Citrus canker is a widespread disease affecting citrus plants worldwide. It is caused by the bacterium Xanthomonas citri. The disease produces lesions on leaves, twigs, fruits, and branches that appear as small, raised spots that eventually rupture, giving a crater-like appearance. Wet weather and temperatures between 20-30 degrees Celsius promote the spread of the disease. Control methods include destroying infected plants, using disease-free nursery stock, pruning infected twigs, and spraying with copper-based fungicides. The bacterium spreads primarily through rain splash and insects like citrus leaf miners.

1. CITRUS CANKER
Dr. Sr. Meena K Cheruvathur
Assistant Professor
Department of Botany
St. Mary’s College Thrissur

2. Citrus canker, Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
CITRUS CANKER
Citrus is a common term used for fruits of Genus Citrus belongs to
family Rutaceae. It is a native of Australia and now cultivated in all
over the world.
 Citrus canker is originated in China. It is a wide spread disease in all
citrus growing areas of the world now.
SYMPTOMS.
The disease occurs on leaves, twigs, thorns, older branches and fruits.
Lesions first appear on the lower side of the leaves as small, round,
watery, translucent spots.
They are raised and become yellowish brown.

3. Citrus canker , Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
CITRUS CANKER SYMPTOMS

4. Citrus canker , Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
 The spots 1mm to 1 cm increase in size and coalesce to form
elongated lesions on fruits and twigs.
In advanced stages surface of the spots become white or
grayish.
Finally centre of the spots ruptures, giving a rough, corky
crater like appearance.
The rough lesions surrounded by yellowish brown to green
raised margin and watery yellow halo.
Spots occurring on midrib of leaves and petioles cause
premature defoliation.
Cankers on twigs cause them to break.

5. Citrus canker, Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur

6. Citrus canker , Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
As the lesions age, gradually increase in size to 5-10mm
over several months.
Large or older lesions may have a crater-like centre, which
can fall out to create a ‘shot-hole’ appearance, occur in
clusters where water pools on the leaf (such as along leaf
margins or tips).
It can follow the feeding tracks of citrus leaf miners,
where the wound provides an entry point for the bacteria.
Multiple lesions on fruit or stems are seen in cases where
the foliage is severely affected.

7. Citrus canker, Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
On larger branches
cankers/lesions are large, irregular,
rougher and more prominent.
Cankers on fruits are similar to
those on leaves, but yellow halo
absent.
In fruits, crater like depression in
the centre is more prominent.
Injury to fruits is only skin deep
and no effect on pulp or juice.

8. Citrus canker, Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
Pathogen
 Gram negative, aerobic bacterium Xanthomonas citri is the
causative organism.

9. Citrus canker, Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
Pathogen
Wet weather ( rainy season) and mild temperature (between 20 -
30 degree) is favorable for disease development.
Presence of free moisture on host surface for at least 20 minutes
support successful infection.
Bacterium enters the host through natural
openings like stomata and through wounds.
It multiply in the intercellular spaces,
dissolves middle lamella and establishes in the
cortical region.

10. Citrus canker, Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
Spread of disease
Bacteria does not survive in soil or infected plant parts fallen on
the ground.
Attacked twigs bearing old lesions on the tree are main source of
perenation of the pathogen.
 Bacteria from the cankers are mainly disseminated by
1. Rain splashes
2. Insects (Citrus leaf miners) and
3. Transfer of disease through infected nursery stock

11. Citrus canker , Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
Control measures
• Very difficult to control.
•Only practical method is destruction of the diseased plants by
burning them.
•Use of disease free nursery stalk.
•Spraying of 1% bordeaux mixture before planting in new
orchards.
•In old orchards, pruning of the affected twigs, Spraying of 1%
bordeaux mixture at periodical intervals especially rainy season.
•Burning of dropped of leaves and twigs.
•The vigour of the plant should be maintained by proper irrigation
and fertilization.
•Proper care given to minimize the attack of leaf miners.
•Rigidly follow quarantine measures.
•Development of resistant varieties

12. Citrus canker , Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur
References:
https://www.agric.wa.gov.au/citruscanker/citrus-canker-declared-
pest?page=0%2C1
https://www.easybiologyclass.com/citrus-canker-symptoms-causal-
organism-and-control-measures-pathology-lecture-notes/
https://www.plantmanagementnetwork.org/pub/php/review/citrus
canker/

13. Citrus canker, Dr. Sr. Meena. K. Cheruvathur, St. Mary’s College, Thrissur