Identification and Selection of Promising Autochthonous Bradyrhizobium Strains to Develop an Inoculant for Lotus angustissimus

Lotus angustissimus is a promising forage legume increasingly used to improve naturalgrasslands in Uruguay. However, a specific rhizobial inoculant for this species has not yet been developed, and the identification of its autochthonous symbionts remains unknown. Instead, L. angustissimus is inoculated with Bradyrhizobium sp. U531 the commercial inoculum for Lotus subbiflorus . We evaluated the symbiotic efficiency of sixteen Bradyrhizobium strains isolated from L. angustissimus nodules in a site without inoculation for 15 years, revealing efficient soil rhizobia suitable for inoculant development. Under controlled conditions, GL3 and GL5 strains significantly exceeded the symbiotic efficiency of strain U531 in L. angustissimus . In L. subbiflorus , strain GL5 exceeded the symbiotic efficiency of strain U531. Genomic and phylogenetic analyses showed that strain GL3 belongs to the species Bradyrhizobium canariense BTA‐1 T , whereas strain GL5 is related to Bradyrhizobium nitroreducens TSA1 T , although average nucleotide identity suggests that it represents a different species. Despite their taxonomic divergence, both strains share a high percentage of identity with the nodBC and nifHK genes of Bradyrhizobium sp. WSM471, suggesting horizontal gene transfer of the symbiotic loci. The presence of denitrification genes ( nap , nor , and nos ) and nitrate‐dependent anoxic growth in both strains was also confirmed. These findings demonstrate, for the first time, that B. canariense GL3 can efficiently nodulate L. angustissimus and L. subbiflorus . Bradyrhizobium sp. GL5, related to B. nitroreducens TSA1 T , is also reported to establish an efficient symbiosis with these legumes. Due to the high symbiotic efficiency of these strains in two hosts, they represent elite candidates for the development of a specific dual‐purpose inoculum.