Heavy-ion beam irradiation enhances polyphenol accumulation and antioxidant activity in sweet potato storage roots without compromising agronomic traits

Heavy-ion beams are attracting attention as a useful approach for mutation breeding because they can induce diverse mutations in crop plants. We investigated the potential of heavy-ion beam irradiation to enhance polyphenol accumulation and related functional properties in sweet potato while maintaining the desirable agronomic characteristics of the parent cultivar. Eighty lines of the cultivar ‘Beniharuka’, comprising 57 lines irradiated with carbon ions and 23 lines irradiated with argon ions, were subjected to primary selection under field conditions based on the yield and morphology of their storage roots. Of the 10 selected lines, line C20-4-2 was selected for detailed analyses because it showed markedly increased polyphenol accumulation without apparent morphological mutation. The total polyphenol content in C20-4-2 reached 976.0 mg gallic acid equivalents 100 g ⁻¹ fresh weight in the peel and 97.3 mg gallic acid equivalents 100 g ⁻¹ fresh weight in the flesh, corresponding to 4.7-fold and 3.0-fold increases, respectively, relative to ‘Beniharuka’. Antioxidant activity was also significantly higher in both tissue types. High-performance liquid chromatography analysis showed that these increases were associated with a coordinated accumulation of chlorogenic acid derivatives, particularly dicaffeoylquinic acids. Notably, 3,5-dicaffeoylquinic acid in the flesh was increased by 18-fold. Peel extracts of C20-4-2 also showed significantly stronger growth inhibitory effects against human colon adenocarcinoma COLO201 cells than those of ‘Beniharuka’, whereas no significant difference was observed in flesh extracts. These findings demonstrate that heavy-ion beam irradiation combined with two-stage selection can generate sweet potato lines with enhanced functional quality without compromising agronomic performance.