Estrutura de população e mapeamento associativo para tolerância ao alumínio em regiões candidatas do loco AltSB de sorgo

• Autor(a) principal: Caniato, Fernanda Fátima
• Data de Publicação: 2009
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1401
• topic: Sorgo - Melhoramento genético; Genética de populações; Sorgo - Efeito do alumínio; Sorghum - Breeding; Population genetics; Sorghum - Effect of aluminum; CNPQ::CIENCIAS BIOLOGICAS::GENETICA::GENETICA VEGETAL

Aluminum (Al) toxicity is one of the most limiting factors for crop growth and development on acid soils. The frequency of Al tolerance accessions in sorghum is low, ranging from 6 to 8%, and allelic variation at the AltSB locus accounts for up to 80% of the phenotypic variation of the trait in some mapping populations, even though the presence of other loci controlling the tolerance has been considered. In this context, identifying patterns underlying the distribution of highly Al tolerant accessions in the context of the species genetic diversity as well identifying polymorphisms associated with allelic variation at the AltSB locus are the goals of this work. Population structure analysis based on 38 SSR markers indicated that the 254 sorghum accessions were organized into six subpopulations and the analysis of aluminum tolerance in this population showed strong evidence that Al tolerance is related to racial differentiation, since the tolerant accessions were detected at higher frequency in subpopulations belonging to the guinea race. With candidate polymorphisms within the 24.6kpb region where the AltSB gene is located, pairwise estimates of linkage disequilibrium were obtained and association mapping was performed using a linear mixed model for appropriate correction of Type I Error. Linkage disequilibrium in the target region decayed to values close to zero within 5000pb, which prevented us to isolate the individual contributions of causative polymorphisms on Al tolerance. However, polymorphisms highly associated with different phenotypic indices used to assess Al tolerance were detected along the sampled region. Emphasis was given to polymorphisms located in the second intron of the AltSB gene, particularly that located at the 6083pb coordinate, which had the greatest contribution to an overall tolerance index represented by the first principal component (PC1), and to an index that reflects induction of root growth upon Al exposure (b index), explaining 10.8 and 13.5% of variation for these traits, respectively. This locus discriminates 8 of the 14 accessions that are highly tolerant to aluminum and occurs at a low frequency in this panel (10%). These features make it a promising locus for marker-assisted selection, and particularly in combination with other loci, can be used to increase the probability of sampling tolerant accessions in widely diverse panels as core collections or breeding populations (i.e. allele mining). The current dataset provides support to future work aimed at revealing the functional structure of the AltSB locus regarding the contribution of polymorphisms in the Al tolerance response, and is also useful to the development of specific markers to guide the identification, selection and pyramiding of new sources of Al tolerance in sorghum.