Methods of analysis for studying cocoa (Theobroma cacao L.) susceptibility to mirids

Two species of mirids, Distantiella theobromae (Dist.) and Sahlbergella singularis Hagl., cause substantial damage to cocoa plantations in West Africa. Cocoa susceptibility to mirid attack was observed in the Côte d'Ivoire in a trial involving progenies obtained from crosses according to a factorial mating design, and in a trial involving clones. As spatial distribution of mirid damage was not uniform within the plots, a method was developed for experimental design of completely randomized single-tree elementary plots, based on analysis of covariance and taking into account the spatial within-plot effect of the damage caused. This method resulted into a more precise estimation of genetic effects and heritabilities adjusting for mirid susceptibility heterogeneity in the field.[PUBLICATION ABSTRACT]