Phenotypic diversity and symbiotic efficiency of Bradyrhizobium spp. strains from Amazonian soils

This work aimed to evaluate the phenotypic diversity and symbiotic efficiency of Bradyrhizobium strains isolated from Amazonian soils, under different land use systems (crop, fallow, pasture, forest and agroforestry system). Total protein profiles obtained by polyacrylamide gel electrophoresis (SDS-PAGE) of 46 strains showed great diversity, while 11 groups presented similarity above 80%. One of these groups contained the reference strain of B. elkanii: BR29, recommended as soybean inoculant. Twenty-two strains, tested in Leonard jars for symbiotic efficiency with Vigna unguiculata (L.) Walp. (cowpea) produced shoot dry matter, N-content, and relative efficiency higher than the control (without N, with inoculation). Production of shoot dry matter and relative efficiency were induced by 13 strains in a way similar to the N-control (with N, without inoculation); five strains induced higher nitrogen content than N-control. Native populations comprise high diversity of strains with variable symbiotic efficiency, and some of them could be recommended for agronomic efficiency assays.