Individual tree variation and selection for yield and vigour : Experience from Côte d'Ivoire

This study entailed a comparison of the performances of 22 single trees selected in a progeny trial in Bingerville (south-eastern Côte d'Ivoire) with those of the clones issued from their vegetative multiplication (plagiotropic cuttings), evaluated in a clonal trial at the same locality. The traits observed were early and adult yield, vigour and yield efficiency. When compared to a seedling control progeny present in both trials, the selected genotypes showed a much lower relative early yield value in the clone trial than in the hybrid trial. This might suggest superiority for early yield of seedling trees in comparison to plagiotropic clonal trees. In addition, a similar level of variation was observed between trees within a seedling progeny and within a clone, suggesting that inter-tree variation is mainly due to environment. Correlation analysis revealed that the values of clones could not properly be predicted from those of the single trees from which they were obtained. On the other hand, the average values of the progenies to which the selected trees belong appeared as better predictors of the values of the clones obtained from these progenies, but the correlations remained rather low (r values of roughly 0.5), even when significant, and only the yield assessed on the trees between their tenth and fifteenth year was a significant predictor. These results seem to indicate a rather poor efficiency in the selection of individual trees for obtaining clones with high early yield. Possibly, data from additional years of harvesting of the clones are necessary before reaching final conclusions on the selection efficiency of individual trees based on yield. These results are in contrast to the significant correlation between individual tree values and clone values for Phytophthora pod rot incidence in the same trials, as published earlier. Under the conditions of these trials, pod rot incidence seems therefore to be a more heritable trait than yield and vigour. An individual tree selection strategy based on combined selection for resistance to black pod and yield is discussed. (Résumé d'auteur)