Dual-phase culture system as a promising strategy to enhance the efficiency of somatic embryogenesis and plant regeneration in oil palm (Elaeis oleifera × E. guineensis)
摘要
Somatic embryogenesis in oil palm plays a crucial role in the large-scale propagation of high-quality plants, and the use of liquid media has shown potential to enhance efficiency. This study aimed to develop a protocol for somatic embryogenesis and plant regeneration in an interspecific oil palm hybrid B351733 (Elaeis oleifera × E. guineensis) using a dual-phase culture system combining semi-solid and liquid media at different stages. Particular attention was given to the optimization of somatic embryo maturation. Embryogenic calli (300 mg), either sectioned or naturally dissociated, were inoculated into a liquid medium, consisting of MS salts and 1.0 mg L−1 2,4-D, and the sedimented cell volume (SCV) was measured over 90 days to establish growth curves. To optimize somatic embryo (SE) maturation, SEs were transferred to semi-solid media containing different combinations of polyethylene glycol (PEG) and/or sucrose, and subsequently evaluated biochemically (total protein accumulation) and histochemically. SEs were then inoculated into a germination medium. During the initial establishment and multiplication phases in liquid medium, both sectioned and dissociated calli showed satisfactory growth, reaching SCVs of 4 mL and 6 mL, respectively. After 90 days in the maturation medium, an average of 46% of the embryogenic calli produced at least one somatic embryo at the globular or torpedo-like stage. Embryos matured on ½ MS medium supplemented with 20 g L⁻1 sucrose exhibited the highest germination rate (22.02%), resulting in complete plantlet formation, whereas other treatments led to reduced shoot and root development. Overall, maturation media containing only sucrose at 45 g L⁻1 yielded the highest number of mature embryos and the best germination performance, with an average of four plantlets per flask. Biochemical and histochemical analyses confirmed increased accumulation of total soluble proteins in somatic embryos (SEs) with higher concentrations of PEG and sucrose in the culture medium. Germination of SEs was more efficient from embryos maturated on sucrose-only media, whereas embryos from PEG treatments exhibited higher oxidation and hyperhydricity. A robust methodology was developed, demonstrating that the dual-phase culture system significantly improved somatic embryogenesis, embryo maturation, and clonal plant propagation efficiency in the interspecific oil palm hybrid studied.