Submitted to: Tropical Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 20, 2011
Publication Date: May 16, 2011
Citation: Emche, S.D., Zhang, D., Islam, M.B., Bailey, B.A., Meinhardt, L.W. 2011. AFLP Phylogeny of 36 Erythroxylum species- genetic relationships among Erythroxylum species inferred by AFLP analysis. Tropical Plant Biology. 4(2):126-133. Interpretive Summary: Cocaine is an illicit narcotic alkaloid that is produced in plants in the genus Erythroxylum. There are many wild species of Erythroxylum and we don’t know how they are related to each other genetically, geographically or taxonomically. We analyzed the DNA of two cocaine producing species (that are grown for illicit markets) and 33 other wild species to determine how they are related to each other. We found all of the Erythroxylum species separated into three main groups that corresponded to their geographical origin. We also found that the cocaine producing Erythroxylum species are more closely related to each other than to any other species. This is the largest genetic analysis of Erythroxylum. The analysis of these species will provide new information to researchers and government agencies to assist and improve control measures of illicit coca cultivation. In addition this information will improve our understanding of this plant and it’s worldwide distribution.
Technical Abstract: The plant genus Erythroxylum is known for four cultivated taxa, Erythroxylum coca var. coca (Ecc), Erythroxylum coca var. ipadu (Eci), Erythroxylum novogranatense var. novogranatense (Enn) and Erythroxylum novogranatense var. truxillense (Ent) that are cultivated primarily for the illicit extraction and processing of cocaine. Despite their economic and medical importance, the evolutionary history of the cultivated species and their closest non-cultivated relatives remains unknown and untested in a modern phylogenetic framework. The aims of this study were to (a) to investigate the relationship among the cultivated taxa and their non-cultivated relatives, and (b) to test the hypothesis of linear progression of the cultivated taxa (Ecc'Ent'Enn) versus the second hypothesis that Ec and En are sister species. Phylogenetic analysis based on 886 AFLP polymorphic fragments was used to compare the relationships among the cultivated taxa and their non-cultivated relatives for 35 Erythroxylum species (132 accessions) spanning the geographic distribution of the genus. Multivariate ordination analysis was used to evaluate the relationship between cultivated and non cultivated taxa from the tropical Americas. A Maximum Parsimony tree constructed for the 35 Erythroxylum species revealed three major clades that represent Africa, Asia-Pacific and the New World species. A small cluster of non-cultivated species was revealed as the most closely related to the cultivated Erythroxylum species. In addition, Ec and En formed distinct, parallel subclades. Our results support the hypothesis that the cultivated species are more closely related to each other than to any other species of Erythroxylum but refute the hypothesis that En descended from Ec. Instead our data suggest an independent, non-linear evolutionary relationship between Ec and En.