Effects of exogenous betaine on alfalfa seed germination and seedling resistance under NaCl stress

As an important osmotic regulator, glycine betaine is could improve plant stress resistance. To explore the effects of exogenous betaine on alfalfa seed germination and seedling stress resistance under NaCl stress, Gannong 3 was selected as the alfalfa in this experiment and moderate salt stress was simulated using an NaCl solution of 150 mmol·L^–1. Additionally, six gradient concentrations of exogenous betaine (0, 10, 20, 30, 40, and 50 mmol·L^–1) and two application modes, via leaf or root, were used as treatments to assess seed germination and potted seedling growth. The physiological mechanism of exogenous betaine in alleviating NaCl stress in alfalfa was explored by analyzing the related indicators during seed germination and seedling growth. The results showed that: 1) after NaCl stress, alfalfa seed germination potential, germination rate, germination index, vigor index, germ radicle length, plant height, tissue water content, chlorophyll, soluble sugar, and free proline decreased significantly, whereas MDA content, and SOD, POD, and CAT activities increased significantly; and 2) after adding different concentrations of exogenous betaine, six germination traits and 8 physiological stress resistance indexes were significantly increased and MDA was significantly decreased. When leaf application was 30 mmol·L^–1 and root injection was 40 mmol·L^–1, the stress resistance effects were optimal. It not only effectively improved salt resistance of alfalfa seeds and seedlings, but also promoted the growth and development of alfalfa in saline environments.