Plant regeneration through direct somatic embryogenesis from leaf explants of Dendrobium

A protocol for induction of direct somatic embryogenesis, secondary embryogenesis and plant regeneration of Dendrobium cv. Chiengmai Pink was developed. Thidiazuron (TDZ) at 0.3, 1 and 3 mg dm(-3) induced 5-25 % of leaf tip segments of in vitro grown plants to directly form embryos after 60 d of culture, and 1 mg dm(-3) TDZ was the best treatment. Somatic embryos mostly formed from leaf surfaces near cut ends, and occasionally found on leaf tips. Higher frequency of embryogenesis was obtained in light than in darkness. During subculture, secondary embryos developed from outer cell layers of primary embryos. All combinations of NAA (0, 0.1, 1 mg dm(-3)) and TDZ (0, 0.3, 1, 3 mg dm(-3)) increased the multiplication rate of embryos. It takes about 8 months from embryo induction, plantlet formation to eventually acclimatization in greenhouse.