Effects Of Salicylic Acid On The Seed Germination And Seedling Growth Of Alfalfa Under Drought Stress

Alfalfa is one of the most widely planted forages in the world.It has the advantages of rich nutrition,strong stress resistance and high yield.As the main forage in our country,the improvement of its quality and yield is an urgent problem to be solved at present.Northwest China is the main forage producing area in our country,and arid environment is the main limiting factor restricting the high-quality and high-yield production of alfalfa.Drought causes serious harm to pastures,especially alfalfa.Faced with the constraints of drought on animal husbandry,we have adopted a variety of methods to alleviate it.Among them,the exogenous application of salicylic acid has been applied in the drought improvement of various crops,but there are few related studies on its effect on the production performance of alfalfa under drought stress.Therefore,this study adopted a completely randomized block method to investigate the effects of different salicylic acid concentrations(0,0.02,0.1,0.5 and 2.5 mmol L^-1)on seed germination,potted seedlings and field seedlings of alfalfa under drought stress.The most effective concentration for improving production performance is selected according to the fuzzy membership function method.The main research results are as follows:（1）For the germination stage of alfalfa seeds,2.5 mmol L-1 salicylic acid treatment could improve the phenotype,germination and physiological index of alfalfa seed under PEG stress.By increasing the seed germination rate and daily germination number,salicylic acid shortens the time to 50%germination,so that the seeds have good germination potential,germination index,seed vigor index,germination peak and coefficient of germination velocity.Daily germination number,daily root length and daily shoot length are promoted,which in turn promotes root and cotyledon growth in alfalfa seeds.（2）For the potted alfalfa seedling stage,0.02,2.5 and 0.5 mmol L-1 salicylic acid treatments improved the phenotype,agronomic traits,photosynthetic pigments,photosynthesis properties,physiological properties,and ionic concentrations of potted alfalfa seedlings under 80%,40%and 20%water stress.Appropriate exogenous application of salicylic acid maintains the plant growth and reasonable nutrient distribution,protects the stomatal shape and photosynthetic capacity of leaves,alleviates oxidative damage and cell membrane damage,and stabilizes the cell osmotic potential of leaves and roots,thereby making the phenotypic development of potted alfalfa seedlings under drought stress is normal.（3）For alfalfa seedlings in the field,treatments of 0.02,0.5,0,CK（No treatment is applied under natural drought conditions）and 2.5 mmol L-1 could improve the agronomic traits,physiological responses and nutrient ions of cultivars WL168HQ,WL353HQ,Central,Longnan 1 and Pioneer under natural drought conditions concentration.Appropriate exogenous application of salicylic acid can increase the activity of antioxidant enzymes and facilitate the accumulation of non-enzymatic antioxidant substances,thereby alleviating the oxidative damage caused by drought stress.In addition,salicylic acid alleviates cell membrane damage caused by drought stress by promoting the accumulation of osmotic regulators and regulating the concentration of inorganic ions.It also stabilizes the antioxidant system and osmotic pressure damage of field alfalfa seedlings under natural drought stress,and finally maintains its agronomic traits and production performance.（4）The effects of salicylic acid on alfalfa seed germination,potted seedlings and field seedlings under drought stress depended on salicylic acid concentration,salicylic acid concentration and water conditions,salicylic acid concentration and variety,respectively.