33
October 1970
Family: Closteroviridae
Genus: Closterovirus
Species: Citrus tristeza virus
Acronym: CTV

There is a more recent description of this virus: DPV 353

Citrus tristeza virus

W. C. Price
Guinobatan Experiment Station, Guinobatan, Albay, Phillippines

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

Transmitted by Meneghini (1946) and Fawcett & Wallace (1946), and described by Kitajima et al. (1964).

Synonym

Citrus quick decline virus (Fawcett & Wallace, 1946)

A virus with highly flexuous filamentous particles, c. 2000 x 12 nm, restricted to the family Rutaceae. Causes a severe disease in only a few species. Common wherever citrus is grown. Transmitted by aphids, not by sap inoculation. Aphids retain virus up to 48 h when starved.

Main Diseases

Tristeza, or quick decline, of commercial varieties of citrus on sour orange root-stock; stem pitting, or stunt bush, of grapefruit; die-back of lime; seedling yellows of sour orange; and decline of Ellendale mandarin and Pera orange.

Geographical Distribution

World-wide in tropical and semi-tropical regions where citrus is grown.

Host Range and Symptomatology

Most varieties of Citrus and a few species in certain other genera of the family Rutaceae, such as Aeglopsis, Afraegle, and Pamburus, are susceptible to infection. A majority are, however, tolerant of commonly occurring strains of the virus. Tristeza is principally a disease of sweet orange or other varieties when grown on sour orange rootstock, and of grapefruit, lime, and calamondin.

Diagnostic species

Citrus aurantifolia (West Indian lime, Key lime, Mexican lime, Galego lime, Kagzi lime). Young leaves on infected seedlings are small, develop yellow flecks along their veins, and become cupped or canoe-shaped; stems are pitted under the bark (Wallace & Drake, 1951).

C. sinensis (sweet orange) plants on C. aurantium (sour orange) rootstock suddenly wilt, decline, and die (quick decline; Fig.1), or develop a characteristic overgrowth at the bud-union and ‘honeycombing’ in the sour orange stock just below the union (Fig.4).

Propagation species

C. aurantifolia is perhaps the best species for maintaining cultures because it displays diagnostic symptoms.

Strains

Many strains, differing in virulence, are found in nature. A few have been isolated experimentally (Grant & Higgins, 1957). The following are probably the most common naturally occurring strains of tristeza virus:

Citrus seedling yellows virus (Fraser, 1952). Causes severe yellowing and stunting of seedlings of Eureka lemon, Seville orange, grapefruit, and citron. (Some authors regard seedling yellows virus as being distinct from tristeza virus, but occurring with it.)

Grapefruit stem pitting virus (Oberholzer, Mathews & Stiemie, 1949); grapefruit stunt bush virus (Anon., 1950). In Australia, S. Africa and S. America, infected trees are stunted and bushy; leaves are sparse, small, rounded, and develop interveinal chlorosis; fruit is small, misshapen, and has thick rind; wood of trunk and large limbs is pitted with longitudinal depressions; main scaffold branches are twisted and distorted. This strain, or a similar one, is responsible for the decline of calamondin trees in the Philippines (Fig.5).

Lime die-back virus (Hughes & Lister, 1949). Causes vein flecking on young leaves, severe pitting of wood of twigs and branches, stunting of trees, and die-back with eventual death.

Ellendale mandarin decline virus (Stubbs, 1952). This strain may be the same as, or similar to, the citrus seedling yellows strain.

Transmission by Vectors

Transmissible most efficiently by the tropical citrus aphid, Toxoptera citricidus (Meneghini, 1946; Costa & Grant, 1951); less efficiently by Aphis gossypii, A. spiraecola, and T. aurantii (Dickson, Flock & Johnson, 1951; Norman & Grant, 1956). Virus can be acquired in a few seconds and transmitted in a few seconds’ feeding. Latent period unknown. T. citricidus can retain the virus for as long as 24 h when not allowed to feed. It has been suggested (Price, 1968) that tristeza virus is a circulative, non-propagative virus. Recent work (Retuerma & Price, unpublished) suggests that it may be both stylet-borne and circulative.

Transmission through Seed

None reported.

Transmission by Dodder

Reported to be transmitted by Cuscuta americana (Knorr & Price, 1954), but not confirmed.

Serology

No antisera have been prepared.

Relationships

Several authors have found that infection of test plants with mild strains of tristeza virus protects them, at least in some cases, from more severe strains. Cross-protection tests have given evidence for relationship of seedling yellows, stem pitting, and Ellendale mandarin decline viruses to the tristeza virus complex (Stubbs, 1964).

Stability in Sap

No information.

Purification

A few flexuous filaments thought to be tristeza virus particles were found in preparations obtained by high-speed centrifugation of sap from leaves (Kitajima et al., 1964; Price, 1966). More recently Bar-Joseph, Loebenstein & Cohen (1970) found large numbers of such particles in preparations made from peeled bark of diseased West Indian lime seedlings. The method was as follows. Grind frozen tissue with mortar and pestle in liquid air. Thaw and extract twice with 0.05 M Tris/HCl buffer pH 7.4 (1 g/12.5 ml). Centrifuge 10 min at 4000 g. then 5 min at 8000 g. To every 100 ml of the supernatant add 4 g polyethylene glycol (M. Wt 6000) and 4 ml 20% NaCl. Centrifuge 15 min at 16,000 g. Suspend pellets in 0.04 M phosphate buffer pH 8.2. Clarify by centrifuging 10 min at 5000 g. Sediment at 29,000 rpm in Spinco No. 30 rotor for 90 min. Suspend in water and centrifuge 10 min at 5000 g.

Properties of Particles

Sedimentation coefficient (s20,w) determined in sucrose density gradients: 140 ± 10 S at zero depth (Bar-Joseph et al., 1970).

Particle Structure

Particles are very flexuous filaments c. 2µm long and 10-11 nm in diameter (Fig.3). Visible in leaf dip preparations, or in large numbers in bark dip preparations, mounted in phosphotungstate.

Particle Composition

No information.

Relations with Cells and Tissues

Flexuous filamentous particles occur in large numbers in phloem cells (Fig.2) but not in other cells. Destruction of phloem tissues in sour orange rootstock is responsible for quick decline of orchard trees.

References

  1. Anon., Agr. Gaz. N.S.W. 61: 365, 1950.
  2. Bar-Joseph, Loebenstein & Cohen, Phytopathology 60: 75, 1970.
  3. Costa & Grant, Phytopathology 41: 105, 1951.
  4. Dickson, Flock & Johnson, Calif. Citrogr. 36: 135, 1951.
  5. Fawcett & Wallace, Calif. Citrogr. 32: 50, 1946.
  6. Fraser, Agr. Gaz. N.S.W. 63: 125, 1952.
  7. Grant & Higgins, Phytopathology 47: 272, 1957.
  8. Hughes & Lister, Nature, Lond. 164: 880, 1949.
  9. Kitajima, Silva, Oliveira, Muller & Costa, Nature, Lond. 201: 1011, 1964.
  10. Knorr & Price, Rep. Fla agric. Exp. Stn 195, 1954.
  11. Meneghini, Biologico 12: 285, 1946.
  12. Norman & Grant, Proc. Fla St. hort. Soc. 69: 38, 1956.
  13. Oberholzer, Mathews & Stiemie, Sci. Bull. Dep. Agric. S. Afr. 287, 17 pp., 1949.
  14. Price, Virology 29: 285, 1966.
  15. Price, Indian Phytopath. 21: 159, 1968.
  16. Stubbs, J. Dep. Agric. Vict. 50: 124, 1952.
  17. Stubbs, Aust. J. agric. Res. 15: 752, 1964.
  18. Wallace & Drake, Calif Citrogr. 36: 136, 1951.


Figure 1

Sweet orange on sour orange rootstock in quick decline phase ot tristeza. (Photo courtesy J. M. Wallace.)

Figure 2

Electron micrograph of filamentous particles in a portion of a phloem cell of a West Indian lime seedling infected with tristeza virus.

Figure 3

Two filamentous particles, c. 2000 x 12 nm in an electron micrograph of a dip preparation from a West Indian lime leaf infected with tristeza virus.

Figure 4

Honeycombing in the sour orange portion of a strip of bark removed from the graft union of a tristeza-diseased pummelo tree on sour orange rootstock.

Figure 5

Stem pitting in the trunk of a calamondin tree infected with tristeza virus. (Photo courtesy D. M. Nora.)