Identification of salt-tolerant henna (Lawsonia inermis L.) germplasm using a fuzzy comprehensive evaluation model at the seed germination stage

Soil salinity is a major constraint for cultivating the economically important medicinal and ornamental shrub henna (Lawsonia inermis L.) in arid regions like Kerman Province, Iran. To address the lack of systematic germplasm evaluation for salinity tolerance, this study quantified the responses of ten geographically distinct henna populations to salt stress (0, 50, and 100 mM NaCl) during the critical germination and early seedling stages. A Fuzzy Comprehensive Evaluation (FCE) framework, based on the membership function values (MFV) derived from trait-specific Salt Tolerance Indices (STI), was used to integrate data from multiple germination parameters, e.g., germination percentage (GP), mean germination time (MGT), germination index (GI), germination vigor index (GVI) and seedling growth traits, e.g., radicle length (RL), plumule length (PL), total seedling length (TSL), seedling fresh weight (SFW). Results identified germplasm J-02 as the most salt-tolerant genotype (mean MFV = 0.536), demonstrating exceptional stability in RL (STI = 1.01) and SFW (STI = 0.90) under severe stress (100 mM NaCl). In contrast, K-01 was highly sensitive (mean MFV = 0.322), suffering severe GVI loss (STI = 0.56) and TSL reduction (34.1%) despite superior control performance. Regression analysis identified SFW as the optimal single-trait predictor for overall tolerance (R² = 0.714 at 50 mM; R² = 0.549 at 100 mM). The FCE model effectively resolved genotype-specific trait conflicts, a finding corroborated by principal component analysis (PCA) and hierarchical cluster analysis (HCA) which provided mechanistic insights: elite performers (e.g., J-02) prioritized seedling elongation, while others (e.g., F-01) excelled in germination under moderate stress. This study establishes J-02 as prime germplasm for saline zones and validates the integration of FCE with multivariate analysis for precision phenotyping in henna breeding programs.