Search

Background: Acid soils comprise up to 50% of the world's arable lands and in these areas aluminum (Al) toxicity impairs root growth, strongly limiting crop yield. Food security is thereby compromised in many developing countries located in tropical and subtropical regions worldwide. In sorghum, SbMATE, an Al-activated citrate transporter, underlies the AltSB locus on chromosome 3 and confers Al tolerance via Al-activated root citrate release. Methodology: Population structure was studied in 254 sorghum accessions representative of the diversity present in cultivated sorghums. Al tolerance was assessed as the degree of root growth inhibition in nutrient solution containing Al. A genetic analysis based on markers flanking AltSB and SbMATE expression was undertaken to assess a possible role for AltSB in Al tolerant accessions. In addition, the mode of gene action was estimated concerning the Al tolerance trait. Comparisons between models that include population structure were applied to assess the importance of each subpopulation to Al tolerance. Conclusion/Significance: Six subpopulations were revealed featuring specific racial and geographic origins. Al tolerance was found to be rather rare and present primarily in guinea and to lesser extent in caudatum subpopulations. AltSB was found to play a role in Al tolerance in most of the Al tolerant accessions. A striking variation was observed in the mode of gene action for the Al tolerance trait, which ranged from almost complete recessivity to near complete dominance, with a higher frequency of partially recessive sources of Al tolerance. A possible interpretation of our results concerning the origin and evolution of Al tolerance in cultivated sorghum is discussed. This study demonstrates the importance of deeply exploring the crop diversity reservoir both for a comprehensive view of the dynamics underlying the distribution and function of Al tolerance genes and to design efficient molecular breeding strategies aimed at

The toxicity caused by Aluminum (Al) is one of the most limiting factors for crop growth and development on acid soils. In sorghum, allelic variation at the AltSB locus accounts for nearly 80% of the phenotypic variation for the trait in some mapping populations, even though other loci controlling Al tolerance do exist. Our previous positional cloning effort led to the identification of a gene belonging to the multidrug and toxic compound extrusion (MATE) family that underlies the AltSB locus. Attempting to identify the molecular determinants of allelic effects at AltSB, we completely sequenced a 24.6kbp region defined by high resolution mapping of AltSB in the parents of a sorghum RIL population, SC283 (Al tolerant) and BR007 (Al sensitive). Six candidates regions containing polymorphisms were subsequently selected for association studies. These candidates regions were genotyped or sequenced in 254 sorghum accessions comprising our association panel. Association tests were performed using a mixed linear model that accounts for multiple levels of relatedness for appropriate Type I error control. Highly significant associations were detected for traits related to Al inhibition of root growth in nutrient solution. An important role in Al tolerance is possibly played by a polymorphism located in the second intron of the AltSB gene, which had a major contribution to an overall Al tolerance index created by principal component analysis. However, this polymorphism is in strong linkage disequilibrium with others in the region, which prevented us to definite the causative nature of the associated loci. Highly associated SNPs are being used to develop tag markers for marker-assisted selection, which can be used for allele mining in diverse sorghum germplasm. (Texte intégral)

Cette communication expose une trajectoire de 10 ans d'appui à l'agriculture familiale dans le Nordeste brésilien. Ce travail collectif fut l'objet d'un partenariat entre l'EMBRAPA-CPATSA et le CIRAD. La première partie du texte résume l'évolution du dispositif de recherche-développement en appui à l'agriculture familiale. La deuxième partie présente les résultats obtenus et plus précisement une analyse de la différenciation spatiale de l'agriculture familiale nordestine