Evaluation of salt tolerance at the seedling stage and related gene mining in mung bean germplasm resources

Soil salinization poses a serious threat to agricultural production. Exploring salt-tolerant germplasm in mung bean is crucial for the effective utilization of saline-alkali soils in China and for promoting the sustainable development of the mung bean industry. In this study, 200 mung bean germplasm accessions were evaluated for salt tolerance (150 mmol L-1 NaCl) at the seedling stage based on 13 phenotypic traits, including plant height, above-ground fresh weight, and root fresh weight. The results showed that the salt tolerance coefficient for root length per unit volume was the highest (0.806), while that for root branching was the lowest (0.591). Significant differences were observed among germplasms in their responses to salt stress, particularly in root dry weight, root length per unit volume, and root fresh weight. Based on salt damage symptoms, 16 highly salt-tolerant and 12 highly salt-sensitive germplasms were identified, with the highest proportion of salt-tolerant accessions found in the North China region. A genome-wide association study (GWAS) based on resequencing data identified 67 SNP loci significantly associated with salt tolerance, corresponding to 348 candidate genes, of which 99 had annotated functions. Among these, Vradi04g09980, Vradi01g06290, and Vradi08g02890 were validated through haplotype analysis as potentially associated with salt tolerance at the seedling stage. These findings provide a valuable foundation for the genetic improvement of salt tolerance in mung bean and for further elucidating the underlying regulatory mechanisms.