Bacterial leaf blight: Xanthomonas oryzae pv. Oryzae
Symptoms:
- Water-soaked to yellowish stripes on leaf blades or starting at leaf tips with a wavy margin
- Leaves with undulated yellowish white or golden yellow marginal necrosis, drying of leaves back from tip and curling, leaving mid rib intact are the major symptoms.
- Appearance of bacterial ooze that looks like a milky or opaque dewdrop on young lesions early in the morning
- Severely infected leaves tend to dry quickly
- Loss in grain yield may be up to 60%.
Factors favouring disease development
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- Presence of rice stubbles and ratoons of infected plants
- Presence of bacteria in the rice paddy and irrigation canals
- Warm temperature (25-30° C), high humidity, rain and deep water.
- Severe winds, which cause wounds and over fertilization are suitable factors for the development of the disease.
- Presence of weeds
- Irrigation water and splashing or windblown rain can disseminate the bacterium from plant to plant.
- The use of trimming tools for transplanting and by handling during transplanting can also trigger new infection.
Identification of pathogen:
- The bacteria causing disease are rods, 1.2 x 0.3-0.5 µm. They are single, occasionally in pairs but not in chains.
- They are Gram negative, non-spore-forming and devoid of capsules.
- Their colonies on nutrient agar are pale yellow, circular and smooth with an entire margin. They are convex and viscid.
Management:
Cultural methods:
- Seed treatment with bleaching powder (100g/l) and zinc sulfate (2%) reduces the bacterial blight (or)
- Seed treatment – Seed soaking for 8 hours in Agrimycin (0.025%) and wettable ceresan (0.05%) followed by hot water treatment for 30 min at 52-54oC(or)
- Soaking of seeds for 8 hours in ceresan (0.1%) and treat with Streptocyclin (3g in 1 litre)
- Spray neem oil 3% or NSKE 5% (or)
- Spray fresh cowdung extract 20% twice (starting from initial appearance of the disease and another at fortnightly interval)
Preventive method:
- Seed treatment with bleaching powder (100g/l) and zinc sulfate (2%) reduce bacterial blight.
- Seed treatment – seed soaking for 8 hours in Agrimycin (0.025%) and wettable ceresan (0.05%) followed by hot water treatment for 30 min at 52-54oC;
- Soaking of seeds for 8 hours in ceresan (0.1%) and treat with Streptocyclin (3g in 1 litre);
- Spray neem oil 3% or NSKE 5%
- Spray fresh cowdung extract for the control of bacterial blight. Dissolve 20 g cowdung in one litre of water; allow to settle and sieve. Use supernatant liquid. (starting from initial appearance of the disease and another at fortnightly interval)
Cultural methods:
- Grow Tolerant varieties (IR 20, IR 72, PONMANI and TKM 6).
- Secure disease free seed
- Grow nurseries preferably in isolated upland conditions
- Avoid clipping of seedlings during transplanting.
- Balanced fertilization and avoid excess N application
- Skip N application at booting (if disease is moderate)
- Drain the field (except at flowering stage of the crop)
- Destruction of weeds and collateral hosts
- Avoid flow of water from affected fields
- Maintain proper plant spacing
Chemical methods:
- Spray Streptomycin sulphate + Tetracycline combination 300 g + Copper oxychloride 1.25kg/ha. If necessary repeat 15 days later.
- Application of bleaching powder @ 5 kg/ha in the irrigation water is recommended at the kresek stage.
- Foliar spray with copper fungicides alternatively with Streptocyclin (250 ppm) to check secondary spread.
- Two sprays of Copper hydroxide 77 WP@1.25 kg/ha 30 DAP & 45 DAP
Source-
- TamilNadu Agritech Portal.
