Résumé
A good knowledge of the diversity of genetic materials as well as the relationship between genotypes is essential for the improvement of plant quality. While genetic identification was based on phenotypic observation of the plant, this type of identification was sometimes doubtful and could never be carried out at an early stage of development. Many techniques are now available to detect the differences between genotypes. Added to the observation of morphological and phenotypical characteristics are those achieved by isoenzymatic and molecular makers on DNA. The development and application of genetic molecular makers offer the opportunity to access the conformity of collection of genetics resources. Among the different molecular makers, RFLPS were the first to be used for the study of the genome of plants, in Cartography as well as in the study of diversity. However, RFLPS require time and a large quantity of DNA to put in place. PCR based techniques could be used to detect polymorphism. This method requires a low quantity of DNA and is convenient for genetic analysis on germ. A new method of extracting cocoa tree DNA have been put in place. Among the methods of marking, using the PCR, the specific locus character and codominants of Micro satellites confer on them a certain advantage compared with techniques which use arbitrary baits. Compared with RFLP, they reveal more allele and more polymorphism. However, the discovery and the development of locus Micro satellite is a costly exercise. Banks enriched in Micro satellite sequences were built in CIRAD. 80 loci are now available. Under the auspices of the IPGRI / CFC project on the preservation and the utilization of genetic resources, 8 of these loci spread over seven different chromosomes were used to examine the conformity of 28 clones which have to be multiplied and transmitted from Reading and Montpellier in relation to clones originally collected and national collections. Micro satellites were established by migration on polyacrylamide gel after PCR for amplification and marking of baits with y - 33p. A first study carried out in 1999 was based on 130 individuals, 13 out of the 28 clones analyzed present identical profiles to the 8 loci identified. In the second year of the project, 140 new individuals were analyzed to confirm the first results and for clones whose identification were not correct, other individuals were analyzed to verify intra-clonal homogeneity. In conclusion, freely usable Micro satellite markers put at the disposal of genetic engineers interested in selection, constitute a powerful tool for the analysis of genetic resources with a view to improving the cocoa tree. (Texte intégral)