Somatic Embryogenesis of Immature Cunninghamia lanceolata (Lamb.) Hook Zygotic Embryos

Two efficient somatic embryogenesis systems were developed in Chinese fir, the most important conifer for industrial wood production in China. Three development stages (cleavage polyembryony, dominant embryo, and precotyledon) of immature embryos derived from 25 genotypes of open-pollinated mother trees were used as initial explants. Cleavage polyembryony-stage embryos with a 12.44% induction rate was the most embryogenic response stage. The highest frequency of embryogenic callus (13.86%) induction was obtained from DCR medium supplemented with 1.5 mg L^-1 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.3 mg L^-1 kinetin (KN). An average of 53.33 early somatic embryos were produced from approximately 0.2 g (fresh weight) embryogenic callus after 2 weeks of incubation on medium supplemented with 50 μmol L^-1 abscisic acid (ABA) and 100 g L^-1 polyethylene glycol (PEG) 6000. About 53% dominant embryos have an embryogenic response after a 6-week cultivation on medium supplemented with 1.0-2.0 mg L^-1 benzyladenine (BA), 0.2 mg L^-1 naphthylacetic acid (NAA) or 2,4-D, and 0.004 mg L^-1 thidiazuron (TDZ). After three successive transfer cultures on medium supplemented with 1.5 mg L^-1 BA, 0.2 mg L^-1 NAA, and 0.004 mg L^-1 TDZ, 4.49-16.51% of the embryos developed into somatic embryos.