Introductory Chapter: Trichoderma the Versatile Fungus to Soil Plant Pathogens Control and Bioprocess Uses

1. Introduction

The Trichoderma mycoparasitism relationship against pathogens may involve events such as location, recognition, direct contact, formation of hook-shaped structures with appressorium function, penetration, folding, and development of parallel hyphae [1, 2, 3, 4]. Some studies report that Trichodema species are efficient in antagonizing phytopathogens with resistance structures considered difficult to be attacked by microorganisms, such as spores, sclerotia, chlamydospores, and microsclerotia [5, 6].

Trichoderma antagonism against sclerotia producers may be imposed by different mechanisms, such as mycoparasitism, antibiosis, competition, resistance induction, and plant growth promotion [1, 7, 8, 9]. The niche competition for space and nutrients besides antibiosis are the most often mechanisms used by biocontrol agents, and one of the main Trichoderma strategies. The fast reproduction and colonization confer more effectiveness on available resources using. By the way, the successful antagonism could be attributed to the combined action of secondary metabolites and hydrolytic enzymes [10]. The wide range of secondary metabolites includes epipolythiodioxopiperazines (ETPs), peptaibols, pyrones, butenolides, pyridines, azaphilones, steroids, anthraquinones, lactones, trichothecenes, and harzianic acid [8]. These metabolites can interfere with the metabolic activities of other microorganisms, promoting growth and sporulation inhibition, reduction in spore germination, in addition to hyphae distortions, and endolysis. Some Trichoderma species are strong cellulases, chitinases, and β-1,3-glucanases producers. These enzymes are involved in the fungi and oomycetes cell wall components degradation process and can interfere in its biosynthesis [2, 11, 12, 13, 14, 15]. Proteases and lipases can also kill some fungi, which are substrate for mycoparasites [5, 16]. Different enzyme cell wall degradation-related are expressed in Trichoderma harzianum in biocontrol when grown on mycelia, sclerotia, or apothecia of S. sclerotiorum. There is probably a synergistic action between the cell wall-degrading enzymes [2].

The Trichoderma mycoparasitism relationship against pathogens may involve events such as location, recognition, direct contact, formation of hook-shaped structures with appressorium function, penetration, folding, and development of parallel hyphae [1, 2, 3, 4, 6, 17, 18, 19]. Some studies report that Trichodema species are efficient in antagonizing phytopathogens with resistance structures considered difficult to be attacked by microorganisms, such as spores, sclerotia, chlamydospores, and microsclerotia [5, 6, 17]. Besides that, Trichoderma application in seeds improves the seed sanity, physiological quality, germination, and early development, as observed for soybean seeds [9].

2. Biological control by Trichoderma

In 2014 there were 177 Trichoderma-based fungicides commercially available in the world [20]. These products contained mainly Trichoderma asperellum, T. hamatum, T. harzianum, and T. viride as active ingredients and were recommended mainly for seed and soil treatments [20]. In Brazil, there are currently 34 formulated products with Trichoderma as active ingredients registered in the Ministry of Agriculture, Livestock and Food Supply (MAPA) [21, 22]. These 34 products are based on four species: T. harzianum, T. asperellum, T. koningiopsis and T. stromaticum. The combination of more than one biocontrol agent is thought to be advantageous, but it depends on the individual strains’ compatibility [23]. Six out of the 34 registered products in Brazil are formulated with one or two Trichoderma and Bacillus amyloliquefaciens strains.

However, it is not known whether these microorganisms are compatible or not or if there is any synergism in their combination. Bacterial genera such as Bacillus and Pseudomonas are potential biocontrol agents of soil-borne pathogens due to the secretion of antibiotics and lytic enzymes in the rhizosphere of plants. Therefore, they are potential agents to be combined with Trichoderma, especially when they do not inhibit each other [23, 24, 25, 26, 27]. However, the compatibility of combinations needs to be evaluated with in vitro and in planta assays [28]. Interactions between Trichoderma and mycorrhyzae are sometimes antagonistic, such as with the ectomycorrhyzal basidiomycetous genus Laccaria spp., where there was clear inhibition of growth, colonization, and spore germination on both partners [29, 30, 31]. However, sometimes these interactions are synergistic, such as with Glomus spp. Although there was an increase in plant biomass in the interaction, microscopical observations clearly showed that Trichoderma was parasitizing this endomycorrhyzal fungus [32].

The fungicides thiophanate methyl+fluazinam, carbendazim+tiram, metalaxyl-M+fludioxonil, fipronil+pyraclostrobin+thiophanate-methyl and carboxine+tiram are compatible with the isolates of Trichoderma spp. The fungicide carboxin+tiram is compatible with the isolates at high concentration of 1000 ppm, thus suggesting that these fungicides can be used in the integrated management with the isolates Trichoderma spp. [9].

3. Conclusion

Trichoderma spp. is a versatile fungus with a high reproductive capacity and with a high potential for application in the biological control of plant diseases. It stands out for the control of phytopathogens with use via seed, soil, straw, and has action or interaction with bacteria, actinomycetes, and mycorrhizas, improving its action in hyperparasitism and antibiosis. It can also be used in the production of biofuels, through the degradation of cellulose, and even pharmacologically.

Acknowledgments

FCJ acknowledges CNPq (National Council for Scientific and Technological Development) for his productivity scholarship. DSJF acknowledges Fundação Araucária (Araucária Foundation to Support Scientific and Technological Development of Paraná) for his productivity scholarship.

Conflict of interest

The authors declare no conflict of interest.