engleski

Genetic diversity and phenotypic characterization of symbiotic bacteria nodulating soybean (Glycine max L.) in continental Croatia

Symbiotic nitrogen fixation enables legumes to supply most of their needs for nitrogen in efficient and ecological manner. Symbiotic associations between legumes and specific group of soil bactera (rhizobia) enable considerable entries of biologically fixed nitrogen into the soil. Rhizobia are considered as one of the best plant partners in providing nutrient during the process of symbiosis with legumes taking advantage of nutrients from rhizosphere. The use of rhizobia as biofertilizer leads to enhanced nutrients composition and plant water uptake and tolerance to both abiotic and biotic stresses. Different studies revealed that the biofertilizers keep the soil fertility well managed in all kinds of macro- and micronutrients. It is also well known that rhizobia play crucial role in mineralization of phosphate and potassium, release of plant growth hormones and production of antibiotics. 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 their 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. From three soil samples 19 indigenous strains of rizobia were isolated, which were then identified at the species level by sequencing 16S rrs genes, while an insight into genetic diversity was obtained by RAPD (Random Amplified Polymorphic DNA) analysis. Phenotypic characterization included the determination of growth at different temperatures, pH values and growth at different salt concentrations, biochemical characterization, antibiotic resistance testing and the use of different carbon sources. Results obtained by sequencing rrs genes showed that 51% of isolates belong to the slow growing genera Bradyrhizobium, while the remaining 49% belong to fast growing genera Rhizobium, Ensifer and Microbacterium. The RAPD method grouped isolates into 20 groups with a similarity of 51%. 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 and SR2 (B. diazoefficiens) and SR3 and SR18 (B. japonicum) have proven to be the best strains, therefore it would be useful to include them in a further selection programme.

nodule bacteria ; biological nitrogen fixation ; soybean ; 16S rRNA sequencing ; RAPD

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