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Bacterial leaf blight (BLB) in paddy

Bacterial leaf blight (BLB) is a major foliar disease of rice caused by the gram-negative bacterium Xanthomonas oryzae pv. oryzae. It is endemic in tropical Asian rice ecologies and is one of the principal diseases shaping fine-grain variety breeding in India.

Identification and symptoms

The diagnostic symptom is a V-shaped yellow lesion advancing inward from the leaf tip along the leaf margins. Lesions later turn straw-white and the leaves wilt and dry. Younger infections may also show a 'kresek' phase in which whole leaves and tillers wilt. Bacterial ooze is visible when freshly cut leaves are dipped in clear water.

Host crops and life cycle

The pathogen survives on infected stubble, weed hosts and seed, and spreads through irrigation water, rain splash and through wounds caused by typhoons, leaf-cutting and mechanical damage. Warm, humid weather, dense canopies and high nitrogen rates accelerate spread, making the boot-to-panicle window the critical risk period.

Damage and economic impact

Severe outbreaks cause leaf desiccation before grain fill and can reduce grain yield substantially. Field trials reported a disease index near 22% under best chemical management and corresponding yields around 56.5 q/ha, compared to higher disease and lower yield under untreated control.

Management

  • Resistant varieties: lines carrying Xa resistance genes such as Improved Samba Mahsuri and Drr Dhan 75 are widely deployed; many older fine-grain varieties including Bpt 5204 are susceptible.
  • Clean seed: certified disease-free seed and hot-water seed treatment reduce primary inoculum.
  • Nutrition: balanced nitrogen, avoiding late luxury N at booting (Paddy Panicle Stage Management, Paddy Panicle Stage Fertilization).
  • Chemical: foliar sprays of streptocycline (streptomycin sulphate + tetracycline) combined with copper oxychloride give the lowest disease incidence and the highest grain response in published trials, outperforming kasugamycin and agrimycin alone.

See also: Paddy Bacterial Leaf Blight, Paddy Blast Disease, Brown Spot Paddy, Drr Dhan 75, Bpt 5204.

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.