Abstract

Plant growth-promoting rhizobacteria play an important role in sustainable agriculture by enhancing crop productivity and suppressing phytopathogens. The present study focused on the isolation and characterization of fluorescent Pseudomonas strains from the rhizosphere of paddy (Oryza sativa L.) cultivated in Gangoh Block, Saharanpur, Uttar Pradesh, India. Seven bacterial isolates were obtained using serial dilution and streak plate techniques, among which Pseudomonas fluorescens MS-05 exhibited the highest production of indole-3-acetic acid and siderophores. Biochemical characterization and 16S rRNA gene sequencing confirmed the identity of the strain, showing 99% sequence similarity with P. fluorescens (NCBI Accession No. PP501522.1). The antagonistic potential of P. fluorescens MS-05 against the storage-deteriorating fungus Aspergillus niger was evaluated using a dual-culture assay. The strain produced a clear inhibition zone of 21.3 ± 1.2 mm after 7 days of incubation, with sustained inhibition of fungal growth observed under prolonged in vitro incubation. Gas chromatography–mass spectrometry (GC–MS) analysis of the bacterial metabolites identified extracellular metabolites, including 2,4-diacetylphloroglucinol and phenazine, previously reported for antifungal activity. Comparative evaluation demonstrated that the cell-free supernatant of P. fluorescens MS-05 exhibited significantly higher antifungal efficacy than the corresponding bacterial broth. This enhanced activity is likely due to the direct availability of extracellular antifungal metabolites, highlighting the functional advantage of metabolite-based, cell-free formulations over whole-cell preparations. Overall, the findings highlight the potential of P. fluorescens MS-05 and its extracellular metabolites as effective bio-priming agents for controlling seed and storage-associated fungal pathogens in paddy. The study emphasizes the importance of metabolite-based biocontrol strategies and provides a foundation for the development of eco-friendly alternatives to chemical fungicides in post-harvest disease management.

Key words: Bio priming, Paddy crop, DAPG (2,4-diacetylphloroglucinol), Phenazine, Germination enhancement, Antifungal activity.