Genetic characterization of cassava ( Manihot esculenta ) landraces in Brazil assessed with simple sequence repeats

Marcos V B M Siqueira,José G Pinto,Eduardo A Bressan,Jurema R Queiroz-Silva,Elizabeth Ann Veasey,Kayo J C Pereira,Aline Borges

doi:10.1590/s1415-47572009005000010

Abstract

Based on nine microsatellite loci, the aim of this study was to appraise the genetic diversity of 42 cassava (Manihot esculenta) landraces from selected regions in Brazil, and examine how this variety is distributed according to origin in several municipalities in the states of Minas Gerais, São Paulo, Mato Grosso do Sul, Amazonas and Mato Grosso. High diversity values were found among the five above-mentioned regions, with 3.3 alleles per locus on an average, a high percentage of polymorphic loci varying from 88.8% to 100%, an average of 0.265 for observed heterozygosity and 0.570 for gene diversity. Most genetic diversity was concentrated within the regions themselves (HS = 0.52). Cluster analysis and principal component based scatter plotting showed greater similarity among landraces from São Paulo, Mato Grosso do Sul and Amazonas, whereas those from Minas Gerais were clustered into a sub-group within this group. The plants from Mato Grosso, mostly collected in the municipality of General Carneiro, provided the highest differentiation. The migration of human populations is one among the possible reasons for this closer resemblance or greater disparity among plants from the various regions.

Highlights

Traditional or slash-and-burn farming is a system with characteristics related to the pre-colonial period, and which is preserved by both indigenous and other populations that employ techniques transmitted culturally by their ancestors (Faraldo et al, 2000)
A total of 42 landraces from the cassava germplasm bank of the Genetics Department of ESALQ/USP, Piracicaba, SP, were assessed according to their geographical origin, with the aim of obtaining a representative sample from different parts of Brazil. These plants were collected from homesteads undertaking traditional farming methods, in several municipalities in five regions of Brazil, and were classified into five groups, according to their place of origin: MG - municipality of Frutal, Minas Gerais State; SP municipalities of Eldorado, Cananéia and Ilha Comprida, in the Vale do Ribeira, São Paulo State; MS - municipalities of Sonora, Pedro Gomes, Rio Verde de Mato Grosso, Costa Rica, Cassilândia, Paranaíba and Inocência, Mato Grosso do Sul State; AM - municipalities of Uarini, Maraã and Alvarães, in the Mamirauá and Amanã Sustainable Development Reserves, Amazonas State; and MT - municipality of General Carneiro, Mato Grosso State (Figure 1; Table 1)
A total of 46 alleles were amplified with nine simple sequence repeats (SSR) loci analyzed in the 42 landraces, the number of alleles observed per locus varying from 3 to 6 alleles (Table 2)

Summary

Introduction

Traditional or slash-and-burn farming is a system with characteristics related to the pre-colonial period, and which is preserved by both indigenous and other populations that employ techniques transmitted culturally by their ancestors (Faraldo et al, 2000). The basic evolutionary unit of traditional farming, the “swidden field”, is where both in situ conservation of landraces from many species of economic importance and genetic amplification of diversity occur, with subsequent benefits to the farmer (Martins, 1994, 2001; Peroni and Martins, 2000; Sambatti et al, 2001). It is common to find numerous varieties in the same field (Elias et al, 2000) Some of these species have received attention by researchers through the focus on genetic characterization, for example sweet potato (Veasey et al., 2007, 2008), yam (Malapa et al, 2005), taro (Jianchu et al, 2001), maize (Louette et al, 1997), bananas (Creste et al, 2003), and most important of all, cassava (Sambatti et al, 2000; Mühlen et al, 2000; Faraldo et al, 2000; Peroni, 2007)

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