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Bacterial leaf blight in paddy (Xanthomonas oryzae pv. oryzae)

Bacterial leaf blight (BLB) is a foliar disease of rice caused by the gram-negative bacterium Xanthomonas oryzae pv. oryzae. It is one of the principal foliar diseases of rice in tropical Asia and a leading target of resistance breeding in Indian fine-grain paddy.

Identification and symptoms

Lesions begin as water-soaked streaks near leaf tips that develop into V-shaped yellow areas advancing inward along the margins. Affected leaves later turn straw-white. Younger infections may show a kresek phase, in which whole leaves and tillers wilt soon after the bacterium enters through wounds. Bacterial ooze can be seen as droplets on freshly cut leaves dipped in clear water.

Host crops and life cycle

The pathogen survives on infected stubble, seed and grassy weed hosts and spreads in irrigation water, rain splash and through wounds. Warm humid weather, dense canopies and excessive nitrogen during booting are the principal triggers for in-season epidemics.

Damage and economic impact

Severe BLB causes leaf desiccation before grain fill, reducing grain weight and head rice recovery. Indian field trials reported the best chemical management combination producing yields around 56.5 q/ha at a disease index of about 22%, while untreated controls suffered substantially greater leaf damage and lower yields.

Management

  • Resistant varieties: lines with Xa genes such as Drr Dhan 75 and Improved Samba Mahsuri are core to control.
  • Clean seed and hygiene: certified disease-free seed and hot-water seed treatment cut inoculum.
  • Balanced nutrition: avoid excess and late nitrogen at boot stage (Paddy Panicle Stage Management).
  • Chemical: streptocycline (streptomycin sulphate + tetracycline) plus copper oxychloride is the most effective combination in published field trials, outperforming kasugamycin and agrimycin alone.

See also: Bacterial Leaf Blight Paddy, Bacterial Panicle Blight Paddy, Paddy Blast Disease, Brown Spot Paddy, Drr Dhan 75.

References

  1. Bacterial leaf blight (Xanthomonas oryzae pv. oryzae). TNAU Agritech Portal.
  2. Management of bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae under field condition. Journal of Pharmacognosy & Phytochemistry, 2017.