Enhanced Plantlet Regeneration in Two Cacao (Theobroma cacao) Clones from Immature Inflorescence Explants

Abstract

Theobroma cacao L. (cacao) is a major tropical crop, grown for its oil-rich seed, which is used in the manufacture of chocolate, its derivatives, and cosmetics. Cacao is cultivated mainly by smallholders and represents a significant export commodity for some developing countries such as Côte d’Ivoire. It is conventionally propagated by seeds, grafting, and cuttings. Somatic embryogenesis offers an alternative method for propagation where large-scale production of planting materials is possible. In the current study, the effect of different concentrations of 2, 4-dichlorophenoxyacetic acid (2, 4-D) and kinetin on induction of somatic embryogenesis and plantlet regeneration in two cocoa clones (coded as C1 and C14) were evaluated. Flowers were collected early in the morning, sterilized, explants excised and cultured on Driver, and Kuniyuki Walnut (DKW) media supplemented with different concentrations of 2, 4-D (9, 10, and 20 µM) and kinetin (0.5, 1, 2.5, 5, 10, and 25 µM) in separate experiments. The frequently used media in somatic embryogenesis of cacao [DKW supplemented with 0.022 µM thidiazuron (TDZ) and 9 µM 2, 4-D] was used as a control. The results of the study showed that explants cultured on media supplemented with 10 µM 2, 4-D and 5 µM kinetin produced the highest (28.0 ± 1.1) mean number of embryos/explant in C1 and this was a 9-fold increase in the number of embryos compared with the control. Explants cultured on media supplemented with 10 µM 2, 4-D and 2.5 µM kinetin produced the highest (7.0 ± 4.0) mean number of embryos/explant in C14 whereas the explants cultured on media supplemented with 20 µM 2, 4-D and 2.5 µM kinetin gave the highest (22.0 ± 1.7) mean number of embryos in clone C1 and C14. The regenerated embryos were germinated and successfully weaned in the green house with a survival rate of 70% being recorded. The paper describes an improved protocol compared with previous work in terms of embryo recovery and survival rate of the elite clones of cocoa through somatic embryogenesis. The results of the current study confirm that somatic embryogenesis of cacao clones is genotype dependent.