Smut is a major sugarcane crop disease caused by the fungus Ustilago scitaminea. The affected plants develop slowly and have a whip-like structure in place of the central shoot, which ruptures to disperse millions of tiny black smut spores. The fungus mainly spreads through diseased setts and soil-borne infections aided by air currents.
Using healthy setts from disease-free regions, destroying smutted clumps, discouraging ratooning of diseased crops, crop rotation with green manure crops, intercropping with companion crops like red gram, and using resistant sugarcane types are all part of proper management. Biological control techniques such as Trichoderma spp. and maintaining healthy soil conditions can be used to manage the disease.
Chemical control methods can be used as a last resort to avoid the development of fungicide-resistant strains. To successfully manage smut disease in sugarcane, integrated pest management strategies incorporating various control methods should be created and implemented.
Smut Disease Management in Sugarcane
The Causal Organisms of Smut Disease
The fungus Ustilago scitaminea is the cause of sugarcane Smut Disease. The fungus grows mainly between the vascular bundles of the host plant, creating a dense mass of intercellular hyphae. The fungi create tiny, echinate, light brown, spherical, and black spores. The epidermis of the host plant is the thin covering that protects the smut whip. The spores can live for up to 10 years on the earth and can also be found in infected plant matter. The spores and sporidia infect the earth by dispersing through irrigation and rainwater.
The Disease Cycle of Smut Disease
During the Smut Disease cycle, teliospores can remain on the earth for up to ten years. The presence of spores and sporidia in diseased plant material and setts facilitates primary dissemination via diseased seed fragments. Rain and irrigation water can disseminate sporidia and spores, resulting in a soil-borne infection.
Smut spores that have developed in the whips and are dispersed by air currents in the field are the main source of secondary spread. The fungus can also live on unrelated hosts like Cyperus dilatatus, Saccharum spontaneum, S. robustum, Sorghum vulgare, and Imperata arundinacea.
Causes/Conditions Favorable for Smut Disease in the Field
Sugarcane smut spreads through teliospores produced in the smut whip, which can be found in the soil or on the plant. The disease is primarily spread through infected seed pieces and secondarily through windblown spores or waterborne spores, or sporidia in the soil. Hot and dry weather is favorable for completing the disease cycle, but the pathogen requires wet conditions for teliospore development.
Symptoms of Smut Disease
- Production of whip-like structures ranging from 25 to 150 cm from the growing point of the canes.
- A translucent silvery membrane covers the whip, enclosing a mass of black powdery spores.
- Initial thin canes with elongated internodes later become reduced in length.
- Profuse sprouting of lateral buds with narrow, erect leaves, especially in the ratoon crop.
- The smutted clumps also produce mummified arrows. The lower portion consists of a normal inflorescence with typical flowers. The upper portion of the rachis is converted into a typical smut whip.
- Occasionally, smut sori may develop on the leaves and stem.
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