Multiple Origins of Lima Bean Landraces in the Americas: Evidence from Chloroplast and Nuclear DNA Polymorphisms

Crop wild relatives that have experienced mul-tiple and independent domestication events provide an excellent model for understanding adaptation processes in crop populations and a fi rst and relevant aspect to investigate is the geographic origin of landraces. The aim of this research was to establish the origin of Meso-american and Andean Lima bean ( Phaseolus lunatus L.) landraces by analyzing chloroplast DNA and ITS polymorphisms in a sample of 59 wild and 50 landrace accessions. Accord-ing to seed size, genetic distance analyses, and haplotype networks, at least two indepen-dent domestication events are proposed. The fi rst one would have taken place in the Andes of southern Ecuador–northwestern Peru and would have given rise to the large-seeded land-races collectively known as the “Big Lima” cul-tivars. The second one would have taken place in central–western Mexico, more likely in the area to the north and northwest of the Isthmus of Tehuantepec. This event, along with post-domestication migrations of landraces in South America, would have given rise to the great vari-ety of small-seeded Mesoamerican landraces that exist today. We did not fi nd any evidence supporting the existence of two discrete groups within Mesoamerican landraces that might cor-respond to the previously proposed “Sieva” and “Potato” cultigroups. A severe reduction in genetic diversity because of domestication, known as the “founder effect”, was detected, which may have implications for the conserva-tion of genetic resources in this species.J.R. Motta-Aldana, M.L. Serrano-Serrano, J. Hernandez-Torres and G. Castillo-Villamizar, Escuela de Biologia, Facultad de Ciencias, Univ. Industrial de Santander-UIS, Cl27 Cra9, Bucaramanga, Colom-bia; D.G. Debouck, Genetic Resources Unit, International Center for Tropical Agriculture (CIAT), Km17 via Cali-Palmira, Colombia; M.I. Chacon S., Facultad de Agronomia, Universidad Nacional de Colom-bia, Cra30 Cl45, Bogota, Colombia. Received 6 Dec. 2009. *Corre-sponding author (michacons@unal.edu.co).