Potential Screening of Indigenous Drought Stress Tolerant Bacteria for Plant Growth Promotion (PGP) Traits: An In-vitro Study

Abstract

Aims: The study aims to formulate relevant microbial consortia against drought stress mitigation with potential drought stress tolerant bacterial isolates by polyethylene glycol 6000 (PEG 6000) different moisture stress levels to mitigate the drought stress which can finally helpful to increase plant and soil health under adverse stress conditions. Study Design:  Source of rhizosphere soil samples from groundnut drought prone areas of Andhra Pradesh. Place and Duration of Study: Department of Agricultural Microbiology, Advanced Post Graduate Centre, Acharya N.G Ranga Agricultural University, Lam, Guntur, 522 034, between June 2017 and July 2020. Methodology: Isolated strains were also tested for further drought stress screening by polyethylene glycol 6000 In-vitro screening was done for different plant growth promotion activities i.e. phosphate solubilization, IAA production, ammonia production, ACC deaminase activity, HCN production and catalase. HCN production, catalase positive, colony morphology, Gram staining and biochemical tests. Results: Fifty-one efficient bacterial isolates were obtained from drought prone rhizosphere soils of groundnut. Isolated strains were also tested for further drought stress screening by polyethylene glycol 6000 at 0% (-0.05 MPa), 10% (-0.65 MPa), 20% (-1.57 MPa), 30% (-2.17 MPa) and 40% (-2.70 MPa). Thirty-seven bacterial isolates were further found to have an enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity which improved plant growth during stress conditions. The In-vitro screening was done for different plant growth promotion activities, twelve bacterial isolates were positive for phosphate solubilization. IAA production was shown by almost all the bacterial isolates. Three isolates were positive for ammonia production. Two isolates were positive for HCN production and all the isolates were found to be catalase positive. Seven isolates were showing maximum plant growth promotion activities and further identified based on colony morphology, Gram staining and biochemical tests. Conclusion: This study suggests that 51 bacterial isolates exhibited the highest tolerance to moisture stress under In-vitro, these are screened and considered as potential isolates against plant growth promoting characteristics. Plant growth promoting bacteria that can modulate physiological response for water shortage, enhanced water or nutrient uptake and transpiration, induction of plant growth hormone signaling and increased antioxidase activity and photosynthetic rate thereby ensuring plant survival under such stressful conditions. In regard to isolates having PGP properties from the research work presented could be studied further under In-vitro and in vivo conditions from different soils with several crops for confirming their use as bio inoculants.