Morpho-physicochemical and antioxidant trait diversity of red mulberry (Morus rubra L.) genotypes from northwestern Iran

Red mulberry (Morus rubra L.) is a valuable fruit species rich in bioactive compounds; however, information on genotype-dependent variation in its physicochemical and antioxidant traits compared to other mulberry species remains limited. Northwestern Iran represents an important center of red mulberry diversity, however limited information is available about the diverse physical characteristics, biochemical composition, and antioxidant potential of local genotypes. This study aimed to quantify physicochemical and antioxidant variation among red mulberry genotypes from this region and to identify superior genotypes with high functional potential. Significant genotypic variation (p < 0.01) was observed for all evaluated traits, demonstrating substantial diversity among the studied genotypes. Fruit weight ranged from 1.53 to 3.97 g, geometric mean diameter from 13.05 to 19.78 mm, and marketability coefficient from 52.58 to 63.4, indicating substantial morphological diversity. Soluble solids content and titratable acidity varied markedly among genotypes (TSS: 13.53 to 16.17%; TA: 0.70 to 1.61%), suggesting pronounced genotype-dependent differences in fruit flavor profiles. Antioxidant-related traits showed wide variability, with total phenolic content (TP) ranging from 268.06 to 941.13 mg GAE·100 g⁻¹ FW, total anthocyanin (TAC) from 0.209 to 0.499 mg g⁻¹ FW, and ascorbic acid from 12.95 to 21.16 mg 100 ml⁻¹ FW. Antioxidant activity values also differed significantly (DPPH: 23.12–92.87%; FRAP: 0.929 − 2.86 mg Fe²⁺ SO₄ g⁻¹ FW). Color analysis revealed that hue angle exhibited the strongest positive correlation with antioxidant traits, indicating fruit color as a reliable indirect indicator of antioxidant richness. These results suggest that fruit color attributes may serve as a rapid, indirect indicator of antioxidant potential in red mulberry. The results demonstrate substantial genetic diversity in fruit quality and antioxidant traits among red mulberry genotypes from northwestern Iran. The pronounced variation observed reflects strong genetic and geographical influences on fruit quality and bioactive composition. Genotypes Ru2, Ru3, Ro4, and Ru4 exhibited superior physicochemical attributes and antioxidant contents, highlighting their potential for breeding programs, conservation, and development of antioxidant-rich functional products.