Salicylic acid exerts effects on regulating flower bud differentiation and nutrient contents in red radish.

Red radish (Raphanus sativus L. var. carminatus) is a characteristic economic crop in China, with flower bud differentiation efficiency directly determining its yield and quality. However, how salicylic acid (SA) affects this process and tuber quality remains unexplored. Here, we investigated different SA concentrations' effects on endogenous hormones (GA3, IAA, CTK), flower bud differentiation, flowering, and pollen traits, alongside leaf soluble sugar, starch, and protein levels. We also applied response surface methodology (RSM) to build a regression model for optimizing SA application parameters, and conducted real-time PCR to detect the expression of flowering-related genes. SA and GA₃ most strongly affected apical buds (F = 45.2, p < 0.001). SA inhibited IAA in apical buds and seedlings (F = 35.8, p < 0.001), while functional leaf IAA peaked at 7% SA. Cytokinin peaked at 3% SA (F = 15.8, p < 0.001). Plant height, node number, leaf number and tubular flower number all reached their maximum values under 5% SA treatment. Starch content at the flowering stage increased significantly under 2% SA treatment, whereas the pre-anthesis protein accumulation reached the optimal level under 4% SA treatment. Pollen formation was significantly enhanced by 7% SA, boosting pollen quantity by 62.4%. The model optimization prediction indicated that the optimal nutrient contents could be obtained with the application of 5.09% SA for 24.82 days, verifying the parameters with <1% prediction error. Real-time PCR showed SA markedly downregulated flowering-related genes (RsGAIe, RsSLY1, RsUBC1h/g/b/i). These findings reveal that exogenous SA coordinately remodels endogenous GA₃-IAA-CTK hormone homeostasis to synchronously modulate flower-bud differentiation and leaf carbon-nitrogen accumulation in red radish (Raphanus sativus L. var. carminatus), and highlight a feasible strategy for manipulating flowering and improving economic traits via SA application. These findings provide a theoretical basis for shortening red radish's flowering cycle and improving its economic traits.