Growth regulators affect the dry weight production, carvacrol and thymol content of Lippia gracilis Schauer

Abstract The essential oil from Lippia gracilis Schauer (Verbenaceae) leaves are rich in thymol and carvacrol with antibactericidal and antinflammatory action. The aim of the present study was to evaluate the effect of growth regulators and their combinations on shoot proliferation, growth, and volatile fraction analysis of Lippia gracilis in vitro . In the first experiment, five different concentrations of 6-benzylaminopurine (BAP) were used: 0.0, 2.22, 3.33, 4.44, and 5.55 μM and three of naphthaleneacetic acid (NAA): 0.0, 2.68, and 5.36 μM, in a factorial design. In the second, the treatments consisted in combination of BAP + TDZ at concentration (μM): 0 + 0, 1.11 + 1.13, 1.33 + 0.91, 0.88 + 1.36, 0.43 + 1.81, and 1.78 + 0.46. At 30 days of culture in ½ Murashige and Skoog (MS) medium, the growth and volatile constituents were evaluated. Growth regulators significantly influenced in vitro growth of L. gracilis . Growth data for the first experiment were predicted from the three-dimensional (3D) response surface of the different variables analyzed. In the second experiment, the presence of growth regulators reduced shoots and root length in all combinations. The combinations among regulators (BAP and TDZ) stimulated the number of shoots per explant, but BAP and NAA induced higher shoot number. Variation in the number, content, and profile of volatile compounds were also observed under the influence of growth regulators. The major constituents ρ-cimene, γ-terpinene, thymol, carvacrol, and E- caryophyllene were identified, independent of the experimental conditions. However, the use of growth regulators significantly reduced carvacrol and thymol levels.