Fraser fir somatic embryogenesis: high frequency initiation, maintenance, embryo development, germination and cryopreservation

Fraser fir (Abies fraseri [Pursh] Poir.) is a coniferous species native to the Southern Appalachian Mountains of the eastern United States. The species has high economic and recreational value but is vulnerable to extinction due to introduced pests and global warming. Somatic embryogenesis technology may assist in the clonal production of desired lines of Christmas trees and safekeeping of rare and valuable germplasm via cryopreservation. We have developed a highly effective medium for initiation of embryogenic tissue from immature or mature seeds of Fraser fir that contains AL salts (Kvaalen et al., in Can J For Res 35:1053–1060, 2005), brassinolide, paclobutrazol and abscisic acid. Using dominant embryos attached to the female gametophyte placed on medium, the highest initiation percentages occurred with precotyledonary stage 3 embryos. When tested with 11 high-value open-pollinated families over 5 years, initiation tests for medium containing brassinolide and paclobutrazol averaged 6–62 % initiation. A maintenance medium was developed that contained AL salts and 1.1 mg L⁻¹ BAP and was able to capture approximately 50 % of the initiations. A maturation medium was developed containing AL salts, maltose, polyethylene glycol 8000 and abscisic acid that produced cotyledonary embryos capable of germination to produce a root and shoot. Culture cryopreservation and retrieval was also demonstrated.