Effect of the inflorescence stages and 2,4-dichlorophenoxyacetic acid concentrations on somatic embryogenesis in oil palm (Elaeis guineensis)

Abstract

Oil palm (Elaeis guineensis) is a globally important vegetable oil crop, contributing over 35% of the world’s oil supply due to its superior oil yield per hectare. To fulfil the global demand for high-quality planting materials, hybrid seeds are not optimal due to their genetic variability. Induction of somatic embryogenesis in floral explants enables mass clonal multiplication of elite genotypes. However, the collection of early inflorescence stages causes significant damage to the palm; thus, exploring the potential of utilising the latter inflorescence developmental stages is important. The effect of floral tissues extracted from different inflorescence developmental stages (18–21; 17th inflorescence considered the most immature externally visible stage) was tested against four concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D; 0, 2, 5, or 10 mg/L) using Murashige and Skoog (MS) medium in a two-factor factorial experiment on direct formation of somatic embryoids under light at 28 ◦C. Forty samples were used for each combination. Direct embryo formation and embryo diameter were recorded at three months and analysed using analysis of variance (ANOVA). No interaction effect was found among the tested factors. The inflorescence stage significantly impacted embryo formation and growth (p < 0.0001). Stage 20 resulted in the maximum embryogenic potential with the highest average number of embryoids (0.82±0.08) and the greatest embryo diameter (1.01±0.08 mm), compared to the other stages. This could be attributed to the higher totipotency and responsiveness of the mitotic cells present in the floral buds. The tested concentrations of 2,4-D did not significantly impact embryo induction, but they did influence embryo growth. The embryo diameter in the presence of 2 mg/L and 5 mg/L 2,4-D was comparable with the absence of the growth regulator (p < 0.01), whereas the lowest size was recorded at the highest growth regulator level, 10 mg/L. These results indicate that, within the tested range, the auxin concentration is not significantly effective in embryogenic induction efficiency. This study emphasises the importance of explant selection during the induction of somatic embryogenesis in oil palm and provides insight toward enhancing an effective clonal propagation method.