Identification and comprehensive evaluation of salt-alkali tolerance throughout the growth period of 155 faba bean germplasms

Soil salinization has become one of the critical abiotic stresses affecting the growth of faba bean. Identifying salt-alkali tolerant germplasm in faba bean lays the foundation for exploring salt-alkali tolerant genes and selecting and breeding salt-alkali tolerant varieties, which is of great significance for the utilization of salinized land. In this study, 155 faba bean germplasm resources from domestic and international collections were subjected to stress treatment with a matrix + mixed salt-alkali (9 g L-1, NaCl+Na2CO3+Na2SO4, pH 10.5) throughout their entire growth period. Seven indicators were measured, including the seedling rate, salt damage index (SDI), plant height, fresh weight, dry weight, chlorophyll content, and nitrogen content. Correlation analysis, principal component analysis, membership function analysis, and systematic cluster analysis were used to comprehensively evaluate and classify the salt-alkali tolerance of various germplasms. A predictive regression equation for salt-alkali tolerance was established using stepwise regression analysis. The results showed as follows: (1) Three faba bean germplasms with salt-alkali tolerance (20 ≤ salt damage index < 40) were identified, constituting 1.94% of the total, while eight germplasms displayed moderate salt-alkali tolerance (40 ≤ salt damage index < 60), comprising 5.16% of the tested germplasms. No highly salt-alkali tolerant (salt damage index < 20) faba bean germplasms were detected. (2) The salt damage index was negatively correlated with plant height, fresh weight, dry weight, chlorophyll content, and nitrogen content (P < 0.01). (3) Five indicators—fresh weight, plant height, salt damage index, chlorophyll content, and seedling rate—can be used as evaluation criteria for assessing salt-alkali tolerance throughout the entire growth period of faba beans. (4) The 155 faba bean germplasms were divided into two major groups, with the salt-alkali tolerant germplasm group exhibiting higher seedling rates, biomass, nitrogen content, and chlorophyll content. These research findings provide reliable materials for studying the mechanisms of salt-alkali tolerance in faba beans, exploring salt-alkali tolerant genes, and selecting and breeding salt-alkali tolerant varieties.