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Title: Dinâmica evolutiva de mandioca (manihot esculenta crantz) em três tipos de solo manejados por caboclos na região do médio Rio Madeira, Amazonas
Authors: Pereira, Alessandro Alves
metadata.dc.contributor.advisor: Clement, Charles Roland
Keywords: Mandioca
Diversidade genética.
Issue Date: 9-Mar-2011
Publisher: Instituto Nacional de Pesquisa da Amazônia - INPA
metadata.dc.publisher.program: Genética, Conservação e Biologia Evolutiva - GCBEv
metadata.dc.description.resumo: Manioc (Manihot esculenta Crantz) is the most important food crop worldwide that originated in Amazonia. Bitter manioc varieties are one of the most important food staples for traditional peoples in Central Amazonia, and a growing body of studies has increased our understanding of the evolutionary dynamics of the crop under traditional cultivation. However, most of these studies have been undertaken in single plots or in communities with access to a single soil type, and, in the case of Amazonia, generally Oxisols and Ultisols in non-flooded upland plateaus on the terra firme, despite the observations that bitter manioc cultivation is also practiced in highly fertile soils. Recently, ethnobotanical observations along middle Madeira River showed that numerous communities of smallholder farmers grow bitter manioc in the highly fertile soils of the floodplain and Amazonia dark earths (ADE), and in the clayey nutrient-poor Oxisols. It was observed that, in this region, farmers manage distinct sets of varieties for each soil type, and those varieties grown in the floodplain and ADE have similar characteristics. Such observations raised the hypotheses that communities in which farmers grow manioc in different soils maintain higher genetic diversity than communities in which manioc is grown on fewer soil types, and that the genetic structure of varieties would be related to soil types, with special emphasis on the relationship of varieties grown in the floodplain with those grown in ADE. To test these hypotheses, this study evaluated the genetic diversity, based on 10 microsatellite markers, of bitter manioc varieties traditionally cultivated in different soil types (namely ADE, Oxisols and floodplain) along the middle Madeira River region. Varieties were sampled in two distinct schemes to evaluate the distribution of genetic diversity on a local scale, as well as intra-varietal genetic diversity. For the first scheme, it was observed that floodplain varieties had greater genetic diversity (Ā= 5.2; HO= 0.606) than varieties grown on ADE (Ā= 4.5; HO= 0.538) and on Oxisols (Ā= 4.2; HO= 0.559). Floodplain varieties were also strongly differentiated from the varieties grown on ADE (FST = 0.108) and Oxisols (FST = 0.093), while these latter two soils were less differentiated (FST = 0.016). For the second scheme, high intra-varietal genetic diversity was observed, along with significant differentiation among varieties, with a tendency for varieties having equivalent names, but grown on ADE and floodplain, to be genetically differentiated. Additionally, gene flow was detected among some of the varieties. When taken together, the results of these two sampling schemes reveal that along the middle Madeira River the traditional farmers maintain high levels of genetic diversity within and among the bitter manioc varieties grown in different soil types. Higher levels of genetic diversity are not necessarily found in the communities in which farmers plant bitter manioc on more than one soil type: higher genetic diversity was observed for communities located in the floodplain. The hypothesis of closer relationships among varieties according to the soil types in which they are grown is partly true, since the varieties are genetically structured among different soil types, but, contrary to expectations, there seems to be an important genetic differentiation between varieties grown in the floodplain and varieties grown in upland soils (ADE and Oxisols). In spite of such differentiation, it was demonstrated that some varieties collaborate to the genetic diversity found within others, irrespective of whether they are from the same soil type or not. This study adds a new component to the discussion on manioc evolutionary dynamics, since it is the first time that differentiation of manioc varieties among environments of cultivation in Amazonia is examined with molecular data.
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