Improving Coconut (Cocos Nucifera) Micropropagation through Enhanced Somatic Embryogenesis
The coconut palm occupies a significant portion of humid tropics contributing to food security, improved nutrition, employment, and income generation. Owing to the genetically diverse nature of seedlings produced, clonal propagation of selected elite coconut genotypes by micropropagation is the ultimate strategy to produce large quantities of genetically uniform, disease free, high quality planting material rapidly. Although, in vitro cloning via somatic embryogenesis seems to provide a convenient alternative due to its potential for rapid and massive propagation, difficulties in the process are still preventing the establishment of an affordable and universal protocol. Some of such major bottlenecks are heterogeneous responsiveness of individual palms and explants to in vitro culture conditions, oxidative browning, and poor somatic embryo multiplication. The objective of the study is enhancing existing somatic embryogenesis protocol through improved media composition and incorporation of better multiplication strategies. Initial calli, generated from unfertilized ovaries, were cultured in Y3 basal medium with auxins (i.e. 2,4-dichlorophenoxyacetic acid [2,4-D] and dicamba) alone and with auxin in combination with calcium ionophore A23187 and/or 22(S),23(S)-homobrassinolide. The number of somatic embryogenic calli produced per initial callus piece was recorded. The media with 2,4-D alone or in combination with calcium ionophore A23187 and/or 22(S),23(S)-homobrassinolide resulted in significantly greater number of somatic embryogenic calli (4.33, 4.41, 4.59, 4.55) compared to the media with dicamba alone or in combination with calcium ionophore A23187 and/or 22(S),23(S)-homobrassinolide (1.7, 1.83, 1.8, 1.92). Effect of incorporating 2,4-D into the media alone or in combination with calcium ionophore A23187 and/or 22(S),23(S)-homobrassinolide is yet to be investigated down the somatic embryogenic pathway in order to enhance the existing in vitro propagation protocol.