In vitro regeneration of Cocos nucifera L. via somatic embryogenesis

Clonal propagation of coconut, a recalcitrant crop propagated mainly by seed, remains the only way for its vegetative propagation. Immature inflorescence, leaves and embryos and plumules derived from zygotic embryos were used as explants. Embryonic calloids were obtained from immature inflorescences of cultivars Bago-Oshiro (BAO), Laguna (LAG) and Rennel Island Tall (RIT) cultured in Branton and Blake's basal medium supplemented with 2,4-D and 2iP for calloid and embryoid induction. Subculture of calloids in BAP-supplemented medium resulted in regeneration of complete plantlets from the three Tall cultivars 17-26 months after initial culture. Two clonal plantlets are now being established in the greenhouse. The success in regenerating plantlets from the three cultivars adopting one in vitro system has established a reproducible system for clonal propagation of coconut using immature inflorescences. Clonal plantlets were also regenerated from immature (7-9 months old) embryo of cultivars Catigan (CAT, dwarf), LAG and Catigan x Baybay hybrid 5-6 months and from plumular tissues excised from mature zygotic embryos of cv. LAG 3-17 months after initial culture. Although plantlets can be produced from immature zygotic embryos and plumular tissues earlier than immature inflorescences, these are not ideal explants because of the unknown performance of zygotic tissues. However, if a more efficient, reliable and economical regeneration system can be developed with these explants than immature inflorescence, the technique could be applied to rapidly mass propagate the elite Makapuno coconut. The work reported has demonstrated the potential of clonal propagation for the mass propagation of coconut, which with further improvements to increase the frequency of plantlet regeneration and successfully establish clonal plantlets in the screenhouse, will enable the large scale production via somatic embryogenesis of this recalcitrant crop. Furthermore, with the available in vitro regeneration system for coconut, the prospect of genetic transformation as a tool in coconut breeding and improvement could be realized