Thymol elicitation during in vitro regeneration of axillary bud explants from a Thymus piperella L. commercial hybrid

Species of the genus Thymus L. (Lamiaceae) are of great interest as medicinal plants, as well as in the extracts and food technology industries due to the richness in bioactive specialized metabolites. Specifically, Iberian endemic species such as Th. piperella L., have a wide range of traditional uses in this sense. However, the micropropagation and biosynthesis of high-added value compounds under in vitro culture conditions has not been studied for this species and its commercial hybrids yet. Therefore, the main objective of this work was to develop a micropropagation protocol of a popularly used commercial hybrid of Thymus. The results obtained showed a good capacity of adaptation and initiation of in vitro culture after the sterilization treatment applied. In addition, the different plant development parameters measured in the multiplication phase showed significantly higher values in Murashige and Skoog (MS) medium supplemented with 0.013 mg/L 2-isopentenyladenine (2iP), or without plant growth regulators, plus 30 g/L sucrose and solidified with 5.5 g/L Plant Agar when compared to the other treatments applied. Finally, the test performed on the content of volatile compounds by HS-SPME-GC/MS revealed that there was a remarkable increase of thymol in the in vitro cultivated plants when compared to the samples from the wild-type plants. Therefore, the results obtained in the present work could be the basis for the development of future studies on the elicitation of this compound by in vitro culture systems with this hybrid, or other plant materials from Thymus piperella chemotypes