Bacterial leaf blight

Causative agent : (Xanthomonas  oryzae pv. Oryzae)  

Symptoms

Two phages a) wilting of plants (kresek phage )    b) leaf blight phage

A. Wilting phage

• Occurs during seedling stage, 3-4 weeks after transplanting roll up. As disease progress the leaf turns yellow to straw color and wilts leading whole seedling to dry up and die.
• Sometime confused to early rice stem borer damage.
• To distinguish kresek symptoms from stem borer, squeeze the lower end of infected seedling between finger.
• Kresek symptoms show yellowish bacterial ooze coming out from cut end and not pull easily from soil.

B. Leaf blight phage

• On older leaf, water soaked to yellow orange stripes are +nt on leaf blade, leaf tip or mechanical injured parts of plant.
• Lesion are wavy margin and progress towards the leaf base.
• On young lesion bacterial ooze resembling a dew .
• Bacterial ooze later dries up and become a yellow to black beads .

Favorable condition:

• favorable temperatures is 25−34°C,
• Relative humidity above 70%
• High nitrogen application.

Survive and spread

• Primary source of inoculum: Seeds, straw, leaves and even stubbles, wild rice & other grasses (Cyperus rotundus & Panicum repens) •
• Secondary infection: occurs though ooze from infected plants/leaves disseminated by rain and other carriers like grasshoppers, leafhoppers externally but not internally.

Management:

• Use of seed from uninfected plants (or seed treatments), Soaking seeds for 8 hrs in Agrimycin (0.025%) followed by hot water treatment for 10 minutes at 52-54 degree C.
• Use of resistance varieties like IR 20, IR 26, Pokhreli Masino etc.
• Foliar spray of Agrimycin 250 ppm + Copper oxychloride 0.05% for 5 times at 12 days interval.
• There are possibilities for biological control by Fluorescent pseudomonads (Anuratha and Gnanamanickam, 1987).