Physiological responses of two apricot-plum hybrids to low temperature stress

• Systematically evaluated cold tolerance in apricot-plum hybrids using integrated phenotypic, anatomical, and physiological indicators. • Low-temperature thresholds for two hybrid apricot-plum dormant branches and flower buds established for cold-tolerance early warning. • Cold tolerance of hybrid apricot-plum dormant branches and buds evaluated via correlation, PCA, and membership function analysis. Low temperature is a major factor limiting the cultivation and productivity of crops. In the Xinjiang region of northwestern China, fruit trees are frequently exposed to severe temperature fluctuations in spring and extreme cold in winter. Apricot-plum hybrid (Prunus domestica × armeniaca ), an interspecific hybrid between plum and apricot, is valued for its unique flavor and high nutritional value. This study compared the cold tolerance of two main cultivars, 'Weidi' (WD) and 'Konglongdan' (KLD), by evaluating one-year-old dormant branches and flower buds through integrated analyses of stress phenotypes, anatomical structure, and physiological biochemistry. Results showed that the periderm and xylem of KLD branches were significantly thicker than those of WD during winter dormancy. After extreme low-temperature exposure, the semi-lethal temperature (LT₅₀) of KLD branches (-22.93 °C) was lower than that of WD (-20.63 °C), with bud burst rate significantly decreasing in both cultivars at ≤ -20 °C. Based on the LT₅₀ range, continuous low-temperature treatments revealed KLD exhibited a significantly longer semi-lethal time (Lt₅₀) under sustained stress. In flower buds, KLD demonstrated a lower LT₅₀, supercooling point, and freezing point, alongside less severe anatomical damage under frost stress. Physiological analyses indicated that KLD's superior performance was associated with reduced membrane lipid peroxidation and reactive oxygen species accumulation, coupled with higher antioxidant enzyme activity and osmoprotectants. A comprehensive evaluation based on membership function analysis confirmed that KLD has stronger cold tolerance than WD. This study provides a scientific basis for freezing injury early warning, cold-resistance breeding, and mechanistic studies in apricot-plum hybrid.