European Origin of Bradyrhizobium Populations Infecting Lupins and Serradella in Soils of Western Australia and South Africa

We applied a multilocus phylogenetic approach to elucidate the origin of serradella and lupinBradyrhizobium strains that persist in soils of Western Australia and South Africa. The selected strains belonged to different randomly amplified polymorphic DNA (RAPD)-PCR clusters that were distinct from RAPD clusters of applied inoculant strains. Phylogenetic analyses were performed with nodulation genes (nodA ,nodZ ,nolL ,noeI ), housekeeping genes (dnaK ,recA ,glnII ,atpD ), and 16S-23S rRNA intergenic transcribed spacer sequences. Housekeeping gene phylogenies revealed that all serradella andLupinus cosentinii isolates from Western Australia and three of five South African narrow-leaf lupin strains were intermingled with the strains ofBradyrhizobium canariense , forming a well supported branch on each of the trees. AllnodA gene sequences of the lupin and serradella bradyrhizobia formed a single branch, referred to as clade II, together with the sequences of other lupin and serradella strains. Similar patterns were detected innodZ andnolL trees. In contrast,nodA sequences of the strains isolated from native Australian legumes formed either a new branch called clade IV or belonged to clade I or III, whereas their nonsymbiotic genes grouped outside theB. canariense branch. These data suggest that the lupin and serradella strains, including the strains from uncultivatedL. cosentinii plants, are descendants of strains that most likely were brought from Europe accidentally with lupin and serradella seeds. The observed dominance ofB. canariense strains may be related to this species' adaptation to acid soils common in Western Australia and South Africa and, presumably, to their intrinsic ability to compete for nodulation of lupins and serradella.