Bacterial Leaf Blight of Rice

In the leaf-blight phase, lesions begin as water-soaked streaks near the leaf tips and margins, then enlarge and turn yellow to straw-coloured with a wavy margin, often extending down the leaf. In humid conditions, droplets of bacterial ooze may form on lesions and dry into small beads. In the kresek phase, young transplanted seedlings wilt, roll, and turn yellow to grey-green before dying, sometimes leading to loss of whole hills.

Xanthomonas oryzae pv. oryzae survives on infected rice residue, in weeds and volunteer rice, and can be carried on seed. The bacteria enter plants through natural openings such as leaf pores (hydathodes) and through wounds, then multiply and move within the water-conducting tissue. They spread within and between fields in irrigation and rain water, in wind-driven rain, and through contact between plants.

• Bacteria survive on residue, weeds, volunteer rice, and seed
• They enter through leaf pores and wounds, especially after storms
• Multiplication in the vascular tissue drives lesion spread
• Irrigation water, rain splash, and wind-driven rain move bacteria between plants

Rice is the primary host. The disease is favoured by warm temperatures, high humidity, heavy rain and wind that wound plants and spread bacteria, deep standing water, and high nitrogen fertilisation that produces lush, susceptible growth. Storms and flooding often precede outbreaks because they injure plants and move inoculum.

• Warm, humid weather with frequent rain and wind
• Deep or stagnant standing water in the field
• High or unbalanced nitrogen that produces lush growth
• Wounding from storms, flooding, or handling during transplanting

Because chemical options are limited for bacterial diseases, management depends heavily on resistant varieties and cultural practices that reduce inoculum, wounding, and spread. Balanced nutrition and careful water management are particularly important.

• Grow resistant varieties suited to the local pathogen populations
• Use clean, healthy seed and remove infected residue and weed hosts
• Apply nitrogen in balanced, split amounts rather than heavy single doses
• Manage water to avoid deep, stagnant flooding where feasible
• Minimise plant injury during transplanting and field operations