Improved formation of embryogenic callus from coconut immature inflorescence explants

Coconut is a crop with high economic potential; however, production is declining mainly because of palm senescence and diseases such as lethal yellowing. Therefore, there is great demand for palms selected for high productivity and resistance to diseases, and the best strategy for their production is micropropagation through somatic embryogenesis. It is currently possible to micropropagate coconut with highly efficient protocols using the plumule as the explant tissue, but these protocols are not useful for propagating an already fruit-bearing palm with known traits and measured performance. The objective of the present study was to define the conditions for the production and multiplication of embryogenic calluses from rachilla explants from immature inflorescences and to determine their capability to form somatic embryos that are able to convert into plantlets. Twenty-five media containing the plant-growth regulators 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (BAP) combined in different concentrations were tested to induce somatic embryogenesis. A medium containing 0.65 mM 2,4-D and no BAP most efficiently induced the formation of callus with embryogenic structures, and through subculturing these structures as explants, embryogenic callus was produced from them and multiplied. Morphological and histological characterization showed that the callus obtained was indeed embryogenic, similar to that obtained from plumule. The results are encouraging and represent a strong basis for further studies aiming at the development of a protocol for massive propagation using rachilla explants from immature inflorescences, therefore enabling the cloning of fruit-bearing palms with known traits and measured performance.