Identification, evaluation and screening of salt-tolerant of soybean germplasm resources at seedling stage

Soil salinization has a significant impact on soybean quality and yield. Therefore, it is crucial to screen salt-tolerant soybean resources for the comprehensive utilization of salinized land. To establish a method for identifying and evaluating salt tolerance in soybean at the seedling stage, we conducted experiments using fresh water and 10 equal-differential gradients of NaCl solutions ranging from 0.9% to 1.8%. These solutions were applied to vermiculite culture medium when the soybean plants reached the stage of two emerged leaves. Results indicated that the 1.2% salinity treatment for 16 days demonstrated the highest interquartile range of salt-tolerant grading among various soybean germplasm resources, thus considered the optimal condition for evaluating salt tolerance in soybean seedlings. A total of 504 soybean germplasm resources from diverse geographic regions at home and abroad were subjected to evaluation using the soybean salt-tolerant evaluation system. Among them, 46, 146, 157, 79, and 76 soybean germplasm resources received salt-tolerant gradings of 1, 2, 3, 4, and 5, respectively. The soybean resources with salt-tolerant grading 1 were further analyzed using the GmSALT3 gene molecular marker. The amplification results of 40 soybean resources (80.96%) were consistent with the GmSALT3 gene molecular marker. To analyze the change in salt stress concentration in the culture medium during the identification of soybean seedlings, a regression equation was established between soil salt content (Y, %) and electrical conductivity (X, mS cm-1): Y=0.278X-0.0618, with a prediction accuracy above 95%. The variation trend of salt content in the culture medium was measured from the beginning of salt treatment until the end of the investigation, and it was found to be maintained at approximately 13 mS cm-1. This study not only provides a technical system for large-scale identification of salt-tolerant soybean seedlings but also serves as a foundation for breeding new soybean salt-tolerant germplasm resources.