Within-plant circulation of systemic elicitor of induced defence and release from roots of elicitor that affects neighbouring plants

Herbivory on the above-ground plant parts can induce the production of volatiles that attract carnivorous enemies of the herbivores. These volatiles may be induced systemically in the damaged plant, In a previous study, we had shown that a systemic elicitor that induces the production of predator-attracting volatiles in lima bean plants can be collected from lima bean leaves by placing spider-mite-infested leaves with their petiole in water. However, it remained unknown to what sites this elicitor was transported within the plant. Here, we show that exposing uninfested lima bean leaves to this elicitor also results in a reduced rate of reproduction in spider mites (Tetranychus urticae). Furthermore, an elicitor can also be collected from whole lima bean plants of which one primary leaf was infested with spider mites. by detaching the other primary leaf and inserting the petiole., that is still connected to the plant, in a vial with distilled water. When uninfested lima bean leaves are incubated in this elicitor solution for three days, this results in the attraction of the predatory mite Phytoseiulus persimilis in an olfactometer. Finally, an elicitor of predator-attracting volatiles was collected from whole infested lima bean plants by placing the plants with their roots in distilled water. Uninfested lima bean plants that were subsequently placed with their roots in this water became attractive to the predatory mite P. persimilis relative to control plants that had been placed with their roots in water in which uninfested bean plants had been incubated previously. These data indicate that herbivore-infested plants may interact with undamaged neighbouring plants through chemical information that is exchanged in the soil. Important issues that need to be addressed next are discussed. The connection of above- and belowground interactions of plants with other organisms will have important consequences for future ecological studies on multitrophic interactions. (C) 2001 Elsevier Science Ltd. All rights reserved.