Smut disease of bajra commonly occurs in many parts of our country such as Tamil Nadu, Andhra Pradesh, and Maharashtra. The infection is visible on scattered grains in the ear and majority of grains escape the damage.
Symptoms of Smut Disease:
The disease can be seen through the manifestation of its symptoms at the grain setting. A few grains generally get replaced by oval to top-shaped sori which are usually two or three times the size of normal grain. They are bright-green to dirty-black in colour and often rupture to expose a black spore-mass. The colour is due to the membrane which is tough and is made up of host tissues.
Causal Organisms of Smut Disease:
The pathogen remains confined mostly to sori, the wall of which is a tough combination of host tissue and fungal hyphae, and surrounds a powdery mass of spores. The spores (teleutospores) are held together in the form of compact balls, which remain persistent even in water. These spore- balls measure 40-150 µm in diameter.
Individual spores are round to irregular, 8-12.5 µm in diam., light-brown in colour, and with slightly roughened wall. They germinate while still held in balls. On germination, a 4-celled pro-mycelium is formed, each cell of which separates and buds out sporidia. The latter may be formed directly on pro-mycelium apically and laterally.
Smut Disease Cycle:
(i) Perennation:
The disease is soil-borne. The pathogen perennates through spore-balls that have fallen onto the ground, remain in soil, and overcome the unfavourable conditions.
(ii) Primary Infection:
The perennating spores germinate at the time of ear formation in the next season. They give rise to sporidia, which are wind-blown and brought onto the florets of the host. The sporidia settle down on the florets, germinate, and quickly cause infection. The latter is always localized. The result of this shoot infection is apparent in the same season when smutted grains appear.
(iii) Secondary Infection:
Secondary infection may occur on late sown crops or on ear emerging out late.
Predisposing Factors:
Disease incidence is higher if conditions are humid. Successive cropping of bajra in the same field also increases considerably the intensity of infection.
Management of Smut Disease:
(i) The only control measures recommended strongly for this disease are the removal of smutted ears, use of clean seeds, hot weather deep ploughing, field sanitation, and crop rotation.
(ii) Attempts are required to raise resistant varieties of this crop against smut disease.
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