Nanoextract of Zataria multiflora Boiss. Enhances Salt Stress Tolerance in Hydroponically Grown Ocimum basilicum L. var. Genovese

In order to investigate the effect of Zataria multiflora Bioss. extract and nanoextract on morphophysiological and phytochemical indices, yield, and essential oil compositions of basil (Ocimum basilicum L. var. Genovese) under salinity stress (0, 25, 50, and 100 mM NaCl), an experiment was conducted as a split-plot design in a basic block with complete randomization and three replications. In the treatment without salinity, nanoextract increased the shoot fresh weight by 34.28%, and regular extract increased it by 8.35% compared to the 0 NaCl without extract. In the treatment without salinity stress, nanoextract decreased the Na content by 17%, and regular extract decreased it by 5%; nanoextract increased the K content by 22.93%, and regular extract increased it by 9.05% compared to the 0 NaCl without extract, respectively. In all salinity concentrations applied, nanoextract showed lower sodium accumulation and higher potassium accumulation rate than regular extract and treatment without extract at the same salinity concentration. The highest total phenols were observed in the 100 mM salinity treatment in both nanoextract and regular extract of Z. multiflora, followed by the 50 mM salinity treatment—nano extract, with 12.33, 11.17, and 10.01 mg GA g−1 FW, respectively. In the non-saline stress treatment, nanoextract increased the proline content by 125%, and regular extract increased it by 79.16% compared to the 0 NaCl without extract. In the treatment without salinity stress, the nano extract increased the level of PAL enzyme by 16.66% and the regular extract by 8.33% compared to the 0 NaCl without extract. The highest antioxidant activity was observed in the 100 mM salinity treatment in both nano extract and regular extract of Z. multiflora, followed by the 50 mM salinity treatment and nano extract with 31.86, 30.60, and 28.21%, respectively. In this study, the results of essential oil analysis indicated the identification of 39 compounds in which linalool, eugenol, carotenoid, methyl chavicol, A-Humulene, and menthol were identified as the main compounds. Among all treatments, Z. multiflora nanoextract, while moderating the effects of stress, showed the highest efficiency in improving the morphophysiological and biochemical traits and essential oil content and secondary metabolites of O. basilicum L. var. Genovese.