Evaluation of physiological response and cold resistance of four alfalfa cultivars to low temperature stress

Four alfalfa (Medicago sativa) cultivars, ‘Zhaodong’, ‘Longmu 801’, ‘Dongnong No. 1’, and ‘Aohan’, were studied. The cold resistance of the four alfalfa cultivars was comprehensively compared by analyzing physiological biochemical indexes and leaf anatomical structure. The relative electrical conductivity, malondialdehyde content, soluble sugar content, free proline content, peroxidase, and superoxide dismutase activity of the alfalfa cultivars increased compared with the control. Among them, ‘Zhaodong’ had the highest increase in each indicator. Through a comprehensive analysis of the membership function, it was concluded that the cold resistance of the alfalfa cultivars from high to low is as follows: ‘Zhaodong’ > ‘Longmu 801’ > ‘Dongnong No. 1’ > ‘Aohan’. By observing the anatomical structure of the alfalfa cultivars, it was found that the blade thickness, palisade tissue thickness, and sponge tissue thickness of ‘Zhaodong’ and ‘Longmu 801’ with strong cold resistance were less than that of ‘Aohan’, which was less cold resistant, and the cell structure was tighter than that of ‘Aohan’.