Bacterial leaf blight of rice

 Bacterial leaf blight of rice

Pathogen :-Xanthomonos oryzae.

Distribution :- this disease has been recorded from Japan, Philippines , china and Mexico, in India, this disease was observed in south India by Srinivasan in 1959. 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.

Symptom:- This disease appears early in august and become quite distinct when the ears are developed. Small water-soaked spots 5 to 10 mm in length are formed along the margin of the leaf blade or along the prominent veins. Gradually several lesion coalesce to form whitish or yellowish blotches .The infection takes place in wounds caused by wind damage, along the margins and prominent veins. In seedling stage, the tips of the leaves are affected. Small droplets of bacterial exudates are formed on the lesions. These droplets harden into yellowish or amber-colored resinous granules. Ultimately the leaves dry up and the plants die. The vascular bundles remain filled with bacteria. In severe infection, the pathogen has been found in the glumes and even in the endosperm of the grain.

The pathogen:- the disease is caused by Xanthomonas oryzae . the bacterium is rod-shaped measuring 0.5 to 0.8 * 1 to 2 microns. They occur singly or in pairs .They are gram negative, aerobic and with a single polar flagellum. They are non-sporing and do not form chains. The colonies found on nutrient agar are waxy-yellow, round, smooth and glistening.

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.

Control measures:-

   Resistant varieties- The most economic and easy method of control is to sow the resistant varieties. Kidama variety is highly resistant for this disease.

Use of fungicides- spraying of copper fungicide alternately with streptocycline has been proved to be useful to some extent. Soaking of seed for eight hours in ceresin (0.1 per cent) and streptocycline has been recommended.

         Thirty- three varieties showed highly resistant reaction during 1987,198 ,1989 , such as IET 9198, IET 4141, RO 2151-64-3-11, RP 2151-165-1,RP 2151-173-8, CR 316-636, IR 226082-91-1-2-2-2-2, ETC