关键词: 香橼, 耐寒性, 寒害指数, 半致死温度（LT₅₀）, 生理特性

Abstract: The cold resistance of 24 Citrus medica strains which have favorable fruit characters was studied by field identification，cell membrane permeability research and cluster analysis；The cold resistant physiological property of ten strains which belong to high cold resistance，medium cold resistance and poor cold resistance respectively were studied under low temperature stress. The results showed that the index of chilling injury was intervenient 2.00 and 3.40，and the range of semilethal temperature（LT₅₀）was–14.84 to–7.07 ℃. The cold resistance of 24 Citrus medica strains was evaluated by cluster analysis based on index of chilling injury and LT50，Chunjiang 4，Chunjiang 5，Chunjiang 6，Xinshiji 9，Xinshiji 10 and Xiangyuan 4 had high cold resistance；Chunjiang 1，Chunjiang 2，Chunjiang 3，Chunjiang 8，Xiangyuan 1，Xiangyuan 2，Xiangyuan 5，Xiangyuan 6，Xiangyuan 7，Xinshiji 1，Xinshiji 3，Xinshiji 4，Xinshiji 5，Xinshiji 6，Xinshiji 7 and Xinshiji 8 had medium cold resistance；Chunjiang 7 and Xinshiji 2 had poor cold resistance. With the temperature decreasing，the contents of MDA，proline and soluble protein，the activities of SOD increased at first and then decreased. In high cold resistance strains，the contents of MDA was low，the contents of proline，soluble protein，and the activities of SOD were high；On the contrary，in low cold resistance strains，the contents of MDA was high，the contents of proline，soluble protein and the activities of SOD were low.

Key words: Citrus medica, cold resistance, index of chilling injury, semilethal temperature（LT₅₀）, physiological property