Riboflavin Enhances Root Development and Antioxidant Defense to Improve Fragrant Rice Seedling Quality

Rice seedlings, with immature defense systems, are highly susceptible to adverse conditions, severely hindering establishment and yield. While exogenous riboflavin regulates rice growth and stress resistance, its role in modulating comprehensive seedling quality (a core yield-determining trait) remains understudied. This study systematically evaluated riboflavin’s effects on two fragrant rice varieties (Meixiangzhan, Nanjingxiangzhan) with four concentrations (0, 10, 20, 40 mg·L⁻¹) at the seedling stage. The key results showed that 20 mg·L⁻¹ riboflavin (optimal concentration) significantly enhanced root architecture (length, surface area, volume, diameter) and coordinated biomass accumulation (leaf/root fresh/dry weights) across three sampling stages (3d, 6d, 9d after treatment). It also elevated chlorophyll a/b, carotenoid contents, antioxidant enzyme (SOD, POD, CAT) activities, and osmolyte (soluble protein, proline) levels, while reducing oxidative damage (MDA, H 2 O 2 )-except for transient leaf-specific fluctuations at 3d. Meixiangzhan showed stronger responsiveness than Nanjingxiangzhan, linked to varietal differences in root traits and redox sensitivity. This study elucidates that riboflavin improves rice seedling quality via synergistic regulation of root development, photosynthetic capacity, and antioxidant homeostasis. As an eco-friendly, cost-effective biostimulant, it offers a practical strategy to enhance transplanting survival, stress tolerance, and yield potential in rice production.