This study aimed to associate the silicon (Si) deposition on sheaths of rice plants with an increase in physical resistance against infection by Rhizoctonia solani. Plants from the susceptible cultivars BR-Irga 409 and Labelle were grown in nutrient solution containing (+Si) or not (-Si) Si. Si concentration on sheaths of plants supplied with Si and inoculated with R. solani significantly increased compared to plants non-supplied with Si, reducing the relative lesion length at 96 hours after inoculation (hai). There were significant differences between -Si and +Si treatments for the force required of a metal needle to pass through the sheaths at 48 and 72 hai. The greater physical resistance at 24 hai was due to the fact that R. solani was growing on sheath tissue without destroying it, which could be proved by the absence of symptoms. After this period, the resistance decreased due to the rapid R. solani growth. However, on sheaths of plants supplied with Si, the force required for the needle to penetrate was higher at 48 and 72 hai. The sheath resistance of plants supplied with Si to infection by R. solani can be explained partly by the greater physical resistance due to Si deposition.
Oryza sativa; puncture; sclerotium; sheath blight
