A Simple and Reproducible Seedling Assay for Rice Sheath Blight Caused by Rhizoctonia solani

Rice sheath blight caused by Rhizoctonia solani AG-1 IA is a major disease of rice. In this study, a simple seedling inoculation method using small nursery trays was developed for pathogenicity assays and resistance screening. Rice seedlings at the 4-5 leaf stage were inoculated with 5-mm-diameter mycelial plugs and incubated at 30°C under humid conditions for 10 days. Disease severity was assessed using relative lesion height (RLH) and the IRRI Standard Evaluation System. Typical sheath blight symptoms developed consistently, and reproducible disease reactions were obtained across 12 rice cultivars in three independent experiments. This method requires minimal space and inoculum preparation, providing a rapid and reproducible system for rice sheath blight research.