Tissue Culture of Cacao (Theobroma cacao L.): Between Somaclonal Variation and Mass Propagation

Abstract

Cacao (Theobroma cacao L.) is an important commercial and agricultural crop. It has been the subject of varied research aimed at optimizing the propagation of materials selected for different traits of interest. Tissue culture is one of the promising tools for this purpose, as well as for plant breeding and other basic research. Somatic embryogenesis (SE) in cacao has been shown to be a viable and cost-effective alternative; the process, standardized by different authors, is associated with significant advantages. However, difficulties related to somaclonal variation have also been identified, which are the main focus of this work. Of the two pathways for inducing SE, direct (DSE) and indirect somatic embryogenesis (ISE), cacao primarily responds to ISE, where an intermediate callus phase is present. Large-scale multiplication has been effectively achieved from primary somatic embryos (PSE) in hormone-supplemented culture media, which has been shown to generate somaclonal variation. It was detected through changes in embryos development and conversion rates, plant morphology and architecture, and supported at the genetic and molecular levels. This work provides an overview of the state of development of plant production technology by SE for cacao and the challenges in terms of scaling, efficiency, and final production costs. The most prominent factors inducing somaclonal variation are also addressed, as well as the anomalies in somatic embryos and cacao seedlings found in different research studies.