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In Ethiopia, the production of livestock has been mainly constrained by low quality feed supply and seasonal fluctuations. The usage of good quality and drought-tolerant forage legumes like white lupin and tree lucerne are recommended to overcome feed constraints. Those legumes fix atmospheric nitrogen when being in symbiosis with rhizobia and thereby reduce the need for synthetic fertilizers. However, they show variations in terms of N2-fixation, calling for screening the best native symbionts. The aim of this study was therefore; to isolate, characterize, and screen potential rhizobia isolates nodulating white lupin and tree lucerne from Ethiopia. A total of 115 bacteria were isolated from both legumes, of which 48.7% were authenticated as rhizobia while the remaining were not. The authenticated rhizobia isolates showed a wide diversity in their response to different eco-physiological stresses and substrate utilization pattern. Majority of isolates grew at pH range of 5 - 8.5, temperatures of 15 - 35ï¯C, and NaCl (w/v) concentration of 0.5% - 2%. Regarding substrate utilization, almost all of the isolates metabolized all C- and N-sources tested. There was a significant variation (p < 0.05) among the strains in terms of inducing nodule number, nodule dry weight and shoot dry weight on sympatric (their own) hosts. Six strains nodulating white lupine induced higher shoot biomass than N-fertilized control plants while there was no significant difference between the highly effective strains of tree lucerne and the N-fertilized control plants. The numerical analysis of 56 phenotypic traits grouped white lupin isolates into four clusters at similarity coefficient of 77%, while tree lucerne isolates were grouped into three clusters at a similarity coefficient 69%, indicating phenotypic diversity of the strains. Isolates that had higher or equal symbiotic effectiveness with the N-fertilized control plants are recommended for field evaluation under different environmental conditions. We also recommend those isolates for molecular characterization and use as inoculants on their host legumes in soils where they perform best.
