Molecular identification and functional characterisation of efficient indigenous Azotobacter strains conferring salinity tolerance in rice (Oryza sativa L.)
TL;DR
Findings demonstrate that the indigenous A. vinelandii strain AztACU1 possesses multifunctional plant growth-promoting traits and effectively enhances salinity tolerance in rice, highlighting its potential as a sustainable biofertiliser for improving productivity in salt-affected agroecosystems.
Abstract
An indigenous Azotobacter vinelandii strain (AztACU1) was isolated from the rice rhizosphere and evaluated for its nitrogen-fixing ability, plant growth-promoting (PGP) traits and potential to enhance salinity tolerance in rice (Oryza sativa L. var. IR64). A total of 10 bacterial isolates were obtained from rice rhizosphere soil and characterised using morphological, biochemical and molecular (16S rRNA gene sequencing) approaches. Nitrogen-fixing efficiency was assessed using the acetylene reduction assay (ARA). Among the isolates, A. vinelandii AztACU1 exhibited the highest nitrogenase activity (131.05 ± 3.16 nmol C₂H₄ mg-1 bacterial protein hr-1). The isolate also showed superior plant growth-promoting characteristics, including siderophore production, hydrogen cyanide (HCN) production, phosphate solubilisation, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, ammonia production and synthesis of salicylic acid, indole-3-acetic acid (IAA), gibberellic acid (GA₃) and zeatin. The 16S rRNA gene sequence of AztACU1 was deposited in the NCBI GenBank database under accession number PZ167826.1. The salinity tolerance-promoting potential of AztACU1 was evaluated in rice plants exposed to 200 mM NaCl. Under salinity stress, inoculated plants exhibited approximately 1.5-fold higher proline accumulation, 2-fold lower malondialdehyde (MDA) content, 2.5-fold lower H₂O₂ accumulation and 1.5-fold lower electrolyte leakage than uninoculated control plants. In addition, inoculated plants showed increased concentrations of endogenous phytohormones (GA₃, IAA and zeatin) and improved growth and yield attributes under saline conditions. These findings demonstrate that the indigenous A. vinelandii strain AztACU1 possesses multifunctional plant growth-promoting traits and effectively enhances salinity tolerance in rice, highlighting its potential as a sustainable biofertiliser for improving productivity in salt-affected agroecosystems.
