Induction of somatic embryogenesis and biochemical characterization of Cordyline australis (G. Forst.) Endl. ‘Red Star’ callus

• The current study presents a method for the regeneration of Cordyline australis (G. Forst.) Endl. ‘Red Star’ through somatic embryogenesis.
• The effect of: 4-amino-3,5,6-trichloropicolinic acid (picloram); 2,4-dichlorophenoxyacetic acid (2,4-D); and 2-methoxy-3,6-dichlorobenzoic acid (dicamba), with a combination of cytokinin 6-benzyladenine (BA) and thidiazuron (TDZ) was tested on the induction of somatic embryogenesis.
• The relationship of phenolic compounds, sugars, peroxidase activity and protein contents in callus was investigated in order to find if these compounds might be the indicators of further embryos development.
• This is the first report on the induction of somatic embryogenesis in this genus with implications for mass clonal propagation.

The current study presents a method for the plant regeneration from stem segments of Cordyline australis (G. Forst.) Endl. ‘Red Star’ through somatic embryogenesis. We tested the effect of 3 kinds of auxin 4-amino-3,5,6-trichloropicolinic acid (picloram), 2,4-dichlorophenoxyacetic acid (2,4-D), and 2-methoxy-3,6-dichlorobenzoic acid (dicamba), with a combination of 2 kinds of cytokinin, 6-benzyladenine (BA) and thidiazuron (TDZ), on the induction of embryogenic callus and its capacity to induce somatic embryogenesis under dark culture condition. The highest percentage of explants forming callus (nodular and friable) was observed on medium containing 25 μM picloram and 0.5 μM BA. The embryogenic callus, with white-yellowish nodular structures, was proliferated in the initial media and finally produced somatic embryos on all media with picloram and 2,4-D. Somatic globular embryos were obtained with a higher frequency from explants cultured on MS medium supplemented with 25 μM picloram and 0.5 μM BA. On this medium, a mean number of 23.0 embryos developed per gram of callus. Globular embryos developed most efficiently into cotyledonary stage on MS medium supplemented with 5 μM picloram and 1 μM BA. The addition of zeatin (5 and 2.5 μM) and NAA (0.5 and 0.25 μM) to the medium was found to be essential for the highest conversion of somatic embryos into plants. Plantlets were successfully acclimatized in the greenhouse with 90% survival rate. Callus was tested for phenolic compounds, sugars, peroxidase activity and protein contents in order to find if these compounds might be the indicators of further embryos development. The embryogenic callus of C. australis with various stages of embryo development had higher level of protein than the non-regenerable one, whereas level of sugars increased only in callus with embryos in cotyledonary stage. Callus with globular embryos contained high concentration of phenolics and low activity of peroxidase, comparing to other types of callus.