Bacterial Leaf Streak (BLS), caused by Xanthomonas oryzae pv. oryzicola, is a destructive disease affecting paddy crops in both tropical and temperate climates. It compromises rice productivity and quality, making its management crucial. The disease thrives under warm temperatures (25°–34°C), high humidity (>70%), and conditions of strong winds or heavy rains. Below is an overview of the disease's symptoms, development, and contributing factors.

Symptoms

1. Early Signs:

   • Small, water-soaked streaks appear between leaf veins.
   • These streaks are initially dark green and translucent.

2. Progression:

   • Streaks grow larger, merge, and turn light brown.
   • Yellow-colored bacterial exudate appears as tiny beads on streak surfaces.

3. Advanced Stages:

   • Leaves turn brown, then gray-white, and eventually die.

Pathogen Characteristics

• Vascular Colonization:

  • X. oryzae pv. oryzicola primarily infects vascular tissues, leading to systemic blight.
  • It enters through water pores (hydathodes), stomata, or wounds in leaves, stems, or roots.

• Bacterial Multiplication:

  • Bacteria proliferate in the epithem (parenchymatic tissue under hydathodes) and spread to xylem vessels.
  • They can exude as slime droplets and re-infect the plant.

Disease Development and Favorable Conditions

1. Climatic Factors:

   • High temperatures (25°–34°C) and humidity (>70%) promote disease.
   • Strong winds and heavy rains facilitate bacterial spread via ooze droplets.

2. Agricultural Practices:

   • High nitrogen fertilization increases susceptibility.
   • Presence of weeds and infected plant stubbles intensifies disease severity.

3. Survival of Pathogen:

   • In temperate regions, the bacterium survives winter in rice stubbles and the rhizosphere of weeds (e.g., Leersia and Zizania).

Key Management Practices

1. Field Sanitation:

   • Remove infected plant debris and control weeds.

2. Nutrient Management:

   • Avoid excessive nitrogen fertilization.

3. Resistant Varieties:

   • Use resistant or tolerant rice cultivars where available.

4. Cultural Practices:

   • Promote proper drainage and minimize water stagnation.

By understanding the symptoms and factors contributing to bacterial leaf streak, farmers can adopt preventive measures and mitigate yield losses effectively.