Repeated subculture of such totipotent callus lines on the original medium resulted in continued proliferation without apparent loss in regeneration capacity for 2 years.
Since our experiments were conducted with only one cultivar, the variants on callusing and embryo formation of other cultivars requires further studies. Also, the genotypic and phenotypic fidelity of the process has to be ascertained before developing any practical cloning protocols. The strong totipotency of callus also provided an opportunity to obtain embryogenic suspension culture, and molecular breeding of this orchid.
In conclusion, this report is the first to show that the embryogenic calli derived from the segments of roots, stems and leaves of Oncidium are able to form somatic embryos in a hormone-free 1/2 MS medium. The optimum combinations of NAA and TDZ significantly promoted the frequency of embryo formation up to 93.8% in root-derived callus. In addition, most of the somatic embryos converted into healthy plantlets with an almost 100% survival rates when transplanted. The optimized procedure required about 12–14 weeks from the initiation of callus to the plantlet formation. This reliable and highly efficient method for embryo formation from callus is essential to establish a cell suspension culture protocol for Oncidium. Furthermore, this method also opens up the prospects of using biotechnological approaches for Oncidium improvement.