Isolation and phenotypic characterization of soybean (Glycine max L.) microsymbionts in continental Croatia

Symbiotic nitrogen fixation enables legumes to supply most of their needs for nitrogen in efficient and ecological manner. Rhizobia are group of prokaryotic organisms with the unique ability to form symbiotic relationships at the root of leguminosis in which they inert atmospheric nitrogen in plants is converted by nitrogenase enzymes. It is assumed that native rhizobial populations are also present in the soils of continental Croatia and that the strains differ from each other in phenotypic and genotypic properties. In order to select the best rhizobia strains, soil samples were collected from three areas of continental Croatia where there is a long tradition of soybean cultivation. Phenotypic characterization included the determination of growth at different temperatures, pH values and growth at different salt concentrations, biochemical characterization, antibiotic resistance testing. Phenotypic characterization has shown significant resistance to environmental stress conditions, particularly resistance to low pH, which is extremely important because Croatia has a lot of acid soils. Strains SR1, SR2 and SR3 have proven to be the best strains, therefore it would be useful to include them in a further selection programme.