Amino acids suppress bacterial and rust diseases by interfering with pathogen entry processes

The increasing demand for environmentally sustainable disease management has stimulated interest in alternatives to chemical pesticides. Amino acids are ubiquitous plant metabolites that have been implicated in defense responses, but their role in disease suppression across pathogen types remains unclear. In this study, we evaluated the protective effects of exogenous amino acids against bacterial and fungal diseases in multiple crop systems. Foliar application of cysteine (Cys), lysine (Lys), and glutamate (Glu), individually or in combination, was tested against cabbage bacterial leaf spot caused by Pseudomonas cannabina pv. alisalensis (Pcal), wheat leaf rust caused by Puccinia recondita, and soybean rust caused by Phakopsora pachyrhizi. In cabbage, amino acid treatments reduced disease symptoms and bacterial populations, with mixtures showing enhanced effects. Mechanistically, amino acids decreased stomatal aperture width and limited bacterial entry, indicating a pre-entry mode of action. In wheat and soybean, amino acid treatments significantly reduced rust severity, primarily through inhibition of appressorium formation without affecting spore germination. These findings demonstrate that amino acids suppress both bacterial and rust diseases by targeting early infection processes. Notably, mixtures of amino acids consistently conferred stronger protection than individual treatments, suggesting additive or synergistic effects. Collectively, our results establish amino acids as potential pre-penetration barriers that interfere with pathogen entry across kingdoms and highlight their promise as sustainable tools for crop disease management.