Manioc is the most important food crop that originated in Amazonia. Many studies have increased our understanding of its evolutionary dynamics under cultivation. However, most of them focused on manioc cultivation in environments with low soil fertility, generally Oxisols. Recent ethnobotanical observations showed that bitter manioc also performs well in high fertility soils, such as Amazonian dark earths (ADE) and the floodplain. We used 10 microsatellite loci to investigate the genetic diversity and structure of bitter manioc varieties grown in different soil types in communities of smallholder farmers along the middle Madeira River in Central Amazonia. The genetic diversity of some sweet varieties and seedlings was also evaluated. Adult individuals showed higher levels of genetic diversity and smaller inbreeding coefficients (A R = 5.52, H O = 0.576, f = 0.086) than seedlings (A R = 4.39, H O = 0.421, f = 0.242). Bitter manioc varieties from the floodplain showed higher levels of genetic diversity (A R = 5.19, H O = 0.606) than those from ADE (A R = 4.45, H O = 0.538) and from Oxisols (A R = 4.15, H O = 0.559). The varieties grown in the floodplain were strongly differentiated from the varieties grown in Oxisols (F ST = 0.093) and ADE (F ST = 0.108), suggesting important genetic structuring among varieties grown in the floodplain and upland soils (ADE and Oxisols). This is the first time that genetic divergence of bitter manioc varieties in cultivation in different Amazonian soils in a small geographic area is reported. © 2012 Springer Science+Business Media B.V.
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