Disease due to a bacterium Xanthomonas citri. This bacterium is of bacillus and gram negative type. In India, this is the most commonly prevalent disease during the rains.
The disease affects the leaves, twigs, thorns and fruits. All green
parts and maturing fruits become more or less covered with brown scabby spots surrounded by dark – brown glossy margins.
The lesions may enlarge to a diameter of 3 or 4 mm become raised and rough and turn brown. The bacteria enter through the stomata and wounds and multiply in the cortex to which they are confined.
The infection can be largely prevented by removing the infected branches and spraying the plants with Bordeaux mixture or spraying 3 to 4 times in a season with antibiotic the streptocycline at the rate of 1 gm in 45 liters of water.
Tungro disease of rice
Disease incited by a virus Rice Tungro virus. The virus is transmitted by a leafhopper.
The symptoms appear first on the emerging leaf. They are mild
interveinal chlorosis (loss of chlorophyll), mild mottling and yellowing. Plant shows stunted growth and symptoms appear on the lower leaves. They turn yellow orange, bend downwards and possess dark brown spots.
Transmission of virus
The leafhopper retains infectivity for a short period only and transmits the virus to another plant immediately after feeding on an infected plant.
Biological agents that are used for control of insects, weeds and
pathogens produced from living organisms are called biopesticides. Microorganisms such as viruses, bacteria, fungi, protozoa and mites may be used as biopesticides.