Abstract: Salinity is recognized as one of the abiotic stresses negetively affecting crop productivity worldwide, which is mainly introduced by the consequence of Na⁺ toxicity. Great advances have been made in screening methodologies for salt tolerant soybean [Glycine max (L.) Merr.] in recent years. But few studies have focused on the evaluation of the relationship of soybean salt tolerance with Na⁺ content in different organs. The objective of our study was to develop a steady, measurable and effective method for salt tolerance evaluation of soybean germplasm based on measuring Na⁺ content in soybean. Twenty nine cultivars were grown in 1/2 Haogland nutrient solution, in which 100 mmol L^–1 NaCl was added when the second pair of simple primary leaves fully expanded. The visual foliar symptom was used to evaluate the scale of the salt tolerance. Roots, stems, leaves, and cotyledons were sampled at eight days after salt treatment. Different parts of the plant were measured by the atomic absorption spectrophotometer. Na⁺ content was extremly correlated with the scale of salt tolerance content in stem, leaf and cotyledon but not in root. Clustering for salt tolerant (including scale of 1 and 2) and salt sensitive (including scale of 3, 4, and 5) soybean cultivars at seedling stage based on Na⁺ contents in stem, leaf and cotyledon. The average Na⁺ contents of leaf and cotyledon from the tolerant cultivars were significantly lower than those from the sensitive culitvars. There was significant difference of Na⁺ contents in roots but there was not in stem between tolerant and sensitive soybean. Therefore, Na⁺ content in leaf and cotyledon can be used for evaluation of salt tolerance in cultivated soybean at the seedling stage. The results indicated that the possibility evaluating salt tolerant soybean cultivars at the seedling stage by Na⁺ content of leaf and cotyledon in hydroponics provides a method for germplasm identification, gene cloning and cultivar development of salt tolerance in soybean.

Key words: Soybean, Germplasm, Seedling stage, Salt tolerance, Na⁺ content