Plant regeneration via somatic embryogenesis in Drimia robusta

A simple efficient in vitro plant regeneration system was developed by direct and indirect somatic embryogenesis of Drimia robusta, a medicinal plant extensively used in South African traditional medicine. Different developmental stages of somatic embryos (SEs: globular embryos, partial pear-shaped embryos and club-shaped embryos), club-shaped cotyledon initiation, plumule initiation and plantlets were directly obtained from leaf explants on Murashige and Skoog (MS) medium containing 3.5 % (w/v) sucrose and different plant growth regulators (PGRs). In MS medium containing 3.5 % (w/v) sucrose and supplemented with 10 mu M picloram, 1 mu M thidiazuron (TDZ) and 20 mu M glutamine, a higher number of SEs and plantlets were achieved. These were established onto half-strength MS medium followed by successful acclimatization (100 %) in the greenhouse. Liquid somatic embryo medium (SEML) containing 500 mg of friable embryogenic callus on MS medium supplemented with different concentrations and combinations of PGRs and organic elicitors produced different stages of SEs. Somatic embryo production was enhanced by 0.5 mu M picloram, 1 mu M TDZ and mebendazole treatment. The highest number of plantlets (9.0 +/- A 0.70) was obtained in SEML containing 0.5 mu M picloram, 1 mu M TDZ and 25 mg l(-1) haemoglobin. All the cotyledon and plumule embryos germinated on half-strength MS medium, however 90 % of SEs germinated on half-strength MS medium containing 0.5 mu M naphthaleneacetic acid. All plantlets were successfully acclimatized in the greenhouse. This first report of D. robusta somatic embryogenesis provides an opportunity to control extinction threats, ensure germplasm conservation and provides a system for analysis of bioactive compounds and bioactivity.