Brown spot, caused by Bipolaris oryzae, is one of the most important diseases of rice and can cause a reduction in yield and grain quality. The effect of silicon (Si) on the resistance of rice grains to brown spot was investigated. Plants from cv. Oochikara and its mutant, defective in the Lsi1 transporter (lsi1 mutant), were grown in hydroponic culture either with Si (+Si; 2 mM) or without Si (-Si). Panicle inoculation with B. oryzae was carried out at the beginning of the milk-grain stage. Panicles were harvested at physiological grain maturity. The supply of Si significantly increased Si concentration in husks compared to -Si plants. Si concentration in husks from cv. Oochikara was up to three times greater than the lsi1 mutant. In the presence of Si, brown spot severity was reduced by 88% in grains from cv. Oochikara and by 53% in grains from lsi1 mutant. Brown spot severity was 77% lower for grains of cv. Oochikara than for the lsi1 mutant, both plant types were grown in the presence of Si. Panicle inoculation reduced significantly the following yield components: number of grains per panicle, the weight of 1000 grains and the percentage of filled grains. Si significantly increased these yield components, especially for inoculated panicles. Considering kernel quality, the panicle inoculation with B. oryzae significantly reduced the yield of husked kernel, yield of whole kernel and kernel diameter, especially for grains from -Si plants. For panicles from +Si plants, the kernel quality was improved under inoculation, compared to -Si plants. Results from this study show that Si improved rice yield and kernel quality in panicles inoculated with B. oryzae. Furthermore the functional Lsi1 gene contributed significantly for increasing the yield of whole kernel and kernel diameter, possibly due to the increasing Si concentration in husks.

This study aimed to investigate the effect of silicon (Si) on the reduction of brown spot severity (BSS), caused by Bipolaris oryzae, and grain discoloration in several rice genotypes. An experiment was conducted in a greenhouse where eight genotypes were evaluated for their response to Si rates and decrease on BSS. The relationship between Si rates and BSS was linear negative. Additionally, a field experiment was conducted including forty-eight genotypes which were grown in upland conditions and evaluated for their response to Si rates and reduction on grain discoloration. The relationship between Si rates and grain discoloration was quadratic negative. Weight of filled grains per panicle increased as the Si rates in the soil increased. Genotypic differences for Si concentration in husk were evident for both non-amended and Si-amended plots. While the Si concentration in husk increased to all genotypes, there was no relationship between grain discoloration and Si concentration in husk for plants from non-amended and Si-amended plots. The genotype CAN-7024 with the highest resistance to leaf brown spot also showed the lowest grain discoloration in comparison to the genotypes Casado and Caqui.