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 vola tiles that attract carnivorous enemies of the herbivores. These volatiles m ay be induced systemically in the damaged plant, In a previous study, we ha d shown that a systemic elicitor that induces the production of predator-at tracting volatiles in lima bean plants can be collected from lima bean leav es by placing spider-mite-infested leaves with their petiole in water. Howe ver, 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 (T etranychus urticae). Furthermore, an elicitor can also be collected from wh ole lima bean plants of which one primary leaf was infested with spider mit es. by detaching the other primary leaf and inserting the petiole., that is still connected to the plant, in a vial with distilled water. When uninfes ted lima bean leaves are incubated in this elicitor solution for three days , this results in the attraction of the predatory mite Phytoseiulus persimi lis in an olfactometer. Finally, an elicitor of predator-attracting volatil es 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 th e predatory mite P. persimilis relative to control plants that had been pla ced with their roots in water in which uninfested bean plants had been incu bated previously. These data indicate that herbivore-infested plants may in teract 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 pla nts with other organisms will have important consequences for future ecolog ical studies on multitrophic interactions. (C) 2001 Elsevier Science Ltd. A ll rights reserved.