Improved secondary embryo production in Quercus alba and Q. rubra by activated charcoal, silver thiosulphate and sucrose: influence of embryogenic explant used for subculture

In somatic embryogenic systems of various oak species, including Quercus alba and Q. rubra, embryogenic lines generally proliferate through generation of nodular embryogenic structures (NS) as a form of repetitive embryogenesis, without embryo development progressing to the cotyledonary stage, or with a low proportion of embryo formation, resulting in the inability to achieve suitable material for plant recovery. In experiments we used previously initiated embryogenic lines derived from 7-year-old trees of Q. alba and Q. rubra. The aim of this work was to improve embryo proliferation and histodifferentiation of lines from these oak species to obtain well-developed embryos and plant regeneration. The effects of activated charcoal, silver thiosulphate (STS) and sucrose concentration on secondary embryo production were investigated. Overall, the best embryo proliferation medium consisted of basal Murashige and Skoog medium containing 0.4 % charcoal and 20 µM STS, and supplemented with 6 % sucrose for Q. alba and 3 % sucrose for Q. rubra. In these conditions, well-developed and singularised torpedo- and cotyledonary-shaped embryos were produced. The developmental stage of the embryogenic explant used for subculture significantly influenced embryo production and differentiation of new secondary embryos, with NS being the most effective explant despite being the smallest explant type in terms of size and fresh weight. Addition of STS in the germination medium also had a positive effect on germination response giving rise to approximately 39 % embryo conversion in Q. alba and 11 % in Q. rubra.This research was partially funded by Ministerio de Economía y Competitividad (Spain) through the project AGL2013-47400-C4-3-R.Peer reviewe