Seed priming with brassinolide improves lucerne (Medicago sativa L.) seed germination and seedling growth in relation to physiological changes under salinity stress

Salt stress is an important constraint to lucerne (Medicago sativa L.) production in many parts of the world. Seeds of 3 lucerne varieties, cvv. Victoria, Golden Empress, and Victor, were used to investigate the effects of seed priming with 5 µm/L brassinolide on germination and seedling growth under a high level of salt stress (13.6 dS/m NaCl solution). The results showed that germination percentage, germination index, and vigour index of lucerne seeds primed with brassinolide were significantly higher than those of the non-primed seeds under salinity stress in each variety. Seed priming with brassinolide significantly increased the shoot fresh weight, shoot dry weight, and root dry weight in 2 varieties, and significantly increased the root length and root vigour in each variety. It also significantly increased the activities of antioxidant enzymes, peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), in Victoria and Victor seedlings. During seedling growth, the primed seeds significantly reduced the malondialdehyde (MDA) accumulation. This suggests that priming lucerne seed with brassinolide at a suitable concentration can improve germination and seedling growth under high-saline soils.