Rapid in vitro multiplication and ex vitro rooting of Rotula aquatica Lour., a rare rhoeophytic woody medicinal plant

Abstract.

Single medium-based efficient protocols for large-scale multiplication of the rare woody aromatic medicinal plant Rotula aquatica Lour. by means of axillary bud multiplication and indirect organogenesis were established using Murashige and Skoog (MS) medium. There were no significant differences with respect to the induction of shoots per node or callus and roots per shoot on media prepared either with tap water and commercial sugar or those prepared with double distilled water and tissue culture-grade sucrose. The most effective medium for axillary bud proliferation was MS medium fortified with 1.0 mg l^–1 N⁶-benzylaminopurine (BAP) and 0.5 mg l^–1 indole-3-butyric acid (IBA), on which shoots were induced at the rate of 15 per node. The excision of node segments from the in vitro-derived shoots and their subsequent culture on medium supplemented with same concentrations of BAP and IBA facilitated enhanced axillary bud proliferation. Callus that developed from the lower cut end of the node explants induced shoots during subculture on half-strength MS medium with 1.0 mg l^–1 BAP and 0.5 mg l^–1 kinetin. The shoots developed rooted best on half-strength MS medium supplemented with 0.5 mg l^–1 naphthaleneacetic acid (NAA). Rooted shoots, following acclimation in the greenhouse, were successfully transferred to field conditions, and 80% of the plantlets survived. When the basal ends of shoots harvested from multiplication medium were dipped in an NAA (0.5 mg l^–1) solution for 25 days, a mean of 5.6 roots per shoot developed; the transfer to small pots facilitated the survival of 75% of the rooted shoots. Ex vitro rooting by direct transfer of the shoots from the multiplication medium to the greenhouse resulted in a 65% survival. Commercial sugar and tap water and ex vitro rooting make the protocol economically advantageous. About 750 plantlets were procured in a 3-month period starting from a single node explant.