V. Laurent

Comparative genetic diversity studies of Theobroma cacao L. using RFLP and RAPD markers

The genetic diversity of 106 genotypes of Theobroma cacao L. was assessed using RFLP and RAPD methods. Thirty-one cDNA probes and 19 primers generated, respectively, 87 and 49 polymorphic bands that were submitted to factorial and cluster analyses. Both RFLP and RAPD bands separated the individuals into three distinctive groups. Some genotypes did not correspond to the currently accepted classification and are considered to have been originally misclassified. The nature of RAPD bands was investigated by Southern analysis. There were as many highly repeated sequences as single copy sequences but the two types of sequences did not structure the variability in the same way. Similar results were obtained with RFLPs and RAPDs with regard to the genetic structure of Theobroma cacao L. Therefore, RAPDs appear to be as efficient as RFLPs for classifying cocoa genotypes.

Genetic diversity in cocoa revealed by cDNA probes.

The variability of the cocoa (Theobroma cacao) nuclear genome was investigated. A total of 203 cocoa clones was surveyed for restriction fragment length polymorphisms (RFLPs) using four restriction endonuclease and 31 seed cDNA probes. A high level of polymorphism has been found. This study points to a structuring of the species that fits with the distinction between the Criollo and Forastero populations. These results combined with previously obtained nuclear rDNA and mtDNA data allow us to propose new hypotheses on the origin and evolution of the different cocoa populations.

The genetic structure of cocoa populations (Theobroma cacao. L.) revealed by RFLP analysis

The genetic structure of 175 genotypes of Theobroma cacao L. was investigated using 27 RFLP/cDNA loci. The number of alleles per locus was never higher than four and a high genetic diversity was found. Criollo genotypes appeared differentiated from Forastero genotypes. A deficiency of heterozygotes was found in all populations and some alleles were fixed in some populations. Within population gene diversity was high. When four morphological groups were considered, Upper Amazon Forastero was the most polymorphic and diverse population. Almost all the alleles of the whole species could be found within this group. Observed heterozygosity was the highest within Criollo and Trinitario populations but a certain proportion of homozygous genotypes was present in all groups.

Chloroplast and mitochondrial DNA diversity in Theobroma cacao.

The variability of cocoa (Theobroma cacao) cytoplasmic genomes has been investigated. A total of 177 cocoa clones was surveyed for restriction fragment length polymorphism (RFLP) in chloroplast DNA and in mitochondrial DNA using two restriction endonucleases and various heterologous cytoplasmic probes. A high level of polymorphism was found for the mitochondrial genome. This study points up a structuring of the species that fits with the distinction between the Criollo and Forastero populations. In contrast to all previous analyses, a higher level of polymorphism is found among the Criollo clones while the Forastero clones form quite a homogeneous group.