Linking aboveground and belowground inducible resistance

Induced resistance of plants against pests and diseases via plant defense responses is well documented and can occur aboveground, in the leaves, and belowground in the roots. A number of recent studies have shown that soil-borne pests can also induce plant resistance aboveground and vice versa. Since plants are frequently exposed to aboveground and belowground pests simultaneously, interactions between induced plant defense responses in the foliage and in the roots can have major implications for induced resistance. On the one hand, induction in one plant part may result in systemically induced resistance in the other part. On the other hand, simultaneously occurring aboveground and belowground induced plant defenses may interfere, for example, when the activities of root feeders alter the effectiveness of induced resistance against foliar herbivores. I will review the literature to show similarities and dissimilarities in aboveground and belowground resistance. I will show how soil dwelling pests such as nematodes and root feeding insects can induce defense responses in aboveground plant parts, and how aboveground pests can influence plant defense responses in the roots. I will discuss the mechanisms involved and provide examples of the consequences of interference between aboveground and belowground plant defense responses for plant damage and insect herbivore performance. Finally, I will show how such aboveground-belowground interactions can influence the reliability of indirect plant defense responses, the attraction by the plant of natural enemies of the attacker.