Biocontrol potential of Pseudomonas fluorescens: Phenazine mediated antifungal activity against phytopathogens

Fungal phytopathogens pose significant threats to plant health and agricultural productivity. Biocontrol agents like Pseudomonas fluorescens offer eco-friendly alternatives to chemical fungicides. In this study, P. fluorescens was isolated from the rhizosphere of Vanda wightii and assessed for its potential as a biocontrol agent against key fungal pathogens.

The antagonistic activity of P. fluorescens was tested against Botrytis cinerea, Colletotrichum gloeosporioides, Fusarium oxysporum, and Rhizoctonia solani using dual plate and cross-streak assays. Siderophore and hydrogen cyanide production were evaluated as possible biocontrol mechanisms. Growth conditions were optimized by varying glycerol, tryptone, pH, and temperature. Phenazine, the main antifungal metabolite, was extracted and characterized using FTIR, HPLC, NMR, and mass spectrometry. Antifungal kinetics and membrane permeability assays were also conducted.

P. fluorescens exhibited strong antagonism, forming clear inhibition zones against all tested pathogens. Optimal growth occurred with 2% glycerol, 2% tryptone, pH 7, and 35 °C. The purified phenazine showed significant antifungal activity, with inhibition zones of 18.29 ± 0.05 mm to 25.90 ± 0.02 mm and a MIC of 2.0 µg/mL against C. gloeosporioides. FTIR and NMR confirmed aromatic and carbonyl groups; HPLC revealed a 20.25 min retention time; and mass spectrometry detected a molecular ion peak at m/z 180.75. Time-course assays showed reduced spore viability at 16 h, while membrane assays indicated nucleotide leakage.

P. fluorescens and its phenazine metabolite demonstrate strong biocontrol potential. Future work should focus on bioreactor-scale production and mode-of-action studies for integrated disease management.