Search Results (3)

Yuca (Manihot esculenta esculenta; cassava, manioc) is a native Amazonian crop represented by myriad landraces. To investigate human influences on its diversification, we conducted field observations and analyzed 13 short tandem repeat (STR) loci in 43 landraces in the Peruvian Amazon. We found a different multilocus genotype (MLG) in every landrace. However, tests for Hardy–Weinberg equilibrium found a deficit of heterozygosity at every locus (p < 0.001 for 12 of 13 loci). Further, the fraction of genetic variance due to landrace differences was greater than expected (38.84%; p = 0.001). This suggested that landrace hybridization is restricted, a finding consistent with our field observations. However, we found an excess of within-landrace heterozygosity (p < 0.001) in 39 of 43 landraces, suggesting they originated through hybridization. Mantel tests identified associations between genetic and geographic distances (p < 0.001), but their correlation coefficients were low (Mantel’s r < 0.21). In addition, AMOVA analyses revealed that differences between landraces collected from five sampled rivers accounted for just 3.05% of observed genetic variance (p < 0.001). Neighbor joining and principal components analyses also revealed little evidence of differentiation between rivers. Finally, in a comparison with a secondary sample, we found that the closest relative of 27 of 28 specimens had a landrace name different from their own, suggesting that traditional nomenclature is a poor indicator of genetic relatedness. Full article

Manioc is an important root crop in the tropics and the most important staple food in the Amazon. Manioc is diverse but its diversity has not yet been clearly associated with environmental or social factors. Our study evaluates how variation in edaphic environments and in social factors influences manioc diversity among five ethnic groups of the Amazon region of Colombia. Inventories of landraces, genetic analysis of manioc diversity, visits to farmers’ swiddens and interviews with farmers were carried out during two years of field work. Morphotypic and genotypic diversity of manioc were large. The different ethnic groups of our study cultivate different sweet and bitter manioc landraces which they select and maintain in accordance with their ancestral rules and norms. Differences in available environments among indigenous communities (such as the presence of different soils) did not markedly affect manioc morphotypic or genotypic diversity, while social factors considerably influenced observed manioc diversity. Manioc diversity was explained by two parallel processes of manioc diversification: volunteer seedling selection and manioc seed exchange. We argue that, for a full understanding of manioc diversity, indigenous knowledge, as well as morphological and genetic variation should be taken into account. Full article

While bitter manioc has been one of the most important staple crops in the central Amazon for thousands of years, there have been few studies of its cultivation in the fertile whitewater landscapes of this region. Anthropological research on bitter manioc cultivation in the Amazon has focused almost exclusively on long-fallow shifting cultivation in marginal upland areas of low soil fertility. This has contributed to the persistence of the oversimplified notion that because bitter manioc is well adapted to infertile upland soils; it cannot yield well in alluvial and/or fertile soils. I hypothesized that bitter manioc cultivation would be well adapted to the fertile soils of the whitewater landscapes of the central Amazon because of the centrality of this crop to subsistence in this region. In this article, I examine one such whitewater landscape, the middle Madeira River, Amazonas, Brazil, where smallholders cultivate bitter manioc on fertile Amazonian Dark Earths (ADE) and floodplain soils, and on infertile Oxisols and Ultisols. In this region, cultivation on fertile soils tends to be short-cycled, characterised by short fallowing (0–6 years) and shorter cropping periods (5–12 months) with a predominance of low starch fast maturing “weak” landraces. By contrast, cultivation on infertile soils is normally long-cycled, characterised by longer fallows (>10 years) and longer cropping periods (1–3 years) with a predominance of high starch slow maturing “strong” landraces. This diversity in bitter manioc cultivation systems (landraces, fallow periods, soils) demonstrates that Amazonian farmers have adapted bitter manioc cultivation to the specific characteristics of the landscapes that they inhabit. I conclude that contrary to earlier claims, there are no ecological limitations on growing bitter manioc in fertile soils, and therefore the cultivation of this crop in floodplain and ADE soils would have been possible in the pre-Columbian period. Full article