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Bacterial leaf blight (BLB) of rice

Causal Organism: Xanthomonas compestris pv. Oryzae

Bacterial blight is a monsoon disease and its incidence and severity is very much influenced by rainfall, number of rainy days, and susceptibility of the cultivar and nitrogen fertilizer application. Severe epidemics recorded in 1979 and 1980 in northwestern India, reducing the grain yields drastically.

Symptoms

The bacterium induces either wilting of plants or leaf blight. Wilting syndrome known as 'Kresek' occurs sporadically in the fields causing serious damage. It commonly occurs within 3-4 weeks after transplantation of the crop. Kresek results either in the death of whole plants or wilting of only a few leaves. Leaf blight phase is the most predominant form of the disease occurring between tillering and heading stage of the corp. Third type of less conspicuous symptoms caused by the bacterium is yellowing of leaves. Such leaves show blighted appearance.

The earliest symptom of the blight phase is the appearance of dull greenish water-soaked or yellowish spots 5-10 mm in length on the leaf towards the tip or margins, leading to tip and marginal dying. The infection soon extends along one or both margins, sometimes to the leaf sheath. As the disease progress, several lesions coalesce to form straw-brown large lesions or blighted portions. The inner margin of the blighted patch in contact with the adjoining green portion of the leaf is ragged or wavy. Occasionally, the lesion may extend from the tip downward along the midrib itself, the leaf margins remaining green. Small droplets of bacterial ooze, pale amber in colour, are found on the affected portions.

Management

  •  Use seed from disease free crop.
  •  Treat the seeds by soaking it for 12hrs in a mixed solution of streptocycline(0.15%) and wetable Ceresan (0.05%) followed by hot water treatment at 52oC-54oC foe 30 minutes.
  •  Growing resistant varieties is the best way to disease management, some of the commercially cultivated resistant varieties to bacterial blight are Ajay, PR 114, Swarna, MTU 4870,HKER 120, IR 36, IR 64 and Saket 4, IR-20,IR-54,Pusa2-21, , Asha and Daya.
  •  If the favorable weather persists and disease is at flare-up stage, it is advisable to withdraw application of nitrogen fertilizer at that stage of crop growth to minimize the effect of disease on yield.
  •  Spray the crop with copper fungicides like Blitox-50 and other formulations of Copper fungicides also will helpful in reducing disease.
  •  Application of Streptocycline @ .6% for spray.
  •  Drain away the water from fields as frequently as possible.
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