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

Abstract

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.