Phylogeography and rhizobia-legume genotypic interactions in common bean (Phaseolus vulgarisL.) and chickpea (Cicer arietinumL.) in Ethiopia

Abstract

Rhizobia are soil borne bacteria that form symbioses with legumes and fix atmospheric nitrogen. The nitrogen fixation potential of the symbionts depends on several factors such as the host and rhizobia types and environmental factors that affect distribution of the rhizobia. We isolated rhizobia nodulating common bean growing in Southern Ethiopia to evaluate their genetic diversity and phylogeography at nucleotide, locus (gene/haplotype) and species levels of genetic hierarchy. Phylogenetically, seven rhizobial genospecies (including previous collections) were determined that had reduced genetic diversity compared to reference strains. The reduction in genetic diversity of the Ethiopian collections was due to absence of some of the Rhizobium lineages known to nodulate beans. R. etli and R. phaseoli were predominant strains of bean nodulating rhizobia in Ethiopia. We found no evidence for a phylogeographic pattern in strain distribution. However, joint analysis of the current and previous collections revealed differences between the two collections at nucleotide level of genetic hierarchy. The differences were due to genospecies R. aethiopicum that was only isolated in the earlier collection.