Plants, including the Arabidopsis thaliana shown here, secrete antimicrobial compounds from their roots as part of their defense against potential pathogens. The plant on the left remains healthy after exposure to the bacterium Pseudomonas syringae. In contrast, the plant on the right was exposed to a strain of Pseudomonas syringae resistant to the antimicrobial compounds. Arrows highlight the signs of disease.

Credit: Jorge Vivanco, Colorado State University