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چکیده
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Background: Moldavian balm (Dracocephalum moldavica L.) is a valuable medicinal plant, yet salinity responses of its Iranian genotypes remain poorly characterized. This study introduces a methodological approach for preliminary screening of salt-tolerant genotypes using a novel composite index. Methods: Ten Iranian genotypes were subjected to three salinity levels (0, 75, and 150 mM NaCl) in a completely randomized design with three replicates (n = 90). Agronomic traits, antioxidant enzyme activities, malondialdehyde (MDA), and essential oil profiles were measured. A novel composite index (STI × YSI) was developed and validated via bootstrap analysis (1000 resamples). Multivariate analyses including principal component analysis (PCA), cluster analysis, and MANOVA were employed for genotype discrimination. Results: Salinity significantly reduced shoot dry weight (by 52%, from 15.21 g to 7.29 g, p < 0.01) while concurrently increasing ascorbate peroxidase (APX) activity (from 0.386 to 0.517 μmol mg⁻¹ protein min⁻¹, p < 0.001). The STI × YSI index resolved the paradox between high baseline yield and hormesis. PCA (83.1% variance explained, KMO=0.76) and cluster analysis (cophenetic=0.82) identified Azarshahr (0.70), Maragheh (0.64), and Ajabshir (0.57) as top-scoring genotypes with stable rankings (>90% bootstrap stability). A biphasic geraniol response (increase at 75 mM, decrease at 150 mM NaCl) supported the growth-defense trade-off theory. SOD and proline responses could not be reliably assessed, as the study's statistical power for these traits was insufficient (0.38–0.45). Conclusion: Azarshahr, Maragheh, and Ajabshir are promising candidates from this preliminary screening. However, these findings require field validation with ion measurements (Na⁺/K⁺ ratio) and increased replication before breeding recommendations. The methodological framework (STI × YSI) offers a robust approach for initial genotype screening.
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