Establishment of a qualified ex vitro-acclimatized whole plant reproduction system using secondary somatic embryos in Panax ginseng

In vitro regenerated ginseng plants from embryos have been successfully ex vitro acclimatized and transplanted to soil as reported in previous studies. However, resprouting of ex vitro acclimatized ginseng in the following year has not been achieved. In this study, we optimized plant regeneration protocol through the somatic embryo culture and acclimatization steps in the soil for Korean ginseng. Primary somatic embryos were induced from the cut cotyledons in hormone-free MS medium with 3% sucrose after 8 weeks. The secondary somatic embryos were induced from transplanted primary embryos in hormone-supplemented MS containing 1 mg/L 2,4-D and 0.5 mg/L BAP for 10 weeks. Two weeks more cultivation in the same medium generated shoots, and shoot elongation and the formation of all above-ground parts of the shoots was achieved in hormone-free MS medium over 6 weeks. Roots were formed in 1/2 MS medium with 1% sucrose and 0.3% of activated charcoal after 12 weeks. Overall, plant generation, from the cotyledon of the zygote to the transplantable plantlet, was about 53% efficient (33 plantlet/61 secondary embryos) and took about 38 weeks. The acclimatization of transplanted plantlets in a soil mixture was 82% efficient. Buds on taproots of adapted plants developed a dormant tendency, and the dormancy of these buds was broken during cold treatment at 4 °C for 3 to 4 months. The system we developed can be effectively utilized for the mass production of Korean ginseng through somatic embryo culture.