Symbiotic and phenotypic characteristics of indigenous rhizobia nodulating faba bean (Vicia faba L.) growing in some parts of Wello, Northern Ethiopia

Nitrogen is one of the most abundant elements in the atmosphere, and BNF is the main source of N for Legumes plants. Faba bean is one of the most important Legumes plants in Ethiopia and widely grown in Amhara regional state.In view of the presence of  heterogeneous agroecologies found in the country, more diversity and effective strains nodulating faba bean are expected. This study was initiated with the objectives of isolation, characterization, and selection of symbiotically efficient faba bean rhizobia from some part of Wello, Ethiopia. The result will contribute for utilizing BNF system of faba bean to increase productivity into lowinput agriculture of the region and the country at large. A total of 132 endophytic bacteria found in the nodule of faba bean (V. faba L.) growing at different farmers' fields in Wello were isolated and characterized based on phenotypic features. Up on authentication, only 70 (53%) isolates were found to be rhizobia (the true symbiont) of faba bean, while the remaining 62 (47%) of the test isolates were found to be non-nodulating nodule endophytes of faba bean. The result of the study showed the presence of diversity in morphological, physiological and symbiotic properties among the tested isolates. Presumptive reactions of the result showed all isolates are fast growing rhizobia, Gram negative rods, except CR absorption by 8 isolates and moderate growth on PGA media by seven isolates. ANOVA of the result indicated that all of the parameters including; nodules number, root fresh and dry weight, shoot fresh and dry weight, symbiotic efficiency were significantly improved by inoculation (p< 0.05). Based on SE (expressed as the ratio of % of SDW of the plant inoculated with the test isolates to SDW of the plant that received KNO₃ - as nitrogen source), 12.9% of the isolates were found to be highly effective and increased the shoot dry weight of host plant by 80-117.6%. Two of the test isolates (FBW140 and 145) in the current study showed better performance in SE%, exceeding 100% over KNO₃ treated plants. Total nitrogen content of the faba bean plant, when inoculated with 21 selected test isolates, showed that four isolates (FBW107, 140, 144 and 145) significantly exceeded that of the plant which received KNO₃ (positive control). The results also revealed that SDW showed significant positive correlation with Shoot and root fresh weight, Root dry weight and nodule number. The relative amount of nitrogen fixed by the majority of selected test isolates, when compared with the commercial inoculant strain (D/sina) was found to be higher as evidenced by accumulation of high shoot fresh and dry weight, root fresh and dry weight and nodule number. The isolates have exhibited diverse and interesting features such as ability to grow on wide range of carbon and nitrogen sources, tolerance to higher and lower temperature, high salt concentration, acidic and alkaline pH and almost all isolates were resistant to Erythromycin (5μg/ml) while sensitive to Kanamycin at (5 and 10μg/ml). The numerical analysis based on 55 phenotypic traits revealed the existence of diversity among the test isolates and categorized all isolates into 3 clusters when 63% similarity was taken as cut point. Generally, the present work while showing the physiological and symbiotic diversity of the test isolates in the study sites, field study aiming at screening of the best nitrogen fixing candidate would be essential before using them as inoculants in areas where the indigenous rhizobia fail to do so.