Covered smut disease of barley occurs in every part of the world where the barley crop is grown. This disease is more common than the loose smut disease of wheat and barley. In India, the disease prevalently occurs in northern part causing considerable damage to the crop in Punjab, U.P., Bihar, and M.P Besides barley, the same fungal pathogen has also been reported on species of Agropyron and Elymus.
Symptoms of Covered Smut Disease:
Symptoms become evident only when the plants are headed and the ears emerge out. Every grain in a smutted ear consists of black mass of teleutospores, which remain held together almost firmly by a persistent membrane of the grain and the basal part of the glume.
Moreover, the spores of a grain are held together due to deposition of a fatty substance. However, the smutted ears may emerge out at about the same time as those of healthy ears but remain shorter and are usually retained within the sheath for a longer time before appearing, or may sometime fail to emerge at all.
Causal Organism of Covered Smut Disease:
The mycelium is septate, dikaryotic, and grows systemically inside the plant. The mycelial cells get transformed into brown, spherical, echinulate teleutospores. The latter are formed exactly in the manner the chlamydospores are formed and hence are also called “chlamydospores”.
On germination, the teleutospores give out a typical 4-called pro-mycelium or basidium which, contrary to the basidium of U. tritici (loose smut of wheat) producing primary hyphae, produce “sporidia” near the septa and at the apex. The sporidia are ovate to oblong, uninucleate and may bud out secondary sporidia. Two sexually compatible sporidia fuse together resulting in a dikaryotic infection hypha.
Covered Smut Disease Cycle:
(i) Perennation:
The pathogen perennates through the teleutospores borne externally on healthy seeds. The latter get contaminated usually at the time of threshing when persistent membrane covering smutted grain is broken and the teleutospores are freed.
(ii) Primary Infection:
When teleutospore bearing seeds are sown, the spores germinate on seed coat simultaneously with the seed germination. The teleutospores produce sporidia on the basidia, the two sporidia of sexually compatible nature (+ and -) fuse together giving rise to dikaryotic infection hypha, which penetrates through the young coleoptile of the growing seedling causing primary infection.
After entering inside the hypha grows systemically along with the growing plant. The symptoms manifest at the time of emergence of the head as the mycelia fill in the floral parts, and produce teleutospores, which replace the kernel.
These teleutospores become free at the time of threshing, get attached with seeds, remain dormant thereupon and serve as the source of primary infection during the next growing season.
(iii) Secondary Infection:
Secondary infection during the growing season is absent. It is because the teleutospores remain held together in situ by persistent membranes and they are released only at the time of threshing after the crop is harvested.
Predisposing Factors:
Soil moisture and soil temperature are the main factors, which predispose host seedling for infection. Deep sowing provides greater moisture in soil and thus results in greater infection. Similarly, a soil temperature of 20°C helps spore germination resulting in greater sporidia production and, therefore, greater infection.
Management of Covered Smut Disease:
(i) Smutted plants must be uprooted and burnt.
(ii) Since the pathogen is externally seed-borne, seed treatment with protectant or systemic fungicides render great help in controlling the disease. Agrosan GN (2.5g/kg seed), Ceresan, Agrosan 5W, Vitavax and Sulphur dust (300 meshes) are some chemicals which effectively control the disease incidence.
(iii) Varieties like BHS 4, BM23, LB873, EB4003, HBL 1 are highly resistant, while varieties like K 12, K 18, K 19, C 50, C 84, CN 294 are moderately resistant. Variety C 613 has been found immune to disease in Punjab.
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