Screening for Ecologically Competent, Nutritional Characteristics and Symbiotically Effective Chickpea Nodulating Mesorhizobium spp. Isolated from Acidic Soils of Ethiopia

Background: Nitrogen fixations are limited in acidic soil due to the sensitivity of legume, rhizobia, and the symbiosis to low pH. However, legumes and their rhizobia show different responses to soil acidity. Objective: The experiment was conducted to screen indigenous Mesorhizobium isolates for their ecological competitiveness and symbiotically effectiveness for enhancing nitrogen fixation in chickpea production. Methodology: A total of 81 genetically diverse indigenous Mesorhizobium spp. were screened for low pH tolerance and their potential to ecological adaptations under in vitro conditions and their symbiotic effectiveness on two chickpea varieties under greenhouse conditions. Results: 62 (77%) strains grew well at low pH 5, and 47 (75.8%) of them were phosphate solubilizers. The species displayed marked differences in their eco-physiological characteristics such as the utilization of different carbon and nitrogen sources, pattern of tolerance to salinity, temperature, Mn2+ and Al3+ toxicity, heavy metals, and inherent resistance to antibiotics. They also displayed significant (p<0.01) differences in their nodulation features (nodule number, nodule dry weight) and yield characters (shoot dry weight) on Natoli and DZ-ck-2011s-2-0042 chickpea varieties. Based on their symbiotic effectiveness (SE), five strains, namely a.15star (ANI95 groups 5C), a.117L2 (ANI95 groups 2D), a.71 (ANI95 groups 4B), a.40L2 (ANI95 groups 8A), and a.200M (ANI95 groups 3A) showed the best performance on both varieties, even out-performed over the commercially available local strain Cp41 and tolerance to different in vitro ecological conditions. Conclusion: Ethiopian acidic soils harbored symbiotically effective, ecologically competent, and phosphate solubilizing Mesorhizobium species. Thus, these strains could be recommended as prospective commercial inoculants provided they can be tested in field trials in acidic soils.