Belowground Defence Strategies in Plants: The Plant–Trichoderma Dialogue

Abstract

Trichoderma spp. are cosmopolitan soil fungi that hold great promise as biocontrol organisms. Their biocontrol capacity was initially thought to be based on their direct suppressive effects on plant pathogens, with most strains showing mycoparasitic potential and producing a large variety of enzymes and secondary metabolites. More recently however Trichoderma was also recognized as an opportunistic plant root colonizer that can trigger induced systemic resistance (ISR) in the plant, typically leading to a more rapid and robust systemic activation of defences after pathogen attack. As our understanding of the Trichoderma-plant interaction advances, it is becoming increasingly clear that Trichoderma is initially also perceived by the host plant as a potential invader. Trichoderma thus needs to find a way to deal with the plant defence response, either by avoiding or suppressing it, in order to establish a durable interaction with their host. In this chapter, we cover our current knowledge on the initial dialogue between Trichoderma and its host, including the defence responses mounted by the host plant and how Trichoderma attempts to circumvent it. Next, we describe how the host plant can benefit from this interaction. Trichoderma colonization can indeed prime the host defence, enabling it to react faster and stronger to subsequent pathogen attack. We then conclude with examples of Trichoderma-induced resistance and direct antagonism against different types of soil pathogens and pests.