Evaluation of Somaclonal and Ethyl Methane Sulfonate-Induced Genetic Variation of Mexican Oregano (Lippia graveolens H.B.K.)

Lippia graveolens, commonly known as Mexican oregano, is an aromatic plant of great industrial, nutritional, and medicinal value, principally for its essential oils. Regeneration via axillary buds was established in MS medium supplemented with 6-benzyladenine (BA) (0.5 mgL(-1)) as a growth regulator. Three genotypes and three stages of cultivation were considered in the study. On average, 3.5, 4.2, and 6.4 shoots induced per explant were obtained for genotypes B, C, and D, respectively. Several doses (0.1, 0.3, and 0.5%) of ethyl methane sulfonate (EMS) and different exposure times (1, 2, and 3 h) were applied to investigate the effect of the chemical mutagen on the formation of axillary buds. Genetic variation among the collected plants, the micro-propagated plants during three sub-cultivations, and the plants regenerated in the presence of the mutagen was evaluated by means of randomly amplified microsatellite polymorphism (RAMP) markers. A high genetic stability was observed in the micro-propagation of Mexican oregano for the three genotypes and three sub-cultivations, presenting 100% of monomorphic bands. The genetic variation observed in the different collections of wild populations (A, R, and V) and after treatment with EMS regarded 34 and 35% of polymorphic loci, respectively.