Loblolly Pine Somatic Embryogenesis: Development of a Maturation Medium and Resulting Embryo Quality

Clonal production of loblolly pine (Pinus taeda L.) through somatic embryogenesis has great potential to meet the increasing industrial demands for highquality uniform raw materials. A major barrier to the commercialization of this technology is the low quality of resulting embryos. Twenty-five newly initiated loblolly pine genotypes were followed through the process of liquid culture establishment, embryo maturation, germination, and retrieval from cryogenic storage. A maturation medium, capable of promoting development of loblolly pine somatic embryos that can germinate, is presented that combines Y2 P6 modified salts, 2% maltose, 13% polyethylene glycol 8000, 5 mg/L abscisic acid, and 2.5 g/L Gelrite. A procedure for converting and acclimating germinants to growth in soil and greenhouse conditions is presented. A set of somatic seedlings, produced from the maturation medium, showed 100% survival when planted in a field setting. Somatic seedlings showed normal yearly growth when compared to standard seedlings from natural seed. Quality of resulting embryos is examined and compared to zygotic embryos using morphology, dry weight, germination performance, and gene expression. All observations support the conclusion that somatic embryos grow approximately halfway through the normal sequence of development and then prematurely discontinue growth.