Embryogenic tissue initiation and somatic embryogenesis in Fraser fir (Abies fraseir [Pursh] Poir.)

Embryogenic suspensor mass (ESM) was established from immature seeds of Fraser fir. The initiation frequency of ESM was dependent on genotype, collection time, medium, and plant growth regulators (PGR) used. The ESM initiation potential was higher with seeds collected in late June (clone 16-273, 4.7%) or early July (clone 16-45, 2.2%) and decreased as the zygotic embryos matured. Excised proembryo stage of zygotic embryos was most appropriate to initiation of ESM. Most of the ESM arose from the seeds that were at the proembryo stage. From the four different culture media we compared, seven ESM lines were obtained: two lines from Murashige and Skoog (MS) medium with 4.4 mu M benzyladenine (BA), one from Schenk and Hildebrandt (SH) medium with 4.5 mu M thidiazuron (TDZ), and four from SH with 4.4 mu M 6-benzyladenine. However, only one ESM line from clone 16-273 (June 24, SH+TDZ) could be proliferated in subsequent culture. Different concentrations of l-glutamine and casein hydrolysate (CH) in the medium were also compared for their effect on ESM proliferation. The highest proliferation rate (1.16-fold) was obtained from SH medium supplemented with 250 mg/L CH and 3.42 mM l-glutamine. In contrast, the lowest rate was noted when 1,000 mg/L CH plus 3.42 mM l-glutamine (0.17-fold) was added to the medium. As for somatic embryo maturation, the highest number of mature precotyledonary (100.1/g(-1) FW ESM) or cotyledonary (64.3/g(-1) FW ESM) somatic embryos was obtained on a medium containing 20 or 80 mu M abscisic acid, 10% polyethyleneglycol, 4% maltose, and 0.3% gellan gum. For germination of the somatic embryos, the cotyledonary somatic embryos derived from maturation medium were transferred on half-strength Litvay medium containing 0.3% gellan gum. The somatic plantlets were recovered from the germination medium and transferred to soils.