Tree resistance can be enhanced by a variety of biotic and abiotic inducers, including nonpathogenic and pathogenic microbes, and herbivores, resulting in enhanced protection against further biotic injury. Induced resistance (IR) could be a valuable tool in sustainable pest management. IR has been actively studied in herbaceous plant species, and, in recent years, in woody plant species, and is fast emerging as an intriguing, eco-friendly concept for enhancing tree resistance. However, before application of IR becomes possible, there is a need to increase our knowledge of the mechanisms of defence in forest trees. A richer understanding of these phenomena will play a critical role in developing sustainable integrated pest management strategies. This review summarizes our current knowledge of IR in forest trees, focusing on inducible defence mechanisms, systemic induction of resistance and phytohormone signalling networks. We conclude by discussing the potential advantages and limitations of applying IR-based management tools in forest systems.
