Deciphering Trichoderma-Plant-Pathogen Interactions for Better Development of Biocontrol Applications

Abstract

Members of the fungal genus Trichoderma (Ascomycota, Hypocreales, Hypocreaceae) are ubiquitous and commonly encountered as soil inhabitants, plant symbionts, saprotrophs, and mycoparasites. Certain species have been used to control diverse plant diseases and mitigate negative growth conditions. The versatility of Trichoderma's interactions mainly relies on their ability to engage in inter- and cross-kingdom interactions. Although Trichoderma is by far the most extensively studied fungal biocontrol agent (BCA), with a few species already having been commercialized as bio-pesticides or bio-fertilizers, their wide application has been hampered by an unpredictable efficacy under field conditions. Deciphering the dialogues within and across Trichoderma ecological interactions by identification of involved effectors and their underlying effect is of great value in order to be able to eventually harness Trichoderma's full potential for plant growth promotion and protection. In this review, we focus on the nature of Trichoderma interactions with plants and pathogens. Better understanding how Trichoderma interacts with plants, other microorganisms, and the environment is essential for developing and deploying Trichoderma-based strategies that increase crop production and protection.

Keywords: ISR; Trichoderma; fungal chemical ecology; mutualistic; mycoparasitism; plant defense; secondary metabolite; volatile organic compounds (VOC).

Figure 1

Trichoderma–plant–pathogen interactions map. Trichoderma produces recognition molecules, i.e., MAMPS (microbe-associated molecular patterns) and effectors, which bind to the PRRs (pattern recognition receptors) and intracellular receptors activating mitogen-activated protein kinase (MAPK) cascades, leading to the reprogramming of several plant pathways related to defense, i.e., induced systemic resistance (ISR), systemic acquired resistance (SAR), and hypersensitive response (HR), as well as interfering with hormonal homeostasis, i.e., ethylene (ET), abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA) pathways. Trichoderma-pathogen interactions takes several forms through the action of its diverse secretome containing volatile organic compounds (VOC), cell wall degrading enzymes (CWDE), reactive oxygen species (ROS), and antimicrobial secondary metabolites (SM). By forming these interactions, Trichoderma increases plant fitness and tolerance against biotic stress either by priming plant defenses, increasing plant growth, or releasing pathogen pressure leading to the enhanced growth response.

Figure 2

A schematic diagram displaying simplified glimpse of possible crosstalks between Trichoderma spp., plant pathogens, other beneficial microbes (i.e., arbuscular mycorrhizal fungi (AMF)) and plants.