Physiological Responses of Rice Plants Supplied with Silicon to Monographella albescens Infection

This study investigated the effect of silicon (Si) on the resistance of rice plants of the cv. 'Primavera' cultivar that were grown in a nutrient solution with 0 (-Si) or 2 mM (+Si) Si to leaf scald, which is caused by Monographella albescens. The leaf Si concentration increased in the +Si plants (4.8 decag/kg) compared to the -Si plants (0.9 decag/kg), contributing to a reduced expansion of the leaf scald lesions. The extent of the cellular damage that was caused by the oxidative burst in response to the infection by M. albescens was reduced in the +Si plants, as evidenced by the reduced concentration of malondialdehyde. Higher concentrations of total soluble phenolics and lignin-thioglycolic acid derivatives and greater activities of peroxidases (POX), polyphenoloxidases (PPO), phenylalanine ammonialyases (PAL) and lipoxygenases (LOX) in the leaves of the +Si plants also contributed to the increased rice resistance to leaf scald. In contrast, the activities of chitinases and beta-1,3-glucanases were higher in the leaves of the -Si plants probably due to the unlimited M. albescens growth in the leaf tissues, as indicated by the larger lesions. The results of this study highlight the potential of Si in decreasing the expansion of the leaf scald lesions concomitantly with the potentiation of phenolic and lignin production, and the greater activities of POX, PPO, PAL and LOX rather than simply acting only as a physical barrier to avoid M. albescens penetration.