Histodifferentiation of oil palm somatic embryo development at low auxin concentration

Large-scale propagation of oil palm (Elaeis guineensis, Jacq.) is difficult due to its single apical meristem. Thus, obtaining plants is mainly through seed germination, and a long growing period is required before oil production is possible. An alternative to large-scale seedling production is indirect somatic embryogenesis. The aim of this study was to analyze the somatic embryogenesis process in oil palm (E. guineensis Jacq.) with amino acids and low concentrations of auxins. The Tenera hybrid was analyzed by cytochemical and ultrastructural methods and was used to regenerate oil palm plants. First, calli were induced in MS culture media supplemented with 2,4-D and picloram. Two types of calli were obtained, characterized by beige or translucent color. Beige calli had embryogenic characteristics, such as large nuclei with prominent nucleoli, and they were multiplied for 8 months in MM culture (half strength MS, 1 mg L^-1 2,4-D, 2 mg L^-1 2iP, 1 mg L^-1 IBA, 250 mg L^-1 citric acid, 10 mg L^-1 cysteine, 100 mg L^-1 inositol, 1 mg L^-1 thiamine, 1 mg L^-1 pyridoxine, 1 mg L^-1 nicotinic acid, 1 mg L^-1 glycine, 200 mg L^-1 malt extract, and 100 mg L^-1 casein hydrolysate). After multiplication, the MCB culture medium (half strength MS, supplemented with 0.25 mg L^-1 NAA, 2 mg L^-1 BAP, MM vitamins and 200 mg L^-1 malt extract, and 100 mg L^-1 casein hydrolysate) was the most efficient for embryo formation, showing meristematic centers with totipotent cells in histochemical analyses. The somatic embryos were developed and germinated in MG medium (half strength MS, 0.45 mg L^-1 IAA, 0.25 mg L^-1 BAP, and MM vitamins), transplanted into polyethylene tubes containing pine bark substrates, and acclimatized in a greenhouse, achieving a 97% survival rate. The use of picloram for callus induction and somatic embryogenesis is advantageous and multiplication in MM medium is an important step for increasing cell mass. The calli with light beige color and nodular structures have meristematic cells with dense cytoplasm and totipotential features that later give rise to protoderm, procambium, and ground meristem during the globular, cordiform, and torpedo embryogenesis phases. In MCB medium, the concentration of vitamins and amino acids are crucial for somatic embryogenesis.