Upper Amazon Forastero cacao (Theobroma cacao L.) 1: An assessment of phenotypic relationships in the International Cocoa Genebank, Trinidad (original) (raw)

Upper Amazon Forastero (UAF) cacao clones account for approximately 60% of cacao cultivation globally, and are widely used in breeding. This study was undertaken at the International Cocoa Genebank, Trinidad to examine the phenotypic relationships among several UAF accession groups, viz., Iquitos Mixed Calabacillo (IMC), Morona (MO), Nanay (NA), Parinari (PA) and Scavina (SCA) and some of their known progenitors, POUND accessions using Cluster Analysis (CA) and Principal Component Analysis (PCA). Some of the IMC, NA and SCA clones clustered with their putative mother trees. The grouping of the IMC clones in a few almost homogeneous clusters suggested that this group was the least diverse phenotypically. More diversity was expressed within the POUND, MO, NA, PA, and SCA groups. The considerable phenotypic diversity in the SCA and MO groups, expressed for traits such as pod index, cotyledon weight and width and pod apex form, seems not to be explained by a single mother tree source for each group. Significant phenotypic diversity in this UAF germplasm sample, measured by the Shannon Weaver Diversity Index (values  0.5) and coefficients of variation (>10%), was observed for some of the traits studied including stamen filament pigmentation, pod apex form, pod index, cotyledon weight and style length. IMC 3 and 63 were among the most phenotypically distinct accessions based on the results of CA and PCA. These results, in conjunction with those from genetic diversity studies, should prove useful for future cacao breeding programmes and will facilitate the formulation of strategies to effectively manage cacao genetic resources -select core and working collections and plan future collections in the wild to increase the genetic diversity of cacao conserved ex situ.