Selection of culture conditions for callus induction and proliferation by somatic embryogenesis of Pinus koraiensis

The induction and proliferation of embryogenic callus are key steps for large-scale propagation of somatic embryogenesis pathway and long-term preservation of coniferous germplasm. Callus can be induced from immature embryos of Korean pine (Pinus koraiensis Sieb. et Zucc.; Pinaceae) as explants, but there are problems, such as low proliferation efficiency, loss of embryogenicity, poor vigor; thus, best conditions for proliferation and culture of immature embryos of Korean pine are not yet clear. To solve the problems with somatic embryogenesis of Korean pine and determine the best culture conditions for callus induction and proliferation, we varied hormone concentration, subculture cycle of proliferation and other plant growth regulators combinations in media to induce callus formation by megagametophytes of three Korean pine families at different developmental stages, then analyzed the effects on embryogenic callus retention and cell proliferation using a quadratic regression orthogonal rotation design. The results showed that the family origin and collection date of explants significantly affected callus induction (induction rate reached 1.67%). Embryogenic maintenance and callus proliferation were best on DCR medium supplemented with 0.25 mg L-1 6-benzyl adenine, 1 mg L-1 naphthaleneacetic acid, 30 g L-1 sucrose, 500 mg L-1, l-glutamine, 500 mg L-1 casein hydrolysis and 6.5 g L-1 agar. In addition, the combination of 2,4-dichlorophenoxyacetic acid + 6-benzyl adenine also had a better proliferative effect on callus. The effects of different combinations of growth regulators on callus proliferation efficiency were significantly different. Transfer to new medium every 13-15 days not only maintained robust callus vigor, but also yielded a larger proliferation coefficient. The techniques and conditions for embryogenic callus induction and proliferation of Korean determined here will serve as a foundation for establishing a large-scale system for somatic embryogenesis and propagation of Korean pine.