Leucaena leucocephala as a trap-host for rhizobium tropici strains from the Brazilian "cerrado" region.
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Using Leucaena leucocephala as a trap-host, 422 strains of rhizobia were isolated from the bean (Phaseolus vulgaris L.) rhizosphere in the Cerrado region of Brazil. Traditional bean-producing areas with no history of rhizobial inoculation were sampled. Colony DNA hybridizations with gene-specific probes were used to identify strains that could be grouped as R. tropici, type I strains (R. leguminosarum bv. phaseoli or R. etli), or as other Rhizobium species. The same typing procedure was applied to 61 isolates from a large collection of strains isolated from bean plants inoculated with the same soil samples. Rhizobium tropici was present at all sites. The population of rhizobia isolated from bean plants was more heterogeneous than rhizobial population isolated from Leucaena. More than 90% of Leucaena isolates could be typed as R. tropici. Strains typed as R. tropici hybridized with R. leguminosarum hup structural genes, but not with R. leguminosarum bv. phaseoli ORF3, and the majority of them had a relative efficiency above 0.75. All the Leucaena strains were found to effectively nodulate beans and most of them yielded higher shoot dry weight than R. tropici strain CIAT899.
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Rhizobium Leguminosarum, Genetic variance, Phaseolus vulgaris endornavirus, Hybridization