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Title: Geographic and genetic population differentiation of the Amazonian chocolate tree

item Motamayor, Juan
item Lachenaud, Philippe
item Wallace, Jay
item Loor, Gaston
item Kuhn, David
item Brown, James
item Schnell Ii, Raymond

Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2008
Publication Date: 4/22/2008
Citation: Motamayor, J.C., Lachenaud, P., Wallace, J., Loor, G., Kuhn, D.N., Brown, J.S., Schnell Ii, R.J. 2008. Geographic and genetic population differentiation of the Amazonian chocolate tree. PLoS One. Available: DOI: 10.1007/s12042-008-9011-4

Interpretive Summary: The classification for cacao germplasm has been confused because of poor management of collections and limited knowledge about the genetic diversity within the species Theobroma cacao L. This research reports a new classification and differentiation hypothesis based on population genetic analyses, by Bayesian and other statistical methods, of microsatellite data of a large sample of T. cacao L. individuals. Using 1241 individuals from many collecting expeditions and 100 microsatellite markers, ten genetic groups were identified. These groups were named according to the geographic location or traditional cultivars most represented in the group; Maranon, Curaray, Criollo, Iquitos, Nanay, Contamana, Amelonado, Parus, Nacional, and Guiana. This new classification reflects more accurately the genetic diversity now available for breeders, rather than the traditional classification as Criollo, Forastero or Trinitario. We propose that germplasm curators, geneticists, and breeders should use this new classification to conserve, manage and exploit cacao genetic resources.

Technical Abstract: Numerous collecting expeditions of Theobroma cacao L. germplasm hae been undertaken in Latin-America. However, this germplasm has not contributed to cacao improvement because its relationship to cultivated selections was poorly understood. Germplasm labeling errors have impeded breeding and confounded the interpretation of diversity analyses. Aiming to improving the understanding of the origin, classification, and population differentiation within the species, analyses using 106 microsatellite markers were performed on 1241 accessions covering a large geographic sampling. After discarding mislabeled samples, 10 genetic clusters, as opposed to the two genetic groups traditionaly recognized within T. cacao, were found by applying Bayesian statistics. Results provided new insights about genetic diversification within the Amazon basin and, lead to propose a new classification of the cacao germplasm that will enhance its management.