Citrus canker.PPTX disease of lemon......

Fawcett and Jenkins (1933) reported that citrus canker disease is originated in India

This disease affects cultivars and hybrids of citrus and citrus relatives including orange, grape wine, mandarin, lemon, lime, tangerine, sour orange and rough lemon.

Because of its rapid spread, high potential damage and impact on export and domestic sales, the disease is a significant threat to all citrus growing countries.

1. Citrus canker Pragya Atrey Department of Microbiology

2. Fawcett and Jenkins (1933) reported that citrus canker disease is originated in India This disease affects cultivars and hybrids of citrus and citrus relatives including orange, grape wine, mandarin, lemon, lime, tangerine, sour orange and rough lemon. Because of its rapid spread, high potential damage and impact on export and domestic sales, the disease is a significant threat to all citrus growing countries.

3. Morphology of the causal organism : (Pseudomonas citri or Xanthomonas citri .) Xanthomonasis small aerobic, rod shaped motile bacterium. It is 5.20×0.5-0.75 micron in size and has single polar flagellum. It forms chains and capsules but no spores. It is a short, rod shaped bacterium , motile by means of a single polar flagellum . It is 1.5- 3u long and 0.5 – 1.5u broad and strictly aerobic.

4. Symptoms : • Plants infected with citrus canker disease have characteristic lesions on leaves, stems and fruits with raised brown, water soaked margins, which develop around the necrotic tissues • A characteristic symptom of the disease on the leaves is the yellow halo that surrounds lesion. • These lesions start as pinpoint spots and attain a maximum size of 2-10mm diameter. • Lesions become visible about 7-10 days after infection on the lower surface. The lesion persists on twigs and branches for several years and support long-term survival of the bacterium. • Old lesions become corky and brown. • On young twigs, lesions are similar to those on leaves but on older twigs, they are more irregular in shape • Severely infected fruits can drop prematurely, leading to reduced yield. • The internal quality of mature fruit with lesions is unaffected and is still edible and usable for juice. • In severe infection defoliation and broken twigs also occurs and lastly entire plant dies.

5. Transmission of Citrus Canker The disease of citrus canker disseminates by the following factors, which include : 1. Plant to plant dissemination : It occurs via the contact of an infected plant with the uninfected one . 2. Improper vegetation : The use of wrong vegetative methods and improper handling of the plants also transmits the infection . 3. Extrinsic factors : It includes environmental factors like wind, rain etc. that favor the dissemination of infection . 4. Insect vectors : Insects transmission is one of the common types of plant disease transmission . 5. Water splashing : It also favors disease propagation .

6. Disease cycle: • Infected twigs having old lesions are the main source of infection . • These lesions ooze bacteria, which are blown away by the wind or dispersed by rain. Healthy plants are infected by these bacteria, which entered through stomata, or wounds (caused by citrus leaf minor phyllocnistiscitrellain feeding activity ). • The bacteria after penetration in to host multiply in the intercellular spaces, dissolve the middle lamella and are established in to the cortex . • Lesions on healthy plants become visible about 7 to 10 days after infection on the underside of the leaves and soon thereafter on the upper surface . • Man is also an important agent of dissemination through infected nursery stock . • High mean temperature (20- 30) coincide with high rainfall favors the development of disease.

7. Control measures: • Eradication of infected trees and burning them. • Applying preventive sprays of copper based Kocide 3000. • Pruning of infected twigs and leaves during the dry season and then spraying the trees with 1% Bordeaux mixture. • Spraying the antibiotics e.g. streptomycin sulphate and phonomycin . • Strictly applying quarantine methods. • Replacing susceptible citrus cultivars with resistant cultivars. • Growing winds breaks to hinder inoculum dispersal. • Developing transgenic plants for e.g. Xanthomonas resistance gene from the rice has been transferred in to sweet orange .

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