Salt Tolerance Identification Of Alfalfa And Mitigation Effect Of Melatonin On Salt Stress

Land salinization is one of the environmental issues of global concern.China’s salinealkali lands are widely distributed and large in area,and land salinization is one of the important environmental factors leading to crop yield reduction.At present,two types of leading technologies have been formed in the improvement and utilization of saline-alkali soil in the world: one is to improve the soil through irrigation and drainage technology;the other is to develop salt-tolerant plants to use saline-alkali soil.Alfalfa(Medicago Sativa L.)is known as the "king of forage".It has the advantages of high crude protein content,good palatability,and high yield,making it widely concerned in China.Compared with most crops,the quality of forage grass is relatively less affected by soil and water,and it is a better material for the development of salt-tolerant plants and the use of salinized land.At the same time,melatonin is found in animals as an antioxidant,but it also plays an important role in alleviating plant abiotic stress in plants.In the present study,the following three aspects were used to screen salt-tolerant cultivars of alfalfa and observe the effects of salt stress and melatonin treatment on alfalfa cultivars with different resistance.(1)Seed germination of 33 alfalfa cultivars was carried out with different concentrations of salt(CK,0.3%,0.6%,0.9%,1.2% and 1.5% Na Cl)to determine the germination potential,germination rate and radicle length,seedling length and other indicators.Using clustering,single factor and one-variable quadratic equation analysis,the salt tolerance classification and the theoretical identification concentration were assessed.(2)A salt-tolerant cultivar and a salt-sensitive cultivar in Experiment 1 were selected to grow to the 5-leaf stage,and salt treatment was conducted.After 14 d of salt treatment,the seedlings were watered with 100 μmol L-1 melatonin.Root and leaf samples were collected on days 1 and 7 after treatment to determine the antioxidant system,photosynthetic pigment,ion content and other related physiological indicators.(3)The seedlings of the two cultivarsgrew under continuous salt stress until half of the leaves were all faded and albino.According to the different appearance indicators,they were divided into CK(no salt treatment),N(no change in leaves),and M(half of the leaves were white),and R(all leaves were white)four groups to measure the physiological indicators.The main results are as follows:1.The roots of alfalfa seedlings are more sensitive to salt stress than the shoots.The salt concentration suitable for salt tolerance screening of alfalfa is 1.24% Na Cl.The salttolerant cultivars of alfalfa are WL16HQ and WL298HQ;and the salt-sensitive cultivars are Queen,Longnan No.1,Aihe No.1,Kehan and WL366HQ.2.Salt stress reduced the photosynthetic pigment content,antioxidant enzyme activity,glutathione and ascorbic acid content of alfalfa,and increased the content of superoxide anion and hydrogen peroxide in the alfalfa body.In addition salt stress increased the content of soluble sugar,soluble protein and sodium ion in the roots.Melatonin can alleviate the damage caused by salt stress,and the salt-sensitive cultivar Kehan had a higher degree of alleviation.With the increase of the salt stress time,the mitigation effect of melatonin on salt-sensitive cultivat Kehan weakened.3.When the apparent state was the same,the alfalfa seedlings of the two cultivars with different salt tolerance had different internal physiological states.The antioxidant enzymes,chlorophyll and other related indicators in the salt-tolerant cultivar WL168HQ performed better.