Introduction: Citrus canker is a plant disease which was originated from Southeast Asia i.e. India. It is a kind of bacterial disease that can cause endemics in most of the areas because it spreads rapidly by many factors which we will also discuss and it has high potential to cause damage that can infect all the surrounding citrus growing fields. Therefore, it can cause huge ecological loss by creating damage to the citrus plant species.
Causative agent: Xanthomonas axonopodis
Host range: Acid lime, sweet orange and grapefruit plants etc.
Endemics: Brazil and the United States
Content: Citrus Canker
- Causative Agent
- Favourable Conditions
- Disease Cycle
- Control Measures
Citrus canker is a disease that mainly occurs in citrus plants which includes lemon, orange, key lime, pomelo, grapefruit plants etc. whose causative agent is Xanthomonas axonopodis.
Xanthomonas axonopodis is a bacteria which is having following features:
Gram reaction: Negative
Motility: It consists of single polar flagella i.e. Xanthomonas axonopodis is having monotrichous flagella.
Respiration: Xanthomonas axonopodis undergo “Aerobic respiration” .
Genome: Xanthomonas axonopodis consist of ds-DNA.
Genome size: The genome size of Xanthomonas axonopodis is 5megabase- pairs.
Enzymes: Xanthomonas axonopodis contains cellulose, pectate lyase, protease, and type-3 proteins which are responsible for the pathogenicity of the bacteria and acts as “Virulence-factors”. All these enzymes induce host susceptibility in plants, which can destroy or infect the entire crop field.
Capsule. The mucilaginous capsule is present in Xanthomonas axonopodis.
Endospore formation: Xanthomonas axonopodis are non-endospore formers.
Effects: Xanthomonas axonopodis can cause effects like the formation of lesions, yellow-brown watery halos which forms irregularly on the leaves, fruits, stem, branches etc.
Based on the distribution of Xanthomonas axonopodis it is of following types:
- Asiatic types of citrus canker: This type of citrus canker is widely distributed in Asia which is caused by X. axonopodis pv. Citri.
- Cancrosis B: This type of citrus canker is widely distributed in South America is caused by X. axonopodis pv. aurantifolii.
Favourable Conditions for citrus canker disease
There are many environmental conditions that favour the disease of citrus canker which is as follows:
- Mild temperature between 20-30 ֯ C.
- Wet weather or humidity.
- Heavy rain
Transmission of Citrus Canker
The disease of citrus canker disseminates by the following factors which include:
- Direct contact uninfected plant with an infected plant.
- Use of wrong vegetative methods.
- Dissemination by environmental factors like wind, rain etc.
Symptoms of Citrus Canker
The symptoms of citrus canker may include:
- The lesions first appear on the lower surface of the leaves as different spots.
- In starting, the lesions appear as small, round, corky.
- Later, margin raises out from the lesions which are yellowish-brown in colour.
- Then in the more advanced stage, the lesions become white to grey in colour which finally ruptures. Then yellow watery halo surrounds the lesion which slowly infects the whole plant body including leaves, stem, branches, fruits, twigs etc.
- Defoliation of leaves.
- The premature death of a plant.
Pathogenicity of Xanthomonas axonopodis
Xanthomonas axonopodis first attack the cuticle of the plant which enters through the stomatal pores of the leaves by the rainwater and through the wound i.e. by any cut in the leaf.
Then in the epidermis Xanthomonas axonopodis undergo multiplication where it increases its number. After multiplication, it occupies in the intercellular spaces in the plant tissue.
Then, it damages the middle lamella and after that enters into the mesophyll cells by infecting it. At last, it infects the lower surface of the leaf and at this stage, first symptoms appear in the form of lesions which is due to malic acid formation due to intense metabolic activity.
Disease Cycle of Citrus Canker
First, the infection starts through the infected leaf or stem which disseminates through rain and wind which carries the inoculum to the uninfected plants. Then the inoculum slowly causes water congestion inside the stomata and mesophyll cells of the plant tissue. Later, the pre-symptoms appear in the form of lesions on the foliage (Leaves), fruits, stems etc.
And, during conditions like rain and irrigation, the bacteria ooze out of the lesions onto the plant surface. Then post symptoms appear with raised margin, sunken centre with a yellow-brown halo that surrounds the lesions. And, again it disseminates through various factors and the disease cycle continues in this way.
Control Measures of Citrus Canker
- Removal or eradication of infected plants which can be done by a burning method where the whole infected area is eradicated by burning.
- Pruning can be also done by which the infected parts of the plants are removed by the pruning scissors.
- Use of disease-resistant varieties of the crop.
- Bordeaux mixture and lime sulphur can use in the form of sprays to combat the disease.
- Neem cake can also use in the field.
- Antibiotic sprays like streptomycin sulphate and phonomycin are found to be very effective against this disease of citrus canker.
Therefore, through all these control measures, the disease of citrus canker can be managed.