Bacillus velezensis GF267 as a multi-site antagonist for the control of tomato bacterial spot.
Some isolates of sporogenic bacteria can reduce the plant disease intensity through different mechanisms. In the present study, 29 isolates of this group of bacteria were evaluated for the control of tomato bacterial spot in order to select strains with multiple modes of action in disease suppression. In the first experiment, tomato seedlings received three applications of the antagonists on leaves or on soil which were then challenged with Xanthomonas perforans after the second application. There was no effect of the dispensing methods and eight isolates significantly reduced the disease intensity when compared to control. These strains were reassessed for disease control, and characterized based on siderophore production and antibiosis. Five isolates significantly reduced disease severity in the second in vivo experiment. Among these, strains GF203, GF264, and GF267 inhibited the development of the pathogen in vitro and were able to produce siderophores. Carbon source utilization profile revealed the strain GF267, besides the greatest reduction in the intensity of bacterial spot, presented a reciprocal competition ability with the pathogen. This strain was identified as Bacillus velezensis and, when applied on soil, increased the activity of peroxidase and polyphenoloxidase, provided increment of chlorophyll content, and reduced the disease intensity. Our study demonstrated B. velezensis GF267 as being a multi-site antagonist, which may have potential application in controlling tomato bacterial spot.