3. HISTORY
The disease has led to the death of millions
of Citrus trees all over the world and has rendered
millions of others useless for production.
Farmers in Brazil and other South American countries
gave it the name "tristeza", meaning sadness in
Portuguese and Spanish, referring to the devastation
produced by the disease in the 1930s.
The virus is transmitted most efficiently by the brown
citrus aphid.
4. ECONOMIC IMPORTANCE
• CTV is the most economically important and damaging virus
of citrus trees.
• It has killed more than 80 million trees worldwide.
• With the spreading of T. citricida the severity and impact has
increased dramatically in Central America and the U.S.
• In Spain there has been a progressive decline in production
from over 40 million sweet orange and mandarin trees.
6. SYMPTOMS
• The three most common groupings of symptoms are decline (quick and
slow), stem-pitting, and seedling yellows.
DECLINE
• Decline is generally exhibited with sweet orange, mandarin, or
grapefruit when they are grafted on infected sour orange rootstock.
• This decline includes chlorotic leaves and general dieback of the
infected tree.
• In this case the infected tree will also show a bulge above the bud union
and honeycombing on the inner face of the original sour orange root
stock bark.
7. STEM PITTING
Stem-pitting is another symptom of CTV that manifests
in most host types under the proper conditions, and
especially in Citrus trees grafted onto sour orange
rootstock.
The host will develop pits in the trunk and stem.
This results is decreased tree vigor and reduced fruit
yield.
This is typically caused by the more virulent strains of
CTV.
8.
9. YELLOW OF SEEDLING
• The third major symptom of CTV infection is seedling
yellows. This tends to occur on sour
orange, Natsudaidai, lemon and buntan. Symptoms
include yellowing of foliage and general dieback.
12. VECTOR
• CTV is a virus that is limited to the phloem tissues of
its host.
• It is transmitted semi-persistently by vectors that
penetrate the phloem to extract sap, mostly the aphid
species that colonize the crop.
• The brown citrus aphid is considerably more efficient at
transmitting the virus than are other aphids that infest
citrus.
14. MODE OF SPREAD
• The aphids require at least 30 to 60 minutes of feeding to acquire the
virus, and remain viruliferous for at least 24 hours.
• T. citricida is much more efficient than the other aphids, and it can
transmit CTV strains causing severe stem pitting or decline that the
other aphids cannot vector.
• The main cultural practice that increases the severity of the CTV is
when the citrus trees are grafted onto the sour orange rootstock.
• Using CTV infected budwood for grafting can transfer the CTV from
the original tree to the new one.
15. PATHOGEN CHARACTERS
CTV is a flexuous rod virus with dimensions of 2000nm long
and 12nm in diameter.
The CTV genome is typically between 19.2 and 19.3 kb long
and consists of a single strand of RNA enclosed by two types
of capsid proteins.
The size of genome makes CTV one of the largest RNA viruses
known.
The CTV genome consists 12 open reading frames which
could encode atleast 17 proteins
16. MANAGEMENT-PREVENTIVE MEASURES
• Check quarantine regulation in the area to avoid
transmission of the disease.
• Use resistant rootstock of e.g. trifoliate orange, Sunki, and
Shiikuwasha have been used for many years.
• Some hybrids, such as Troyer citrange or Swingle
citromelo, show promise as resistant root-stock.
• Keep nurseries and greenhouses free of insect vectors.
• Do not transport suspicious citrus material to other farms.
18. BIOLOGICAL CONTROL:
Some field experiments with parasitoid wasps or gall midges are
ongoing, which could naturally control some of the aphids in
citrus grooves.
Use commercially available formulations (natural pyrethrum,
fatty acids), insecticidal soaps or horticultural oils (plant or fish
oils) to control populations.
Aphids can also be wiped out by spraying the leaves of the plant
with a mild solution of water and a few drops of detergent.
19. REFERENCES
• Tripathi. D.P., Introductory Plant Virology, Kalyani
Publishers, New Delhi.pg:351-353
• Thind. T.S., Diseases of fruits and vegetables and
their management, Kalyani Publishers, New
Delhi.pg:70-82
