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CTV stem pitting on a budded citrus tree Photo: placeholder pending image-fill pass

Citrus tristeza virus (CTV)

Citrus tristeza virus (CTV) is a phloem-limited Closterovirus and one of the most economically important plant viruses worldwide. It is the single virus responsible for the historic decline of millions of budded citrus trees on sour-orange and rough-lemon rootstocks across India, Brazil, Argentina, Spain and California through the 20th century. In India, CTV was the principal driver of the 1960s-80s collapse of mandarin orchards in the Coorg (Citrus Coorg Mandarin Karnataka) and Khasi (Citrus Khasi Mandarin Northeast) belts and remains a major component of the broader citrus decline complex (Citrus Die Back Citrus Decline Complex).

Identification and symptoms

CTV causes three distinct syndromes depending on virus strain and rootstock-scion combination:

  • Quick decline (seedling-yellows / bud-union decline): in mandarin or sweet orange budded on sour orange or susceptible rough-lemon rootstocks, the tree wilts within weeks of an apparent first symptom; leaves yellow and drop, feeder roots die back, fine pitting appears at the bud union, and the tree often dies in a single season. This is the classic "tristeza" (Spanish for sadness) syndrome.
  • Stem pitting: in grapefruit, acid lime and some sweet orange and mandarin selections, longitudinal pits develop in the wood under the bark; the tree survives but yields drop progressively, fruit size shrinks and orchard productive life shortens.
  • Symptomless infection: in pummelo (Citrus Pummelo Shaddock Cultivation), Rangpur lime, lemon on its own roots and many mandarin selections on tolerant rootstocks, infection is latent.

Confirmation is by indicator-plant inoculation onto Mexican lime, by ELISA against CTV coat protein, or by RT-PCR of phloem extract.

Hosts and lifecycle

All commercial Citrus species are hosts; the response depends on rootstock-scion combination and on the CTV strain (mild, severe, stem-pitting). The virus is transmitted in three ways:

  • Aphid vectors: the brown citrus aphid (Toxoptera citricida) is the most efficient natural vector and is the principal agent of CTV spread in the Northeast, Coorg and Kerala. The black citrus aphid (Toxoptera aurantii), the cotton aphid (Aphis gossypii) and the spirea aphid (Aphis spiraecola) are less efficient but ubiquitous secondary vectors.
  • Infected budwood and budded plants: the dominant long-distance pathway. A single infected mother tree in a nursery can produce thousands of contaminated budded plants distributed across districts.
  • Mechanical: budding and grafting knives can carry CTV between trees in a nursery if not sterilised.

Once a tree is infected, CTV remains in the phloem for the life of the tree; the rate of disease expression depends on rootstock-scion susceptibility and strain virulence.

Damage and economic impact

CTV is the historic largest single cause of citrus orchard loss in India. The Coorg mandarin belt fell from a 1960s peak to less than a fifth by the 1990s, principally because of CTV on rough-lemon rootstock. The Khasi mandarin belt has reverted largely from budded to seedling plantings for the same reason. In Punjab Kinnow (Citrus Kinnow Mandarin Punjab), CTV stem-pitting strains are an increasing concern as the older orchards on Jatti khatti rootstock age. CTV interacts with HLB (Citrus Greening Hlb Candidatus) and Phytophthora gummosis; co-infected trees decline faster than singly infected trees.

Management

There is no curative treatment. ICAR-CCRI Nagpur and ICAR-IIHR recommend prevention-by-rootstock and indexed-planting:

  • Tolerant rootstocks: replace sour orange and susceptible rough-lemon selections with Rangpur lime (Rangpur Lime Rootstock) on most Indian sites; X-639 and Volkamer lemon are also tolerant on heavy soils. Sour orange is now used only on calcareous high-pH sites where Rangpur lime fails.
  • Indexed planting material: source budded plants only from accredited screenhouse nurseries that ELISA- or RT-PCR-test mother trees. This is the single most cost-effective intervention.
  • Mild-strain cross-protection: deliberate inoculation of nursery plants with a mild CTV strain ahead of exposure to severe strains; used in Brazilian and South African Pera sweet-orange industries and trialled by ICAR-CCRI for stem-pitting management in Kinnow.
  • Vector management: monitor and control Toxoptera citricida on tender flush, particularly in the Northeast. Imidacloprid 0.005% or thiamethoxam 0.025% is effective.
  • Sanitation: remove and burn severely declining trees on susceptible rootstocks; sterilise budding tools with sodium hypochlorite.

See also: Citrus Die Back Citrus Decline Complex, Citrus Greening Hlb Candidatus, Rangpur Lime Rootstock, Rough Lemon Jamberi Rootstock.

Sources

  1. Citrus tristeza virus. ICAR-Central Citrus Research Institute, Nagpur.
  2. Citrus tristeza virus. CABI Compendium.
  3. Citrus virus indexing. ICAR-Indian Institute of Horticultural Research.