Abstract

Although manioc is well adapted to nutrient-poor Oxisols of Amazonia, ethnobotanical observations show that bitter manioc is also frequently cultivated in the highly fertile soils of the floodplains and Amazonian dark earths (ADE) along the middle Madeira River. Because different sets of varieties are grown in each soil type, and there are agronomic similarities between ADE and floodplain varieties, it was hypothesized that varieties grown in ADE and floodplain were more closely related to each other than either is to varieties grown in Oxisols. We tested this hypothesis evaluating the intra-varietal genetic diversity and the genetic relationships among manioc varieties commonly cultivated in Oxisols, ADE and floodplain soils. Genetic results did not agree with ethnobotanical expectation, since the relationships between varieties were variable and most individuals of varieties with the same vernacular name, but grown in ADE and floodplain, were distinct. Although the same vernacular name could not always be associated with genetic similarities, there is still a great amount of variation among the varieties. Many ecological and genetic processes may explain the high genetic diversity and differentiation found for bitter manioc varieties, but all contribute to the maintenance and amplification of genetic diversity within the manioc in Central Amazonia.

Highlights

  • Manioc (Manihot esculenta Crantz ssp. esculenta) was domesticated in southwestern Amazonia at least 7,000 years ago (Allem, 1994; Olsen and Schaal, 1999) and today is cultivated in all tropical countries (Lebot, 2009)

  • Manioc is well adapted to nutrient-poor Oxisols of Amazonia, ethnobotanical observations show that bitter manioc is frequently cultivated in the highly fertile soils of the floodplains and Amazonian dark earths (ADE) along the middle Madeira River

  • Because different sets of varieties are grown in each soil type, and there are agronomic similarities between ADE and floodplain varieties, it was hypothesized that varieties grown in ADE and floodplain were more closely related to each other than either is to varieties grown in Oxisols

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Summary

Introduction

Manioc (Manihot esculenta Crantz ssp. esculenta) was domesticated in southwestern Amazonia at least 7,000 years ago (Allem, 1994; Olsen and Schaal, 1999) and today is cultivated in all tropical countries (Lebot, 2009). Esculenta) was domesticated in southwestern Amazonia at least 7,000 years ago (Allem, 1994; Olsen and Schaal, 1999) and today is cultivated in all tropical countries (Lebot, 2009). It is grown for its tuberous starchy roots, which are the primary source of carbohydrates for more than 800 million people (Lebot, 2009). ADE are anthropogenic soils, located on upland plateaus, associated with Amerindian settlements from the

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