Multiplication via micropropagation in cocoa

The therm plant micropropagation includes all the in vitro vegetative propagation techniques. Some of these techniques have been applied to Theobroma cacao L., and the most important efforts were made for microcuttings and somatic embryogenesis that will mainly be considered in this paper. Microcutting: After the definition, a bibliographic synthesis will be presented, focusing on the limitations of the technique. In order to a better knowledge of the physiology of the explants, a programme was recently followed at Cirad. It consisted in trying to identify the main important factors responsible for the generally poor reactivity of buds in vitro, and analysing the rooting and acclimation of the shoots. Parameters related to the vegetal material were considered. The physiological stage of growth reached by the branches from which the explant were taken, the position of the nodes on the branch with respect to the apex and the age of the donor plant had a considerable influence on culture initiation and response. Identification of limiting factors of single-nodes culture: Because of the clear differences of reactivity of single-nodes explants and cotyledonary explants, they were chosen as a reference to identify the limiting factors of the cultures. An histological analysis of the evolution of the nodes during the primary culture (25 days), an analysis if the water status of the explants clearly demonstrated some differences between the two explants. The consequence of the desinfection step on the water status of single-nodes was studied. Rooting and acclimatisation: Rooting capacity of bud shoots was compared for two genotypes: Amelonado and Spontaneous Guyanese. Somatic embryogenesis: After the definition, a bibliographic synthesis will be presented, focusing on the limitations of the technique. Research developed at CIRAD will be presented on the subject. Embryogenic capacity: The protocol defined by Li et al. (1998) has been tested on 23 genotypes. The efficiency of each step of the process has been determined. Origin of the somatic embryos: histological analysis: The somatic embryos were demonstrated to be of multicellular origin. Comparison with coffee and banana somatic embryogenesis: Cocoa somatic embryogenesis will be compared in term of number of plants produced from a fixed amount of starting material. The limitations of the protocol will be identified. Preliminary results on improved embryo growth and conversion. (Résumé d'auteur)