Improving micropropagation of Mentha × piperita L. using a liquid culture system

In the current study, in vitro shoot proliferation and plant regeneration of Mentha × piperita L. (peppermint) cultivar ‘Black Mitcham’ was compared in semi-solid and liquid culture systems. Shoot tips from field-grown plants were used as explants to study shoot proliferation response on either Murashige and Skoog (MS) or Chee and Pool (C2D) medium containing varying levels of 6-benzylaminopurine (BAP), kinetin, and 6-γ,γ-dimethylallyl aminopurine (2iP). Differences in leaf ultrastructure and antioxidant capacity of greenhouse-grown and micropropagation-derived plants were studied to identify potential changes occurring during in vitro culture. Among the various media treatments tested, the maximum number of shoots was produced on the C2D medium with 4.0 μM BAP (40.7) followed by the MS medium with 4.0 μM BAP (32.2). Among the rooting treatments, shoots on the MS medium with 1.0 μM indole-3-butyric acid (IBA) produced the maximum number of roots (14.4). The number of shoots produced in Liquid Lab Rocker® (LLR) vessels containing liquid C2D medium with BAP (103.4) was significantly higher than that produced on semi-solid medium (40.7). No differences were observed in the leaf ultrastructure and antioxidant capacity of leaf extracts obtained from greenhouse-grown and micropropagation-derived plants. The study indicates that the liquid culture system under the described conditions can enhance peppermint micropropagation, with plant material being potentially valuable for use in herbal supplements and essential oil production.