📄 Diseases of Rice — BLB, Tungro, False Smut
Diseases of Rice — BLB, Tungro, False Smut.
This lecture covers three additional major diseases of rice: Bacterial Leaf Blight, Tungro, and False Smut. These diseases can cause severe yield losses in endemic areas across South and Southeast Asia.
Bacterial Leaf Blight (BLB)
Causal Organism
Xanthomonas oryzae pv. oryzae (Xoo)
Symptoms
- Kresek phase: Seedlings wilt and die within 2-3 weeks of transplanting — the most destructive phase
- Leaf blight phase: Water-soaked lesions starting from leaf tips and margins that turn yellow to white and extend along the veins
- Bacterial ooze (milky droplets) on leaf surface in early morning
Disease Cycle
The bacterium survives in infected plant debris, weed hosts, and seed. It enters through wounds and hydathodes. Spread is facilitated by rain splash, irrigation water, and wind-driven rain.
Favorable Conditions
- Heavy rainfall, strong winds causing leaf injuries
- High nitrogen fertilization
- Temperature: 25-34 degrees C
- Clipping of seedling tips during transplanting
Management
- Use resistant varieties carrying Xa genes (Xa4, Xa21)
- Avoid clipping of seedling leaf tips before transplanting
- Balanced nitrogen application
- Seed treatment with Streptomycin sulphate + Tetracycline (300 ppm)
- Spray Copper oxychloride (0.25%) at disease onset
Tungro Disease
Causal Organism
A double virus complex:
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This lecture covers three additional major diseases of rice: Bacterial Leaf Blight, Tungro, and False Smut. These diseases can cause severe yield losses in endemic areas across South and Southeast Asia.
Bacterial Leaf Blight (BLB)
Causal Organism
Xanthomonas oryzae pv. oryzae (Xoo)
Symptoms
- Kresek phase: Seedlings wilt and die within 2-3 weeks of transplanting — the most destructive phase
- Leaf blight phase: Water-soaked lesions starting from leaf tips and margins that turn yellow to white and extend along the veins
- Bacterial ooze (milky droplets) on leaf surface in early morning
Disease Cycle
The bacterium survives in infected plant debris, weed hosts, and seed. It enters through wounds and hydathodes. Spread is facilitated by rain splash, irrigation water, and wind-driven rain.
Favorable Conditions
- Heavy rainfall, strong winds causing leaf injuries
- High nitrogen fertilization
- Temperature: 25-34 degrees C
- Clipping of seedling tips during transplanting
Management
- Use resistant varieties carrying Xa genes (Xa4, Xa21)
- Avoid clipping of seedling leaf tips before transplanting
- Balanced nitrogen application
- Seed treatment with Streptomycin sulphate + Tetracycline (300 ppm)
- Spray Copper oxychloride (0.25%) at disease onset
Tungro Disease
Causal Organism
A double virus complex:
- Rice Tungro Bacilliform Virus (RTBV) — causes stunting
- Rice Tungro Spherical Virus (RTSV) — needed for vector transmission
Vector
Green leafhopper (Nephotettix virescens) — transmits the virus in a semi-persistent manner
Symptoms
- Yellow to orange discolouration of leaves starting from tips
- Stunted plant growth, reduced tillering
- Delayed or incomplete panicle emergence
- Interveinal chlorosis; rusty brown spots in some varieties
Favorable Conditions
- High leafhopper populations (especially during monsoon season)
- Presence of virus-infected staggered plantings acting as reservoirs
- Temperature: 25-30 degrees C
Management
- Grow resistant varieties (e.g., Vikramarya, Bharani)
- Synchronous planting to avoid green bridges
- Control vector with Imidacloprid or Thiamethoxam
- Rogue out infected plants early
- Use light traps to monitor leafhopper populations
False Smut (Green Smut)
Causal Organism
Ustilaginoidea virens (Teleomorph: Villosiclava virens)
Symptoms
- Individual rice grains transformed into large velvety green to greenish-black spore balls
- Spore balls may be 1 cm or more in diameter and are enclosed by glumes initially
- Usually a few grains per panicle are affected
- Infected grains produce ustiloxins (mycotoxins) — a food safety concern
Disease Cycle
The pathogen infects during the booting stage through floral parts. Chlamydospores and sclerotia in soil serve as primary inoculum. Ascospores from sclerotia initiate infection.
Favorable Conditions
| Factor | Condition |
|---|---|
| Temperature | 25-30 degrees C |
| Humidity | >90% RH during booting |
| Nitrogen | Excessive application |
| Rainfall | Continuous cloudy weather before heading |
Management
- Avoid excessive nitrogen fertilization
- Spray Propiconazole 25 EC or Copper hydroxide at the boot leaf stage
- Use clean certified seed
- Remove and destroy infected panicles before spore dispersal
Summary Cheat Sheet
| Disease | Type | High-yield exam point |
|---|---|---|
| BLB | Bacterial | Kresek and leaf blight phases are diagnostic |
| Tungro | Viral complex | Green leafhopper transmits the virus complex |
| False smut | Fungal | Green smut balls and mycotoxin concern |
References
1 source
References
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