Somatic embryogenesis in oak (Quercus spp.)

The present review summarizes the factors involved in controlling the proce ss of oak somatic embryogenesis as a method for vegetative plant propagatio n and includes also data on artificial seed production, cryopreservation an d transformation. One major limitation. the inability to initiate embryogen ic cultures from mature trees, has: been recently overcome. Leaves from sel ected cork oak trees with an age of 50 yr and more have been used to, initi ate somatic embryogenesis (SE) with a frequency of up to 20%. These finding s offer encouraging prospects for cloning proven superior plant material an d to integrate this propagation system into, tree improvement programs. Onc e thr process of SE has been initiated, the multiplication cycle proceeds v ia secondary embryogenesis. which can bt maintained indefinitely. Problems are reported by the formation of anomalous embryos. The mutability of somat ic. embryogenic cell lines of various oak species has been monitored by flo w cytometry and molecular markers. No somaclonal variation was detected app lying random amplified polymorphic DNA (RAPD) or amplified fragment length polymorphism (AFLP) markers. whereas DNA-content measurements via now cytom etry revealed tetraploidy in some cell lines after several years of continu ous subculture. Maturation and low germination frequencies are the main bot tlenecks for a broader use of this technique. Recently attention has been o n embryo quality and parameters for conversion capacity such as high endoge nous cytokinin level and low abscisic a id (ABA) level. Although oak is pro bably the species that is the most well-developed system for a broadleaved forest tree, data on growth performances of somatic embryo-derived plants a re rare.