Basil (Ocimum basilicum L.), a globally significant medicinal plant of the Lamiaceae family, contains valuable volatile oils, polyphenols, and flavonoids with wide applications in food, pharmaceutical, and cosmetic industries. This study evaluated salinity stress responses across 13 basil cultivars, quantifying growth, morphological, and biochemical changes under 90 mM NaCl. Salinity stress (90 mM NaCl) significantly reduced shoot biomass across all cultivars (p < 0.01), with Variegated showing maximum reduction (59.8%) versus Bush/Light Purple cultivars (31%). Essential oil content increased in all cultivars except Dark Opal under 90 mM NaCl (p = 0.003), with Lettuce showing a 12-fold rise (0.05–0.60% v/w), though yield (mL/plant) declined in most cultivars due to biomass reduction. Cluster analysis revealed genotype-specific tolerance mechanisms: Purple cultivars demonstrated specify osmotic adjustment through 58% higher proline accumulation and 33% lower MDA levels than sensitive genotypes. Bush and Light Purple exhibited superior salt tolerance (31% biomass reduction), ideal for cultivation in saline soils, while Lettuce and Afghan showed enhanced essential oil production (up to 12-fold increase) under 90 mM NaCl, offering potential for phytochemical extraction. The observed diversity in stress responses provides valuable genetic resources for breeding climate-resilient cultivars, supporting sustainable medicinal plant production.
