6-benzylaminopurine induces somatic embryogenesis in staminodia of new genotypes of Theobroma cacao L. from the Papaloapan Basin of Mexico and reveals differences with T. bicolor Bonpl.

Abstract

Abstract Theobroma cacao and T. bicolor belongs to most important agricultural crops of the Mexican tropics. Currently, propagation of these crops is carried out by seed, which means that demand exceeds production. In this context, somatic embryogenesis is an alternative to this isues. Thus, we evaluated the presence of embryogenic genotypes of T. cacao and T. bicolor in the Papaloapan Basin of Mexico with the idea of implementing this technology in the region. The analysis of the phenotypic expression of the floral whorls revealed that 6-benzylaminopurine in combination with 2,4-dichlorophenoxyacetic acid, induces different morphogenetic responses of the genotypes evaluated in the primary callus phase of T. cacao, unlike T. bicolor. The staminodia presented the highest percentage of caulogenesis in T. cacao, while T. bicolor presented the highest frequency of caulogenesis in staminodia and carpels. Some calli differentiated in the root, being to a greater extent those derived from staminodes of T. cacao. The calli of T. bicolor did not differentiate. A parallel study using thidiazuron as an inducer revealed a similar behavior in obtaining callus in both species, however the rhizogenesis from staminodes was 50% lower in the evaluated genotypes of T. cacao. Staminodes were the only ones that presented primary somatic embryogenesis in 66% of the T. cacao genotypes evaluated using benzylaminopurine. Finally, the secondary somatic embryogenesis was evaluated from cotyledons, reaching a 60% success rate, of which 95.48% were normal somatic embryos. Both types of embryogenesis were characterized morphologically using optical and/or scanning electron microscopy.