Sheath rot, also known as sheath blight or ShB, is a devastating disease that affects paddy or rice crops worldwide. It is caused by the fungal pathogen Rhizoctonia solani, which attacks the sheath that surrounds the base of the rice plant. Sheath rot can lead to significant yield losses if not properly managed, making it a major concern for rice farmers.
The symptoms of sheath rot can vary depending on the stage of infection and environmental conditions. Initially, small water-soaked lesions appear on the rice leaf sheaths and stems. As the disease progresses, these lesions expand, turn brown, and develop a characteristic dark-brown border. Infected plants may exhibit wilting or bending at the infection site, leading to a characteristic lodging of the crop. Additionally, severe cases may cause the panicles to rot and shrivel, preventing grain development and further reducing yield potential.
Several factors contribute to the development and spread of sheath rot in paddy fields. High humidity, prolonged leaf wetness, and warm temperatures favor the growth and reproduction of the pathogen. Overcrowding of plants and excessive nitrogen fertilization provide ideal conditions for the disease to thrive. ShB is mainly spread through infected plants or plant debris, water, and even farm equipment. It can also be carried over from one season to another through infected seeds or soil.
To effectively manage sheath rot, farmers can adopt various preventive and control strategies. Crop rotation is an important practice that can break the disease cycle, as the fungus is host-specific and cannot survive without a rice crop. Proper field hygiene and the removal and destruction of infected plant debris can help reduce the pathogen’s survival and spread. Adequate spacing between plants allows better air circulation, reducing humidity and promoting faster drying of the leaf sheaths.
Applying biological control agents or fungicides can also help prevent and control sheath rot. Several fungal antagonists, such as Trichoderma and Bacillus species, have shown promising results in suppressing the growth of R. solani. Chemical fungicides can be used as a last resort if cultural and biological methods are insufficient. However, it is essential to follow appropriate application guidelines and rotate between different active ingredients to prevent the development of fungicide resistance.
Plant breeders are continuously working to develop rice varieties with improved resistance to sheath rot. Resistant cultivars offer long-term solutions by minimizing the impact of the disease on yield and reducing the need for chemical inputs. Farmers should seek advice from local agricultural extension services or agronomists to identify resistant varieties that are suitable for their region.
In conclusion, sheath rot in paddy is a significant issue that affects rice productivity worldwide. By employing a comprehensive approach that combines cultural practices, biological control agents, and resistant cultivars, farmers can effectively manage and minimize the impact of this devastating disease. Timely action, vigilance, and proper crop management strategies are crucial to mitigating the risk of sheath rot and ensuring a healthy and productive rice harvest.