Genetic diversity in cocoa germplasm of southern Cameroon revealed by simple sequences repeat (SSRS) markers

The range of polymorphism of about 194 cocoa accessions collected in farms in Southern Cameroon during field surveys and 71 Trinitario and Upper Amazon clones available in genebanks on-station wasassessed using 13 SSR markers. The gene diversity, genetic differentiation and genetic similarities were analysed for the different populations. In total, 282 alleles were detected within all the populations studied. The farm accessions were strongly differentiated based on their geographical origin, with accessions coming from the East province clustering together with local Trinitario accessions from the genebank. Accessions from the Centre-South provinces clustered with Amazon and hybrid accessions, suggesting more uptake of seed garden materials in farms in these provinces. The genetic diversity parameters indicate that the farmers’ planting material is not highly diverse, and is genetically close to parental genotypes available in genebanks. However, some promising Upper Amazon clones (T-clones) that have also been used as parents of released hybrid varieties were genetically distant from the accessions. This result suggests that the progenies of these parents have so far been poorly used in the cocoa farms surveyed. The consequences of these findings for cocoa breeding in Cameroon are discusse

Phenotypic diversity of cacao (Theobroma cacao L.) on farms and in the gene bank in Cameroon

A survey was undertaken in the 2 major cocoa producing areas (Southern and Western) of Cameroon to study the morphological diversity existing in cacao farms in relation to genetic diversity in gene bank accessions. A total of 300 farm accessions (FA) were selected in the field which were compared to 77 gene bank accessions distributed into 4 groups (AGs) according to their origin. The 17 quantitative and qualitative descriptors used in this study were related to leaf (flush colour), flower (ligule colour), pod (weight, length, width, apex form, shape, rugosity, colour, husk hardness, basal constriction and pod index) and seed (number, length, width, dry weight and colour) characters. For the qualitative characters evaluated, considerable morphological variation was observed using the Shannon Weaver diversity index (SWDI) within FA and gene bank accessions. Among the FA, a differentiation between southern and western regions was only possible when using quantitative pod traits. Mean quantitative traits values of FA were not too different than those of most gene bank AGs, except for a few traits of agronomical interest (seed weight and pod index). No significant variation was observed for seed traits in all FA groups (southern/western). The morphological structure (quantitative traits) showed spatial differentiation between western and southern FA and a closer relationship between gene bank and some farm accessions. Furthermore, a molecular study done earlier using microsatellite profiles of the same FA did not show any genetic difference between FA of both regions, suggesting that the agro-morphological performance of FA is rather due to non-genetic factors. In contrast, microsatellites have shown that most of the gene bank accessions were genetically distant from the FA, suggesting the low intake of some breeders' genotypes to farmers' fields. The level of diversity found in farmers' germplasm could enhance the gene bank and current breeding programs

Gamma-irradiation of cacao (Theobroma cacao L.) pollen: Effect on pollen grain viability, germination and mitosis and on fruit set

International audienc

Participatory cocoa (Theobroma cacao) selection in Cameroon: Phytophthora pod rot resistant accessions identified in farmers fields

As part of a participatory selection programme, promising individual trees were selected in 2004 in cocoa farms of southern and western Cameroon regions for yield and for low incidence of Phytophthora pod rot (Ppr) caused by Phytophthora megakarya. The aim of this study was to compare the levels of resistance to Ppr between farm accessions (FA), introduced and local genebank accessions (GA). In total, 234 FA were grafted in the nursery together with 22 introduced GA and 73 local GA, and tested for resistance to P. megakarya by leaf disc inoculations. The introduced GA, that were reported as resistant to Ppr in other countries, proved to be more resistant than the selected FA and unselected FA and also more resistant than the 3 control clones for Ppr resistance used in the study. However, approximately 10% of the FA were as resistant as the average of the introduced GA, showing the potential of selection for resistance to Ppr in farmers’ fields. The average level of resistance of the FA was relatively higher than that of the local GA. The FA selected for yield and low Ppr incidence in the field were more resistant in the leaf disc test than the unselected FA. The use of FA and of farmers’ knowledge in the participatory selection process is valuable in obtaining Ppr-resistant cultivars

Genetic diversity in cocoa germplasm of southern Cameroon revealed by simple sequences repeat (SSRS) markers

The range of polymorphism of about 194 cocoa accessions collected in farms in Southern Cameroon during field surveys and 71 Trinitario and Upper Amazon clones available in genebanks on-station was assessed using 13 SSR markers. The gene diversity, genetic differentiation and genetic similarities were analysed for the different populations. In total, 282 alleles were detected within all the populations studied. The farm accessions were strongly differentiated based on their geographical origin, with accessions coming from the East province clustering together with local Trinitario accessions from the genebank. Accessions from the Centre-South provinces clustered with Amazon and hybrid accessions, suggesting more uptake of seed garden materials in farms in these provinces. The genetic diversity parameters indicate that the farmers’ planting material is not highly diverse, and is genetically close to parental genotypes available in genebanks. However, some promising Upper Amazon clones (T-clones) that have also been used as parents of released hybrid varieties were genetically distant from the accessions. This result suggests that the progenies of these parents have so far been poorly used in the cocoa farms surveyed. The consequences of these findings for cocoa breeding in Cameroon are discussed