Pathology ppt

BACTERIAL LEAF BLIGHT OF RICE

BACTERIAL LEAF BLIGHT OF RICE

• Pathogen : Xanthomonas campestris p var

oryzae Class : Schizomycetes Order: Pseudomonadales Family : Pseudomonadaceae

• History : It was 1st reported in Japan during 1884 & in India during the year 1951 in Maharashtra. Later on,in 1962 the disease broke out in the form of epidemics in Bihar and other parts of North India. Now this disease is found to be prevalent in all parts of country.

Symptoms

Leaf blight

kreseck

yellowing

Symptoms

• The disease appears early in August and becomes quite distinct when the ears developed.

• The symptoms of the disease may vary depending upon growth stage of the crop. There are 3 types of symptoms

Leaf blight Kreseck /wiltYellow leaf

• Leaf blight : this symptoms will appear 4-6 weeks after transplanting.

Appearance of small circular water soaked spot on the margins of the leaf & this spots also extends to leaf sheath, also later this spots turn yellow & becomes necrotic & results in drying of leaf.

• Under humid conditions creamy white color bacterial oozes comes out from the young lessions in the morning hours.

• Yellowing stage : Here individual leaf becomes yellow later wilting & dies.

• Kreseck / wilt : this is the most destructive stage & Kreseck degenerations / wilting.

Young plants are more susceptible which shows sudden wilting. The bacteria multiplies in vascular bundels , exudation of bacterial ooze at the cut end portion of leaf.

Etiology

• The bacteria is rod-shaped measuring 0.5 to 0.8 * 1 to 2 µ. They occur singly or in pairs. They are Gram –ve , aerobic and with a single polar flagellum. They are non-sporing and do not form chains.

Infection

• Infection takes place through wounds. The nitrogenous fertilization of the crop increases the incidence of the disease. If the seedlings are infected, the disease intensifies, after transplanting.

Predisposing factors

Rainy weather, dull windy days and a suitable temperature of 22 c to 26 c, clipping of tip of ̊ ̊leaves of seedling during transplanting , excess application of nitrogenous fertilizer favor the incidence of the disease.

• PSI : bacterial cells present on seeds, stubbles & in soil. Here collateral host like Leessia hexandra, Cyprus rotundus plays a major role.

• SSI : bacterial cells spread through irrigation water and rain from one field to another.

Management

• Removal, collection and burning of diseased plant parts straw left over in the field after harvest

• Burning of choffy grains near the threshing yard

• Irrigation canal, paddy field should be kept free from weed , avoid movement of irrigation water from field to field

• Selection of healthy seeds for sowing.• Avoid clipping of tip of the leaves• Judicious use of nitrogenous fertilizer • Growing of resistant varieties Swarna, Ajay,

IR20• Spraying of the crop with streptocyclin @ 0.6 g/litre.

Plant

health is

wealth