Effects Of Brassinolide On Seed Germination,Physiological Response,and Production Performance Of Alfalfa Under Drought Stresse

Alfalfa（Medicago sativa L.）is a world-recognized high quality forage grass with the advantages of high protein and good palatability.Drought is a limiting factor for plant production,which seriously affects the growth,yield and quality of alfalfa,and has become one of the main limiting factors for the development of forage industrialization in China.Brassinolides（BRs）are highly oxygenated phytosteroid phytohormones that play an important role in improving plant resistance,quality and yield,and have good application potential in agricultural production.In this study,the alfalfa variety Suntory was used as the test material,and three experiments were designed:First,after seed soaking with different concentrations of 2,4-epibrassinolide（EBR）,the germination was observed under 15%PEG stress.Second,control the water holding capacity of potted alfalfa to 30%（severe drought,D1）,60%（moderate drought,D2）,and 80%（normal water supply,N）,respectively.Third,randomly selected field plots,followed by spraying the EBR concentration in the pot experiment,and observed the effect of EBR on the production performance of alfalfa.The three experiments were combined to explore the effects of EBR on seed germination characteristics,physiological and biochemical responses and growth performance of alfalfa in response to drought,and to screen the best EBR application concentration in order to provide a reference for improving the growth of alfalfa under drought stress and the field application of EBR.The main results are as follows:1.15%PEG significantly inhibited alfalfa seed germination.EBR treatments significantly increased the germination rate,germination potential,radicle length,and germ length of alfalfa seeds.In the process of seed germination,the seedlings treated with EBR were more resistant to drought,which showed that the levels of O₂?^?and H₂O₂ were lower,the activities of SOD and POD were higher,and the accumulation of proline was more.Based on the above indicators,the drought resistance effect of EBR with 0.1μmol L^-1 was the best at the germination stage.2.After foliar spraying with an appropriate concentration of EBR,it can promote the growth of alfalfa while relieving drought stress.0.1μmol L^-1 EBR significantly promotes the production of photosynthetic pigments under drought stress,regulates photosynthetic gas parameters,and effectively inhibits the excessive accumulation of MDA,H₂O₂,and O₂?^?,increasing the content of osmotic regulators and enhances the activities of SOD,POD,and APX.It can promote the synthesis of As A,GSH,and polyphenols,thereby improving the response of alfalfa to drought stress and increasing the growth under normal water holding conditions.In addition,most indicators were significantly correlated,and the principal component analysis results of groups D1,D2,and N could explain 76.7%,80.8%,and 73.6%of the total variables,respectively.3.In the field test,foliar spraying of 0.01μmol L^-1 EBR improved the growth indicators of alfalfa such as dry and fresh weight,plant height,stem diameter,number of leaves,and leaf area.Compared with the control,the fresh weight and dry weight of alfalfa treated with 0.01μmol L^-1 EBR increased by 24.02%and 30.72%,respectively.The total dry weight of 1μmol L^-1 EBR treatment decreased significantly.An appropriate concentration of EBR also reduces oxidative damage by regulating the antioxidant system and osmotic adjustment substances,improving the growth of alfalfa.The indicators were clustered into two categories,and most of them had significant correlations.The first principal component（60.6%）and the second principal component（18.8%）could explain 79.4%of the total variables.In addition,higher concentrations of EBR had a growth-inhibiting effect.In summary,exogenous application of EBR at a concentration of 0.01-0.1μmol L^-1 can significantly promote the germination of alfalfa seeds under drought stress,improve the growth of potted alfalfa with different water holding capacity,and have good results in field application.Therefore,the appropriate concentration of EBR can be used for the forage production of alfalfa to promote growth and increase hay yield.