Phaseolus vulgaris is nodulated in northern Spain by Rhizobium leguminosarum strains harboring two nodC alleles present in American Rhizobium etli strains: biogeographical and evolutionary implications

Abstract

In this study a collection of rhizobial strains were isolated from effective nodules of Phaseolus vulgaris in a wide region of northern Spain, which is the major producer region of this legume in Spain. The analysis of their core genes, rrs, atpD, and recA, and the 16S-23S intergenic spacer showed that all isolates belong to the phylogenetic group of Rhizobium leguminosarum and some of them were identical to those of strains nodulating Vicia or Trifolium. None of the isolates was identified as Rhizobium etli; however, all of them carry the nodC alleles alpha and gamma harboured by American strains of this species. These alleles were also found in strains nodulating P. vulgaris in southern Spain identified as R. etli. These results suggest that R. etli was carried from America to Spain with common bean seeds, but that they could have found difficulties persisting in the soils of northern Spain, probably because of the climatic conditions. The symbiotic genes of this species could have been transferred, after the arrival of P. vulgaris, to strains of R. leguminosarum already present in northern Spanish soils.