Integration of two herbivore-induced plant volatiles results in synergistic effects on plant defense and resistance

Plants can use induced volatiles to detect herbivore‐ and pathogen‐attacked neighbors and prime their defenses. Several individual volatile priming cues have been identified, but whether plants are able to integrate multiple cues from stress‐related volatile blends remains poorly understood. Here, we investigated how maize plants respond to two herbivore‐induced volatile priming cues with complementary information content, the green leaf volatile (Z)‐3‐hexenyl acetate (HAC) and the aromatic volatile indole. In the absence of herbivory, HAC directly induced defense gene expression, while indole had no effect. Upon induction by simulated herbivory, both volatiles increased jasmonate signaling, defense gene expression and defensive secondary metabolite production and increased plant resistance. Defenses and resistance in dual‐volatile exposed plants were more strongly induced than in plants exposed to single volatiles. Induced defense levels in dual volatile‐exposed plants were significantly higher than predicted from the added effects of the individual volatiles, with the exception of induced plant volatile production, which showed no increase upon dual‐exposure relative to single exposure. Thus, plants can integrate different volatile cues into strong and specific responses that promote herbivore defense induction and resistance. Integrating multiple volatiles may be beneficial, as volatile blends are more reliable indicators of future stress than single cues.