Comprehensive evaluation of freezing tolerance in prickly ash and its correlation with ecological and geographical origin factors.

Low temperatures are a key factor affecting the growth, development, and geographical distribution of prickly ash. This study investigated the impact of ecological and geographical factors on the freezing tolerance of prickly ash germplasm. Thirty-seven germplasm samples from 18 different origins were collected, and their freezing tolerance was comprehensively evaluated. The correlation between freezing tolerance and the ecological and geographical factors of their origins was also analyzed. Significant differences in freezing tolerance were observed among germplasm from different origins. The semi-lethal temperature of the germplasm ranged from - 12.37 to 1.08 °C. As temperatures decreased, the relative conductivity (REC) and catalase (CAT) activity of the germplasm gradually increased, while soluble sugar (SS), soluble protein (SP), free proline (Pro), and Peroxidase (POD) activities decreased and then increased. Superoxide dismutase (SOD) activity initially increased and then decreased. A comprehensive evaluation of freezing tolerance was conducted using a logistic equation, membership function, and cluster analysis. Germplasm from Tongchuan and Hancheng (Shaanxi Province, China), Asakura (Japan), and Yuncheng (Shanxi Province, China) exhibited the highest freezing tolerance, whereas those from Rongchang (Chongqing Municipality, China), Qujing (Yunnan Province, China), and Honghe (Yunnan Province, China) had the lowest. The correlation analysis revealed a significant positive correlation between freezing tolerance and latitude, and a significant negative correlation with the temperature of origin. Germplasm from higher latitudes showed higher SS content, SOD and CAT activities, stronger antioxidant enzyme activity, and better freezing tolerance compared to those from lower latitudes. REC was lower in germplasm originating from low-temperature areas than in those from high-temperature areas. Additionally, SP, Pro content, SOD, and POD activities were higher, indicating effective scavenging of active oxygen free radicals. No significant correlation was found between altitude and longitude of origin and freezing tolerance. However, at similar latitudes, prickly ash from higher altitudes displayed higher antioxidant enzyme activity and stronger freezing tolerance compared to those from lower altitudes. These findings provide a scientific basis for breeding prickly ash cultivars suited to different ecological regions.