Comparative Evaluation of Three Temporary Immersion System Bioreactors for Improved In Vitro Propagation and Terpene Production in Myrtus communis L

Myrtus communis L. is an aromatic and medicinal plant commonly used in the pharmaceutical, food, and cosmetic industries for its bioactive compounds. Temporary immersion systems (TISs) are an efficient and cost-effective in vitro propagation method for enhancing biomass and secondary metabolite production under controlled conditions. This study aimed to compare the effect of three different TIS bioreactors (SETIS™, Plantform™, and ElecTIS) and a conventional semisolid culture on relative growth rate (RGR), photosynthetic pigments, stomatal function and terpene content. The results showed that all bioreactors increased biomass production, with the highest RGR achieved in ElecTIS (7.1) after 28 days of culture. SETISTM induced 80% rooting and better stomatal density and functionality, resulting in a 98% survival rate of plants in acclimatization. Moreover, chlorophylls and carotenoids were significantly enhanced during rooting, particularly in SETIS™ and Plantform™. GC-MS analysis identified 14 volatile compounds, with myrtenyl acetate, linalool, and α-pinene as the dominant constituents. Rooted shoots cultured in Plantform™ and SETIS™ accumulated the highest terpene concentrations (341.5 and 326.4 μg g−1 FW, respectively), which exceeded those of semisolid cultures. These findings demonstrate that TIS bioreactors, particularly SETIS™, represent a promising tool for the efficient production of biomass and terpenes, depending on the selection of the appropriate culture conditions, bioreactor type, and plant development stage.