METHODS OF ANALYSIS FOR STUDYING COCOA (THEOBROMA-CACAO L) SUSCEPTIBILITY TO MIRIDS

Two species of mirids, Distantiella theobromae (Dist.) and Sahlbergell a singularis Hagl., cause substantial damage to cocoa plantations in W est Africa. Cocoa susceptibility to mirid attack was observed in the C ote d'Ivoire in a trial involving progenies obtained from crosses acco rding to a factorial mating design, and in a trial involving clones. A s spatial distribution of mirid damage was not uniform within the plot s, a method was developed for experimental design of completely random ized single-tree elementary plots, based on analysis of covariance and taking into account the spatial within-plot effect of the damage caus ed. This method resulted into a more precise estimation of genetic eff ects and heritabilities adjusting for mirid susceptibility heterogenei ty in the field.