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To develop a simple and reliable inoculation technique allowing to differentiate minor differences in susceptibility of rice cultivars to sheath blight caused by Rhizoctonia solaniKühn, the effects of different pathogen and host factors on disease development were investigated under greenhouse conditions. The most critical factor affecting uniform development of sheath blight was the amount of inoculum. Approximately 0.2 mg of inoculum placed inside the leaf sheath with a few drops of sterile water invariably induced single discrete, uniform-sized lesions, irrespective of the type of inoculum used (i.e., mature sclerotium, immature sclerotium, or mycelium). Considering the ease of maintaining uniformity of inoculum, the use of immature sclerotia is recommended. This inoculation method is not only simple, rapid, and highly reproducible, but it also allows to distinguish minor differences in susceptibility under greenhouse conditions.