Improvement of somatic embryo maturation and shoot formation in somatic embryogenesis of Asian coconut varieties

• Zygotic embryo germination and embryogenic callus formation are genotype dependent. • First report of glutamine improving somatic embryo maturation in coconut. • Gibberellic acid positively influences mature somatic embryo shoot formation. • This study contributes to the optimization of somatic embryogenesis. Somatic embryogenesis is one of the identified pathways that has the potential to clonally propagate coconut at scale, but considerable improvements are needed prior to commercialization. Once formed, the maturation process for somatic embryos and their subsequent shoot formation, are the key processes that need to be improved to achieve a high throughput plantlet propagation system. Therefore, this study evaluated the impact of various plant growth regulators, medium additives, and partial desiccation on somatic embryo maturation and shoot formation on Asian varieties. This study showed that zygotic embryo germination and embryogenic callus formation were genotype specific. A significant improvement in somatic embryo maturation (from 57 to 83 %) was first reported using l -glutamine (1.4 mM) and marginal improvements were obtained with gibberellic acid (GA 3 ; 0.5 µM), adenine sulphate (27 µM) or partial desiccation. Shoot formation from mature somatic embryos also significantly increased from 17 % to 30 % with ca. 5.6 shoots produced per mature somatic embryo clump with the addition of GA 3 (1.0 or 2.0 μM) to the medium. These amendments are important improvements to the coconut somatic embryogenesis protocol, and once tested on a wider range of varieties, may allow for the widespread application of somatic embryogenesis to rapidly produce coconut plantlets.