Diseases in Wheat

Loose Smut

Caused by: Fungus

Causal Organism: Ustilago nuda tritici

Symptoms:

• Generally, diseased plants are indistinguishable from the healthy plants before heading but diseased plants produce heads earlier than healthy plants.
• Terminal symptom in all the varieties is the production of black powder in place of wheat grains in the ears. Almost every ear of the diseased plant is converted ino black powder.
• The black powder is a mass of olive-green microscopic spores of the smut fungus.
• When spores are blown to flowers of healthy plants, they germinate on the female organ, stigma and lead to infection of the developing seed.
• The smut fungus thus reaches in the mature grain and remains dormant there until germination of the grain.
• From superficial examination at harvest time, infected grains are sown in the following season; the fungus inside the seed becomes active as the germination starts.
• The fungus grows inside the plant first behind the growing point, keeping pace with apex of the growing shoot.
• As the ear formation starts, there is an accumulation of the fungus in the floral parts, which are completely destroyed due to formation of the black powder.

Control Measures:

• Growing of loose smut resistant varieties like Raj 2296, K-8027, K-8251, HW-657, HW-240, Raj-6276, VL-646, VL-719 etc. is the best method of control.
• Since loose smut fungus totally depends on wheat seed for its survival and carry over from one season to another, growing of disease free seed is the only alternative method of control available at present for large scale adoption. Treat the seed with Vitavax at the rate of 2.5 g per kg of seed before planting.
• At the time of ear emergence, visit the seed crop regularly and locate plants with diseased ears. Uproot the entire plants while covering the diseased ears with a paper envelope so that black powder does not spread. Destroy it by burying under the ground or by burning.
• Solar heat treatment of infected seed is highly valuable in the hot summer areas of the plains to make seed disease free. On a bright sunny day in the last week of May or first week of June. Soak the seed in water for about four hours in the morning and then dry it under hot sun in the afternoon. Store the well dried seed for use in next wheat season. The seed soaking activates the dormant fungus in the seed and heat of the sun kills it.