Manifestation of embryogenic potential in culture of zygotic embryos of Quercus robur L.

For the initiation of somatic embryogenesis early cotyledonary stage of zygotic embryo explants (from 15th July until late August) was suitable. The highest frequency of differentiation of somatic embryos was obtained on cotyledons of zygotic embryos cultured on basal modified medium MS (with 1/2 concentration macronutrients) or WPM medium containing 500 mg•l^-1 glutamine, proline and casein hydrolysate and supplemented with 2,4-D (1,0-2,0 mg•l^-1) and BAP (0,5-1,0 mg•l^-1). The development of somatic embryos was direct and indirect and the process was continuous over a long period. Primary somatic embryos were able to produce secondary embryos. Repetitive somatic embryogenesis led to the proliferation of a large number of new somatic embryos on their cotyledons, hypocotyl or radicula. The process of embryo differentation is asynchronous - various stages of somatic embryos could be observed in embryogenic culture. A somatic embryo conversion was rare on tested media. Embryo germination occured on medium containing BAP (0,1 mg•l^-1) or on medium with ABA and GA₃ (each 0,2 mg•l^-1) after a previous culture on WPM medium without plant growth regulators supplemented with sorbitol (6%). The embryo germination occurred also on WPM medium with 0.2 mg•l^-1 BAP when cultures were mantained at 2^oC for 4 weeks. Only 8 somatic embryos developed into plantlets. Their transplantation to <em>in vivo</em> conditions was unsuccessful.