Robinson, J. Y.; Shepard, H. S.; Ambachew, D.; Eyegheleme, P. J.; May, J. C.; Mmbaga, M.; McLean, J. A.

Biological control agents can offer an eco-friendly and more sustainable alternative to conventional chemical pesticides, providing protection against destructive pathogens, such as Phytophthora capsici, while reducing potential environmental harm associated with synthetic pesticide use in agricultural production systems. This work demonstrates the biocontrol effectiveness of various Bacillus species, including Bacillus vallismortis, Bacillus amyloliquefaciens, Bacillus thuringiensis, and Bacillus subtilis, against the widespread plant pathogen, Phytophthora capsici. Our studies showed that Bacillus thuringiensis and Bacillus subtilis promote plant growth and provide protection against Phytophthora capsici in both in vitro and in vivo greenhouse studies, while Bacillus vallismortis and Bacillus amyloliquefaciens were effective in vitro but not in vivo. Specifically, Bacillus thuringiensis was observed to both hinder the growth of Phytophthora capsici and enhance plant resilience to this oomycete pathogen. To probe the molecular interactions between biocontrol agent and pathogen, a dual culture of Bacillus thuringiensis and Phytophthora capsici was analyzed in situ using a mass spectrometry imaging workflow that implemented desorption electrospray ionization. This imaging approach spatially investigated the complex biochemical interactions that serve as the molecular foundation for the effectiveness of these biological control agents in crop protection, including antagonistic interactions that may be fundamental to their method of action. Herein, we demonstrate the benefits of biological control agent application in tomato cultivation, including enhanced pathogen control and plant growth, and showcase the strengths of desorption electrospray ionization-mass spectrometry imaging when applied to the spatially-resolved molecular characterization of agriculturally relevant microorganisms.