Objective   Physiological responses and cold resistance of Crassulaceae plants under low-temp stress were studied to facilitate selection of germplasms for new variety breeding and cultivation.

  Method   Eight physiological indicators were employed to gage the cold tolerance of 4 varieties of Crassulaceae under the temperature at 9, 6, 3, 0 or −3 ℃. A mathematical model that combined the principal component analysis and the membership function method was formulated for the evaluation, which was subsequently verified by testing the recovery of normal plant growth.

  Result   Crassulaceae plants of different varieties differed significantly in their physiological reactions to the low-temp stress. In general, MDA and Pro contents of the plants increased with decreasing temperature, but soluble sugar, water, and photosynthetic pigment varied among the 4 varieties. Under −3 ℃, Crassula Campfire responded with the greatest increases on relative water content and MDA release, C. oblique Gollum with a mostly stabilized photosynthetic pigment, and Sedum lucidum Obesum with the fastest soluble sugar and Pro accumulations. The 8 physiological indicators were clustered into two principal components that showed a biologically significant cumulative contribution rate of 90.59%. The cold resistance of the varieties was ranked as S. lucidum Obesum＞x Sedeveria Blue Elf＞C. oblique Gollum＞C. Campfire, which agreed with the result obtained by the plant growth recovery test.

  Conclusion   S. lucidum Obesum had a survival rate of 85.5% under −3 ℃ and grew well with stable morphological characteristics after the cold stress treatment. In contrast, C. Campfire was limited in adapting to low temperatures and survived at a rate of merely 25.5% under the same condition.