Microscopic analysis of rice resistance to sheath blight mediated by silicon

Sheath blight, caused by the fungus Rhizoctonia solani Kühn, is one of the most important and destructive diseases affecting rice production in the world. Although silicon (Si) is able to reduce the sheath blight intensity, the mechanisms of resistance mediated by this element remain unknown. Thus, this study aimed to investigate at the microscopical level the effect of Si on rice resistance to infection by R. solani. Rice plants from cultivars BR-Irga-409 and Labelle were grown in nutrient solution containing 0 or 2 mM of Si and inoculated at the maximum tillering stage using pieces of toothpick colonized by R. solani. Both cultivars supplied with Si showed intense and homogeneous deposition of Si in the leaf sheaths tissue colonized by R. solani. The highest Si concentration on the leaf sheaths of plants of both cultivars contributed to reduce the sheath blight symptoms. Using light microscopy and scanning electron microscopy, it was observed reduced fungal growth on the leaf sheaths of plants from both cultivars which were supplied with Si. Sections of the leaf sheaths of plants from both cultivars supplied with Si exhibited intense autofluorescence in tissues near to the necrotic areas due to R. solani colonization. In conclusion, the supply of Si to rice plants played an important role in reducing the sheath blight symptoms.

Rhizoctonia solani ; autofluorescence; x-ray microanalysis; light microscopy; scanning electron microscopy; mineral nutrition