Evaluation of salinity tolerance and germplasm screening of buckwheat during germination under salt stress

Soil salinization is a major abiotic stress factor threatening the sustainable development of global agriculture and severely limiting the production potential of buckwheat and other salt-sensitive crops. To screen salt-tolerant buckwheat germplasm and establish a reliable evaluation model, 160 buckwheat accessions were subjected to a germination test using the double-layer filter paper method. Two types of salt stress—neutral salts (NaCl, Na2SO4) and alkaline salts (NaHCO3, Na2CO3)—were applied at five concentration gradients. Five germination parameters, including germination potential (GP), and four seedling growth traits, including root length (RL), were measured to calculate the salt tolerance index (STI) for each trait. Multivariate statistical analyses were conducted to comprehensively evaluate salt tolerance and identify key indicators. Results showed that the salt tolerance coefficients of the nine measured traits varied across salt types and concentrations, with significant correlations observed among some traits. The germination inhibition threshold for alkaline salts (0.10%) was significantly lower than that for neutral salts (0.25%), and the inhibition strength followed the order: Na2CO3 > NaHCO3 > Na2SO4 ≈ NaCl (at high concentrations). Principal component analysis (PCA) extracted two principal components from the nine STI traits for each salt type, explaining 80.12%-84.07% of the total variance. PC1 (germination vigor factor, contribution 54.60%-58.13%) included vigor index (VI), germination index (GI), and germination rate (GR), while PC2 (biomass factor, contribution 25.21%-27.96%) included fresh weight (FW), dry weight (DW), and shoot length (SL). A comprehensive salt tolerance score (D value) was calculated for each accession using membership function analysis. Cluster analysis grouped the 160 accessions into five categories: highly tolerant (HT), tolerant (RT), moderately tolerant (MT), sensitive (SS), and highly sensitive (HS). Fourteen accessions with high tolerance were identified across all four salt types. Stepwise regression analysis was used to construct optimal linear prediction models. Under NaCl, Na2SO4, and NaHCO3 stress, VI, GI, FW, SL, and GR were significantly correlated with the D value (R2 = 0.994-0.999, P 2CO3 stress, GI, FW, SL, and RL were significantly correlated (R2 = 0.998, P 0.01), suggesting these traits can serve as reliable salt tolerance indicators. Among them, VI demonstrated greater discriminatory power than the traditional GR, making it a promising comprehensive physiological index. These findings provide a phenotypic foundation for identifying salt-tolerant buckwheat germplasm and support future genome-wide association studies (GWAS) to uncover quantitative trait loci (QTLs) and genes involved in salt tolerance.