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

Abstract

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. Key words: Theobroma cacao L., farm accessions, morphological diversity, breeding.