Phenolic Compounds in Crop Protection: Mechanisms in Plant–Pathogen Interactions

Plant pathogens cause significant crop yield losses in both agronomic and horticultural ecosystems. During this ongoing evolutionary arms race between plants and pathogens, plants have evolved a diverse array of constitutive and induced defense responses to survive, where secondary metabolites, especially phenolic compounds, are ubiquitous and driven by selective pressures from microbial pathogens. These compounds aid plant health by conferring tolerance and resistance to various biotic and abiotic stresses. Recent advances in omics techniques have provided many ways to extract and quantify these plant compounds and to understand their antimicrobial activity, offering a potential opportunity for sustainable plant disease management strategies. This review emphasizes the role of phenolic compounds as critical secondary metabolites in plant defense and provides a summary across a wide array of agronomic (cereals, legumes, root crops, leafy crops, fodder crops) and horticultural (vegetables, fruits) crops. We explored the distinct mechanisms of phenolic compounds acting as antimicrobials and their differential production in response to pathogenic microbes. We have also highlighted current knowledge gaps to guide future research toward sustainable crop protection by using these compounds in Integrated Disease Management strategies.