*2.9. Measurement of the Polyphenolic Profile*

For the measurement of the phenolic profile, 5 μL samples extracted according to the procedure described by Vallverdu-Queralt et al. [24] were analyzed by ultrahigh performance liquid chromatography (UHPLC; Dionex Ultimate 3000, Thermo Fisher ScientificTM, Waltham, MA, USA) and Orbitrap high-resolution mass spectrometry (HRMS; Thermo Fisher ScientificTM, Waltham, MA, USA) according to the protocol detailed by El-Nakhel et al. [25]. The chromatographic separation of polyphenols was carried out with a Luna Omega PS column (1.6 μm, 50 × 2.1 mm, Phenomenex, Torrance, CA, USA) set at 25 ◦C, in which the mobile phases consisted of water (A) and acetonitrile (B), both containing 0.1% formic acid (*v*/*v*). The Q-Exactive Orbitrap mass spectrometer was set in a fast negative/positive ion switching mode with two scan events (Full ion MS and all-ion fragmentation, AIF) for all compounds of interest. The calibration and accuracy of the equipment was monitored using a standard reference mixture (Thermo Fisher ScientificTM, Waltham, MA, USA). Data processing was performed with Quan/Qual Browser Xcalibur software, v. 3.1.66.10 (Thermo Fisher ScientificTM, Waltham, MA, USA). Polyphenols were expressed as mg kg−<sup>1</sup> dw.

#### *2.10. Mineral Concentration*

The measurement of cations (K, Ca, Mg, and Na) and anions (Nitrate, P, and Cl) of basil leaves was carried out by ion chromatography coupled with an electrical conductivity detector (ICS3000, Thermo ScientificTM DionexTM, Sunnyvale, CA, USA) according to the detailed protocol of Formisano et al. [26]. By comparing peak areas, the integration and quantification of mineral concentration was performed using the z ChromeleonTM 6.8 Chromatography Data System software (Thermo ScientificTM DionexTM, Sunnyvale, CA, USA) data of samples with those of certified reference standards.

All treatments were analyzed in triplicate and the concentrations of the concentrations of anion and cations were expressed in g kg−<sup>1</sup> dw, except for the for the nitrate, expressed in mg kg−<sup>1</sup> fw.

#### *2.11. Statistics*

Statistical analysis was performed with IBM SPSS 20 software (Armonk, NY, USA) for Microsoft Windows 11. A two-way analysis of variance (ANOVA) was applied to assess the significance of the effects and interactions between the cultivar factors (CV) and salt stress (S). The mean effect of CV factor was compared by one-way analysis of variance, and the mean effect of S was compared by Student's *t* test. Statistical significance of the CV × S interaction and the CV factor was determined using the Tukey–Kramer HSD test at the level of *p* < 0.05. All data were presented as mean ± standard error.

#### **3. Results**

#### *3.1. Biometric Parameters*

Except for total fresh weight and fresh leaf weight (Figure 2A,B), the biometric parameters shown in Figure 3 and Supplementary Table S1 were significantly affected by the interaction between cultivar (CV) and stress (S) factors. Compared to the Control, salt treatment (Salt) reduced the total fresh and leaf weight by 51.52 and 47.32%, regardless of the cultivar (Figure 2A,B). The highest total fresh weight was found in the cultivar Cinnamon, followed by 'Anise' and 'Lemon'. Relative to fresh leaf weight, no significant differences were observed between 'Cinnamon' and 'Anise', unlike 'Lemon', which showed the lowest value (40.11 g plant−1). Compared to the Control, Salt treatment reduced the number of leaves by 39.15, 16.11, and 44.54% in 'Anise', 'Cinnamon', and 'Lemon', respectively (Figure 3B). A similar trend was observed for the leaf area, with the lowest value obtained from the Lemon × Salt interaction (725.29 cm2; Figure 3C). This latter interaction also resulted in the lowest total dry weight (6.20 g plant−1; Figure 3D). Differently, the percentage of dry matter of all cultivars increased significantly after salt treatment.
