Course – M. Sc.
Botany Part 1 Paper III
Topic – Loose Smut of Wheat
Prepared by – Dr. Santwana Rani
Coordinated by – Prof. (Dr.) Shyam Nandan Prasad
Loose Smut of Wheat
➢ The disease loose smut of wheat is caused by ustilago nuda tritici.
➢ Incidence is more in north than in south India.
➢ Country wide loss is about 2-3%of total yield.
➢ There was a loose smut epidemic in Punjab, Haryana and western U.P. in 1970-75.
Distribution:
➢ All wheat growing regions of India.
➢ Particularly in Punjab, Haryana, U.P. and certain regions of M.P.
Symptoms:
➢ Symptoms appear after ear emergence.
➢ Diseased ear emerged first than normal in some varieties
➢ Mostly all ears is converted into a black mass of spores
➢ All the floral parts of the head, except the rachis and pericarp membrane, are invaded by
mycelium of the fungus and converted into loose aggregation of smut spores(teliospores).
➢ Significant reduction in tillering.
➢ Except awns all parts of ear converted into smut spore.
➢ Black powder in ear-covered by slivery membrane.
➢ Membrane burst later & smut spore release.
➢ Group of smut spore called sorus.
➢ High respiration and low dry weight.
Causal agent: Etiology
Pathogen - Ustilago nuda tritici. (Syn. U. segetum var. tritici)
Systematic position:
Kingdom: Fungi
Phylum: Basidiomycota
Sub phylum: Ustilaginomycotina
Class: Ustilaginomycetes
Order: Ustilaginales
Family: Ustilaginaceae
Genus: Ustilago
Species: U tritici (Pers.)
Pathogen characters:
➢ It is an internally seed borne fungal disease.
➢ It causes systemic infection.
➢ The teliospores of the fungus are pale, olive brown, spherical to oval in shape, about 5-9 micro
diameter and are adorned with minute echinulations on the wall.
➢ They germinate readily in water, each spore producing one four celled germ
tube(promycelium).
➢ The promycelial cells fuse and give rise to the germ tubes that enter the ovary through the
stigma and become established in the embryo, remaining dormant until seed germination.
➢ Its presence is revealed only when the plant matures and a smutted ear emerges.
Mycelium characters:
➢ The Primary mycelium consists of hyaline, slender, septate hyphae with a single haploid nucleus
in each cell. (Monokaryotic or haplo mycelium).
➢ The Secondary mycelium consist of hyphae with two haploid nuclei in each cell. (Dikaryotic
hyphae).
Epidemiology: mode of spread.
Primary spread: (Dormant mycelium)
➢ It is internally and externally seed borne and is systemic.
➢ The fungus is carried over in the seed as dormant mycelium.
➢ When the planted seed germinates the mycelium becomes active.
➢ It grows along with the plant and when the panicle is produced the mycelium reaches the
ovaries and transforms the ovaries into a mass of black smut spores teliospores.
Secondary spread: (Teliospores)
➢ Secondary spread occurs through wind borne teliospores spores. The sporidia infect the healthy
flowers. The mycelium enters the ovary and remains in the seed as dormant mycelium.
Favourable conditions:
➢ Cold climate (16 -22°C).
➢ Humid weather 60-85%.
Disease cycle:
➢ Ears of infected plants emerge early.
➢ The spores released from the infected heads land on the later emerging florets and infect the
developing seed.
➢ When infected seed germinates the fungus grows and thus the new plant get infected.
Disease control and Management:
➢ Treat the seed with Carboxin (Vitavax) @ 2g/kg seed before sowing.
➢ Grow resistant varieties like Sonalika, Kalyan 227, PV18, WG307, NP13 and C302.
➢ Burry the infected ear heads in the soil, so that secondary spread is avoided.
➢ Spraying of fungicides like Carboxin (Vitavax) 0.125% or Tebuconazole (Folicur) 0.2
➢ Hot water treatment (Jenson, 1886):
• Soak the seeds in water @ 26-30°C for 5 hours to induce dormant mycelium to grow.
• Then immerse the seeds in hot water a @ 54°C (129°F) for 10mins to kill the mycelium.
• Drying of seed.
➢ Solar treatment (Luthra and Sattar, 1954 in Punjab):
• In May- June -Soak the seeds in cold water for 4 hours from 6AM to 10AM.
• Spreading and drying of seeds on brick floor in bright sun (44°C) for 4 hours from 10AM to
5PM in the afternoon.
