Phenotypic diversity, symbiotic effectiveness and plant growth promoting characteristics of rhizobia nodulating chickpea (Cicer arietinum L.) from central and south gondar zones, Ethiopia.

In Ethiopia, chickpea productivity is below half of its potential, which could be due to various environmental constraints, including low soil nutrients, the absence of compatible strains, low rhizobia population in the soil, pests, and diseases. Identifying efficient and superior rhizobia strains from the local agroecology has paramount importance for enhancing chickpea production and improving soil fertility. This study aimed to isolate and characterize the phenotypic, symbiotic effectiveness and plant growth promoting properties of chickpea nodulating rhizobia from major chickpea producing districts of central and south Gondar zones. Nodule samples were collected from farmer fields, and the rhizobial isolates were isolated and subjected to presumptive tests. The symbiotic effectiveness of each isolate was undertaken in sand pot culture under greenhouse conditions, and the highly effective isolates were evaluated for their physiological tolerance, carbohydrate and amino acid utilization, intrinsic antibiotic resistance, and plant growth promoting properties. Outstanding isolates were subjected to molecular characterization. A total of 89 isolates were isolated, and 82 were confirmed during a preliminary test. Based on the symbiotic effectiveness evaluation, 25 isolates were highly effective. The ecophysiological test result showed that all isolates grew at a temperature range of 20–35 °C, whereas 32% and 36% grew at 10 and 45 °C, respectively. All isolates were able to grow at 1% and 2% NaCl concentrations, whereas 16% were tolerant to 5%. All isolates grew at a pH range of 6.0-8.5, and almost half were tolerant to pH 5. Isolates also showed versatility in utilizing different amino acid (43–100%) and carbon (62.5–100%) sources. Four isolates were resistant to all tested antibiotics, and others showed 37.5–87.5% resistance to the tested antibiotics. Five isolates solubilized tricalcium phosphate with solubilization indices ranging from 1.09 to 1.25. Thirteen isolates were capable of producing indole acetic acid, and 3 isolates were found to inhibit the growth of Fusarium oxysporum. Based on their overall performance, three isolates (GUCR 19, 30 and 55) were selected and identified under the genus Mesorhizobium. In this study, we identified symbiotically effective, competitive and stress tolerant strains that also exhibited plant growth promoting properties, making them potential candidates for inoculant production. This study had a lot of significance for improving the productivity of chickpea on a sustainable basis.