Co-inoculation of indigenous Pseudomonas oryzihabitans and Bradyrhizobium sp. modulates the growth, symbiotic efficacy, nutrient acquisition, and grain yield of soybean

Abstract

Soil microbes play a vital role in improving plant growth, crop productivity, and soil health through solubilization of essential nutrients. Present investigation was conducted to access the efficacy of Bradyrhizobium sp. LSBR-3 and the indigenous phosphate-solubilizing Pseudomonas oryzihabitans LSE-3 in improving the symbiosis, nutrient accumulation, and yield of soybean. The isolate LSE-3, selected on the basis of phosphate solubilization, was screened for beneficial traits, antagonistic activities, and pathogenicity. The levels of indole acetic acid production (50.34 ± 2.35 μg mL-1), phosphate solubilization (184.4 ± 7.4 mg L-1), biofilm formation (optical density at 560 mm, 1.389 6 ± 0.04), siderophore production (121.46 ± 1.61 μg mL-1), and 1-aminocyclopropane-1-carboxylate deaminase activity (0.51 ± 0.07 mmol α-ketobutyrate μg-1 protein h-1) were significantly higher with the dual inoculants (LSBR-3 and LSE-3) than with the single inoculant LSBR-3. The plant growth-promoting traits of single and dual inoculants were evaluated for the synergistic effects on soybean under field conditions. Soybean plots treated with LSBR-3 + LSE-3 exhibited improvement in seed germination, plant height, plant biomass, and chlorophyll content compared with the uninoculated control. Dual inoculant treatments resulted in significantly higher symbiotic efficacy evidenced by increased nodulation (40.0 ± 0.75 plant-1), nodule biomass (188.52 ± 6.29 mg plant-1), and leghemoglobin content (11.02 ± 0.83 mg g-1 fresh nodule), and significantly increased activities of phosphatase (75.16 ± 3.17 and 58.77 ± 6.08 μg p-nitrophenol g-1 h-1 for alkaline and acid phosphatase, respectively) and dehydrogenase (32.66 ± 1.92 μg triphenylformazan g-1 h-1) compared with the control. Dual inoculation with LSBR-3 and LSE-3 enhanced the uptake of macro- and micronutrients, reduced Na content in shoots, and resulted in 10.85% higher grain yield and ca. US$96.80 ha-1 higher profit compared with the control. This is the first report on the effectiveness of combined inoculation of LSE-3 and LSBR-3 in promoting the growth, symbiotic efficacy, and yield of soybean for sustainable agriculture.