In this article we will discuss about:- 1. Symptoms of Covered Smut of Barley 2. Causal Organism of Covered Smut of Barley 3. Disease Cycle 4. Control.
Symptoms of Covered Smut of Barley:
The diseased plants head at about the same time as healthy plants. They are recognizable by their blackened ears that emerge from the leaf sheaths. All the ears in a diseased plant and all the grains in a diseased ear are attacked by the disease. All the grains in a diseased ear are transformed into masses of spores which are held in place by persistent, tough, greyish-white membrane.
The covered masses of spores are not released from their enclosing membranes until threshing time, unless the membrane is broken accidentally. Because the membrane is often prematurely ruptured, covered smut is difficult to distinguish from loose smut.
Causal Organism of Covered Smut of Barley:
This disease is caused by Ustilago hordei (Pers.) Lagerh. The chlamydospores are dark-brown to charcoal-black in mass usually sub-spherical or spherical smooth-walled, and lighter coloured on one side. When young, the chlamydospores are dikaryotic and with maturity karyogamy takes place.
Germination takes place readily in water or damp soil by the formation of a septate promycelium during which meiosis of the diploid nucleus takes place. A large number of sporidia are produced which multiply by budding, germinate by germ tubes, or fuse with each other producing dikaryotic condition.
Disease Cycle of Covered Smut of Barley:
When the masses of spores are broken open as the barley is threshed after harvesting, innumerable spores are released. Many of the spores lodge on healthy kernels and remain dormant until the seed is sown when the barley seed begins to germinate the spores also germinate and infect the seedling along the epicotyl by dikaryotic infection hyphae.
After the fungus has entered the seedling, its hyphae continue to grow with the shoot and eventually replace the grains by masses of spores. A warm, moist, acid soil favours seedling infection. The greatest number of seedlings are infected at a soil temperature range of 50°F. to 70°F. during the germination period.
Disease cycle of Covered Smut of barley is presented in Figure 372.
Control of Covered Smut of Barley:
Since covered smut of barley is an externally seed-borne disease, most effective control measure will be seed treatment with fungicides. Treatment of barley seeds with fungicides like, Ceresan, Spergon, Agrosan successfully controls the disease. Use of disease resistant varieties also helps to reduce losses.
Sowing seeds in a moderately dry soil will aid in checking the disease, since moist soils are favourable for infection. Rate of infection is reduced when barley is raised in a neutral or alkaline soil than in an acid soil.