Rice blast or rotten neck of rice

Catalogue Type
Plant Diseases Catalogue
Scientific Name
Pyricularia oryzae (Perfect stage- Magnaporthe grisea)
Family
Magnaporthaceae/Pyriculariaceae
Distinguishing Characters
-Symptoms may occur in any parts of the plant above ground like in leaf, leaf sheath, culm, panicle, glumes.
- First symptoms appear on the leaf.
- Initially, pin head size spots occur in the leaf lamina (color of these spot is light brown).
- in the later stage, the spots become circular, oval or elongated.
- Different races of the pathogen are seen in different region for example the blast spots in surkhet are much different than that in chitwan. (in surkhet very large spots are seen)

- In culm, symptoms are different.
- Brown to black lesions are found. Sometimes those lesions completely encircle the culm. If such ring formation is in earlier stage, grains are not filled only the chaffy (Vus) grains are formed. If such ring formation is in later stage, panicle hang down and even break and fall off.
- In glumes also the black lesions are found. In those lesions sometimes ash colored fungus growth is noticed where spores are also found.
- The color of circular spots sometimes changes to bluish. That is due to conidia formation. In such spots heavy sporulation occurs.
Host Crop
Rice
Photo of Pathogen
Photo of Damaged Crop
Description

Management

  • Development of resistant varieties: Sabitri and makwanpur-1 are the most common resistant varieties against blast.
  • Agronomic practices:
    • Planting time/ date: Early planting ( 7-10 days before regular) helps in minimizing the blast.
    • Planting density: Thin planting will reduce the disease as high density increases humidity which is favorable for the pathogen. ( more than 90% humidity is required by pathogen to thrive and multiply)
    • Nutrient management: High Nitrogen application increases the disease infestation whereas high Potassium increases the resistancy.
  • Silicon, if present in the rice leaf resist the disease. So, the plants in wet nursery suffer much less blast attack than that of dry nursery as silicon is absorbed only in the wet condition.
  • Direct control by fungicide application:
    • Non-systemic fungicide: Diethane M45 can control the blast  but easily is washed off by rain.
    • Systemic fungicide: Hinosan @ 0.1% for spray
  • Biological control:
    • Fungi: Trichoderma harzianum
    • Bacteria: Pseudomonas fluorescens
    • Pseudomonas works more effectively is isolated and multiplied from the same locality.
    • Practically, Biocontrol is not impressive as we cannot maintain the ideal conditions for action of biological agents.(as we cannot manipulate the micro climatic condition around the crops)