Selection of putative relic cacao (Theobroma cacao L.) genotypes in farmers' fields in Trinidad and Tobago
Keywords:cacao, relic genotypes, collections, principal component, analysis
AbstractTrinidad and Tobago is a repository of putative relic cacao genotypes, given its long history of cultivating cacao from the 1700s onwards. As part of a project conducted between 2009 and 2011, funded by the World Bank Development Market Place, World Bank Project TF 093747 (DM 2008), 106 putative, ancient cacao varieties were collected from farms throughout Trinidad and Tobago to be conserved and utilized to preserve traditional quality (flavour) attributes. The objective of this article is to provide information on agronomic and phenotypic traits of 94 of these 'relic' accessions collected in farmers' fields (FA). These are presumed to be relic Criollos or Trinitarios (selected pre-and post-1930s), and were selected over six cocoa production zones in Trinidad and Tobago. In addition, data for 31 regional Trinitario cacao accessions, which are conserved at the International Cocoa Genebank Trinidad (ICGT) were assessed. Morphological assessment of the selections was based on 22 phenotypic traits including characteristics of economic interest, viz. bean number (BN), individual dried bean weight (DBW), total wet bean weight (TWBW) and pod index (PI), which ranged from 26.4 to 58.0 (CV 16.3%); 0.6g to 2.12g (CV 22.6%); 42.5 to 228g (CV 24.2%) and 10 to 57 (CV 27.5%), respectively. Significant differences (p < 0.0001) were found among the production zones for BN and DBW only. Four zones had selections with significantly higher BN and all six had selections with superior TWBW relative to the ICGT clones studied. No association between cotyledon colour and leaf petiole hairiness was found, suggesting independent inheritance of these traits used for preliminary identification of 'Criollo-like' genotypes in the field. FAs from Tobago generally had selections with paler cotyledons, implying relatively more pronounced Criollo ancestry. Principal Component (PC) scores 1 and 2 accounted for 74.7% of the phenotypic variation expressed by the accessions studied in terms of five traits, based on Principal Component Analysis (PCA). PI and TWBW were major contributors to PC 1, while for PC 2, the major contributors were BN and DBW. The results of PCA and cluster analyses suggest that a phenotypically diverse and unique selection of genotypes was collected from the farmers' fields, relative to studied ICGT types, several of which displayed 'Criollo-like' and Trinitario characteristics (large, plump seeds/beans with pale cotyledons) and favourable yield potential. These can be utilized to enhance the genepool at the ICGT, for breeding to introgress favourable Trinitario genes into national recurrent breeding programmes and for commercial cultivation.