The role of cytokinins and thidiazuron in the stimulation of somatic embryogenesis in key members of the Restionaceae

Rushes are important understorey species and comprise a significant component of pre-mined ecosystems. Re-establishment of rushes into disturbed sites has often been problematic. Several cytokinins and thidiazuron were investigated for the stimulation of somatic embryogenesis in key members of the Restionaceae. Somatic embryogenesis was observed for Desmocladus flexuosus (R.Br.) B.G. Briggs & L.A.S. Johnson with benzyladenine (BA) at 1, 5 or 15 muM alone and 1 muM 2,4-dichlorophenoxyacetic acid (2,4-D). The response to zeatin (Z) and 2iP-6-gamma-gamma-dimethyl-allyamino-purine (2iP) was negligible. For Baloskion tetraphyllum (J.J.H. de Labillardiere) B. G. Briggs & L.A.S. Johnson and Lyginia imberbis R.Br., BA, Z and 2iP were ineffective in stimulating any response.Somatic embryogenesis was achieved for B. tetraphyllum on 1/2-strength Murashige Skoog (1/2 MS) +1 muM 2,4-D, with an estimated 14000 somatic embryos produced from 1 g of plant material. All somatic embryos converted into plantlets and were successfully transferred to soil.Investigation of thidiazuron (TDZ) at 5 and 10 muM and 1 muM 2,4-D demonstrated that young coleoptiles (5-7 days) of B. tetraphyllum produced significantly more somatic embryos (168-fold more) than did older coleoptiles (>14 days). For D. flexuosus, leaf basal portions produced somatic embryos on 5 and 10 muM TDZ, and 5 muM TDZ +1 muM 2,4-D. Proliferation of 'secondary somatic embryos' was also successful when somatic embryos were initiated on 10 muM TDZ and transferred to 1/2 MS (similar to9-fold increase).This study demonstrated variation in response among species of the same family, with D. flexuosus responding to BA and TDZ and B. tetraphyllum responding only to 2,4-D. The protocol investigated has the potential to be commercially viable with over 14000 somatic embryos produced in 6 weeks for B. tetraphyllum.