Pellicularia sasakii

Pellicularia sasakii (also known as Rhizoctonia solani) is a destructive fungal pathogen belonging to the order Cantharellales. It is the primary cause of sheath blight, one of the most serious diseases affecting rice production worldwide. The pathogen is classified as a soil-borne fungus capable of attacking various host plants, but it causes the most significant damage in paddy rice fields.

The characteristic symptoms of the disease appear as irregular, water-soaked spots on the leaf sheaths near the water line. As the infection progresses, these lesions expand and develop grayish-white centers with dark-brown margins. In severe cases, the fungus spreads to the upper leaves and stems, leading to the collapse of the plant and significant reduction in grain yield and quality.

The life cycle of Pellicularia sasakii centers on the formation of sclerotia, which are compact masses of hardened mycelium. These sclerotia serve as the primary inoculum, surviving in the soil, irrigation water, and infected crop residues. Under favorable conditions, the sclerotia germinate, producing mycelia that infect the lower parts of the rice plants through direct contact.

Environmental factors are critical for the spread of this pathogen. High humidity levels exceeding 90% and temperatures ranging from 25°C to 30°C are optimal for the rapid growth of the fungus. Dense crop canopy and high nitrogen fertilization levels further exacerbate the disease spread by creating a humid and vulnerable environment within the field.

Control strategies for sheath blight focus on integrated pest management (IPM). Key measures include the use of resistant rice cultivars, appropriate water management to reduce moisture at the canopy level, and balanced nitrogen fertilization. Fungicide applications, particularly those containing triazoles or strobilurins, are commonly employed during critical growth stages to mitigate the economic impact of the disease.