Morpho-anatomical characterization of secondary somatic embryogenesis in Azadirachta indica

Background and Aims: Meliaceae species are extremely recalcitrant during germination and in vitro processes. Therefore, this research focuses on characterization and optimization of a highly efficient system by secondary somatic embryogenesis in Azadirachta indica, which is an important step for enhancing secondary metabolite production and regeneration in recalcitrant species. Material and Methods: Leaf and cotyledon sections were induced in MS medium supplemented with benzylaminopurine (BAP) alone, or combined with 1-naphthaleneacetic acid (NAA) and, abscisic acid (BA) with thidiazuron (TDZ). Key results: Azadirachta indica developed primary somatic embryos with BAP. Shoot and root formation occurred at low concentrations of BAP, while somatic embryogenesis was favored under high levels of BAP or TDZ. Primary and secondary somatic embryos were evidenced continuously and asynchronously. The highest amount of somatic embryos was obtained with cytokinins. However, the concentration might be significant to differentiate between primary and secondary embryos. Moreover, the auxins are key for inducing histodifferentiation in embryos. Shoot induction occurred after transfer of the embryos to hormone-free MS medium. The shoots were rooted in MS1/2. Conclusions: The secondary somatic embryos were distinguished and characterized during the whole process and the efficient system was established with cotyledon sections at short term, which offers several advantages such as the production of metabolites. Key words: abscisic acid (BA), asynchronous embryogenesis, benzylaminopurine (BAP), cyclic somatic embryogenesis, thidiazuron (TDZ). Antecedentes y Objetivos: Las especies de Meliaceae son extremadamente recalcitrantes durante la germination y en los procesos in vitro. Por lo tanto, este estudio esta enfocado en caracterizar y optimizar un sistema altamente eficiente de propagation a traves de embriogenesis somatica secundaria en Azadirachta indica, paso importante para la produccion de metabolitos secundarios, la propagacion o regeneracion de estas especies recalcitrantes. Materiales y Metodos: Las secciones de hojas y cotiledones fueron inducidos en medio MS suple-mentado con bencil-aminopurina (BAP) sola o combinada con acido 1-naftalenacetico (NAA) y acido abscisico (BA) con tidiazuron (TDZ). Resultados clave: Azadirachta indica desarrolla embriones somaticos primarios con BAP. La formation de tallos y raices ocurre en bajas concentraciones de BAP, mientras la em