Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2003
Publication Date: 8/3/2003
Citation: Johnson, E.L., Saunders, J.A., Helling, C.S., Mischke, B.S., Emche, S.D. 2003. Identification of erythroxylum taxa by aflp dna analysis. Phytochemistry. 64:187-197.
Interpretive Summary: Coca, used collectively to describe the four cocaine-bearing species of Erythroxylum plants, is the target of major eradication efforts in three Andean producer nations. However, accurate identification of coca species/varieties by classical botanical keying is very difficult. In this research, the genetic fingerprinting method of AFLP (Amplified Fragment Length Polymorphism) was modified in order to establish relatedness among 132 known and unknown samples of coca leaf. The major accomplishments were that: (a) all types of coca were genetically distinguishable; (b) all 38 samples of coca from Colombia, collected by USDA during 1997-2001, appear to be unique variants of one species, E. coca var. ipadu; and (c) some geographic grouping of coca within Colombia is distinguishable. This research will be of interest broadly to scientists involved with plant identification, but especially to agencies dealing with trends in illicit coca and cocaine production and suppression.
Technical Abstract: Erythroxylum coca, indigenous to the Andean region of South America, is grown historically as a source of homeopathic medicine. However, in the last century, cultivation of E. coca var. coca and three closely-related taxa for the production of illicit cocaine has become a major global problem. Two subspecies, E. coca var. coca and E. coca var. ipadu, are almost indistinguishable phenotypically; a related cocaine-producing species also has two subspecies (E. novogranatense var. novogranatense and E. novogranatense var. truxillense) that are phenotypically similar, but morphologically distinguishable. The purpose of this research was to discover unique AFLP DNA patterns ("genetic fingerprinting") that characterize the four taxa and then, if successful, to evaluate this approach for positive identification of the various kinds of coca. Of 11 AFLP primers tested, a combination of five proved optimal in differentiating the four taxa as well as a non-cocaine-bearing species, E. aerolatum. This method of DNA fragment separation was more selective and faster, for coca identification, as compared with analyses based on flavonoid biochemical profiles. Using the 5-primer AFLP approach, 138 known and unknown coca leaf samples were evaluated. Of these, 38 were collected in 1997-2001 from illicit coca fields in Colombia, and all were genetically differentiated from coca originating in Peru and Bolivia. Based on the DNA profiling, we believe that the Colombian coca now represents a hybridization of E. coca var. ipadu. Geographical profiling within Colombia also seems feasible, suggesting movement patterns for the germplasm as new production areas are developed.