Citrus canker Caused By: Xanthomonas axonopodis.

2. Citrus canker
Xanthomonas axonopodis pv. citri.

3. Citrus canker
 Causal Organism:
 Xanthomonas axonopodis pv. citri.
 A bacterial disease that causes significant damage to citrus
species.
 including oranges, sour oranges, grapefruit, lemons and limes.
 Citrus canker is most severe in hot, wet areas.

4. History
 Citrus canker was first identified in the United States near the Florida-Georgia
border in 1910.
 From 1910 to 1931, 257,745 grove trees and 3,093,110 nursery trees in 26
counties were destroyed.
 From Pakistan it was first reported in Punjab and after which it becomes
epidemic throughout the country.

5. Symptoms
 Leaf Lesions:
 Citrus canker lesions start as pinpoint spots maximum size of 2 to 10 mm
diameter.
 The eventual size of the lesions depends mainly on the age of the host tissue at
the time of infection and on the citrus cultivar.
 Lesions become visible about 7 to 10 days after infection on the underside of
leaves and soon thereafter on the upper surface.
 A characteristic symptom of the disease on leaves is the yellow halo that
surrounds lesions
 A more reliable diagnostic symptom of citrus canker is the water-soaked margin
that develops around the necrotic tissue.

7.  Fruit and Stem Lesions
 Citrus canker lesions on fruit and stems extend to 1 mm in depth, and are
superficially similar to those on leaves.
 Infection of fruit may cause premature fruit drop but if the fruit remain on the
tree until maturity such fruit have reduced fresh fruit marketability.
 On stems, lesions can remain viable for several seasons. Thus, stem lesions can
support long-term survival of the bacteria.

9. Pathogen
 The bacterium Xanthomonas axonopodis pv. citri is a rod-shaped, gram-negative.
 colonies on laboratory media are usually yellow due to ‘xanthomonadin’ pigment
production.
 The maximum and optimum temperature ranges for growth are to 39°C (95 to
102°F) and 28 to 30°C (82 to 86°F), respectively.

10. Disease Cycle
 Bacteria propagate in lesions in leaves, stems, and fruit. When there is free
moisture on the lesions, the bacteria ooze out and can be dispersed to infect new
growth.
 Wind-driven rain is the main dispersal agent.
 wind aids in the penetration of bacteria through the stomatal pores or wounds
made by insects (leaf miner).
 Multiplication of bacteria occurs mostly while the lesions are still expanding.
 And numbers of bacteria produced per lesion is related to general host
susceptibility.
 The bacteria remain alive in the margins of the lesions in leaves and fruit until
they fall to the ground.

11. Management
• Carefully destroy infected fruit and leaves
• Replace susceptible citrus cultivars with resistant cultivars such as Valentia late,
Seedless lemon and Long lemon
• Spray Bordeaux mixture to help reduce the intensity of this disease
• Copper based fungicides are also considered to be good for the control of citrus
canker
• Leaf miner control can reduce disease pressure considerably, for this purpose
spray Imidacloprid 40 ml or 7.9% Bifenthrin (e.g. Talstar) 20ml
 When using a pesticide, always wear protective clothing and follow the
instructions on the product label, such as dosage, timing of application, and pre-
harvest interval.