Changes in the winter oilseed rape microbiome affected by Xanthomonas campestris pv. campestris and biocontrol potential of the indigenous Bacillus and Pseudomonas isolates

Abstract

Plant pathogenic bacterium Xanthomonas campestris pv. campestris (Xcc) was recently described as a pathogen of winter oilseed rape in Serbia. A metabarcoding approach was used to study bacterial community composition changes in the phyllosphere and rhizosphere of different winter oilseed rape types (lines, cultivars, and hybrids) naturally infected with Xcc. This study also aimed to examine the potential of indigenous Bacillus and Pseudomonas isolates to suppress Xcc. Infection with Xcc leads to depletion of bacterial diversity in the plants' phyllosphere and explicitly decreasing the abundance of genera such as Exiguobacterium, Massilia, and Pantoea with potentially beneficial properties. Strains identified as Bacillus velezensis X5-2, Bacillus megaterium X6-3, and Pseudomonas orientalis X2-1P obtained from oilseed rape phyllosphere were found to be effective against Xcc in vitro and in vivo when applied as a whole-culture and as a cell-free supernatant. The greenhouse in vivo tests on winter oilseed rape plants with three selected biocontrol strains lead to a disease reduction of 82.37% and 72.47% in preventive and curative treatments, respectively. Genetic screening showed potential for the biosynthesis of surfactin, kurstakin, bacillomycin D, and iturin in B. velezensis X5-2, as well as surfactin and kurstakin in B. megaterium X6-3. Gene phcA encoding phenazine-1-carboxylic acid was detected in P. orientalis X2-1P. The chemical composition of ethyl acetate and benzene extracts of three biocontrol strains obtained by GC-MS and HPLC-ESI-qTOF/MS analyses indicates numerous volatile organic compounds (alkenes, benzenes, carboxylic acids, indoles, pyrazines, etc.), lipopeptides, and/or antibiotics, for many of which antimicrobial potential is proven. We assume that this wide range of metabolites is responsible for the exhibited biocontrol activity against Xcc. These results recommend all three biocontrol strains for further studies for use as agents for biocontrol of bacterial blight-like disease caused by Xcc of oilseed rape.