Burkholderia gladioli C101 metabolites protect tomato plants against Xanthomonas perforans infection

Abstract

Root-associated bacteria can mitigate plant diseases which is mediated in part by their production of bioactive metabolites. This has fostered efforts to identify microorganisms with biocontrol efficacy and the development of novel ways to deploy biocontrol agents in agriculture. In this study, we explored the antagonistic potential of a diverse collection of rhizobacteria isolated from soybean rhizosphere against a broad range of plant pathogenic bacteria, fungi and oomycetes. Burkholderia gladioli C101 was identified as a rhizobacterial isolate that produced potent and heat-stable active secondary metabolites that inhibited the growth of many plant pathogens. A draft genome for B. gladioli C101 predicted the presence of many biosynthetic gene clusters (BGCs), including several with high % identity to known BGCs from Burkholderia and other bacterial taxa. A major limitation for biocontrol agents affiliated with genera that are potential opportunistic animal pathogens such as Burkholderia species is the need to conduct rigorous risk assessment of these isolates for crop use. Therefore, we explored the use of cell-free supernatants of B. gladioli C101 to limit plant pathogen growth. To test the effectiveness of cell-free supernatant as a foliar spray, an experiment was conducted under greenhouse conditions on control of the foliar bacterial spot pathogen, Xanthomonas perforans on tomato. A significant reduction in bacterial spot disease severity was observed in greenhouse experiments when cell-free supernatants were applied prior to or after inoculation of tomato plants with X. perforans. Reduced disease severity was observed in a dose-dependent manner, suggesting that the bioactive metabolites produced by B. gladioli C101 have applicability in plant disease management.