Screening and identification of abiotic stress-responsive efficient antifungal Pseudomonas spp. from rice rhizospheric soil

Plant growth-promoting rhizobacteria (PGPR) are a collection of microorganisms often used to support and promote plant development and combat plant infectious diseases with various biological control methods. The most significant restricting factors for agricultural productivity worldwide are abiotic constraints. In the present study, seven bacterial isolates from the rice rhizosphere were selected for detailed tests based on results obtained in experiments determining the ACC deaminase synthesis and drought tolerance at –0.30 MPa PEG level. Screening results of the stress tolerance analysis of the seven isolates for elevated temperature (50°C), alkalinity (10% NaCl), and drought (–1.2 MPa) showed that abiotic stress resistance was less prevalent in DRO2, DRO13, and DRO43 isolates than in DRO17, DRO28, DRO35, and DRO51 isolates. During the study, it was observed that DRO17, DRO28, and DRO51 tended to maintain similar cell density at –0.73 MPa PEG level, as observed at –0.30 MPa stress condition. No bacterial growth was observed at higher PEG level (–1.12 MPa) for any bacterial isolate. Four strains of Pseudomonas (DRO17, DRO28, DRO35, and DRO51) exhibited salinity and temperature tolerance. Antifungal screening using the bangle method showed that DRO35 was highly antagonistic towards Rhizoctonia solani 4633, followed by Fusarium moniliforme 4223, with an inhibition of 64.3% and 48%, respectively. The DRO28 isolate exhibited 72.5% growth inhibition for Fusarium moniliforme 4223, while the DRO51 isolate showed 38.2% growth inhibition for Bipolaris hawaiiensis 2445. DRO17 reduced the growth of Rhizoctonia solani 4633, and Curvularia lunata 350 by 36% and 31%, respectively. In conclusion, the screening of bacterial strains with promising stress tolerance and antifungal characteristics could support farmers to achieve the required positive outcomes in the agriculture field.