Optimization of Key Technologies for Induction of Embryogenic Callus and Maturation of Somatic Embryos in Korean Pine (Pinus koraiensis)

Abstract

Somatic embryogenesis (SE), which leads to the formation of embryonic callus (EC) tissue, is the most promising method for large-scale production and selective breeding of woody plants. However, in many species, SE suffers from low induction and proliferation rates, hindering the production of improved plant materials. We investigated the effects of the explant sterilization method, 4 °C cryopreservation, basal medium, ethylene removal, liquid medium supplementation, and a combination of PGRs on embryogenic callus (EC) induction of Korean pine, using immature embryos of Korean pine as explants. The effects of sucrose and maltose on EC proliferation and maturation were investigated. The differences in the maturation ability of EC somatic embryos before and after cryopreservation were evaluated using the induced embryonic cell lines. The results showed that zygotic embryos (ZEs) performed better than megagametophytes (MGs) as explants. The induction rate of EC was significantly increased after 28 days of cryopreservation at 4 °C. The induction rate of EC in the #5 family increased from 10.00% to 62.8%. The EC induction rate of the five families cultured with the DCR basal medium was higher than that with the mLV basal medium. Among them, the induction rate of the #5 family cultured with the mLV basal medium was 23.3%, while that with the DCR basal medium was 60.9%, an increase of 2.6 times. There was no significant difference in the maturation ability of EC somatic embryos before and after cryopreservation. In conclusion, this study provides a method to improve the EC induction rate and maturation ability of Korean pine.