Identification of Salt-Tolerant Germplasm and Salt-Responsive Genes in Brassica napus Through Phenotypic and Transcriptomic Analyses

China’s edible oil self-sufficiency rate is only about 30%, and approximately 100 million acres of saline-alkali land are potentially available for rapeseed cultivation. However, salt stress severely inhibits rapeseed growth and yield, making the breeding of salt-tolerant varieties and the study of underlying molecular mechanisms urgent priorities. In this study, 1609 Brassica napus accessions were screened for salt tolerance, and the highly salt-tolerant material ‘Xiangnong Saline-Alkali Oil No. 1’ (XNSA01) was identified. Subsequent physiological, hormonal, transcriptomic, and functional analyses were conducted to characterize its salt-tolerance mechanisms. Salt stress significantly activated antioxidant defense and stress-related hormone responses in XNSA01, accompanied by significant accumulation of proline, abscisic acid, and salicylic acid. Transcriptome analysis identified five candidate salt-responsive genes, among which BnaA10g15320D, BnaA02g04730D, and BnaC07g08360D were closely associated with antioxidant enzyme activities and endogenous hormone contents. In particular, BnaA02g04730D showed a significant negative correlation with MDA content. Yeast heterologous expression and transgenic validation further demonstrated that BnaA02g04730D enhanced salt tolerance by increasing antioxidant enzyme activities and reducing membrane lipid peroxidation. These findings provide a useful basis for the breeding of salt-tolerant rapeseed varieties and for further investigation of salt-tolerance mechanisms in B. napus.