Screening of Safflower Genotypes for Enhanced Flavonoid and Anthocyanin Content under Water-Limited Conditions

Drought is the main abiotic stress limiting safflower production in semi-arid regions, with flavonoid and anthocyanin pathways playing a key role in antioxidant defense. A two-year field experiment in Arak, Iran, evaluated 38 safflower genotypes under full irrigation and terminal drought stress, measuring total flavonoid and anthocyanin contents. Drought increased average flavonoids by 6.3% (from 0.1395 to 0.1483 mg QE g⁻¹ DW) and anthocyanins by 8.1% (from 0.00382 to 0.00413 mg g⁻¹ DW). A three-way ANOVA showed significant effects of irrigation and year on both traits, with year accounting for 62.8% of anthocyanin variance, while genotype effects were not significant (p = 0.953 and p = 0.496), indicating high residual variability (75.8% and 23.2%). Using eight drought-tolerance indices, Variety 31 ranked first for flavonoid stability (STI = 1.311), and Variety 14 ranked first for anthocyanin stability (STI = 1.952). Variety 14 was the only genotype among the top five for both traits. The correlation between flavonoid and anthocyanin contents was weak and non-significant (r = −0.06, p = 0.187), suggesting independent regulation of these two phenylpropanoid branches. These results introduce Variety 14 as a promising multi-trait parent for drought-resilience breeding and highlight that interannual climatic variation, rather than genotype, is the primary factor influencing anthocyanin accumulation in safflower petals.