Comprehensive evaluation of the salt tolerance of Melilotus officinalis at the seedling stage

Understanding the salt tolerance of forage grass at the seedling stage is essential for the success of cultivated grassland planting. In this study, the growth rate, chlorophyll content, seedling height, survival rate, dry weight, and number of green leaves were measured under various salt concentrations (0, 50, 100, 150, 200 mmol·L⁻¹) at the seedling stage using a hydroponic method. Moreover, the salt tolerance comprehensive evaluation value (D value) of 68 Melilotus officinalis germplasms was comprehensively calculated using principal component analysis, the subordination function, and the index weight method, based on the salt tolerance coefficient of each individual index. The results revealed that the single index of different germplasm materials showed a significant positive correlation under salt stress (P < 0.01). Based on a cluster analysis of the D value, the 68 M. officinalis germplasms were divided into 6 highly salt-tolerant, 20 moderately salt-tolerant, 27 mildly salt-sensitive, and 15 salt-sensitive accessions. Moreover, stepwise regression analysis was performed on the D value and salt tolerance coefficient, and the survival rate, chlorophyll content, and number of green leaves were determined to be good criteria for salt tolerance evaluation in M. officinalis accessions at the seedling stage. This study provides a theoretical basis for the establishment of M. officinalis-cultivated grasslands on saline-alkaline land.