Cocoa (T. cacao) is a neotropical, small, evergreen tree and native to the undergrowth of the Amazon forest (South America), and belongs to the Malvaceae family. It is cultivated around the world, for its seeds mainly used in the manufacture of chocolate and cosmetics. Côte d’ivoire is the world’s leading cocoa producer accounting for more than a third of the global supply. Cocoa plays a key role in the economy of the country contributing to 15% of its GDP, 40% of its exports, and supporting more than 6 million people (Conseil Café Cacao, 2014; ICCO, 2012). Theobroma cacao is generally a heterozygous plant with a high variability for agronomic and quality traits. Seed propagation, while efficient, is problematic, since many of the trees are unproductive. The number of planting materials produced by rooted cuttings and grafting are unbalanced and far below the quantity needed to supply farmer’s demand. Therefore, there is a need to accelerate the production of the elite cocoa planting materials by using alternative methods such somatic embryogenesis. Somatic embryo production and plantlet regeneration have been achieved in a large number of genotypes (Li et al., 1998; Maximova et al., 2002).
Despite the current progress in this area, the reported efficiencies of somatic embryogenesis and plant regeneration obtained remain low. Furthermore, the practical utilization of this technology for clonal propagation remains hindered by an inability to induce somatic embryogenesis from a majority of elite cocoa genotypes. For these applications to be technically and economically feasible, it is essential to optimize the system variables to obtain high multiplication rates of quality somatic embryos. This is in view of the fact that different cocoa genotypes react differently to different callus-inducing hormones (Traore and Guiltinan, 2006). Plant growth regulators play a key role by intervening in the reactions that lead to a reorientation of the program of gene expression. This expression can lead either to an unorganized growth of the cells (callus) without embryogenesis or to a polarized growth leading to a somatic embryogenesis (Dudits et al., 1995).
In T. cacao, Li et al. (1998) added 18 µm 2,4-D and 45.4 nm thidiazuron in DKW medium basal salts (Driver and Kuniyuki, 1984) while López-Baez et al. (2000) used 2,4-D or 2,4,5-T (1 mg·L−1) and Kin or 2 Isopentyladenine (2-ip) (0.25 mg·L−1) in a modified Murashige and Skoog (MS) salts (Murashige and Skoog, 1962). These two systems resulted in somatic embryos production but some differences in efficiencies were apparent. The DKW basal salts media appears to be superior to MS media for cocoa tissue culture and although modifications of MS have given adequate results, most laboratories have switched to DKW based media (Guiltinan and Maximova, 2000). Although the different combinations have been reported to enhance somatic embryogenesis efficiency, it remains evident that different clones vary in their response given to carbohydrate sources, plant growth regulators, or basal media (Guiltinan and Maximova, 2000).
The present study was aimed at improving the induction of T. cacao somatic embryogenesis by combining several auxins and cytokinins. To the best of our knowledge, 3,4-D and dicamba have never been evaluated for induction of somatic embryogenesis of T. cacao.
Ajijah, N., Hartati, R.S., Rubiyo, R., Sukma, D. & Sudarsono, S. 2016 Effective cacao somatic embryo regeneration on kinetin supplemented DKW medium and somaclonal variation assessment using SSRS markers Agrivita 38 1 80 92
Ajijah, N., Rubiyo, & Sudarsono, 2014 Callogenesis and somatic embryogenesis of cacao using thidiazuron through one step of callus induction (in Indonesian). J. Penelitian Pertanian Tanaman Industri 20(4):179–186. <http://www.ejurnal.litbang.pertanian.go.id/index.php/jptip/article/view/2580/2220>.
Chehmalee, S. & Te-chato, S. 2008 Induction of somatic embryogenesis and plantlet regeneration from cultured zygotic embryo of oil palm J. Agr. Tech. 4 2 137 146
Conseil Café Cacao 2014 Programme Quantité-Qualité-Croissance « 2QC » 2014-2023. Le Conseil de Régulation, de Stabilisation et de Développement de la filière café-cacao. Dec. 2016. <www.conseilcafecacao.ci/docs/Programme_2Qc_2014-2023.pdf>.
Dudits, D., Györgyey, J., Bögre, L. & Bakó, L. 1995 Molecular biology of somatic embryogenesis, p. 267–308. In: T. A. Thorpe (ed.) In Vitro Embryogenesis in Plants. Kluwer Academic Publishers, Dordrecht
Guiltinan, M.J. & Maximova, S. 2000 Recent advances in the tissue culture of cocoa from somatic embryos to bentwood gardens: A short review. In Abstr. Ingenic Workshop on the New Technologies and Cocoa Breeding, Kota Kinabalu, Malaysia
International Cocoa Organization (ICCO) 2012 How many smallholders are there worldwide producing cocoa? What proportion of cocoa worldwide is produced by smallholders? Aug. 2016. <http://www.icco.org/faq/57-cocoa-production/123-how-manysmallholders-are-there-worldwide-producing-cocoa-what-proportion-of-cocoa-worldwide-isproduced-by-smallholders.html>.
Kouassi, K.M., Koffi, K.E., Konkon, N.G., Gnagne, M., Koné, M. & Kouakou, T.H. 2013 Influence of plant growth regulators on somatic embryogenesis induction from inner teguments of rubber (Hevea brasiliensis) seeds Afr. J. Biotechnol. 12 16 1972 1977
Li, Z., Traoré, A., Maximova, S.N. & Guiltinan, M.J. 1998 Somatic embryogenesis and plant regeneration from floral explants of cocoa (Theobroma cacao L.) using Thidiazuron In Vitro Cell. Dev. Biol. 34 293 299
López-Baez, O., Moreno-Martmnez, J.L. & Pacheco-Rodas, S. 2000 Advances in cocoa Theobroma cacao propagation by somatic embryogenesis in Mexico. In Abstr. 3′ Ingenic Workshop on the New Technologies and Cocoa Breeding, Kota Kinabalu, Malaysia
Maximova, S.N., Alemano, L., Youg, A., Traoré, A., Ferrier, N. & Gultinan, M.J. 2002 Genotype variability, efficiency and cellular origin of primary and secondary somatic embryogenesis of Theobroma cacao L. the chocolate tree In Vitro Cell. Dev. Biol. 38 252 259
Michaux-Ferrière, N. & Carron, M.P. 1989 Histology of early somatic embryogenesis in Hevea brasiliensis. The importance of timing of subculturing Plant Cell Tissue Organ Cult. 19 243 256
Murashige, T. & Skoog, F. 1962 A revised medium for rapid growth and bioassays with tobacco tissue cultures Physiol. Plant. 15 473 497
Traore, A. & Guiltinan, M. 2006 Effects of carbon source and explants type on somatic embryogenesis of four cacao genotypes HortScience 41 753 758
Zuyasna,, Hafsah, S., Fajri, R., Syahputra, O.M. & Ramadhan, G. 2012 The effect of picloram concentrations and explants types on the induction of somatic embryo on North Aceh Cocoa genotype. Poster, Proc. 2nd Annu. Int. Conf. Syiah Kuala Univ. 2012 and The 8th IMT-GT Uninet Biosc. Conf. Banda Aceh, Vol. 2 Number 1