Investigating the role of the plant in the interaction with the facultative symbiont Trichoderma spp.

Synthetic chemicals are widely used in agriculture for plant pest control but have serious negative effects both on human health and the environment. Besides, their production is energyconsuming, thus adding to their environmental cost. In this context, the use of Biological Control Agents (BCAs) as an alternative to conventional practices for plant pathogens control can significantly reduce the environmental and health impact of agriculture. Among the most popular BCA used in agriculture are rhizosphere-competent fungi of the genus Trichoderma, which exert beneficial effects on growth and disease resistance of interacting plants. Although they are widely used as bio-fertilisers and bio-pesticides in commercial formulates, knowledge on the molecular mechanisms underlying the plant response to the interaction is still lacking. Besides a direct plant pathogen control, Trichoderma spp. can also activate Induced Systemic Resistance (ISR), and sensitize plants to respond faster and/or more intensely to pathogen attack. The cross-talk that occurs between the fungal BCA and the plant is important both for the reciprocal identification of each player in the interaction and for obtaining beneficial effects. To contribute to the understanding of the plant role in the interaction, we investigated genetic variability among wild and cultivated tomato lines in their ability to interact with T. atroviride and T. harzianum and demonstrated that indeed the plant response to either Trichoderma species changes with the plant genotype both in terms of stem and root growth and in terms of induced defence mechanisms against the pathogen Botrytis cinerea. These findings indicate that the plant response to the interaction is under genetic control in tomato and demonstrate the feasibility of plant breeding aimed at obtaining tomato genotypes with improved ability to benefit from rhizosphere colonisation by Trichoderma strains. Besides, we demonstrate for the first time that Trichoderma is able to induce long-lasting over-expression of defence genes of the salicylic acid pathway in the absence of a pathogen, while its ability to stimulate plant resistance is accompanied by increased transcription of jasmonate-responsive genes upon pathogen challenge.