In vitro biocontrol potential of indigenous Bacillus velezensis strains in suppressing black rot disease in cabbage cv. Futoški

Serbian autochthonous cabbage cv. Futoški is susceptible to various pathogens, including the bacterium Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot, resulting in significant economic losses. This study aimed to provide an environmentally friendly solution for controlling black rot in cabbage cv. Futoški by exploring the potential of indigenous Bacillus spp. strains. Bacillus spp. strains were isolated from the phyllosphere and rhizosphere of cabbage cv. Futoški plants, with and without black rot symptoms. The potential antagonistic activity of their whole cultures and cell-free supernatants was tested in vitro, against Xcc strain XccFC231, also isolated from the cv. Futoški. Phylogenetic analysis was performed based on concatenated sequences of the 16S rRNA, rpoB, and gyrA genes to identify the most potent biocontrol candidate(s). The presence and/or absence of lipopeptide genes in candidates was checked using specific primers, targeting the synthesis of bacillomycin D, fengycin, iturin, kurstakin, and surfactin. Of the 115 isolated Bacillus spp. strains, 52 exhibited antagonistic activity of whole cultures, while nine (BFC3, BFC55, BFC68, BFC73, BFC81, BFC88, BFC98, BFC102, and BFC114) demonstrated activity of supernatants (Ø 12–19 mm) as well. All nine biocontrol candidates were identified as Bacillus velezensis. Except for BFC98, the rest of the candidates showed potential to produce bacillomycin D, while six strains (BFC3, BFC55, BFC68, BFC88, BFC98, and BFC102) exhibited potential for iturin production. The nine isolated B. velezensis strains show potential for future use in managing black rot on cabbage cv. Futoški, and could potentially be used on other Brassicaceae.