Genetically diverse lentil- and faba bean-nodulating rhizobia are present in soils across Central and Southern Ethiopia

In total 196 bacterial isolates were obtained from root nodules of lentil (Lens culinaris) and faba bean (Vicia faba) grown on soil samples collected from 10 different sites in central and southern parts of Ethiopia. All isolates were identified as members of the genus Rhizobium by using recA gene sequence analysis. In the recA phylogenetic tree 195 rhizobial strains were classified into nine genospecies. The phylogeny of symbiotic genes nodC and nifH revealed five and six distinct groups respectively, largely dominated by symbiovar viciae. A multivariate analysis showed that environmental variables of the sampling sites considered in this study had more effect on the distribution and composition of the genospecies than the host legumes of the strains. Twenty representative strains, selected based on their isolation site, host plant and nodC group, were able to nodulate all lentil, faba bean, field pea (Pisum abyssinicum) and grass pea (Lathyrus sativus) plants in a greenhouse test in axenic conditions. The majority of the rhizobial strains were effective nitrogen-fixing symbionts for all tested legumes, indicating their potential to serve as broad host-range inoculants in agriculture. The present work suggests the presence of taxonomically and symbiotically diverse rhizobial species for legumes in the Viciae tribe in Ethiopia.Peer reviewe

Lentil- and Faba bean- Nodulating rhizobial genospecies obtained from Central and Southern Ethiopia are diverse in their phenotypic and symbiotic properties

In our previous study, we isolated and genetically characterized various faba bean and lentil symbionts belonging to diverse Rhizobium genospecies from the soils of Ethiopia. Twenty lentil- and faba bean- nodulating rhizobial strains representing different isolation site, genospecies grouping, host plant and symbiotic gene groups were selected for this study. The aim of the study was to phenotypically characterize the test strains and to explore their nodulation and symbiotic properties to ultimately select those suited for inoculant purposes. Strain EAL 110, a commercial inoculant strain for faba bean, was used as a reference strain to compare the nodulation status (nodule number, nodule dry weight, shoot dry weight, total nitrogen and symbiotic efficiency scores) of the test strains. In vitro experiments were conducted to assess the effects of different eco-physiological stresses (pH, salinity, temperature, antibiotics and carbon and nitrogen substrates assimilation) on their growth. The greenhouse sand-pot experiment showed that the different strains displayed variations in their symbiotic performance on both legume hosts. The consequent results show strain EAL 110 (SE% = 85 with both lentil and faba bean) has still maintained its desired symbiotic property. However, 9 strains with lentil and 5 strains with faba bean from our collections have outperformed (≥85% SE) the reference control strain EAL110 (p<0.001). Of these strains, strain L33b, L53c, F32a and F42 have shown their phenotypic and symbiotic advantage over the remaining treatments under a controlled environment and should thus be selected for further tests to screen their ability of maintaining these traits in natural (field) settings for future bio-inoculant formulation