Objective This study identified and compared cold tolerance in different Chimonanthus praecox cultivars, analyzed their physiological responses to low-temperature stress, and screened cold-tolerant cultivars for cold northern regions, providing elite germplasm and theoretical support for its landscape application.

Method One-year-old branches from 51 C. praecox cultivars were treated with gradient cooling from −34 to −10 ℃, with 4 ℃ as the control. The relative electrical conductivity (REC) was measured, and the semi-lethal temperature (LT₅₀) was calculated by fitting the Logistic equation. Representative cultivars with high cold resistance and low-temperature sensitivity were primarily screened. Their physiological indices related to cold tolerance were further determined, including osmotic regulators (soluble sugar, soluble protein, proline), antioxidant enzymes (superoxide dismutase, peroxidase) and malondialdehyde (MDA) reflecting membrane damage. Finally, the cold resistance of all cultivars was comprehensively evaluated by principal component analysis and the subordinate function method.

Result (1) The relative electrical conductivity of the 51 C. praecox cultivars all showed an S-shaped curve, with their semi-lethal temperatures (LT₅₀) ranging from −28.71 to −17.59 ℃. Five highly cold-tolerant cultivars (C25, C27, C33, C39, C51) and five low-temperature-sensitive cultivars (C10, C11, C42, C46, C49) were screened for further measurement of cold-resistance physiological indices. (2) With decreasing treatment temperature, the relative electrolyte leakage and malondialdehyde (MDA) content of the 10 representative cultivars increased continuously, while the protective physiological indices, including peroxidase (POD) and superoxide dismutase (SOD) activities as well as soluble sugar (SS), soluble protein (SP) and proline contents (Pro), all increased first and then decreased. Compared with the low-temperature-sensitive cultivars, the highly cold-tolerant cultivars displayed slower membrane damage, higher peak values and a milder decline in the protective physiological indices. (3) The comprehensive evaluation showed that the cold hardiness of the 10 selected C. praecox cultivars, consisting of five highly cold-tolerant and five low-temperature-sensitive genotypes, ranked in descending order as follows: C27, C39, C25, C51, C33, C49, C46, C10, C42, C11.

Conclusion Highly cold-tolerant C. praecox cultivars showed lower cell membrane damage, stronger antioxidant enzyme activity, and enhanced osmotic adjustment capacity. The highly cold-tolerant C. praecox cultivars C27, C39, C25, C51 and C33 screened in this study can serve as suitable germplasm for landscape application in cold northern regions, laying a critical germplasm foundation for breaking the popularization bottleneck of C. praecox in these areas.