Bacillus and Pseudomonas spp. strains induce a response in phenolic profile and enhance biosynthesis of antioxidant enzymes in Agrobacterium tumefaciens infected tomato plants

Some antagonistic bacteria contribute to the management of plant diseases by stimulating the host natural defense and/or by providing direct biocontrol of pathogens. The objective of this study was to evaluate the biocontrol performances and the ability to induce a systemic response to crown gall of four strains belonging to Bacillus and Pseudomonas genera. Evaluation of in vitro antagonistic ability showed that the four bacteria had a different spectrum of activity against the three tested strains of Agrobacterium tumefaciens. A delay in time of appearance and a significant reduction of the tumor size were observed in tomato plants obtained by bio-primed seeds and stem inoculated with A. tumefaciens . Seed priming with antagonistic strains stimulated some systemic defense mechanisms in tomato plants that can be related to the reduction of disease symptoms induced by A. tumefaciens . Both antagonists and A. tumefaciens strains induced variations in phenol content and peroxidase activity while polyphenol oxidase activity was mainly affected by the single A. tumefaciens strain. The response was different in relation to the various combinations of antagonist/pathogen, however Pseudomonas brassicacearum EPR3 strain was the most effective strain.