Concentration-Dependent Effects of Hydrogen Peroxide Seed Priming on Seed Vigor and Phytochemical Quality of Thai Rat-Tailed Radish Microgreens

Hydrogen peroxide (H2O2) is a signaling molecule involved in seed germination and secondary metabolism, with its biological effects varying with concentration. This concentration-dependent response is important when applying H2O2 seed priming for microgreen production. However, its effects on seed vigor and phytochemical quality remain poorly characterized in Thai rat-tailed radish (Raphanus sativus var. caudatus) microgreens. This study evaluated H2O2 seed priming (100, 200, 400, and 800 mM) for its effects on germination, oxidative status, microgreen growth, phytochemical accumulation, and antioxidant capacity. Priming with 100 mM H2O2 showed the most favorable overall effects on seed performance among the concentrations tested, increasing germination percentage, germination index, and germination after accelerated aging by 22.6%, 36.5%, and 62.1%, respectively, while reducing mean germination time by 32.0% compared with non-primed seeds. Higher concentrations (400–800 mM) increased seed H2O2 and malondialdehyde contents, suggesting greater oxidative burden. Moderate concentrations (100–200 mM) resulted in higher total phenolic content, phenolic acid accumulation, and antioxidant capacity, particularly in ABTS and FRAP assays, without significantly affecting microgreen growth or biomass. H2O2 priming produced a biphasic concentration-response pattern consistent with a hormetic response, with 100 mM H2O2 providing the most favorable response across several seed vigor and phytochemical quality traits.