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Abstract

Plants emit a large variety of volatile organic compounds during infection by pathogenic microbes, including terpenes, aromatics, nitrogen‐containing compounds, fatty acid derivatives, as well as the volatile plant hormones, methyl jasmonate and methyl salicylate. Given the general anti‐microbial activity of plant volatiles and the timing of emission following infection, these compounds have often been assumed to function in defense against pathogens without much solid evidence. In this review we critically evaluate current knowledge on the toxicity of volatiles to fungi, bacteria and viruses and their role in plant resistance as well as how they act to induce systemic resistance in uninfected parts of the plant and in neighboring plants. We also discuss how microbes can detoxify plant volatiles and exploit them as nutrients, attractants for insect vectors, and inducers of volatile emissions that stimulate immune responses that make plants more susceptible to infection. Although much more is known on plant volatile‐herbivore interactions, knowledge of volatile‐microbe interactions is growing and it may eventually be possible to harness plant volatiles to reduce disease in agriculture and forestry. Future research in this field can be facilitated by making use of the analytical and molecular tools generated by the prolific research on plant‐herbivore interactions.