**3. Problems in oil palm tissue culture**

The oil palm clones are frequently generated via indirect somatic embryogenesis, in which the plantlets were produced from the growth of callus and differentiate into somatic embryos. The process is usually induced from seeds, hence, making seed propagation most common for oil palm somatic embryogenesis. However, seeds propagation often cause difficulties in terms of low germination of the seeds. Due to the hard woody and sturdy structure of oil palm, there is very few choices of explants that can be used to induce somatic embryogenesis. Apart from the seeds, immature leaves are another explant of oil palm that is often be opted.

Oil palm is one of recalcitrant plants, meaning that its explants are more difficult to be developed into plantlets as compared to other plant species. While somatic embryogenesis is well known for its low efficiencies in producing small number of plantlets, the other main setbacks of this method in oil palm breeding are the difficulties in initiating somatic embryogenesis out of embryo cell cultures as well as to fully convert those somatic embryos into whole plantlets. It was reported that immature leaves explants of oil palm has been able to generate callus up to 52%, while other explants such as zygotic embryos and immature inflorescence produced higher rate of callus induction [2]. Despite of these reported adequate efficiencies, the callus induction rate from an explants are highly dependent of its genotype. Many explants could only regain totipotency during the culture process at around 1–5% in order to initiate callus, thus, making somatic embryogenesis is very inefficient procedures [3]. The development of somatic embryogenesis into whole plantlets is also often problematic. This is due to the failure of shoot or root development or induction, whereby, results in low regeneration rate of oil palm clones [4, 5].

The combination of low efficiency of somatic embryogenesis induction, limited explants choices, and low regeneration rate into complete explants, making oil palm breeding via tissue culture is impossible without embryos proliferation process is carried out. However, by producing large number of embryos in one culture may

produce risk of somaclonal variation. Another way to increase regeneration rate in oil palm culture is by using explant of prolific breed. Although the selection of this breed requires large screening process at molecular level to identify the best genotype, it could be developed as a tool that possibly provide long-term benefits [6, 7].
