Asexual stage: pyricularia oryzae ( p. grisae )
Sexual stage: Magnaporthe grisea
First time reported in Nepal in 1966 A.D.
The typical symptoms appear on leaves, leaf sheath, rachis, nodes and even the glumes are also attacked.
- Small water soaked bluish green specks,soon enlarge diamond shaped spots with grey centre and dark brown margin.
- In infected nodes, irregular black areas that encircle the nodes can be noticed.
- The affected nodes may break up and all the plant parts above the infected nodes may die (Node blast).
- The collar of a rice plant refers to the junction of the leaf blade and the sheath.
- Necrosis at the union of the two tissues.
- Collar infections can kill the entire leaf and may extend a few millimeters into and around the sheath.
Neck or Panicle blast:
- The neck of the rice plant refers to that portion of the stem that rises above the leaves and supports the seed head or panicle.
- At the flower emergence, the fungus attacks the peduncle which is engirdled, and the lesion turns to brownish-black.
- Referred to as rotten neck/neck rot/neck blast/panicle blast.
- In early neck infection, grain filling does not occur and the panicle remains erect like a dead heart caused by a stem borer. In the late infection, partial grain filling occurs.
- Lesions can be found on the panicle branches, spikes, and spikelets.
- The lesions are often gray brown discolorations of the branches of the panicle, and, over time, the branches may break at the lesion.
- Brown spots, blotches, and occasionally the classic diamond-shaped lesion often seen on leaves.
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