GENETIC-ANALYSIS OF A FEW QUANTITATIVE CH ARACTERS OF COCOA (THEOBROMA-CACAO L) FLOWERS - THEIR MERITS FOR EVALUATING THE DIVERSITY OF THE SPECIES

This study involved estimating the genetic parameters of several quant itative characters of cocoa flowers using a 12 x 12 half-diallel, set up in Togo. The aim was to evaluate the merits of these characters as descriptors for a study of the diversity of the species. Observations were carried out on five flowers per tree and five to ten trees per cr oss. Measurements concerned the length and diameter of the ovary, the length and width of the sepal, the length of the style, the length of the staminodium; in addition, the length: width ratio for the sepal an d length: diameter ratio for the ovary were calculated. These characte rs own an essentially additive transmission, and their heritabilities are variable. The highest values were obtained for style length, stami nodium length and sepal length. The coefficients of genetic correlatio ns observed between the characters differed from the coefficients of p henotypic correlations. The style length, staminodium length, sepal le ngth and ovary length: diameter ratio were the variables the least gen etically correlated between them and had the highest heritability, whi ch confirmed the merits of these four characters as descriptors. The c oefficients of variation within families were relatively high compared to the residual variation coefficients, which showed the extent of th e variability within the progenies and the value of within-hybrid bree ding. A principal components analysis with the general combining abili ty of the different parents made it possible to distinguish between th e origins of the parents (Upper Amazonian, Lower Amazonian, Trinitario or Criollo). This confirmed the merits of this type of descriptors fo r studying genetic variability in cocoa and guiding hybridization work .