necrotic lesions; systemic vein-clearing, followed by necrosis of the petioles and leaf veins, dwarfing, leaf twisting and rosetting (Fig.3, Fig.4). Symptoms are much more severe at 20°C than at 10°C.

The virus infects inoculated leaves of Nicotiana clevelandii and N. bigelovii without causing definite symptoms, and does not infect N. tabacum.

Propagation species

Brassica pekinensis is a good source of virus for purification but, because systemic infection is unusual, it is less satisfactory for maintaining cultures. The virus can be maintained in B. rapa.

Assay species

Brassica pekinensis gives satisfactory local lesions.

Strains

Only two isolates have been recorded (Broadbent & Heathcote, 1958; Lister, 1958); there is no evidence for any difference between them.

Transmission by Vectors

Probably transmitted by biting insects (Martini, 1958), but no details have been published.

Transmission through Seed

No information.

Transmission by Dodder

Not recorded.

Serology

The virus is a good immunogen; rabbits immunized by one intravenous plus two intramuscular injections (with adjuvant) gave antisera with specific titres in precipitin tube tests of 1/8192 (Hollings & Stone, 1969). The precipitates are granular (somatic). In gel-diffusion tests, a single reaction line is formed; good reactions are obtained with crude infective sap.

Relationships

No serological relationships were found to any of twenty-seven other isometric viruses (Hollings & Stone, 1969).

Stability in Sap

In Brassica pekinensis sap, the thermal inactivation point is 85-90°C, rarely 95°C, the dilution end-point is 10-5-10-6 and infectivity survives at least 30 days at laboratory temperature. Lyophilized sap containing 7% dextrose + 7% peptone and stored under vacuum at laboratory temperature retained infectivity for at least 5 years.

Purification

The following method gives good yields (Hollings & Stone, 1969): preparations from Brassica pekinensis may yield 10-14 mg virus per kg leaf tissue. Harvest inoculated leaves of B. pekinensis 10-15 days after inoculation. Homogenize leaves at room temperature with 0.05 M phosphate buffer (pH 7.6) containing 0.1% thioglycollic acid using 1.5 ml buffer/g leaf. Express through cheesecloth and add 9.3 ml n-butanol to every 100 ml extract. Shake the extract for 5 min, and store it at 2°C for 12-48 h. If this step is omitted, most of the virus may be lost. Concentrate the virus by one or more cycles of differential centrifugation. Purify further by density gradient centrifugation; dialyse the virus-containing fractions against 0.03 M phosphate buffer + 0.5% NaCl for 18 h before pelleting the virus.

Properties of Particles

Sedimentation coefficient (s20,w) at infinite dilution: 112 S.

In immunoelectrophoresis at c. 4°C, using 0.9% Ionagar in 0.03 M phosphate buffer pH 7.6, the virus migrates as a single antigenic component towards the anode at a rate of 2.40 x 10-6 cm2 sec-1 volt-1.

A260/A280: 1.56.

Amax(260)/Amin(241): 1.30.

Particle Structure

Particles are isometric, about 28 nm in diameter in phosphotungstate (Fig.5).

Particle Composition

RNA: Molar percentages of nucleotides: G25; A26; C22; U27.

Protein: Particles contain a protein of M. Wt 27,700 (M. Hollings, O. M. Stone & R. Barton, unpublished).

Relations with Cells and Tissues

All tissues are infected; no inclusion bodies have been reported.

Notes

Several viruses induce similar symptoms in cruciferous crops. Turnip rosette can be distinguished serologically from the isometric viruses turnip crinkle, turnip yellow mosaic and radish mosaic, and unlike the last two has only one sedimenting component. The following are also useful distinguishing features. Turnip crinkle virus sediments at 129 S and induces local lesions in Chenopodium amaranticolor, C. quinoa, Tetragonia expansa and Datura stramonium. Turnip yellow mosaic and turnip crinkle viruses cause chlorotic local lesions in Brassica pekinensis. Radish mosaic virus induces necrotic local lesions in B. pekinensis, Nicotiana clevelandii and N. tabacum and has a thermal inactivation point of 68-70°C.

Another virus common in cruciferous crops, turnip mosaic, has filamentous particles, is aphid-borne, and causes severe systemic mottle and crinkling in Nicotiana clevelandii.

References

  1. Blencowe & Broadbent, Rep. Rothamsted exp. Stn 1956: 105, 1957.
  2. Broadbent & Heathcote, Ann. appl. Biol. 46: 585, 1958.
  3. Hollings & Stone, Zentbl. Bakt. ParasitKde, Abt II 123: 237, 1969.
  4. Lister, Pl. Path. 7: 144, 1958.
  5. Martini, Proc. 3rd conf. Potato Virus Diseases, Lisse-Wageningen, 1957: 106, 1958.


Figure 1

Local lesions in Brassica pekinensis 7 days after inoculation.

Figure 2

Systemic infection in B. pekinensis, showing dwarfing, leaf twisting and veinal necrosis.

Figure 3

Systemically infected B. rapa plant c. 4 weeks after infection.

Figure 4

B. rapa plants, (left) healthy; (right) infected, showing total absence of harvestable root 4 months after infection.

Figure 5

Virus particles from purified preparation, mounted in potassium phosphotungstate. Bar represents 100 nm.