Screening and evaluation of salt tolerance of 80 alfalfa varieties at the seedling stage

To screen salt-tolerant alfalfa (Medicago sativa) varieties at the seedling stage and establish the corresponding evaluation methods, we measured plant height, root length, leaf width, leaf thickness, stem diameter, fresh weight, dry weight, chlorophyll content, and tissue water content in 80 foreign alfalfa varieties treated with 1.2% NaCl using the hydroponic method. Salt tolerance of alfalfa seedlings was evaluated using difference, correlation, principal component, regression, and cluster analyses. The results showed that under salt stress, the coefficients of variation of the nine indicators among the different varieties ranged from 0.119 to 0.604. Salt stress had strongly significant effects on root length, fresh weight, dry weight, and relative tissue water content of alfalfa seedlings (P < 0.01) and had significant effects on leaf width (P < 0.05). The four principal components represented a data volume of 68.545% for the nine original indicators. Principal component analysis showed that fresh weight, relative tissue water content, root length, and leaf width were the main indicators of salt tolerance in alfalfa seedlings. Regression analysis showed that using salt tolerance measures (D) to evaluate salt tolerance at the seedling stage was more objective and reasonable. Cluster analysis divided the 80 alfalfa varieties into four grades, including 3 varieties with the strongest salt tolerance, 28 varieties with strong salt tolerance, 36 varieties with weak salt tolerance, and 13 varieties with the weakest salt tolerance. On this basis, alfalfa varieties with strong salt tolerance at seedling stage were screened: ‘WL354HQ’ ‘Arola’ and ‘Juneng 801’. These results provide a theoretical basis for screening salt-tolerant genes and breeding new varieties of alfalfa.