Optimizing silicon concentration and application stage enhances physiological performance and yield of rice under bacterial leaf blight stress

Bacterial leaf blight (BLB) reduces rice productivity, and silicon (Si) may enhance plant tolerance; however, the optimum application stage and concentration remain unclear. This study investigated rice responses to different Si application stage and concentrations under BLB stress using a greenhouse factorial experiment. A greenhouse factorial experiment was arranged in a randomized complete block design (RCBD), with foliar Si treatments imposed at two application stages, the seedling stage (SS) and tillering stage (TS), and five concentrations of 0, 1.0, 1.5, 2.0, and 2.5 mL L⁻¹. Si application improved rice performance under BLB stress, with stronger responses at TS than SS. Compared with SS, TS increased net photosynthetic rate, transpiration rate, and grain yield by 37.8%, 21.6%, and 26.4%, respectively. Among the treatment combinations, 1.5 mL L⁻¹ Si applied at TS showed the most consistent improvement by enhancing photosynthetic gas exchange, photosynthetic pigments, antioxidant enzyme activities, soluble protein, soluble sugars, starch, non-structural carbohydrates (NSC), and Si and nitrogen (N) accumulation, while reducing oxidative damage. This treatment reduced the disease severity index (DSI) to 35.90%, lowered the area under the disease progress curve (AUDPC) to 1308.97 units, achieved the highest control efficiency of 29.59%, and increased grain yield by 63.9% compared with the corresponding control. Principal component analysis and hierarchical clustering confirmed that the TS application of 1.5 mL L⁻¹ Si was associated with improved physiological stability, reduced disease severity, and better yield performance. Therefore, 1.5 mL L⁻¹ Si at the tillering stage may enhance rice tolerance under BLB stress.