Résumé
Cacao (Theobroma cacao L.) was cultivated by the Mayas over two thousand years ago. The type of cacao cultivated by the Mayas constitutes what is called the morphogeographic group Criollo, also known as Theobroma cacao L. subsp. cacao. Criollo cacao was thought to originate in Central America and to have evolved parallely and independently from the cacao type originating from the Amazon basin. Cacao populations from the Amazon basin are included in the second morphogeographic group, called Forastero. The Forastero group consists mainly of Theobroma cacao L. subsp. sphaerocarpum. In order to better understand the origin and the genetic basis of the cacao type cultivated by the Mayas, a study was performed using RFLP and microsatellite markers. Samples of Criollo trees were collected from ancient Venezuelan, Colombian, Nicaraguan and Mexican plantations, from the Lacandón rainforest of Mexico (where wild Criollo trees have been reported), and from areas where, presumably, Mayan people cultivated cacao (States of Yucatan and Michoacan, México). In addition, Criollo trees from several germplasm collections in Venezuela, Costa Rica and Mexico were also studied. RFLP and microsatellite analyses revealed a high level of homozygosity and a significant molecular similarity between the Criollo samples from all the geographical origins (except between those from the germplasm collections), despite the contrasting morphological traits that differentiate them. Criollo from germplasm collections appeared generally to be more heterozygous and variable, perhaps due to partial introgressions of Forastero genes. The low genetic variability encountered among the Criollo varieties, suggests that the Criollo group probably originated from a few individuals and that man participated in the spread of these individuals in Central America. (Texte intégral)