Assessment of genetic diversity on a sample of cocoa accessions resistant to witches' broom disease based on RAPD and pedigree data

Abstract

Genetic diversity in cocoa (Theobroma cacao L.) has been assessed based on morphological and molecular markers for germplasm management and breeding purposes. Pedigree data is available in cocoa but it has not been used for assessing genetic relatedness. The geneitic diversity of 30 clonal cocoa accessions resistant to witche´ broom disease, from the CEPEC series, were studied on the basis of RAPD data and pedigree information. Twenty of these accessions descend from the TSA-644 clone, originated from a cross between the Upper Amazon germplasm called Scavina-6, the main source of resistance to witches' broom disease, and IMC-67. The ten remaining clones come from different sources including Amazon and Trinitario germplasm. RAPD data was collected using 16 primers and pedigree information was obtained from the International Cocoa Germplasm Database. Genetic similarities, genetic distances and coefficient of parentage were calculated using available software. Relatively low genetic diversity was observed in this germplasm set, probably because of great genetic relatedness amongst accessions studied and the poor representation of the germplasm. The TSA-644 descendants were more diverse than the other accessions used in the study. This might be due to the origin of the TSA clone, which was derived from highly divergent genotypes. Association between genetic similarities based on RAPD data and coefficient of parentage, based on pedigree data, was very low, probably due to the homogeneity of the breeding stocks and poor pedigree information. These findings are useful to cocoa breeders in planning crosses for the development of hybrid and clonal cultivars.