Trichoderma

Nascimento, V. C., Rodrigues-Santos, K. C., Carvalho-Alencar, K. L., Castro, M. B., Kruger, R. H. & Lopes, F. A. C., 2022, Trichoderma: biological control efficiency and perspectives for the Brazilian Midwest states and Tocantins, Brazilian Journal of Biology (e 260161) 82, pp. 1-9 : 2-3

2. Trichoderma : an Effective BCA

Fungi of the genus Trichoderma belong to the phylum Ascomycota, class Sordariomycetes and family Hypocreaceae with easily perceived phenotypic characteristics, ranging from macroscopic fungal parasites to the rhizosphere (De Abreu and Pfenning, 2019). Despite being mesophilic, these fungi are distributed throughout the globe, mostly in tropical and temperate climate regions (Machado et al., 2012).

Currently, it is estimated that the diversity of fungi varies from 2.2 to 3.8 million species ( Calaça et al., 2022), and just over 375 species of Trichoderma are accepted and can be identified through molecular phylogeny ( Cai and Druzhinina, 2021). The genus Trichoderma has fungi that are present in the soil, acting as macroscopic parasites and rotting organic matter, considered environmental opportunists ( Druzhinina et al., 2011). Trichoderma fungi are defined by some common phenotypic characteristics (eg. green colonies) ( Figure 1 ), such as wide geographic distribution, rapid growth, and highly capable of parasitizing or preying on other fungi and, in the case of some species, they can establish beneficial interactions with plants, resulting in the promotion of growth and induction of resistance to diseases and abiotic stresses ( Harman et al., 2004).

As aforementioned, the Trichoderma genus is effective against different phytopathogens for its high capacity to be found in different soils and substrates. In addition, Trichoderma shows an accelerated growth that favors habitat colonization.These fungi can grow in soils without agricultural crops and inactivate structures of infection and resistance to existing pathogens (Lucon et al., 2014). Thus, Trichoderma isolates can act preventively and not only curatively and can be applied before diseases emerge.

Several studies have proved the effectiveness of Trichoderma isolates against phytopathogens found in the soil, responsible for root infection and incidence of rot in plants, such as fungi of the genera Fusarium , Rhizoctonia , and Sclerotinia (Lucon et al., 2014) . Such an effectiveness of Trichoderma in controlling these phytopathogens occurs due to its antagonist actions, which can be classified as i) mycoparasitism – secretion of hydrolytic enzymes acting on the host’s cell wall, ii) competition for space or nutrients, and iii) production of metabolites interfering with pest development ( Bettiol, 2001) ( Figure 2 ).

Mycoparasitism allows the organism of the genus Trichoderma to have a biotrophic and saprophytic nutrition, through which the enzymes secreted by these fungi prevent the germination of spores, growth of hyphae, and the development of sclerotia and chlamydospores (resistance structures) of other species, including pathogens ( Druzhinina et al., 2018; Monte et al., 2019). Expanding its antagonistic role, Trichoderma species rely on the production of a vast diversity of secondary metabolites that present antibiotic properties to many species, enhancing the effectiveness of population control of other species, as target pests ( Hermosa et al., 2014; Monte et al., 2019).

Fungi of the Trichoderma genus feed through their hyphae, which secrete hydrolytic enzymes, thus allowing to break the host’s cell wall (Monte et al., 2019). A large number of genes can encode enzymes, such as β-1-3- glycanases, N-acetyl-glucosaminidase (NAGase), chitanase, and proteases; these enzymes identify mycoparasitism as an ancestral character of genus (Kubicek et al., 2011; Lopes et al., 2012). Thus, the enzyme arsenal of the genus Trichoderma can degrade several compounds in superficial cell from different hosts, allowing these fungi to parasitize other fungi.

Another mechanism used by fungi of the Trichoderma is competition for space and nutrients. Competition is a process related to the interaction between two or more organisms engaged in the same resource, such as nutrients, water, light, space, growth factors, oxygen, among others (Machado et al., 2012). Thus, fungi of the Trichoderma genus are known to be excellent competitors, preventing access to space and nutrients, resulting in inhibited growth of phytopathogenic populations; in addition to influencing plant growth and productivity.

Figures

Figure 1. Trichoderma isolates collected in Brazil. (A) Isolate T. harzianum ALL-42 grown on PDA (Potato Dextrose Agar) medium; (B) Isolate T. asperellum T-00 grown on PDA (Potato Dextrose Agar) medium.

Figure 2. Interaction mechanisms ofTrichoderma spp.and phytopathogens.(A) Yellow,red, and blue correspond to the antagonistic actions of Trichoderma from contact with phytopathogens;(B) Contact of fungal hyphae (Trichoderma spp.ingreen and phytopathogens inorange). Elements in pink correspond to the process of competition for space (long base) and nutrients (rectangles). Blue circles correspond to the metabolites produced by Trichoderma. Yellow stars represent the enzymes produced by Trichoderma in the mycoparasitic process.