Effect of osmoregulatory on the secondary somatic embryogenesis of cocoa (Theobroma cacao L.)

Abstract

Cocoa (Theobroma cacao L.) is the raw material for the worldwide chocolate industry. To ensure high quality and efficient field production, the industry relies on a uniformity of elite cocoa plants, which can be achieved through vegetative propagation methods like somatic embryogenesis. However, the low yield rate in the multiplication and regeneration of cocoa plants remains a challenge for basic research. To obtain a greater number of secondary somatic embryos (SSE) in cocoa, the effect of three osmoregulators on the disc cells of primary somatic embryos (PSE) of cocoa was studied. PSE was induced from cocoa staminodes of genotype I52. Epicotyls were selected from PSE at the torpedo and cotyledon stages, segmented into 3 mm discs, and placed in a secondary callus growth medium. The explants were transferred to embryo development medium 3, where they were exposed to the osmoregulatory polyethylene glycol (PEG), mannitol, and sorbitol at the following concentrations: 0%, 1%, 3%, and 5%. D-Mannitol at 3% and D-Sorbitol at 1% increased the number of SSE at the torpedo, globular, and cotyledon stage per explant. The culture medium with 1% PEG significantly increased the formation of SSE in the globular and cotyledonal stages. The results presented a positive effect of the osmoregulators on the formation of cocoa SSE.