Growth and abscisic acid responses of Medicago sativa to water stress at different growth stages

A pot experiment was conducted in a green-house with three alfalfa (Medicago sativa) cultivars, Aohan, Zhongmu No.l and Sanditi, to examine the morphological and physiological responses of alfalfa to water stress. The response of alfalfa to water stress at different growth stages was generally similar, but varied among cultivars. At the branching, flowering and podding stages, the shoot biomasses of Aohan and Zhongmu No.l were greatly affected by, and responded quickly to, water stress. The shoot biomass of Sanditi was not affected by mild water stress, hut had a slight response to moderate and severe water stress. The root/shoot ratios in Aohan and Zhongmu No.l were more sensitive to water stress than in Sanditi, with the root/shoot ratio in Aohan increasing most significantly. At flowering, the root/shoot ratio was the highest and the effect of water stress the greatest. The abscisic acid (ABA) concentration in the roots of Aohan and Zhongmu No. 1 increased under water stress, while in Sanditi there was only a slight or delayed response of ABA concentration.