title: Predominant populations of indigenous soybean-nodulating Bradyrhizobium japonicum strains obtained from organic farming systems in Minnesota.
abstract: OBJECTIVE
  Bradyrhizobium from organic fields in Minnesota were isolated and genotyped to assess diversity of soybean-bradyrhizobia in organic farming systems that can be used to improve soybean productivity.
  
  
  RESULTS
  Soil samples were collected from 25 organic fields in Minnesota during May to July 2012. Soybean (cv. Lambert) was used as a host to trap indigenous bradyrhizobia in each sample. Genetic diversity of Bradyrhizobium strains (n=733) was determined using the horizontal, fluorophore-enhanced, repetitive extragenic palindromic-PCR (HFERP) DNA fingerprinting technique and the soybean-bradyrhizobia were classified into 79 different genotypes. Of these, 15 dominant genotypes were found and were highly similar (>92% fingerprint similarity) to serotypes USDA 127 (40.4%), USDA 4 (31.8%) and USDA 123 (15.5%), which were the three main populations of soybean-bradyrhizobia in organic fields.
  
  
  CONCLUSIONS
  Bradyrhizobium japonicum serogroup USDA 4 strains were found to make up a previously unrecognized, predominant rhizobial population in the organic farming soils examined. The relative abundance of strain USDA 4 was negatively correlated with that of USDA 127 and this relationship may be influenced by the levels of NO3 -N and other soil edaphic factors.
  
  
  CONCLUSIONS
  The local community of bradyrhizobia can be affected by applying inoculant bacteria to organic fields. Based on these results, soybean production in organic farms may be improved by displacing strains similar to USDA 4 with those better at nitrogen fixation and competitive ability than indigenous strains.
authors: Department of Soil, Water and Climate, BioTechnology Institute, University of Minnesota, St. Paul, MN, USA.
authors: M
authors: M
authors: Wongphatcharachai
authors: C
authors: C
authors: Staley
authors: P
authors: P
authors: Wang
authors: K M
authors: KM
authors: Moncada
authors: C C
authors: CC
authors: Sheaffer
authors: M J
authors: MJ
authors: Sadowsky
mesh_terms: D020369:Bradyrhizobium / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D014644:Genetic Variation; D005838:Genotype; D008910:Minnesota; D009586:Nitrogen Fixation; D058871:Organic Agriculture; D016133:Polymerase Chain Reaction; D053204:Root Nodules, Plant / Q000382:microbiology*; D012988:Soil Microbiology; D013025:Glycine max / Q000254:growth & development / Q000382:microbiology*; D013559:Symbiosis
keywords: Bradyrhizobium japnicum; genotyping; indigenous population; organic farms; serotyping; soybean-bradyrhizobia