Genetic relationships and genome selection signatures between soybean cultivars from Brazil and United States after decades of breeding.

Soybean is one of the most important crops worldwide. Brazil and the United States (US) are the world's two biggest producers of this legume. The increase of publicly available DNA sequencing data as well as high-density genotyping data of multiple soybean germplasms has made it possible to understand the genetic relationships and identify genomics regions that underwent selection pressure during soy domestication and breeding. In this study, we analyzed the genetic relationships between Brazilian (N = 235) and US soybean cultivars (N = 675) released in different decades and screened for genomic signatures between Brazilian and US cultivars. The population structure analysis demonstrated that the Brazilian germplasm has a narrower genetic base than the US germplasm. The US cultivars were grouped according to maturity groups, while Brazilian cultivars were separated according to decade of release. We found 73 SNPs that differentiate Brazilian and US soybean germplasm. Maturity-associated SNPs showed high allelic frequency differences between Brazilian and US accessions. Other important loci were identified separating cultivars released before and after 1996 in Brazil. Our data showed important genomic regions under selection during decades of soybean breeding in Brazil and the US that should be targeted to adapt lines from different origins in these countries.

Genetic Diversity and Selection Footprints in the Genome of Brazilian Soybean Cultivars.

Although Brazil is currently the largest soybean producer in the world, only a small number of studies have analyzed the genetic diversity of Brazilian soybean. These studies have shown the existence of a narrow genetic base. The objectives of this work were to analyze the population structure and genetic diversity, and to identify selection signatures in the genome of soybean germplasms from different companies in Brazil. A panel consisting of 343 soybean lines from Brazil, North America, and Asia was genotyped using genotyping by sequencing (GBS). Population structure was assessed by Bayesian and multivariate approaches. Genetic diversity was analyzed using metrics such as the fixation index, nucleotide diversity, genetic dissimilarity, and linkage disequilibrium. The software BayeScan was used to detect selection signatures between Brazilian and Asian accessions as well as among Brazilian germplasms. Region of origin, company of origin, and relative maturity group (RMG) all had a significant influence on population structure. Varieties belonging to the same company and especially to the same RMG exhibited a high level of genetic similarity. This result was exacerbated among early maturing accessions. Brazilian soybean showed significantly lower genetic diversity when compared to Asian accessions. This was expected, because the crop's region of origin is its main genetic diversity reserve. We identified 7 genomic regions under selection between the Brazilian and Asian accessions, and 27 among Brazilian varieties developed by different companies. Associated with these genomic regions, we found 96 quantitative trait loci (QTLs) for important soybean breeding traits such as flowering, maturity, plant architecture, productivity components, pathogen resistance, and seed composition. Some of the QTLs associated with the markers under selection have genes of great importance to soybean's regional adaptation. The results reported herein allowed to expand the knowledge about the organization of the genetic variability of the Brazilian soybean germplasm. Furthermore, it was possible to identify genomic regions under selection possibly associated with the adaptation of soybean to Brazilian environments.

Tolerance to aluminum toxicity by tropical leguminous plants used as cover crops

Leguminosas herbáceas são plantas de cobertura utilizadas como adubo verde que também atuam na recuperação de solos agrícolas. Devido aos benefícios econômicos e ambientais da adubação verde, tem aumentado consideravelmente a adoção desta técnica no Brasil. Entretanto, não há informações sobre estas espécies quanto à toxicidade de alumínio (Al). O presente estudo teve como objetivo avaliar 17 espécies de leguminosas quanto a tolerância ao alumínio. Também foram incluídas nos testes, três cultivares de soja e duas de milho. Houve uma grande diferença entre as espécies testadas, possibilitando de acordo com a metodologia empregada, a seguinte classificação: muito tolerantes (Mucuna nivea, M. deeringiana, M. aterrima Vigna unguiculata cv. BR 17 e Lablab purpureus cv. Rongai); tolerante (Cajanus cajan cv. IAPAR 43, Canavalia brasiliensis, Calopogonium mucunoides, Cajanus cajan cv. Fava larga, e Crotalaria paulina); moderadamente tolerante (Crotalaria ochroleuca, Canavalia ensiformis, Crotalaria spectabilis, e C. mucronata); sensível (Neonotonia wightii, Crotalaria breviflora e C. juncea cv.IAC-KR1). As três cultivares de soja foram classificadas em moderadamente tolerante (Biloxi) e tolerantes (IAC 13 e IAC 9).