Pathogen-triggered exudation in woody plants: Molecular mechanisms and ecological impacts

Woody plants, critical components of ecosystems and urban environments, face significant threats from biotic agents that compromise their health and longevity. Pathogen-induced exudations, gummosis, wetwood, bleeding, and oozing, are critical yet poorly understood physiological responses compromising the health of woody plants across global ecosystems. This review synthesizes advances revealing how diverse pathogens (bacteria, fungi, oomycetes, viruses, nematodes) subvert host physiology to trigger exudate formation through molecular cascades that disrupt vascular integrity, reprogram defense gene expression, and drive cellular degradation. Exudates emerge from a paradox: while serving as host defense mechanisms, they concurrently act as vectors for secondary infections and alter soil microbiomes. Environmental stressors, intensified by climate change, amplify exudation by weakening tree resilience and enhancing pathogen virulence. Critically, chronic exudation accelerates tree decline, linking localized symptoms (twig/branch colonization) to landscape-scale mortality. We highlight the ecological duality of exudates as both disease biomarkers and ecosystem modulators of nutrient cycling. Integrating multi-omics tools and ecological frameworks, we propose holistic strategies to mitigate pathogen impacts. Future research must decipher host-pathogen crosstalk and harness resilience traits to safeguard forests and urban trees in an era of global change.