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Figure 1. Structure among all accessions as revealed by principal component analysis (PCA) on the among open pollinated varieties variance–covariance matrix of allele frequencies (data from Dubreuil et al., 2006). Axis 1 can be interpreted as the opposition between Northern Flint and tropical materials. Axis 2 can be interpreted as the opposition between the non-Northern Flint origins of northern American and European materials, respectively. Northern American populations were identified according to racial classification (ASW, American southwestern; ASD, American southern Dent; ACB, American Corn Belt; ANF, American Northern Flint). Other American origins were identified according to the country of origin: Arg, Argentina; Bol, Bolivia; Chl, Chili; Cos, Costa Rica; Cub, Cuba; Dom, Dominican Republic; Ecu, Ecuador; Gua, Guatemala; Mex, Mexico; Pan, Panama; Per, Peru; Uru, Uruguay; Ven, Venezuela; Win, West Indies. European origins were identified according to the country or region of origin (Als, Alsace; Bul, Bulgaria; Cze, former Czechoslovakia; Fra, central France; Gal, Galicia; Ger, Germany; Ita, Italy; Pol, Poland; Pyr, Pyrenean; SpS, southern Spain; Ukr, Ukraine; Yug, former Yugoslavia).
