Somatic embryogenesis and plantlet regeneration in American ginseng (Panax quinquefolium L.)

Somatic embryogenesis in American ginseng (Panax quinquefolium L.) was investigated from three explant sources (root, leaf and epicotyl) with Murashige and Skoog (MS) medium containing different growth regulators. Mature roots and leaves obtained from 3- to 5-yr-old field-grown plants, and seedling leaves and epicotyls from plantlets grown in vitro, were evaluated. From root and epicotyl explants, callus development Tvas optimal with 3,6-dichloro-o-anisic acid (dicamba) (9.0 mu M) and kinetin (KN) (5.0 mu M) as the growth regulators. When these calluses were transferred after 3 mo. to dicamba alone (9.0 mu M), somatic embryo formation was observed at an average frequency of 15.6% in root explants;after an additional 3 mo., and 2% in epicotyl explants after an additional 6 mo. No plantlets were recovered because the embryos germinated to form shoots with no roots. From leaf explants, callus growth was optimal,vith alpha-naphthaleneacetic acid (NAA) at 10.0 mu M and 2,4-dichlorophenoxyacetic acid (-2,4-D) at 9.0 mu M. Somatic embryos developed on this medium, with the highest frequency (40%) obtained after 3 mo. from seedling-leaf explants. Calluses on mature leaves formed somatic embryos after 7 mo. with NAA/2,4-D at an average frequency of 30%. Transfer of these somatic embryos to 6-benzyladenine/gibberellic acid (4.4/2.9 mu M) promoted shoot development but no roots were observed. Up to 100% of germination was observed within 6 wk on half-strength MS salts containing activated charcoal (1%) and on NAA/2,4-D (5.0/4.5 mu M) with charcoal (1%). On the latter medium, somatic embryos enlarged and frequently gave rise to new somatic embryos after a brief callusing phase. The embryos germinated through a two-stage process. involving the elongation of the root followed by the formation of a shoot. The highest recovery of ginseng plantlets from germinated embryos was 61.0%. Following transfer to potting medium and maintenance under conditions of high humidity and low light intensity, the plantlets elongated and developed new leaves, A high percentage (50%) of these plants have been acclimatized to soil.