Grain Smuts Of Sorghum // Plant Pathalogy Notes By : Mr. Rohit Jirobe //

 Grain Smuts Of Sorghum

Smut is a fungal disease, characterised by a mass of black spores on the grains in the ears.

The grains infected with fungus are called smutted grains.

There are seven types of smuts in Sorghum (Sorghum vulgare).

Among them, four types of smuts are seen in India. They are-

1. Covered smut 2. Loose smut 3. Long smut 4. Head smut

1. Covered Smut

Covered smut is a fungal disease in Sorghum, characterised by smutted grains. It is also known as kernel smut, short smut or grain smut. It is caused by the fungus Sphacelotheca sorghii. Covered smut is seen in the USA, Italy, Africa, Sri-Lanka, Asia and Australia. In India it is prevalent in Tamilnadu, Karnataka, Andhra Pradesh,

Maharashtra, Gujarat and Uttar Pradesh. Covered smut is a serious disease in Sorghum.

It is responsible for a loss of 25% of the total grain yield.

Because of this disease, several million crores of money have been lost every year.

Causal organism

Covered smut of Sorghum is caused by the fungus, Sphacelotheca sorghii.

This pathogen is included under the class Basidiomycetes.

It is present inside the sorus. The L.S. of smutted grain shows a central portion called columellum surrounded by a peridium.

The peridium is protected by a tough wall. The columellum consists of host tissues in the grain. It is made up of

parenchyma and vascular elements. The peridium consists of a mass of dark-brown spores. The spores are smooth and thick-walled. They are 5-9 u in diameter. The peridium is covered by a thick sorus wall. At maturity, the sorus wall ruptures and hence the spores get exposed. The spores are called teliospores. Teliospores remain viable for 10 years too. The spores germinate and give rise to four-celled promycelia. Each cell produces a single sporidium. The sporidium later on becomes a teliospore.

Symptoms

Covered smut appears only during the grain formation in ears. It shows the following symptoms: 1. Sori are formed in the place of normal grains.

2. They are oval to cylindrical in shape.

3. They are 5-5 mm long and 3-5 mm broad.

4. The sori are dirty-grey in colour.

5. Each sorus is covered with a tough membrane.

Dissemination / Disease Cycle: 

Covered smut of Sorghum is a seed-borne disease.

The seeds may be contaminated while threshing the grains.

The spores of this pathogen germinate at the seed surface and 

produce primary hyphae.

When the seeds germinate into seedlings, the primary hypha penetrates

 the radicle or mesocotyle region.

The hypha later on grows along the meristem and reaches the flowers. When the ovary becomes a seed, cells of the fungal hypha become teliospores. As a result, the seed becomes a smutted grain.

The soil temperature around 25 °C and medium moisture are found to be ideal for the maximum infection.

The teliospores are released after rupturing the sorus wall around the peridium.

The released spores contaminate the fresh seeds and soils.

After releasing the spores, the columellum remains exposed.

Control Measures

1. Treating the seeds with sulphur dust (2g/kg) before sowing, controls the disease effectively.

2. Steeping the grains in 2% Cuso, solution for 15 minutes is recommended for the disease control.

3. Thiram and copper carbonate at the rate of 2-4 g/kg of seed is useful to control the disease.

4. Growing resistant varieties is an effective technique to keep the disease in control. The important varieties that resistant to covered smut are -Milo, Hegari, Feterita, Shantung, etc.

5. Collection of seeds from smutted plants should strictly be avoided.