ARS | Publication request: Characteristics of Rhizobia Nodulating Beans in the Central Region of Minnesota.

Submitted to: Canadian Journal Of Microbiology
Publication Acceptance Date: August 18, 2004
Publication Date: August 18, 2004
Citation: Van Berkum, P.B., Bernal, G.R., Tlusty, B., Esteves DE Jensen, C., Graham, P.H. 2004. Characteristics Of Rhizobia Nodulating Beans In The Central Region Of Minnesota. Canadian Journal Of Microbiology.

Interpretive Summary: Bean is an important grain legume that benefits from biological nitrogen fixation through a symbiosis with soil bacteria collectively known as rhizobia. In agriculture, the benefit is enhanced efficiency of crop production. Management of biological nitrogen fixation usually involves the inoculation of the appropriate bacterial cultures at the time of sowing. These bacterial cultures are available to the farmer as inoculants manufactured in industry. However, in Minnesota there has been a long history of bean cultivation on former prairie land without inoculation of the crop with the appropriate strains of rhizobia. Yet, the crop has always produced well. Therefore, the question to be answered was from where did the rhizobia originate, a prairie legume or were they transmitted into the region? From this study based on extensive characterization it was concluded that the rhizobia are related to those nodulating the prairie legume Dalea purpurea (violet prairie clover) and two bean species of Meso-American and Andean origin. Therefore, bean in Minnesota is nodulated both by indigenous rhizobia and those originated from South and Central America. This information will be useful to scientists and ecologists with interest in bacteria and rhizobia including nitrogen fixation in bean and/or prairie ecosystem improvement.

Technical Abstract: Until recently, beans (Phaseolus vulgaris L.) grown in Minnesota were rarely inoculated. Because of this we hypothesized that bean rhizobia collected in Minnesota would either share characteristics identifiable with R. etli of Mesoamerican or Andean origin, introduced into the region as seed-borne contaminants, or be indigenous rhizobia from prairie species such as Dalea spp. The latter organisms have been shown to nodulate and fix N2 with Phaseolus vulgaris. Rhizobia recovered from the Staples, Verndale and Park Rapids areas of Minnesota were grouped according to the results of BOXA1R-PCR fingerprint analysis into five groups, with only one of these having banding patterns similar to two of four R.etli reference strains. When representative isolates were subject to fatty acid methyl ester (FAME)- and 16S rRNA sequence-analysis the results obtained differed. 16S rRNA gene sequences of half of the organisms tested were most similar to R. leguminosarum. Rhizobia from Dalea spp, an important legume in the prairie ecosystem, did not play a significant role as the microsymbiont of beans in this area. This appears to be due to the longer time needed for them to initiate infection in Phaseolus vulgaris. Strains of R.tropici IIB, including UMR1899 proved tolerant to streptomycin and captan, commonly applied as seed treatments for beans. Local rhizobia appeared to have very limited tolerance to these compounds.