Trichoderma Species: Our Best Fungal Allies in the Biocontrol of Plant Diseases-A Review

Abstract

Biocontrol agents (BCA) have been an important tool in agriculture to prevent crop losses due to plant pathogens infections and to increase plant food production globally, diminishing the necessity for chemical pesticides and fertilizers and offering a more sustainable and environmentally friendly option. Fungi from the genus Trichoderma are among the most used and studied microorganisms as BCA due to the variety of biocontrol traits, such as parasitism, antibiosis, secondary metabolites (SM) production, and plant defense system induction. Several Trichoderma species are well-known mycoparasites. However, some of those species can antagonize other organisms such as nematodes and plant pests, making this fungus a very versatile BCA. Trichoderma has been used in agriculture as part of innovative bioformulations, either just Trichoderma species or in combination with other plant-beneficial microbes, such as plant growth-promoting bacteria (PGPB). Here, we review the most recent literature regarding the biocontrol studies about six of the most used Trichoderma species, T. atroviride, T. harzianum, T. asperellum, T. virens, T. longibrachiatum, and T. viride, highlighting their biocontrol traits and the use of these fungal genera in Trichoderma-based formulations to control or prevent plant diseases, and their importance as a substitute for chemical pesticides and fertilizers.

Keywords: Trichoderma; antibiosis; biocontrol agent; bioformulations; mycoparasitism; secondary metabolites.

Figure 1

Direct biostimulation and biocontrol properties of Trichoderma species. Beneficial Trichoderma spp. exert fungal-root communication via diffusible and volatile compounds, regulation of the stress hormone ethylene, and production of phytohormones, such as auxins (indole-3-acetic acid). Some of the plant-protecting mechanisms of Trichoderma include parasitism, antibiotic and secondary metabolites production, or activation of the induced systemic resistance (ISR). Trichoderma can trigger both growth-stimulating effects and plant defense action by the elicitation of salicylic acid (SA), ethylene (ET), and jasmonic acid (JA) dependent pathways against several types of potential plant pathogens such as nematodes and fungi.

Figure 2

Examples of Trichoderma secondary metabolites involved in plant interactions with growth-promoting effects (A) and secondary metabolites involved in mycoparasitism with antibiotic effect (B).