Root inoculation with beneficial soil microbes enhances indirect plant defenses induced by insect feeding and egg deposition

Tuğcan Alınça, Ezio Peria, Livio Tortaa, Salvatore Guarinob, Stefano Colazzaa, Bart Lievens, Antonino Cusumanoa

This is a plain language summary of a Functional Ecology research article which can be found here.

Plants are sessile organisms, yet they have adopted sophisticated ways to defend themselves against insect pests. One of these strategies consists of mounting early defenses which are activated even before the herbivore reaches the crop-feeding stage. For example, plants can kill the eggs of herbivores by recruiting carnivore insects which develop on the pest eggs. These carnivore insects, called egg parasitoids, follow the scent of plants induced by pest eggs (i.e. “oviposition-induced plant volatiles”). Plants can also mount early defenses against biotic stressors with the aid of beneficial soil microbes, yet it is not known if such beneficial microbes can help the plant get rid of noxious herbivore eggs.

In this study, we show that plant colonization with beneficial soil microbes can influence the strength of plant responses to insect feeding and egg deposition, further disentangling complex plant-insect-microbe interactions. Remarkably, we found that root inoculation with the beneficial soil microbe Trichoderma harzianum T22 enhanced the attraction of the egg parasitoid Trissolcus basalis towards tomato plants carrying eggs of the pest Nezara viridula. Furthermore, chemical analysis showed that root inoculation with T. harzianum T22 of tomato plants resulted in changes in the composition of oviposition-induced plant volatiles, which was consistent with the behavioral observations.

In this work, we evaluated the effects of inoculation with the beneficial soil fungus Trichoderma harzianum strain T22 on a tritrophic system consisting of tomato, the southern green stink bug Nezara viridula and its associated egg parasitoid Trissolcus basalis. We found that root inoculation with beneficial soil microbes enhanced plant defenses induced by insect feeding and egg deposition which resulted in an increased attraction of the egg parasitoid towards plants carrying pest eggs (Credit: Antonino Cusumano)

In modern agriculture, there is an urgent need to develop sustainable cropping systems. In this perspective, the use of beneficial soil microbes such as Trichoderma may be of high interest for sustainable pest control, as they enhance not only plant growth but also plant defenses against phytopathogens and herbivores, including eggs of insect pests.