The role of Trichoderma in belowground-aboveground interactions between plants and insects

In recent years, the reduction of use of agrochemicals have received much attention due to environmental pollution and human health problems caused by their overuse. For this purpose, the search for green alternative practices has increased and interest for the genus Trichoderma has considerably increased in the last decade. Fungi of the genus Trichoderma are agronomically important for their beneficial effects on plant growth and development. The use of root symbionts has gaining popularity as an alternative practice for pathogen control, while no product has been marketed specifically for insect control to date. In this thesis, indirect effects of Trichoderma harzianum T-22 has been evaluated in the laboratory and in the field. The laboratory study focused on two aphids that attack tomatoes, Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae) and Myzus persicae (Sulzer) (Hemiptera: Aphididae). In this study, the response of two different clones of the aphid (referring to French and Spanish clones) to plants colonized by the fungus was investigated. Trichoderma harzianum results in a worsening of fitness in the French clone, but not in the Spanish clone. The influence of T. harzianum on the behavior of aphids belonging to the two clones was also investigated, since this is an aspect that may have considerable importance in virus transmission. In dual choice test, aphids of both clones preferred control plants to those colonized by Trichoderma, probably because of the repellent effect of the volatiles produced by the latter. Feeding behavior of M. euphorbiae, monitored using Electrical Penetration Graph (EPG) technique, was not affected by treatment with T-22, and both clones were able to reach the phloem and feed. As for M. persicae, previous studies are lacking. In laboratory conditions, M. persicae was attracted to tomato plants colonized by T. harzianum and performed better on them. In field experiments, the indirect effects on interactions between arthropods and Trichoderma will be evaluate on tomato and zucchini plants, among the most important crops in Italian horticultural production. The importance of field studies lie in the fact that Trichoderma-plant-insect interaction occurs under conditions of greater complexity and the result may be different from that recorded in the laboratory. Moreover, plants in the field can be simultaneously attacked by different pest species, activating different resistance pathways, and are also subjected to variable abiotic conditions. In this study, plant inoculation with T. harzianum T-22 significantly altered arthropod community in the field.