Foliar-Applied Betaine Mitigates Drought-Provoked Yields and Quality Losses in Potato Through Redox-Centered Antioxidant Regulatory Networks

Drought stress triggers an excessive reactive oxygen species burst, disturbs cellular redox homeostasis, and impairs potato (Solanum tuberosum L.) growth, tuber yields, and quality. Exogenous betaine (Bet) is an effective osmoprotectant mitigating abiotic stress injury in many crops; however, the systematic evaluation of Bet application conditions and its molecular mechanisms in drought-stressed potato remains limited. In this study, morphological and physiological assays were used to screen the optimal Bet concentration and effective foliar-spraying growth stage. Foliar 10 mM Bet exerted the strongest protection, restoring plant growth, enhancing antioxidant enzyme activities, and strengthening antioxidant defense to limit the further progression of drought-associated oxidative injury. Relative to the drought-only control, 10 mM Bet applied at the maturation stage markedly improved photosynthetic performance, tuber yields, and nutritional quality. Transcriptomic profiling revealed that Bet reversed drought-triggered transcriptional perturbations and activated antioxidant, cell-wall remodeling, and hormone signal-transduction pathways. Weighted gene co-expression network analysis identified three key modules linked to drought tolerance and Bet-mediated mitigation. Six hub genes, including StGS2 (antioxidant-associated function), StXTH5 (cell-wall modification), StLOX1 (stress signaling), and StCERK1 (stress perception), were validated via RT-qPCR as candidate genes associated with the betaine-responsive drought response. Mechanistically, Bet strengthened reactive oxygen species-scavenging capacity to limit the further progression of drought-associated oxidative injury, alleviated drought-induced photosynthetic inhibition and maintained photosynthetic functions, and modulated stress-related hub-gene expression. These findings show that exogenous Bet alleviates drought damage by coordinating multi-level physiological and molecular pathways, providing a feasible agronomic practice for water-limited potato production and a molecular reference for Bet-regulated drought tolerance in tuber crops.