Incidence des facteurs agro-écologiques sur l'épidémiologie de la pourriture brune des fruits du cacaoyer au Cameroun : contribution à la mise en place d'un modèle d'avertissements agricoles

Black pod disease, caused by Phytophthora megakarya, is the main cause of cocoa harvest losses in Cameroon. Present in almost all cocoa production areas and mainly controlled by chemicals, the disease is a major constraint with regard to economical, social and environnemental aspects. To diminish this constraint, it is necessary to move from systematic to integrated protection, which basic principle is a better control, that is to plan interventions according to actual risks. The aim of this study was to optimize interventions in the various cocoa production zones in Cameroon. It is a contribution to the elaboration of a disease warnings system, in order to better advise cocoa farmers as far as potential epidemic risk is concerned. Cross correlation and multiple regression analyses have allowed to establish relationships between the disease incidence and the climatic variables, notably the rainfall. Spatio-temporal analysis allowed to demonstrate in some fields the agregation of trees bearing diseased pods, indicating the existence of disease foci. Field experiments were carried out in order to assess the impact of weekly phytosanitary pod removal on disease progress, potential production and final harvest. The generalized linear mixed model proved to be the most appropriate for comparing the two treatments (without and with pod removal). This trial allowed a better evaluation of the respective roles of primary and secondary inoculum in the spread of the disease. The present study is therefore an important step towards a better understanding of components of the pathosystem, such as dispersal mecanisms, quantitative relations between the disease incidence and the climatic variables and the spatio-temporal dynamics of the epidemics. The epidemiological and practical implications of the results are discussed. (Résumé d’auteur)