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The effect of silicon (Si) on sheath blight (Rhizoctonia solani Kühn) of rice was studied under greenhouse conditions. The predominant commercial rice cultivars ‘BR-IRGA 409’, ‘Metica-1’, ‘EPAGRI-109’, ‘Rio Formoso’, ‘Javaé’, and ‘CICA-8’, were grown in pots containing low-Si soil amended with 0, 0.48, 0.96, 1.44 or 1.92g Si pot⁻¹. Plants were inoculated at the maximum tillering stage. For all cultivars, Si concentration in straw increased more than 60% as the rates of Si increased from 0 to 1.92g pot⁻¹. Incubation period of R. solani was slightly prolonged with increasing Si rates and ranged from 53 to 64h depending upon the cultivar. Total number of sheath blight lesions, total area under the relative lesion extension progress curve, severity of sheath blight, and the highest relative lesion height on the main tiller decreased by 37%, 40%, 52% and 24%, respectively, as the rate of Si increased from 0 to 1.92g pot⁻¹ …