Slide 2: Almost all the plants on earth are affected by disease producing micro-organisms. It I not possible to study all the diseases affecting all the plants. Therefore, we will study only few diseases that affect important plants like rice, wheat, sugar-cane and ground nuts.
Rice I san important major crop in our country. From the time of sowing, till the time of harvest, there is possibility of getting diseases from pathogenic organisms like bacteria, viruses or fungi.
Leaf Blight in Rice : Leaf Blight in Rice Is caused by a bacteria mostly in high yielding variety of rice. The disease occurs during the months of July to October and is characterised by the presence of a long yellow or straw coloured lines with wavy margins on leaf. The diseased leaf dries up from the ti to base. In severe infection, entire paddy crop gives a burnt appearance. Bacteria spread from affected leaves to healthy leaves through droplets of water or by direct contact of healthy leaf with an affected leaf. Even seeds are affected by this disease. Sowing of infected seeds lead to the reappearance of the disease in the next crop. Infected seeds should be treated with chemicals or hot water before sowing.
Blast of Rice : Blast of Rice Is produced by a fungus.
Symptoms are prominent on leaves. Infection also occurs on leaf sheaths and stem parts including the grain. Steam and leaf are covered with fluffy white hyphae of the fungus. Plant cells in the infected area are killed by the fungus and the art with dead cells changes its colour to brown. Central part of the spot appear pale yellow with a dark brown border. If the leaves are infected early, they drop off. Grain fans off it the infection occurs below the grain.
Wheat Rust : Wheat Rust The most common fungal disease in wheat is Wheat Rust
Brown of rust coloured pustules appear on leaves and stem. Infection causes premature falling of leaves and reduces yield, a variety of wheat resistant to rust diseases have been developed.
A common disease in sugar-cane is red rot. Leaves are affected by disease. The inner part of cane become red in colour. Diseased cane should not be allowed to grow in the field and it should not be used for sowing in the next season. Sugar-cane plants with this disease should be taken out and burnt far away from the field. Disease resistant varieties should be used to prevent the attack of this fungal disease.
Tikka Disease : Tikka Disease A common disease in ground nut is Tikka disease.
In the diseased condition, many circulars spots appear on the surface of the leaf . The conidia of the fungus present in soil or those present in the fruit shell is the source of infection. Use of fungicides controls the disease.
Points to Remember: : Points to Remember: Study of diseases is known as pathology.
Disease producing organisms are known as pathogens.
Pathogens are present among bacteria, viruses, fungi and protozoa's.
Study of plant diseases is called plant pathology.
Leaf blight in rice gives burnt appearance in the field.
Blast of rice, Wheat rust, Red rot in sugar-cane are produced by a fungus.
Tikka disease in ground nut is characterised by circular spots on leaves.