Enhanced suppression of Pseudomonas coronafaciens pv. garcae, the etiological agent of coffee plant bacterial halo blight, by a four-phage cocktail in in-vitro and ex-planta studies: biological and kinetic profiling

Bacterial blight of coffee caused by Pseudomonas coronafaciens pv. garcae (Pcg) poses a significant threat to coffee production. This study reports the isolation and characterization of four lytic bacteriophages - PCG-05T, PCG-06T, PCG-07T, and PCG-09T - as potential biocontrol agents against Pcg. Isolated using multiple Pcg strains, the phages exhibited differential host specificity, plaque morphology, and lytic efficiency. Adsorption kinetics and one-step growth analyses revealed fast binding (PCG-06T and PCG-07T) and high burst sizes (PCG-05T and PCG-09T). In addition, phages PCG-06T and PCG-09T also displayed broad host range and strong lytic activity, with low frequencies of emergence of bacterial resistant mutants (≤10 −3 ), with all phages positioning themselves as promising candidates for phage therapy. Electrostatic and diffusion analyses suggested that adsorption efficiency was influenced by surface charge interactions, with PCG-06T showing enhanced binding due to a higher (less negative) Zeta potential. In vitro inactivation assays demonstrated MOI-dependent suppression of Pcg populations, with phage cocktails yielding superior reductions - up to 6.17 log CFU/mL - especially at MOI 10000. Ex planta assays on artificially contaminated coffee plant leaves further confirmed significant bacterial inactivation, achieving up to 4.08 log CFU/mL reduction after 36 h. Despite slight regrowth at later time points, phage persistence remained stable, highlighting the potential of high-MOI applications for effective short-term control. Genomic screening confirmed the absence of undesirable genes, reinforcing safety for agricultural use. While results are promising, further studies on formulation, environmental stability, and field efficacy are needed to optimize phage-based interventions for controlling Pcg in coffee plantations.