Comprehensive evaluation of salt tolerance in flax (Linum usitatissimum L.) germplasm based on a multi-trait approach during germination and early seedling growth

Salinity is a major abiotic stressor that limits flax productivity, particularly during germination, a critical stage for early physiological responses and successful crop establishment. Evaluation of germination under saline conditions is an effective approach for identifying salt-tolerant germplasms. Salinity tolerance in the evaluated flax germplasms was evaluated under four sodium chloride (NaCl) concentrations (0, 50, 100, and 150 mM). Germination and seedling growth traits were measured. A quantitative framework blending Principal Component Analysis (PCA), Fuzzy Membership Function Analysis ( \(\:D\) -value), and quadratic regression-based \(\:{IC}₅₀\:\:\) estimation was used to assess germplasm tolerance. NaCl caused a concentration-dependent inhibition of all measured traits, with seedling vigor trait (SVI) showing the lowest IC50, identifying it as the most sensitive indicator. Principal Component Analysis (PCA) effectively captured multi-trait variance and indicated that germination kinetics become increasingly important under severe stress. The integrated D -value framework identified G-2 as the top performer under mild stress (50 mM), G-1 as highest at moderate stress (100 mM), and G-8 as highest at severe stress (150 mM). Both G-1 and G-8 consistently ranked among the tolerant germplasms across all salinity levels, while G-6 was consistently the most sensitive germplasm, with G-7 and G-4 also ranking among the sensitive germplasms at most salinity levels. Quadratic regression analysis identified approximately 118.0 mM NaCl as the optimal screening concentration for discriminating among germplasms. The study shows considerable genetic diversity in flax salt tolerance and recommends specific robust, tolerant, and most sensitive germplasms as reliable screening checks for future flax breeding programs.