Secondary somatic embryogenesis in Cork oak: influence of plant growth regulators

Abstract Cork oak (Quercus suber L.) is one of the most important Mediterranean forest tree species, and the Maâmora forest-Morocco is considered to be the world largest cork oak stand. Clonal propagation of Quercus suber via somatic embryogenesis is an alternative to conventional tree propagation methods. However, complete maturation of somatic embryos is considered the major bottleneck for mass propagation of Quercus suber during somatic embryogenesis. This study focuses on influences of cytokinins on secondary somatic embryogenesis. Cytokinins showed a negative effect on the induction of secondary somatic embryogenesis. For the various concentrations tested, the number of secondary somatic embryos was significantly reduced except in the case with low dose of 2iP, which showed a slight increase. Abscisic acid (ABA) may be beneficial at low concentrations between 0.3 and 0.5 mg/l. The best number of secondary embryos was given at 0.5 mg/l ABA with an average number of 5 embryos from each primary embryo, which represents a slight increase below 10% compared to control medium. Also, we found that the number of responsive embryos presenting secondary somatic embryos based on their cotyledons decreased once adding ABA. Phenylurea derivatives TDZ and DPU do not promoted the process of secondary somatic embryogenesis. DPU showed no significant effect with a similar response to that of the control medium and TDZ showed an inhibitory effect. Gibberellic acid (GA3) partially blocked the process of somatic embryos multiplication, but promoted remarkably the germination of cotyledonary embryos without requesting a particular protocol. Our results provide a new insight into embryo development, establishing the basis for further research toward improvement of secondary somatic embryogenesis in Moroccan cork oak.