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 DiseaseÂ
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 FieldÂ
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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Percentage of the Yield Loss Due to Smut Disease in Sugarcane
Among sugarcane diseases, smut is notable for the damage it can do to susceptible cultivars. There have been reports of up to 60% production losses among susceptible varieties. The smut fungus is particularly dangerous to ratoon cane crops.
Smut Management in Sugarcane by Cultural Method
- Growing resistant and moderately resistant sugarcane varieties lessen smut disease.
- Discourage ratooning of sick crops with over 10% infection to stop disease spread.
- Cajanus cajan, as a companion crop between sugarcane rows, can greatly limit secondary disease spread.
- Sugarcane smut disease can be controlled by treating seed setts with Areated Steam Therapy (AST) at 50 C for 1 hour, in hot water for 30 minutes, or at 52C for 18 minutes.
- Smut whips can be rigged with gunny bags/polythene bags and boiled for an hour to control the illness. To stop disease spread, uproot and burn diseased masses.
Smut Management in Sugarcane by Chemical Method
Treatment of the seed sets with fungicides like Triadimefon at 1 gram in 1 liter of water or Carbendazim at 1 gm in 1 liter of water for 10 minutes is required for chemical control of smut disease in sugarcane. Smut disease can be less common in fields by treating seed sets with benzimidazole fungicides before sowing. Chemical fungicides should only be used sparingly and when essential. Excessive use can wreak ecological destruction and produce pathogens with resistant strains.
Smut Management in Sugarcane by Organic/Natural Method
Organic control of smut disease in sugarcane involves removing infected stalks and destroying all residues of infected plants. Disease-free seeding material can be ensured by dipping sugarcane cuttings in a 52°C hot water bath for 30 minutes or in a 50°C hot water treatment for 2 hours.
Preventive Measures for Control of Smut Disease
Planting resistant varieties, using disease-free planting materials, adopting broad crop rotation, and using heat therapy for breeder seed production are all preventative measures to control smut disease in sugarcane. Co 86249, CoG 93076, CoC 22, CoSi 6, and CoG 5 are examples of resistant and moderately resistant varieties that should be favored.
Pre-treating sugarcane cuttings with hot water or fungicides guarantee the planting material is disease-free. Reduced soil pathogen populations aid in breaking the cycle of illness through extensive crop rotation. Heat treatment using moist hot air or water produces disease-free breeder seed material.Â
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Conclusion
Smut disease, a serious fungal disease, destroys sugarcane crops globally. Smut disease causes whip-like formations and black spores. Cultural, physical, chemical, biological, natural, and organic means can control smut disease. However, disease-free planting material, crop rotation, and heat treatment are the best ways to handle the disease. These steps can control the disease and ensure a healthy sugarcane crop.
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