Loose Smut is a fungal disease that primarily damages wheat fields in India. It is a disease of wheat crops caused by the fungus Ustilago nuda tritici. The fungus infects the wheat plant during its early growth stages. It produces smut fragments that replace the developing kernels, leading to reduced yields and lower-quality grain.
It is especially harmful in Punjab, Uttar Pradesh, and certain parts of Madhya Pradesh. According to Luthra, in 1953, the Disease caused enormous financial losses, with an estimated loss of more than 50 million rupees per year in India. Kangiari is the native name for sickness in Punjab. It generates smut spores that replace growing kernels, resulting in decreased yields and worse grain quality.
Loose Smut disease management in Wheat
The causal organism of Loose Smut disease
- The causal organism of Loose Smut disease is a fungus, Ustilago nuda tritici, with hyaline mycelium that turns brown near maturity.
- The mycelium is septate, dikaryotic, and grows systemically inside the plant.
- At maturity, mycelial cells transform into brown, spherical, echinulate teleutospores that serve as infective agents.
- The teleutospores germinate, producing pro-mycelium or basidium consisting of four uninucleate cells.
- Unlike other smut-causing fungi, the basidium does not produce basidiospores but instead germinates to produce uninucleate hyphae.
- A pair of sexually compatible uninucleate primary hyphae fuse to form a dikaryotic hypha, also known as the “infection hypha,” which causes infection in the plant.
Disease cycle of Loose Smut disease
Perennation
The pathogen survives in the form of dormant mycelium within the infected kernel. This mode of survival is unique to loose Smut, as other smut diseases of wheat plants survive as fragments on the surface of the seed.
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Primary infection
The dormant mycelium becomes active during seed germination and growth of the seedling, spreading systemically through the plant. The mycelium turns brown when mature and accumulates in the floral parts. Teleutospores form and are spread by the wind into adjacent flowering plants.
The teleutospores germinate and produce sexually compatible primary hyphae that fuse and give rise to dikaryotic mycelium (infection hyphae). The infection hyphae penetrate the flower and become established in the embryo’s tissues before the kernels mature. The mycelium becomes dormant within the scutellum of the kernel.
Secondary infection
Although the teleutospores can germinate on flowers of healthy plants, the mycelium becomes inactive and remains dormant within the seed, leading to no secondary infection cycle during the same growing season.