A genetically safe Burkholderia cenocepacia strain P3 suppresses Cercospora zeina via siderophore-mediated iron deprivation

• Isolation of B. cenocepacia P3 with broad-spectrum antifungal activity against maize pathogens. • Siderophores pyochelin and ornibactin synergistically suppress C. zeina via iron deprivation. • Genomic safety confirmed: lacks virulence genes BCESM and cblA, not genomovar II. • P3 promotes plant growth via phosphate solubilization, nitrogen fixation, siderophores. • Optimized fermentation enhances siderophore yield for biocontrol application in maize. Gray leaf spot (GLS), caused by Cercospora zeina , is a devastating fungal disease of maize worldwide. This study reports the isolation of a novel rhizobacterium, strain P3, from the maize rhizosphere, which was identified as Burkholderia cenocepacia based on phylogenetic analysis of 16S rRNA and dnaG genes. Strain P3 exhibited broad-spectrum antifungal activity against multiple pathogens and demonstrated plant growth-promoting traits. Genomic analysis confirmed the absence of major virulence genes, supporting its environmental safety. Fermentation conditions for siderophore production were optimized, achieving a yield of 85.5 % siderophore units under optimal conditions (sucrose 5 g/L, asparagine 3 g/L, pH 7.0, 32 °C). The fermentation supernatant of P3 inhibited C. zeina growth dose-dependently, causing hyphal membrane damage and reactive oxygen species accumulation. Two siderophores, pyochelin and ornibactin, were identified and shown to synergistically suppress fungal growth under iron-limited conditions. Greenhouse trials demonstrated that pretreatment with strain P3 significantly reduced lesion area and disease severity in maize plants challenged with C. zeina . These results indicate that B. cenocepacia P3 is a promising, environmentally friendly biocontrol agent with strong potential for integrated management of gray leaf spot.