The reaction of IR 50, TRY 3, and IR 36 cultivars of rice to R. solani challenge, the causal agent of sheath blight, and its toxic metabolite was studied. Differential response of these cultivars to the pathogen and/or toxin inoculation was observed in detached leaf sheaths and greenhouse-grown plants. The observations were based on disease scoring, electrolyte leakage, and also microscopic views of infection cushions. The Osmyb4 gene expression was studied in the tissues from all these experiments and a correlation between the level of expression and disease response of the varieties was found at least in some experiments. The mechanisms regulated by Osmyb4 might have a lower but significant contribution to the tolerance of rice cultivars to sheath blight.