Plant Regeneration via Somatic Embryogenesis in Larix principis-rupprechtii Mayr

Prince Rupprecht’s larch (Larix principis-rupprechtii Mayr) is a native conifer in North China with great economic and ecological values. Somatic embryogenesis (SE) is a powerful tool for the mass clonal propagation in plants. In this study, we described a high-efficiency SE system via indirect pathways and investigated the effect of genotype, culture conditions and phytohormones on SE. Immature zygotic embryos (IZEs) of L. principis-rupprechtii Mayr were used as explant materials. In the induction stage, embryogenic tissues (ETs) were induced on mLV medium supplemented with 2.0 mg L−1 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.0 mg L−1 6-benzylaminopurine (6-BA). The initiation frequencies showed significant differences (p < 0.05) among 20 genotypes of open-pollinated mother trees with the highest induction frequency reaching 30%. For tissue proliferation, proliferation in liquid medium was more efficient compared with proliferation in semi-solid medium, providing a multiplication rate of 3.12 in an 8-day subculture period. As a necessary exogenous plant growth regulator (PGR) for somatic embryo maturation in conifers, abscisic acid (ABA) was optimized at 16 mg L−1 in this system. Next, an orthogonal test on osmotic pressure factors showed 50 g L−1 sucrose, 7 g L−1 phytagel and 75 g L−1 polyethylene glycol (PEG) was the optimal combination for somatic embryo maturation in L. principis-rupprechtii Mayr. Moreover, the dispersion culture method provided a more efficient somatic embryo maturation, up to 545 per gram of fresh weight (FW). Finally, 2 g L−1 of active charcoal (AC) was found to increase the somatic embryo germination rate to 63.46%. The improved protocol of SE will serve as a foundation for establishing mass propagation and genetic transformation of L. principis-rupprechtii Mayr.