engleski

Selection of stress-tolerant indigenous rhizobia nodulating alfalfa (Medicago sativa L.)

Soil bacterium, Sinorhizobium meliloti is of enormous agricultural value because of its ability to fix atmospheric nitrogen in symbiosis with an important forage crops such as alfalfa. The main aim of this study was to evaluate the stress tolerance of indigenous S. meliloti strains to adverse environmental conditions. Twenty rhizobial strains, isolated from different regions in Croatia, were genotipically characterized to assess diversity amongst natural field population. Stress tolerance assays were performed in order to select indigenous rhizobia with possible higer tolerance to unfavorable soil conditions. The growth of the strains was studied at different pH values, temperatures, carbohydrate sources and different concentrations of NaCl. Biochemical characteristics of rhizobial isolates and the susceptibility to different antibiotics were determined as well. The results showed that most of the strains can grow at temperatures higher than optimal and that strains tolerate both acidic and alkaline environment. It was found that indigenous strains can tolerate extremely high concentrations of NaCl. Lactose agar assay indicates that three isolates probably belong to the genus Agrobacterium. Urease activity was determined in most strains while only a few strains expressed catalase activity. The results showed that all indigenous rhizobial strains belong to the group of fast-growing rhizobia. In comparison to the reference strain, higher resistance of indigenous S. meliloti strains was determined. The results of 16S rDNA genotyping using PCR/RFLP analysis showed that 14 isolates could be assigned to S. meliloti while RAPD and ERIC-PCR fingerprints revealed significant genetic diversity among indigenous rhizobial strains. Better understanding of rhizobial response to adverse environmental conditions is of potential value for improving rhizobial inoculants and efficiency of symbiotic nitrogen fixation.Book

biological nitrogen fixation ; phenotypic characterization ; alfalfa (Medicago sativa L.) ; Sinorhizobium meliloti

nije evidentirano