Although many important crops originated in Amazonia, the general patterns of their evolutionary histories are still obscure. Currently a major global food crop, manioc originated in southwestern Amazonia and was dispersed throughout the lowland Neotropics before the European conquest. However, little is known about the origin of the bitter and sweet landraces, nor the routes by which these were dispersed in Brazil and beyond. We used a non-systematic Brazil-wide sample of 494 manioc landraces from 11 geographic regions, and ten nuclear microsatellite markers to analyze the genetic diversity of sweet and bitter manioc. Bayesian simulations highlighted the bitter–sweet divergence and also suggested the existence of two groups of sweet manioc (circum-Cerrado and general Brazil) and two groups of bitter manioc (upper Negro River and general Brazil), while the relationships among geographic regions were depicted with clustering analysis. Overall we suggest that: (1) manioc was initially domesticated to be sweet, was then dispersed from southwestern Amazonia into both the Amazon basin and the Cerrado; (2) that bitter manioc arose from the general Brazilian sweet manioc landraces, almost certainly in Amazonia, where bitter manioc became most important and was dispersed both throughout Amazonia and along the Brazilian coast, but especially to the upper Negro River, where it became most diverse. Our study adds insights to the knowledge about how native Amazonian crops have been managed across their history of domestication. © 2019, Springer Nature B.V.
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