276
July 1984
Family: Alphaflexiviridae
Genus: Potexvirus
Species: Tulip virus X
Acronym: TVX


Tulip virus X

W. P. Mowat
Scottish Crop Research Institute, Invergowrie, Dundee, UK

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 Mowat (1982).

A virus with filamentous particles c. 495 nm x 13 nm. It is sap-transmissible to several herbaceous hosts but infection of most species is erratic. Reported only from tulips in UK. No vector known.

Main Diseases

Tulip is the only known natural host. The virus causes chlorotic and necrotic light brown to grey elongated streaks or elliptical markings in leaves (Fig.1). Tepals develop narrow streaks of intensified pigmentation (Fig.2); occasionally a streak lacks pigment or is necrotic. There is no information on the effects on flowers of white or yellow cultivars.

Geographical Distribution

Reported only from two locations in Scotland (Mowat, 1982), but probably of wider distribution because the symptoms in tulip may be confused with those induced by other viruses.

Host Range and Symptomatology

Tulip is the only known monocotyledonous host. The virus was transmitted by inoculation of sap to 22 of 42 other plant species in 10 of 14 families (Mowat, 1982). Infection is unreliable in most host species, including Lycopersicon esculentum and Nicotiana benthamiana, the only solanaceous hosts known. Infection of Chenopodium amaranticolor and C. quinoa is reliable.

Diagnostic species

Chenopodium amaranticolor. Chlorotic local lesions (Fig.4) and systemic chlorotic lesions, some in the form of rings or line-patterns (Fig.3).

Nicotiana clevelandii. Not infected.

Propagation species

C. quinoa. Inconspicuous chlorotic local lesions and systemic mottle.

Assay species

C. amaranticolor is a satisfactory local lesion host.

Strains

None distinguished.

Transmission by Vectors

No information. Infection of tulips by manual inoculation is only moderately efficient, and natural spread by contact between plants cannot be assumed.

Transmission through Seed

No information.

Serology

The virus is a good immunogen and reactions were obtained in microprecipitin tests at antiserum dilutions up to 1/4096. Double diffusion precipitin tests can be done in 0.4% agarose gels containing 0.85% NaCl by using sonicated sap from infected leaves of Chenopodium quinoa as a source of antigen.

Relationships

In morphology, structure and composition of particles, the virus resembles members of the potexvirus group. Distant serological relationships were detected to the definitive potexviruses (Koenig & Lesemann, 1978) hydrangea ringspot and viola mottle but particles of tulip virus X did not react with antisera to bamboo mosaic, cactus X, clover yellow mosaic, foxtail mosaic, lily X, narcissus mosaic, nerine X, plantain X or potato X viruses (Mowat, 1982).

Stability in Sap

Infectivity in sap extracts from Chenopodium quinoa survived dilution to 10-9, heating for 10 min at 60°C but not 65°C, or storage at c. 20°C for 30 days or at -20°C for 1 year (Mowat, 1982).

Purification

(Mowat, 1982). Extract sap from fresh or frozen leaves in 0.067 M phosphate buffer containing 10 mM EDTA (pH 7), precipitate the virus particles twice from 8% (w/v) polyethylene glycol (M. Wt 6000) in the presence of 0.2 M NaCl and further purify by two or more cycles of differential centrifugation. Yields of 500 µg virus particles per g leaf are readily obtained. Preparations are strongly birefringent and are satisfactory sources of nucleic acid for M. Wt estimations and for preparing orientated specimens for X-ray diffraction (Radwan, Wilson & Duncan, 1981). Clarification of leaf extracts with charcoal and DEAE cellulose powder followed by filtration through Celite (McLean & Francki, 1967) also gives good yields of particles (c. 100 µg per g leaf).

Properties of Particles

Sedimentation coefficient (s20,w) about 102 S (Fig.7; Mowat, 1982). Particles tend to aggregate: a 118 S component consistently detected in infective sap and in purified preparations is an end-to-end dimer (Fig.7; Mowat, 1982).

A260/A280: 1.28-1.33.

Particle Structure

The virus particles are slightly flexuous filaments (Fig.8) of modal length 495 nm and diameter 12.5 nm in 2% sodium phosphotungstate at pH 6.0. Particles have a helical structure with a pitch of about 3.25 nm and a true repeat in five turns of the helix (Radwan et al., 1981). Optical diffraction patterns indicate that there are 7.8 or 8.8 sub-units per turn of the helix (Radwan et al., 1981); the latter value fits the hypothesis of Richardson, Tollin & Bancroft (1981) that, in the potexvirus group, the number of sub-units per turn of the helix is close to but slightly less than 9. X-ray diffraction patterns indicate that the RNA is located at a radial position of 3.3 nm and that particles have an axial hole of about 1.5 nm radius (Radwan et al., 1981).

Particle Composition

Nucleic acid: (W. P. Mowat, unpublished data): RNA, probably single-stranded, c. 8% of the particle weight (estimated from A260/A280 ratio), M. Wt (x 10-6) 2.05 ± 0.12 (estimated by electrophoresis of glyoxal-denatured RNA in agarose gels).

Protein: A single polypeptide, M. Wt c. 22,500, estimated by electrophoresis in polyacrylamide/SDS gels; an additional polypeptide, M. Wt c. 19,000, possibly representing a degradation product of the larger polypeptide, was detected rarely (W. P. Mowat, unpublished data).

Relations with Cells and Tissues

Spindle-shaped and occasionally loop-shaped inclusion bodies are visible by light microscopy in epidermal cells of leaves of Chenopodium amaranticolor (Fig.5, Fig.6) and resemble those described for narcissus mosaic virus (Stefanac & Ljubesic, 1974) and cactus virus X (Amelunxen & Thaler, 1967).

Notes

The symptoms induced by the virus in tulip resemble those caused by, or associated with, several other viruses. For example, the streaks of intensified pigmentation in tepals resemble those induced by lily symptomless virus (which are narrower) and tobacco rattle virus (which are usually wider). The foliar symptoms somewhat resemble those of Augusta disease (caused by tobacco necrosis virus) but the plants are not distorted. However, the elliptical markings in leaves (Fig.1) are probably characteristic of infection by tulip virus X. The virus may be recognised by the characteristic line-pattern symptom induced in systemically infected leaves of Chenopodium amaranticolor (Fig.3), and by its failure to infect Nicotiana clevelandii combined with the detection of particles of the potexvirus type by electron microscopy of leaf extracts. Particle morphology alone is not unequivocal confirmation of the presence of tulip virus X because potato virus X also infects tulip (Mowat, 1981). Serodiagnosis remains the most reliable means of identification.

References

  1. Amelunxen & Thaler, Z. PflPhysiol. 57: 269, 1967.
  2. Koenig & Lesemann, CMI/AAB Descr. Pl. Viruses 200, 5 pp., 1978.
  3. McLean & Francki, Virology 31: 585, 1967.
  4. Mowat, Rep. Scott. Crop Res. Inst., 1980: 97, 1981.
  5. Mowat, Ann. appl. Biol. 101: 51, 1982.
  6. Radwan, Wilson & Duncan, J. gen. Virol. 56: 297, 1981.
  7. Richardson, Tollin & Bancroft, Virology 112: 34, 1981.
  8. Stefanac & Ljubesic, Phytopath. Z. 80: 148, 1974.

Acknowledgements

Photographs: Scottish Crop Research Institute.


Figure 1

Leaf of naturally infected tulip cv. Smiling Queen showing chlorotic and necrotic lesions.

Figure 2

Streaks of intensified pigmentation in tepals of experimentally infected tulip cv. Paul Richter.

Figure 3

Systemically infected leaves of Chenopodium amaranticolor.

Figure 4

Inoculated leaf of Chenopodium amaranticolor.

Figure 5

Spindle-shaped and loop-shaped inclusions in epidermal cells of Chenopodium amaranticolor.

Figure 6

Spindle-shaped and loop-shaped inclusions in epidermal cells of Chenopodium amaranticolor.

Figure 7

Schlieren patterns produced by partially purified virus preparation sedimenting from left to right; S1 and S2 are the regularly occurring slower (102 S) and faster (118 S) components, respectively.

Figure 8

Virus particles in sap from Chenopodium quinoa stained with 2% potassium phosphotungstate, pH 6.5. Bar represents 200 nm.