Plants have evolved resistance traits that negatively affect attackers, and tolerance traits that sustain plant growth despite herbivore damage. These mechanisms often co-occur in a mixed-defence strategy, balancing resistance and tolerance. These plant defences can be enhanced upon interaction with soil microorganisms. Here, we investigated the effects of volatiles emitted by soil-borne fungi on plant defence to insect herbivory, and on plant phenology. We exposed roots of Brassica rapa plants to volatiles emitted by four...