Evaluating biocontrol potential of Bacillus velezensis against Xanthomonas campestris pv. campestris on cabbage cv. Futoški under greenhouse conditions

Bacillus velezensis is recognized as a species with remarkable biocontrol potential against a wide range of plant pathogens, including the bacterium Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot of Brassicaceae crops. This study aimed to establish the most suitable technique for application of four B. velezensis strains (BFC55, BFC88, BFC102, and BFC114) against Xcc on cabbage cv. Futoški. The efficacy of three application techniques (seed-soaking, preventive and curative foliar spraying) was evaluated on cabbage plants under the controlled greenhouse conditions in two independent experiments. Simultaneously, the efficacy of whole cultures and cell-free supernatants of B. velezensis strains were tested. The disease intensity was scored 14 days after inoculation using the Horsfall–Barratt scale. Upon the end of the experiment, fresh and dry biomass, as well as chlorophyll and epidermal flavonoid content and nitrogen balance index were measured for all treatments. Among the compared treatments, preventive application showed the greatest disease suppression (89.71–93.09%) ability, while the curative exhibited the lowest efficacy (55.00–75.68%). The highest efficacy was observed after preventive application of strain BFC88 in the form of whole culture (93.09%). Preventive treatment showed increased epidermal flavonoid accumulation compared to all other application treatments, along with a decrease in fresh/dry biomass ratio. Preventive treatment has been highlighted as the most effective method for controlling black rot in cabbage cv. Futoški in comparison to other treatments. The demonstrated efficacy of tested strains in greenhouse conditions suggests their potential for successful application in the field.