Anthocyanin-Associated Metabolic Traits Are Linked to Drought Adaptation in Purple Sweet Potato

Anthocyanin accumulation is an important quality trait in purple sweet potato, but its associations with drought responses across tissues and developmental stages remain unclear. Jizishu 1 (JZ1) and Xuzishu 8 (XZ8) were evaluated under control (D0), moderate drought (D1), and severe drought (D2) in 2019 and 2020, with three independent replicate tanks per genotype × water regime per year. Anthocyanin content, physiological traits, endogenous hormones, and anthocyanin-related gene expression were measured across sampling stages. Drought generally reduced leaf relative water content and increased relative electrolyte conductivity. Leaf anthocyanin content generally peaked at 80 d, whereas storage-root anthocyanin continued to accumulate through 120 d. Hormone contents varied with sampling stage, antioxidant enzyme activities generally increased during early and middle stages, and proline and soluble sugars accumulated during later stages. Both D1 and D2 generally increased IbCHI, IbANS, and IbMYB1 expression relative to matched D0 controls, with D1 often producing higher expression than D2. Under D1, leaf IbANS expression in XZ8 and IbMYB1 expression in JZ1 reached 21.08- and 23.13-fold relative to D0 at 80 d, respectively. In storage roots, the corresponding values for IbANS and IbMYB1 in XZ8 were 17.54- and 16.98-fold at 100 d. These findings indicate that anthocyanin accumulation was associated with broader physiological and transcriptional changes under drought, with distinct tissue- and stage-dependent patterns.