High-frequency, direct bulblet induction from rhizome explants of Curculigo orchioides Gaertn., an endangered medicinal herb

Abstract

An efficient and reproducible method for inducing a large number of bulblets from rhizome explants of Curculigo orchioides Gaertn., an endangered medicinal herb, has been developed. The rhizome pieces, measuring about 1 × 1 cm (length × width), were cultured on Murashige and Skoog (MS) medium supplemented with different concentrations of the cytokinins 6-benzylaminopurine, kinetin, and thidiazuron (TDZ) alone or in combination with 1-naphthalene acetic acid or indole-3-butyric acid (IBA). Of the three cytokinins used, TDZ at 7 μM gave the maximum response, with 82% of the cultures responding with an average number of 15.4 bulblets per explant. The addition of auxins with cytokinin considerably increased the response. The optimum induction occurred on MS medium supplemented with 7 μM TDZ and 0.5 μM IBA. On this medium, 88% of the cultures responded with an average number of 21.4 bulblets per explant. Experiments were also carried out to investigate the role of the sugars sucrose, mannose, and glucose along with 7 μM TDZ and 0.5 μM IBA. The results indicate that sucrose and mannose at particular concentrations have critical roles in promoting in vitro bulblet induction. The maximum result was observed on MS medium supplemented with 7 μM TDZ, 0.5 μM IBA, and 200 mM mannose. On this medium, 97% of the cultures responded with an average number of 26.8 bulblets per culture. Several secondary bulblets developing from the leaf blades of primary bulblets were produced when the latter were transferred to MS basal medium for further development. Out of the 45 bulblets transferred to soil, 40 survived. This protocol can be used for the rapid micropropagation of this endangered medicinal herb.