Antagonistic activity and genomic insights of leaf-endophytic bacteria as biocontrol agents against major Brassica pathogens

Abstract

Plant diseases significantly threaten global agriculture, especially in horticultural crops such as Brassica species, where bacterial and fungal pathogens cause substantial economic losses. This study aimed to isolate and characterize endophytic bacteria with potential biocontrol activity against Xanthomonas campestris, Pectobacterium versatile, Sclerotinia sclerotiorum, and Leptosphaeria maculans. A collection of 79 bacterial endophytes was obtained from Brassica leaves, and their antagonistic potential was evaluated. Three isolates, Pantoea agglomerans Bru13, Bacillus velezensis Bro5, and Bacillus subtilis Bro11, demonstrated consistent pathogen inhibition and plant growth-promoting traits, including phosphate solubilization and siderophore production. Antimicrobial assays revealed that cell-free supernatants (CFS) from Bro5 and Bro11 exhibited about 45% inhibition of bacterial pathogens and up to 100% of antifungal activity, with peptide and secondary metabolite fractions being the most effective. Those from Bro5 inhibited 100% bacterial pathogens and about 40% fungal ones. Whole-genome sequencing identified biosynthetic gene clusters related to antimicrobial production, including phenazines, thiopeptides, surfactins, and bacillaene, supporting their biocontrol potential. In planta assays confirmed disease suppression, with Bro5 reducing X. campestris propagation by 70% and minimizing necrotic lesions caused by fungal pathogens by up to 35%. These results highlight the potential of P. agglomerans Bru13, B. velezensis Bro5, and B. subtilis Bro11 as effective biocontrol agents. Their ability to produce broad-range antimicrobial compounds, inhibit several pathogens, and enhance plant health suggests promising applications in sustainable agriculture not only for Brassica spp. but also other horticultural and field crops.