In vitro regeneration of Cyrtanthus species: ornamental plants with medicinal benefits

Abstract

Cyrtanthus (Amaryllidaceae) is a genus of perennial geophytes, endemic to the southern African region. Destructive and indiscriminate harvesting of bulbs for medicinal and ornamental purposes has led to intensive decimation of the populations of most of these species in their natural habitats. The aim of this study was to develop in vitro regeneration systems for Cyrtanthus contractus, Cyrtanthus guthrieae, and Cyrtanthus obliquus using twin-scale explants from mature bulbs. Twin scales from the three species were cultured on solid Murashige and Skoog (MS) medium with different concentrations of 6-benzyladenine (BA) and α-naphthaleneacetic acid (NAA) under 16/8-h light/dark conditions at 25±2°C. The best shoot induction responses were obtained on MS medium containing 4.4 μM BA+1.1 μM NAA (3.1 shoots/explant) for C. contractus and C. guthrieae and 6.7 μM BA+2.7 μM NAA for C. obliquus. When the best shoot induction medium for each species was investigated for the effect of cytokinins on shoot organogenesis, using different concentrations of BA, kinetin (Kin), meta-topolin (mT), zeatin (ZT), and thidiazuron (TDZ), the medium that produced the best shoot induction for C. guthrieae also produced the highest number of shoots per explant, whereas the highest numbers of shoots per explant were obtained with 10 μM TDZ for C. contractus and 10 μM BA for C. obliquus. Superior quality shoots in all three species were obtained from MS medium supplemented with Kin and mT. Regenerated shoots were rooted successfully on half-and full-strength MS medium without plant growth regulators, transferred to organic soil mix, and successfully acclimatized in the greenhouse. The micropropagation protocols described provide rapid and cost-effective methods for in vitro propagation for application to the conservation and domestication of Cyrtanthus species.