Comparing the Effect of Plant Growth Regulators on Callus and Somatic Embryogenesis Induction in Four Elite Theobroma cacao L. Genotypes

Abstract

The effect of plant growth regulators on callus and somatic embryogenesis induction in four Cocoa (Theobroma cacao) genotypes was studied. Flower explants were harvested early in the morning and cultured on Driver and Kuniyuki Walnut (DKW) medium supplemented with 1 mg·L−1 of five auxins type (2,4 dichlorophenoxyacetic acid (2,4-D), 3,4 dichlorophenoxyacetic acid (3,4-D), 2,4,5 trichlorophenoxyacetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 3,6-dichloro-2-methoxybenzoic acid (dicamba) in combination with 0.25 or 0.5 mg·L−1 of two cytokinins type (benzylaminopurine (BAP) and 6-furfurylaminopurine [kinetin (Kin)] in a factorial experiment. The plant growth regulators 2,4-D and 2,4,5-T proved to have a broad spectrum action on somatic embryogenesis induction compared with 3,4-D or picloram. There were no significant differences between the two concentrations of cytokinins. However, Kin was found to be more effective in promoting somatic embryogenesis than BAP. Combining 1 mg·L−1 2,4,5-T or 2,4-D with 0.25 mg·L−1 Kin had a broad spectrum action on embryogenesis induction. On the other hand, combining mg·L−1 picloram with 0.5 mg·L−1 Kin or 1 mg·L−1 3,4-D with 0.25 mg·L−1 Kin was only able to induce somatic embryogenesis in a few of the genotypes evaluated. The protocol developed during the current study differs from earleir works as the callus (derived from explants cultured on DKW media) was taken directly to embryo development media as opposed to earlier works in which the callus was taken through a secondary media before being transferred to an embryo development media.