Diversité génétique et sélection du cacaoyer (Theobroma cacao L.) au Cameroun : approches participatives, phénotypique et moléculaire

Efombagn Mousseni Ives Bruno. 2008. Diversité génétique et sélection du cacaoyer (Theobroma cacao L.) au Cameroun : approches participatives, phénotypique et moléculaire. Rennes : ENSAR, 149 p. Thèse de doctorat : Biologie et agronomie : Ecole nationale supérieure agronomique de Rennes

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Encadrement : Manzanares-Dauleux, Maria

Abstract : Genetic diversity of cacao (Theobroma cacao L.) accessions in farmers' field and genebanks in Cameroon was studied with 12 microsatellite markers and several phenotypic traits of agronomic interest. Knowledge of farmers on their planting material was collected within the framework of a participatory selection progamme, and subsequently compared with molecular and phenotypic data. The molecular assessment of the farm accessions (FA) and genebank accessions (GA) shows that farmers and breeders accessions are closely related. GA belong to three main genetic groups of the cacao species: Upper Amazon Forastero (UA), Lower Amazon Forastero (LA) and Trinitario (Tr). The genetic diversity among FA could be largely explained by the contribution of six reference genomes (Amelonado, Criollo, Iquitos Mixed Calabacillo, Nanay, Parinari and Scavina) supposed to be at the origin of cultivated cacao populations in Cameroon. The genes from the Amelonado group predominated in the FA whereas those from Scavina and Criollo were less represented. The large molecular and phenotypic diversity and the presence of private alleles among FA show the potential for selection of this material. This potential was further demonstrated by the identification of several resistant genotypes among FA tested for resistance to Phytophthora pod rot (Ppr), the major cacao production constraint in the country. The results from Ppr evaluations suggest also that farmers' knowledge on the field resistance of individual cacao trees might be exploited efficiently in the participatory breeding programme. Parentage analyses indicate that only 46% of all the FA appears to originate from the biclonal seed gardens (BSGs). Despite the predominance of self-incompatible progenitors in BSGs, more than half of the BSG-derived FA was the product of setting. Only 25% of these accessions corresponds to the true hybrid combinations proposed to the farmers. The adoption of proper techniques for seeds production and multiplication in BSGs and the use of the results of this study in genetic improvement of cacao in Cameroon are discussed. (Résumé d'auteur)

Mots-clés Agrovoc : Theobroma cacao, Sélection, Variation génétique, Phylogénie, Banque de gènes, Résistance aux maladies, Caractère agronomique, Amélioration des plantes, Participation, Agriculteur, Phénotype, Microsatellite, approches participatives

Mots-clés géographiques Agrovoc : Cameroun

Classification Agris : F30 - Plant genetics and breeding
H20 - Plant diseases

Champ stratégique Cirad : Axe 1 (2005-2013) - Intensification écologique

Auteurs et affiliations

  • Efombagn Mousseni Ives Bruno, ENSAR (FRA)

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