The goal of DNA barcoding is to find a simple, cheap, and rapid DNA assay that can be converted to a readily accessible technical skill that bypasses the need to rely on highly trained taxonomic specialists for identifications of the world's biota. This is driven by a desire to open taxonomic identifications to all user groups and by the short supply of taxonomists that do not even exist in many groups. Although DNA barcoding is being rapidly accepted in the scientific literature and popular press, some scientists warn that we are being too hasty in wholeheartedly embracing this technique. Dr. David Spooner, a researcher with the USDA and an expert in the potato and tomato family (Solanaceae), offers just such a cautionary note against accepting this technique without closer examination in his recent article, "DNA Barcoding will Frequently Fail in Complicated Groups: An example in Wild Potatoes" in the June 2009 issue of the American Journal of Botany.
One of the critical issues surrounding the DNA barcoding debate is that using a section of DNA may not adequately distinguish among closely related species or complex groups. Moreover, in plants, there is still much debate over which gene sequence region should be used and its reliability. In animals, the 5' segment of mitochondrial cytochrome oxidase subunit I (COI) is relatively established as a barcoding marker, but Spooner highlights many groups where COI fails to distinguish species. The COI region fails completely for plants because it evolves at a slower rate in plants and has a much more variable sequence. The search for alternative barcoding regions in plants is especially problematic. Although several gene sequences have been proposed for plants, none of them serves as a universal barcode marker. Regions that have been proposed for plants include a section of the nuclear ribosomal DNA: the internal non-transcribed spacer region (ITS); and various plastid regions to includ
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American Journal of Botany