Comparison of two protocols for somatic embryo induction in a Sulawesi elite Theobroma cacao L. clone

The objective of the present work was to evaluate the induction and development of somatic embryos from staminode and petal explants of the 'Sulawesi 2' cacao clone using the protocol developed by Guiltinan and Maximova (2010) and the modified protocol of Fontanel et al. (2002). Immature flower buds were collected from the experimental station of Tadulako University, Indonesia. Primary Callus Growth (PCG) and Secondary Callus Growth (SCG) medium formulation from Guiltinan and Maximova (2010) and the IND1 medium from Fontanel et al. (2002) were used to induce callus and somatic embryo formation. A high frequency of staminode explants produced callus on the PCG and IND1 medium. Although sustained growth of callus was found after each subculture on SCG medium and prolonged culture (18 weeks, six subcultures) on Embryo Development (ED) medium, direct somatic embryo from petal explant was only achieved when cultured on IND1 medium. Globular-staged somatic embryos, occurred at a rather low frequency, with 8% of petals forming direct somatic embryogenic tissue. These results indicate that the IND1 medium from Fontanel et al. (2002) is valuable to induce a direct somatic embryogenic response on petal explants and indirect somatic embryogenesis on staminode explants of 'Sulawesi 2'. Our study confirms the embryogenic competence of this Sulawesi elite cacao clone cultured by means of the Fontanel et al. (2002) modified protocol.