Using antagonistic soil bacteria and their cell‐free filtrates to control the black rot pathogen Xanthomonas campestris pv. campestris

Abstract Xanthomonas campestris pv . campestris (Xcc) is a phytopathogenic bacteria, and it is the causative agent of black rot in crucifers. Recent studies have shown that Bacillus species have strong biological control on Xanthomonas . One of the mechanisms of this control is secondary metabolites production. A collection of 257 bacteria isolated from a suppressive soil was evaluated for in vitro antagonistic activity against X. campestris , and 92 isolates (44.6%) were able to inhibit its growth. Among the 92 isolates evaluated in the double‐layer technique, 51 (55.43%) inhibited Xcc growth on the inhibition tests with cell‐free filtrates ( CFF ) in liquid medium. Thirteen of these isolates presented 50% or more growth inhibition, and five isolates presented 100% growth inhibition of Xcc. The CFF of the isolate TCDT ‐08, which belongs to the Paenibacillus genus, was used for in vivo tests with kale crops. The artificial inoculation of kale with Xcc‐629 IBSBF pretreated with CFF from the isolate TCDT ‐08 demonstrated that the bacterium loses the ability of colonizing kale and of causing black rot. A Paenibacillus sp. isolate has strong inhibitory activity against X. campestris pv. c ampestris , and further studies can result in the use of this isolate to protect kale from Xcc infection.