title: Site-specific distribution and competitive ability of indigenous bean-nodulating rhizobia isolated from organic fields in Minnesota.
abstract: Organic dry bean production systems have received increasing interest in many regions of the US, including Minnesota. Thus, improving biological N2 fixation would be highly beneficial for organic crop production. To date, only limited work has been done to select efficient N2-fixing rhizobia for organic dry bean production. In this study, soil samples from 25 organic fields in Minnesota, with a previous cropping history of dry beans, soybeans or both, were collected during May to July 2012. Genetic diversity of indigenous dry bean-rhizobia (511 isolates) was determined by using horizontal, fluorophore-enhanced, repetitive, extragenic, and palindromic-PCR (HFERP) DNA fingerprinting and isolates were classified as belonging to 58 different genotypes. The more abundant rhizobia isolated from bean nodules comprised 35.6% of the population. None of the isolates were identical to commonly-used commercial strains used in the U.S., including Rhizobium tropici CIAT899. Seventeen predominant genotypes were shown to represent two main species, Rhizobium leguminosarum bv. phaseoli (67.1%) and Rhizobium etli (30.2%). One of the indigenous strains, orgK9, displayed efficient N2-fixation and competitive ability relative to the commercial strains tested. The lack of large numbers of indigenous dry bean-rhizobia at most study sites will be useful to avoid competition problems between inoculant strains and indigenous rhizobia. This will allow inoculation with highly effective N2-fixing rhizobia, thus resulting in improved crop productivity. Our results highlight the existence of site-specific rhizobial genotypes in different organic fields and identify strains that may prove useful as novel inoculants for organic dry bean production systems.
authors.affiliation: Department of Soil, Water, & Climate, and BioTechnology Institute, University of Minnesota, St. Paul, MN 55108, USA.
authors.forename: Manoosak
authors.initials: M
authors.lastname: Wongphatcharachai
authors.affiliation: Department of Soil, Water, & Climate, and BioTechnology Institute, University of Minnesota, St. Paul, MN 55108, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.affiliation: Department of Soil, Water, & Climate, and BioTechnology Institute, University of Minnesota, St. Paul, MN 55108, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Staley
authors.affiliation: Department of Soil, Water, & Climate, and BioTechnology Institute, University of Minnesota, St. Paul, MN 55108, USA.
authors.forename: Chan Lan
authors.initials: CL
authors.lastname: Chun
authors.affiliation: Department of Soil, Water, & Climate, and BioTechnology Institute, University of Minnesota, St. Paul, MN 55108, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Ferguson
authors.affiliation: Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108, USA.
authors.forename: Kristine M
authors.initials: KM
authors.lastname: Moncada
authors.affiliation: Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108, USA.
authors.forename: Craig C
authors.initials: CC
authors.lastname: Sheaffer
authors.affiliation: Department of Soil, Water, & Climate, and BioTechnology Institute, University of Minnesota, St. Paul, MN 55108, USA. Electronic address: sadowsky@umn.edu.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sadowsky
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics*; D014644:Genetic Variation / Q000235:genetics; D009586:Nitrogen Fixation; D058871:Organic Agriculture; D027805:Phaseolus / Q000382:microbiology*; D012231:Rhizobium / Q000235:genetics*; D012988:Soil Microbiology
chemical_list: D004269:DNA, Bacterial
keywords: Dry beans; Genetic diversity; N(2)-Fixation efficiency; Organic farms; Phaseolus vulgaris; Rhizobia