In Vitro Propagation as a Strategy for Improving Phytochemical Production and Supporting Conservation of Tunisian Lavandula stoechas

Lavandula stoechas (Lamiaceae) is a highly valued medicinal plant due to its rich content of bioactive secondary metabolites, particularly rosmarinic acid. This study aimed to develop an efficient in vitro propagation protocol from seeds and to evaluate the influence of 6-benzylaminopurine (BAP) on morphogenesis and phenolic compound production while comparing the antioxidant and antifungal activities of methanolic extracts from in vitro cultured and wild-growing plants. Seeds were germinated on half-strength MS medium under different sucrose concentrations and temperatures. Nodal explants from seedlings were cultured on full-strength MS medium supplemented with 0, 1, 2, or 3 µM BAP. Methanolic extracts were analyzed for total phenolic content, rosmarinic acid concentration (HPLC), antioxidant activity (DPPH and ABTS assays), and antifungal activity against phytopathogenic fungi. Rapid germination occurred on day 3 on half-strength MS medium with 1% sucrose at 20 °C. The highest biomass production was achieved with 3 µM BAP. In vitro cultured plants accumulated fivefold-higher total phenolic content (217.73 mg GAE g−1 DW) than wild plants (43.23 mg GAE g−1 DW), with significantly higher rosmarinic acid levels. Antioxidant activity was markedly stronger in extracts from plants grown with 1–2 µM BAP, whereas antifungal activity remained limited. These results demonstrate that in vitro propagation with optimized BAP concentrations is an effective strategy for enhancing bioactive metabolite production and supporting the conservation of Tunisian L. stoechas.