Bacillus thuringiensis promotes systemic immunity in tomato, controlling pests and pathogens and promoting yield

Plant pathogens and pests pose an increasing threat to worldwide food security. To improve and strengthen food security under increasingly difficult environmental, economic, and geopolitical conditions, the prospect of using microbial biocontrol agents becomes increasingly desirable. One of the most studied, and commercially used, biopesticide microorganisms is the entomopathogenic, gram-positive, soil bacterium Bacillus thuringiensis (Bt). While Bt has been known for many years as an insecticidal microorganism and used extensively in agriculture, its possible anti-phytopathogen and plant growth-promoting activities have received comparatively limited attention thus far. Here, we examine the ability of Bt to promote systemic immunity in tomato plants. We investigate how Bt influences plant immunity and disease resistance against several fungal and bacterial plant pathogens, as well as several arthropod pests. In order to determine which component of Bt (i.e., Bt spores or pure crystals) is responsible for the observed effects on pathogens or pests, we dissected the different fractions present in a commercial preparation and assessed their effects on pest and pathogen control. As previously reported in the Bt literature, our results indicate that proteins produced by Bt are likely the primary acting components against pests. In the case of pathogens, however, it appears that both the Bt spores and proteins directly act against pathogens such as the fungus Botrytis cinerea. Bt Spores and produced proteins also both induce plant immunity. Understanding the different Bt mode of action mechanisms will help in developing cost-effective and safe plant protection strategies for enhancing food security. Taken together, our findings suggest that Bt could be used in broad-spectrum pest and disease management strategies. Pending validation in agricultural settings, Bt products on the market could have additional uses in sustainable pest management and plant growth promotion.