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Agricultural crops :: Cereals :: Rice

Bacterial leaf blight: Causal organism: Xanthomonas oryzae pv. oryzae

Symptoms

  • Bacterial blight syndrome exhibits three types of symptoms: leaf blight, kresek (the seedling blight or wilt phase) and the pale-yellow leaf.
  • The disease has been referred to as “bacterial leaf blight” to indicate that the “leaf blight” phase of the syndrome is the most distinct and commonly observed symptom.
  • Seedlings in the nursery show circular, yellow spots in the margin, that enlarge, coalesce leading to drying of foliage.
  • “Kresek” symptom is seen in seedlings, 1-2 weeks after transplanting.
  • The bacteria enter through the cut wounds in the leaf tips, become systemic and cause death of entire seedling.
  • In grown up plants water soaked, translucent lesions appear near the leaf margin.
  • The lesions enlarge both in length and width with a wavy margin and turn straw yellow within a few days, covering the entire leaf.
  • As the disease advances, the lesions cover the entire lamina which turns white or straw coloured.
  • Milky or opaque dew drops containing bacterial masses are formed on young lesions in the early morning.
  • They dry up on the surface leaving a white encrustation.
  • The affected grains have discoloured spots.
  • If the cut end of leaf is dipped in water, it becomes turbid because of bacterial ooze.

Pathogen Character:

  • The bacterium is aerobic, gram negative, non spore forming, rod with size ranging from 1-2 x 0.8-1.0􀀀m with monotrichous polar flagellum.
  • Bacterial colonies are circular, convex with entire margins, whitish yellow to straw yellow colored and opaque.

Favourable conditions / Epidemiology:

  • Clipping of tip of the seedling at the time of transplanting
  • Heavy rain, heavy dew, flooding, deep irrigation water
  • Severe wind and temperature of 25-30 0 C
  • Application of excessive nitrogen, especially late top dressing
Bacterial leaf blight
 
 

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