RESUMO
There are two major centres of genetic diversification of common bean (Phaseolus vilgaris L.), the Mesoamerican and the Andean, and the legume is capable of establishing nitrogen-fixing symbioses with several rhizobia; Rhizobium etli seems to be the dominant species in both centres. Another genetic pool of common bean, in Peru and Ecuador, is receiving increasing attention, and studies of microsymbionts from the region can help to increase our knowledge about coevolution of this symbiosis. We have previously reported several putative new lineages from this region and here present data indicating that strains belonging to one of them, PEL4, represent a novel species. Based on 16S rRNA gene sequence phylogeny, PEL4 strains are positioned in the Rhizobium phaseoli/R. etli/Rhizobium leguminosarum clade, but show unique properties in several morphological, physiological and biochemical analyses, as well as in BOX-PCR profiles ( < 75% similarity with related species). PEL4 strains also differed from related species based on multilocus sequence analysis of three housekeeping genes (glnII, gyrB and recA). Nucleotide identities of the three concatenated genes between PEL4 strains and related species ranged from 91.8 to 94.2%, being highest with Rhizobium fabae. DNA-DNA hybridization ( < 47% DNA relatedness) and average nucleotide identity values of the whole genomes ( < 90.2%) also supported the novel species status. The PEL4 strains were effective in nodulating and fixing N2 with common beans. The data supported the view that PEL4 strains represent a novel species, Rhizobium ecuadorense sp. nov. The type strain is CNPSo 671(T) ( = UMR 1450(T) = PIMAMPIRS I 5(T) = LMG 27578(T)).
Assuntos
Rhizobium , DNA Bacteriano/genética , Equador , Ácidos Graxos/química , Dados de Sequência Molecular , Tipagem de Sequências Multilocus , Hibridização de Ácido Nucleico/genética , Peru , Phaseolus , Filogenia , RNA Ribossômico 16S/genética , Rhizobium/classificação , Análise de Sequência de DNA , Simbiose/genéticaRESUMO
Biological nitrogen fixation (BNF) has global economic and environmental importance, but has often not been considered in soybean [Glycine max (L.) Merrill] breeding programs. Knowing the genetic diversity and structure of a population within a germoplasm represent a key step for breeding programs. This study aimed at determining the structure of the population and diversity of soybean with regard to BNF and protein content in grain. In total, 191 accessions were evaluated, including 171 commercial soybean cultivars, developed and released by public institutions and private companies in Brazil, and 20 ancestral lines. The genotypes were chosen to represent four genetic groups: 128 Brazilian public genotypes, 20 exotic, and 43 genotypes from private companies. Soybeans were genotyped with 22 SSR markers, previously described as associated with BNF and protein content. Genetic diversity was evaluated using the DARwin 5.0 software. Population structure was inferred by principal component analysis and by the STRUCTURE software. The accessions were distributed in two groups: one clustering approximately 50 % of the accessions, from Brazilian public and private companies; the other one clustering 45 % of the accessions, including Brazilian, exotic and private germoplasms. Some accessions (5 %) were not grouped in any cluster. Principal component analysis explained 29 % of the total variance and there was a tendency to cluster the accessions into two groups. Similar results were obtained with the STRUCTURE, clearly showing two subpopulations. There is variability for BNF and protein content amongst both modern germoplasms cultivated in Brazil and ancestral lines. This variability could be better explored in soybean breeding programs to improve these traits.
Assuntos
Fixação de Nitrogênio , Melhoramento Vegetal , Glycine max/genéticaRESUMO
Biological nitrogen fixation (BNF) has global economic and environmental importance, but has often not been considered in soybean [Glycine max (L.) Merrill] breeding programs. Knowing the genetic diversity and structure of a population within a germoplasm represent a key step for breeding programs. This study aimed at determining the structure of the population and diversity of soybean with regard to BNF and protein content in grain. In total, 191 accessions were evaluated, including 171 commercial soybean cultivars, developed and released by public institutions and private companies in Brazil, and 20 ancestral lines. The genotypes were chosen to represent four genetic groups: 128 Brazilian public genotypes, 20 exotic, and 43 genotypes from private companies. Soybeans were genotyped with 22 SSR markers, previously described as associated with BNF and protein content. Genetic diversity was evaluated using the DARwin 5.0 software. Population structure was inferred by principal component analysis and by the STRUCTURE software. The accessions were distributed in two groups: one clustering approximately 50 % of the accessions, from Brazilian public and private companies; the other one clustering 45 % of the accessions, including Brazilian, exotic and private germoplasms. Some accessions (5 %) were not grouped in any cluster. Principal component analysis explained 29 % of the total variance and there was a tendency to cluster the accessions into two groups. Similar results were obtained with the STRUCTURE, clearly showing two subpopulations. There is variability for BNF and protein content amongst both modern germoplasms cultivated in Brazil and ancestral lines. This variability could be better explored in soybean breeding programs to improve these traits.(AU)