Optimization of in vitro propagation of Coleonema album, a highly utilized medicinal and ornamental plant

•Direct organogenesis from shoot-tip explants was achieved.•Meta-topolin was more effective than BA and TDZ for in vitro shoot production.•Auxins had an additive/synergistic effect with meta-topolin on shoot production.•A high survival frequency of regenerated plants was recorded.

Coleonema album is an aromatic, medicinal and ornamental plant that is in high demand in the traditional medicine market. In order to meet the increasing demand while conserving those populations in the wild, this study was aimed at developing an efficient in vitro propagation protocol for C. album. The effect of different cytokinins [four meta-topolins in comparison with 6-benzyladenine (BA), kinetin (KIN) and thidiazuron (TDZ)] on direct organogenesis from shoot-tip explants was examined. Each cytokinin was tested at 2.5, 5.0, 7.5 and 10.0 μM. The effect of combining auxins with the optimal cytokinin concentration on shoot proliferation was also investigated. At equimolar concentrations, all treatments with BA, meta-topolin (mT, except 10 μM), meta-topolin riboside and meta-methoxytopolin tetrahydropyran-2-yl significantly increased shoot production when compared to KIN. The optimum cytokinin concentration for shoot production was 5.0 μM mT with 14.5 shoots regenerated per explant. The exogenous addition of auxins further increased shoot proliferation (up to 18 shoots per explant). The findings suggest an additive or synergistic effect of auxin with mT in this study. Regenerated shoots rooted on half-strength Murashige and Skoog medium supplemented with indole-3-butyric acid (IBA) were successfully acclimatized with a survival frequency above 70%.