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Bacterial leaf blight

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1. This disease occurs mostly in low altitude areas of Tripura, Meghalaya and Arunachal Pradesh during July to September. The disease is caused by Xanthomonas campestris pv. Oryza.

2. The bacterium induces either wilting of plants or leaf blight. Leafblight phase is most commonly seen and typical symptoms are yellow to straw coloured stripes with wavy margins, generally on both edges of the leaves. These stripes start from the tips, extend downward and cover the entire leaf. The blighting may extend to the leaf sheaths and culms, killing the tiller or whole clump.

3. The phase usually appears 4-6 weeks after transplanting. The most destructive phase of the disease is 'kresek' or wilt resulting from early systemic infection. The leaves roll completely, droop and turn yellow and grey and ultimately the whole plant wilts and dies.
4. The kresek affected clumps may be confused with stem borer attack. However, borer affected tillers can be easily pulled out, which is not so in kresek' affected tillers. To distinguish 'krisek'; symptoms from stem borer damage, the lower part of the plant should cut off and squeeze between the fingers. Yellowish bacterial ooze will appear at the cut ends if the kresek is present.

5. Primary infection may result from diseased seeds, stubble, straw, and weed hosts such as Cyprus rotundas, C. deforms and Leticia exedra.

6. Thebacteria enter through hydathodes or wounds of the plant. It multiplies in the plant and becomes systemic in vascular bundles causing plugging of the water-conducting tissue, which results in wilting of plants.

7. The bacteria disseminated through irrigation water and wind-borne rain. The disease spreads fast under favourable weather conditions like incessant rains, strong wind and warm temperature (22-26°C). Plants in shade and close-planted crops supplied with high doses of nitrogen show more disease incidence.

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Photo Courtesy: 
Dr.Krishna Veni (DRR)
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