Rhizobium Co-Inoculation Enhances Productivity of Common Bean (Phaseolus vulgaris L.) and Soil Health under Salinity Stress

Soil salinity is a major abiotic constraint that severely limits crop production, whereas beneficial legume-rhizobia symbioses can alleviate stress effects and enhance crop yield performance. In this study, pre isolated Rhizobium phaseoli R9 and Mesorhizobium ciceri R6 strains were evaluated individually and in co inoculation on common bean (Phaseolus vulgaris L.) grown in saline soils (5.6 dS m⁻¹). The experiment was established using a randomized complete block design (RCBD) with three replications at the Experimental Station of the Institute of Agriculture and Agrotechnologies of Karakalpakstan during the 2024–2025 growing seasons. Bacterial inoculations showed potential to increase plant height, root and shoot biomass, grain yield, number of nodules per plant, nodule dry weight, and root length of common bean. Co-inoculation was particularly effective, increasing the dry weights of shoot, root, leaf, grain, and husk by 47.6%, 28.0%, 32.1%, 39.6%, and 22.2%, respectively, compared with the control. Likewise, the highest grain yield (1.85 Mg ha⁻¹) was produced under co inoculation, exhibiting a 44.5% increase compared with the uninoculated control. Chemical analysis showed that co inoculation (R6+R9) increased oil and protein content by 18.2% and 27.4%, respectively, over the control. The results show a strong correlation (R2=0.89) between increased nodule weight and common bean grain yield. The application of biological interventions markedly improved multiple indicators of soil fertility and biological activity, with the R6 + R9 co-inoculation treatment producing the highest concentrations of humus (0.85 g kg⁻¹), total N (1.05 g kg⁻¹), total P (1.15 g kg⁻¹), nitrate-N (6.72 mg kg⁻¹), available P₂O₅ (46.0 mg kg⁻¹), and exchangeable K₂O (180 mg kg⁻¹) compared with the control. It might be concluded that co-inoculation of Rhizobium strains could be the most effective nature-based solutions strategy for enhancing agricultural productivity and ecosystem restoration under saline conditions.