Enhancing in vitro propagation of Melissa officinalis L.: Assessing the role of plant growth regulators as a pathway to sustainable production

The availability of an effective propagation protocol remains crucial to fulfil the increasing demand for Melissa officinalis L. in the global market. Melissa officinalis L., commonly known as lemon balm, is a widely used herb in the cosmetic, food, and pharmaceutical industries with increasing demand for its essential oil and extracts. This study aimed to enhance the in vitro propagation technique of M. officinalis, using different plant growth regulators. Three cytokinins (6-benzylaminopurine, kinetin, and meta -topolin) with concentrations ranging from 1.0 to 15.0 µM were evaluated for shoot proliferation. In vitro regenerated plants were acclimatized in the glasshouse for 8 weeks. The application of 5.0 µM meta -topolin produced the highest average number of shoots (11.75 ± 0.73) per nodal explant. Shoot proliferation was not further enhanced with the application of 1-naphthalene acetic acid concentrations (1.0, 3.0, and 5.0 µM) when combined with meta- topolin. Regenerated shoots rooted well in both half-strength and full-strength Murashige and Skoog medium devoid of plant growth regulators. With no morphological differences observed, the rooted plantlets on full-strength and half-strength Murashige and Skoog medium achieved a 100 % survival rate after successfully acclimatizing in the glasshouse. The optimized protocol can lead to the production of more than 350 000 in vitro shoots per nodal explant in 6 months, making this protocol applicable for a large scale, more efficient, and cost-effective propagation of M. officinalis . • Highest mean shoot number of 11.75 ± 0.73 per nodal explant with 5.0 µM meta- topolin. • Regenerated shoots rooted on plant growth regulator-free half-strength medium. • Rooted plantlets acclimatized successfully with a 100 % survival rate. • Potential production of at least 350,000 in vitro shoots per nodal explants in 6 months.