# Fungi of the _Trichoderma_ Genus: Future Perspectives of Benefits in Sustainable Agriculture
## 5 Application of _Trichoderma_ Fungi in Promoting Plant Growth
### Induction of Plant Resistance to biotic Stress  
The induction of plant systemic resistance to stress by _Trichoderma_ sp. is a complex process based on many related chemical reactions. When a potential pathogen is detected, these microorganisms send signals to the plants, leading to an increase in the number of active enzymes and defense metabolites produced by these organisms [21; 63; 87], such as xylanase, chitinase, lipoxygenase, phenyl ammonia-lyase, peroxidase, polyphenol oxidase, terpenoid, pathogenesis-related proteins (PR proteins), phytoalexins (coumarin, lubimin, phytotuberol, resveratrol, rishitin, soleetivone), and antioxidants (abcsisic acid (ABA), glutathione) [124]. The accumulation and increase in the concentrations of these elicitors are associated with the activation of the immune system in the plant, which includes Induced Systemic Resistance (IRS) directed at heterotrophic pathogens and Systemic Acquired Resistance (SAR) directed at biotrophic and hemibiotrophic pathogens [32; 113]. The IRS response is associated with the synthesis of jasmonic acid (JA) and ethylene (ET), which are responsible for chlorosis, rapid aging, and the death of infected tissue. In contrast, the SAR response is associated with the synthesis of PR proteins and salicylic acid (SA), which limit the spread of pathogens in the plant by inducing programmed death of the infected cell [55; 58; 154; 155; 156] (Table 3). [PERSON] et al. [157] documented that _T. harzianum_, when used to infect bean, in response to the threat of _R. solani_, synthesized greater amounts of ergosterol and squalene, which then activated the bean's defense mechanisms and limited pathogen growth. Maintaining adequate levels of ergosterol and squalene ensures the stability and integrity of plant cell membranes, which are barriers against attack by pests. [PERSON] et al. [158] proved that the treatment of cucumber with _T. atroviride_ induced the accumulation of volatile organic compounds and salicylic acid derivatives, which stimulated its immune system against _R. solani_. The inoculation of plants with the analyzed isolate resulted in enhanced activity of defense enzymes (guaiacol peroxidase, phenylalanine ammonia lyase, polyphenol oxidase, syringaldazine peroxidase), accumulation of phenolic and hydrogen peroxide, as well as decreased lipid peroxidation. In addition, _T. atroviride_ increased the deposition of lignin and callose in cucumber cells, thus protecting its vascular system and assimilation cells from pathogen action. Treatment with the test strain significantly enhanced the fresh weight of the shoot and dry weight of roots by 55% and 77%, respectively, compared to the control. In contrast, [PERSON] et al. [159] reported that in response to the threat of _B. cinerea_, _T. longbrachiatum_ activated signaling pathways associated with salicylic acid, jasmonic acid, and ethylene in cucumber. The treatment of plants with the analyzed strain caused a significant increase in the concentration of phytohormones SA, JA, and ET, thus leading to the induction of resistance, synthesis of defense metabolites, and inhibition of the pathogen growth by 49.62% on the fourth day. In addition, _T. longbrachiatum_ enhanced root length, plant height, and fresh weight of cucumber by 48.68%, 10.82%, and 27.44%, respectively. Similarly, [PERSON] et al. [160] found that _T. asperellum_ activated the expression of genes associated with the synthesis of jasmonic acid and ethylene, thereby inducing IRS and SAR resistance against _B. cinerea_ in tomato and reducing the disease incidence by 38%. Root length and seed germination rate were also increased by 37.86% and 5.55%, respectively.