Effects of drought stress on physiology and antioxidative activity in two varieties of Cynanchum thesioides

Cynanchum thesioides (Freyn) K. Schum. with higher drought tolerance has received much research attention in arid and semiarid areas of China. However, no full evaluation of drought resistance had been made. In the current study, we compared relative water content, water saturation deficit, root vitality, root–cap ratio, photosynthetic pigments and ten physiological indices in C. thesioides and C. thesioides (Freyn) K. Schum. var. australe (Maxim.) Tsiang et P.T. Li. seedlings under a gradient of drought stress. The ten indices included superoxide dismutase, peroxidase, catalase, ascorbate peroxidase and malondialdehyde, hydrogen peroxide, superoxide, proline, soluble protein and sugar content of leaves and roots. Based on the analysis of average membership functional values, the drought tolerance of C. thesioides var. australe was better than C. thesioides. In the future, C. thesioides var. australe should be given priority when selecting varieties for use as medicines in arid and semiarid areas of China.