12th botany neet school

Citrus canker, Tungro disease of rice

Citrus canker

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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.

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Other links 

Plant physiology – photosynthesis and its significance

BIOLOGY IN HUMAN WELFARE Introduction & Food production

Aims of plant breeding

Aspects of plant breeding and Types

Hybridization in plant breeding

Polyploid breeding, Mutation breeding, Breeding for disease resistance

Genetic engineering, Improved varieties, Role of biofertilizers

Green manuring, Mycorrhiza as biofertilizer

Benefits from biofertilizers

Crop diseases and their control, Rice – Oryza sativa

Groundnut or peanut – Arachis hypogea

Biocontrol of insect pests Bacterial pesticides

Genetically modified food

Bio war, Genetically Modified Organisms (GMO) in biological warfare

Biopiracy, Bioresources, Biomolecules, Biopatent, Biotechnology

Sustainable agriculture

Medicinal plants including microbes

Commonly Available Medicinal Plants

Microbes in medicine

Economic importance of Food plant Rice

Oil plant Groundnut Economic importance

Fibre plant – Cotton Economic importance

Timber yielding plant Teak Economic importance

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