BACILLUS -MEDIATED SUPPRESSION OF MACROPHOMINA PHASEOLINA IN STRAWBERRY VIA ANTIBIOSIS AND PAL-ASSOCIATED DEFENSE ACTIVATION

Macrophomina phaseolina, the causal agent of charcoal rot, severely constrains strawberry production, and its management relies on broad-spectrum fungicides with documented environmental and public-health risks. Plant growth-promoting rhizobacteria (PGPR) therefore represents a sustainable alternative. This study evaluated Bacillus subtilis, B. amyloliquefaciens, and B. thuringiensis against M. phaseolina and their ability to induce host defense, monitored through phenylalanine ammonia-lyase (PAL) activity. Antagonism was assessed in vitro, and disease severity and PAL activity were evaluated in greenhouse experiments on two major local strawberry cultivars (Albion and Camarosa), with and without M. phaseolina. Non-inoculated and Bacillus-only controls were included. B. subtilis produced the highest in vitro inhibition of M. phaseolina (percentage inhibition of radial growth, PIRG = 38.82± 1.21%), significantly exceeding (P ≤ 0.05) B. amyloliquefaciens and B. thuringiensis. In the greenhouse (cv. Albion), B. amyloliquefaciens provided the greatest disease control (disease severity index, DSI = 53.3 ± 1.9%; percentage disease control, PDC = 46.7%) relative to the pathogen-inoculated control (DSI = 100%), followed by B. thuringiensis (DSI = 66.6 ± 2.4%; PDC = 33.4%), whereas B. subtilis was least effective (DSI = 73.3 ± 2.1%; PDC = 26.7%). Conversely, B. subtilis induced the highest PAL activity (32.41 ± 1.14 nmol h⁻¹ g⁻¹ FW), a 43.0% increase over the pathogen-inoculated control (22.67 ± 0.76 nmol h⁻¹ g⁻¹ FW). All three Bacillus treatments significantly increased PAL activity (P ≤0.05) relative to the pathogen-inoculated control, indicating activation of host defense responses. These findings support integrating Bacillus-based bioagents into strawberry charcoal rot management.