In vitro propagation of a carvacrol-producing type of Lippia origanoides Kunth: A promising oregano-like herb

In vitro culture techniques are sustainable alternatives to the large-scale production of economically important plant species. Lippia origanoides Kunth (Verbenaceae) is an essential oil-producing species that is used for medicinal purposes and as a spice. The plant has been recently classified into five different chemical types, two of which are rich sources of carvacrol and thymol. Carvacrol has been associated with the oregano scent; thus, species bearing carvacrol-rich essential oils are considered to be economically important due to their potential use as an ingredient in food, cosmetics and pharmaceutical industries. In this work, we evaluated the effects of different plant growth regulators (PGRs) on the in vitro development and volatile composition of L. origanoides. In vitro cultures were maintained in an Murashige and Skoog (MS) basic medium without supplementation with growth regulators or with different concentrations of cytokinins (kinetin and 6-benzylaminopurine) and auxin (indole-3-acetic acid). Volatiles were obtained by simultaneous distillation and extraction (SDE) and were analyzed by gas chromatography (GC) and by gas chromatography coupled to mass spectrometry (GC-MS). Plants that had been developed in a medium supplemented with PGRs presented changes in their chemical profile, but carvacrol and thymol relative percent contents were increased with no PGRs. The major compounds found in the volatile fractions: myrcene (1.3-5.1%), p-cymene (5.7-20.0%), gamma-terpinene (4.3-10.6%), linalool (2.5-4.8%), thymol (5.3-10.7%), carvacrol (29.7-45.5%) and (E)-caryophyllene (2.5-5.1%). MS + 4.6 mu M of kinetin (KIN) significantly influenced the development of L. origanoides in an in vitro culture, which resulted in plants with high shoot length, fresh/dry biomass and increased rhizogenesis. The results showed that in vitro culture is an important and useful biotechnological tool for the optimization of terpene synthesis.