**2.3 Macro and micro nutrient uptake**

It has been reported that plant nutrient uptake can be improved resulting in plant growth promotion. Microorganisms play a major role in accelerating nutrient uptake. *Trichoderma* is one of those microorganisms that contribute to nutrient uptake [24].



#### Trichoderma*: A Biofertilizer and a Bio-Fungicide for Sustainable Crop Production DOI: http://dx.doi.org/10.5772/intechopen.102405*

#### **Table 3.**

*Trichoderma improving macro and micro nutrient uptake by crops.*

In a sugarcane study, there was an increase in nitrogen, potassium, phosphorus and organic carbon after the inoculation with *Trichoderma viride* [25]. Nutrient availability, as well as uptake, is improved by the presence of *Trichoderma* in the rhizosphere. The nutrient uptake is improved because of the conversion of the required nutrients

from being unavailable to the plant to an available form. For example in acidic soils the applied chemical fertilizer is converted to an unavailable form to the plant, forming complexes that may be even toxic to the plant such as aluminum complexes [26]. Its the ability to colonize roots well that gives it an advantage over other microorganisms and enables the crop to receive more from it than others. Therefore, it provides a better and sustainable fertilization as it will be present in the root system as endophytes as well as root colonizers for a longer time than chemical fertilizers. Chemical fertilizers get used up as they do not multiply as microorganisms do. Sustainability is one of the potential benefits that *Trichoderma* provides as a biofertilizer. Other farmers apply microorganisms to improve fertilizer use efficiency by mobilizing nutrients that have accumulated in the soils yet are not available to the plant (**Table 3**) [34].

### **3.** *Trichoderma* **as a biofungicide**

Agriculture is an indispensable part of any country to feed the millions of people. However, production is hampered by various plant diseases posing serious yield reductions threatening global food security. Disease management employs mainly synthetic fungicides. However, with the mounting concern for human health and environmental risks, and the loss of pesticides to resistance, the search for nonchemical alternatives has been a focus of much research for more than three decades. Biocontrol agents have emerged as an important component of plant disease management, and may provide an alternative to synthetic fungicides.

*Trichoderma* species, free-living and cosmopolitan fungi found abundantly in the soil, decaying organic and vegetable matter, were first reported as biocontrol agents in the early 1930s in the control of root rot causing *Armillaria mellea* in citrus [35].

They are successful antagonists having biocontrol abilities against a broad range of economically important phytopathogenic fungi such as *Phytophthora, Rhizoctonia, Sclerotium, Phythium, Fusarium, Sclerotinia, and Galumannomyces. Trichoderma harzianum, Trichoderma viride and Trichoderma koningii* are the main species viz. presently mass-produced by entrepreneurs [36–40].

*Trichoderma* species have been of particular interest as biocontrol as due to their rapid growth and capability of utilizing different substrates, species of this genus are often predominant components of the soil mycoflora in various ecosystems. Their ability to produce hydrolytic enzymes, secondary metabolites and degradation of xenobiotics is also an additional advantage that have an important economic impact [31, 41–43].

Competition for nutrient and ecological niche, mycoparasitism and antibiosis are the major biological mechanisms involved in their direct antagonistic activity against plant pathogenic fungi [43–45]. They can also achieve an indirect effect of antagonism on the target pathogen by interacting with the host tissue, inducing host resistance which protects against the pathogen, promoting plant and root growth as well as improving plant stress tolerance. Many successful biocontrol agents use a combination of different modes of action to produce a higher level of antagonism [38, 46].

#### **3.1 Antibiosis as a mechanism of pathogen control**

Antibiosis involves the production of various antimicrobial compounds by *Trichoderma* strains that inhibit or reduce the growth and/or proliferation of phytopathogens [44]. Most *Trichoderma* strains also produce volatile and non-volatile toxic metabolites that inhibit colonization by antagonized microorganisms; among these

Trichoderma*: A Biofertilizer and a Bio-Fungicide for Sustainable Crop Production DOI: http://dx.doi.org/10.5772/intechopen.102405*

metabolites, the production of harzianic acid, alamethicins, tricholin, peptaibols, antibiotics, 6-penthyl-a-pyrone, massoilactone, viridin, gliovirin, glisoprenins, heptelidic acid and others have been described [47–50]. This phenomenon has been observed in various fungi including *Trichoderma*, which can produce a multitude of compounds with antagonistic properties including cell wall degrading enzymes such as cellulase, xylanase, pectinase, glucanase, lipase, amylase, arabinase, and protease, volatile metabolites such as 6-n-pentyl-2H-pyran-2-one (6-PAP) [51–53], and several antibiotics such as trichodermin, trichodermol, gliovirin, gliotoxin, viridin, herzianolide, pyrones, peptaibols, ethylene and formic aldehyde [50, 54, 55]. In general, strains of *T. virens* with the best efficiency as biocontrol agents can produce gliovirin [50].

#### **3.2 Mycoparasitism**

Mycoparasitism, direct contact of an antagonist with a fungal pathogen, involves sequential events, including pathogen recognition, attack and subsequent penetration of the host cell and death [10]. In this process, *Trichoderma* species initially produce cell wall degrading enzymes at low levels in an attempt to identify its prey. Upon recognition, growth towards the direction of the target pathogen area is induced together with a higher production of cell wall degrading enzymes (CWDEs), mainly chitinases, glucanases and proteases [56, 57]. *Trichoderma* species will then attach to their prey by binding to the carbohydrates present in the *Trichoderma* to the lectins of the fungi, followed by coiling around the pathogen's hyphae and appressoria development to penetrate the hyphae, which are subsequently attacked and degraded through the production of hydrolytic enzymes and secondary metabolites. Other CWDEs constituting hydrolysing polymers such as β-1,6-glucans and α-1,3-glucans are reported to further ensure complete disintegration of fungal mycelia or conidia [43, 58].

#### **3.3 Competition in the rhizosphere**

Starvation is the most common cause of death for microorganisms, so the limited availability of and competition for micro- and macro nutrients results in the biological control of fungal phytopathogens [59]. *Trichoderma* exhibits a better capability of absorption and mobilization of nutrients from the soil in comparison to other rhizospheric microorganisms; therefore, the biocontrol of fungal pathogens using *Trichoderma* involves the coordination of numerous strategies, such as the competition for nutrients, which is considered among the most important [60, 61]. In most filamentous fungi, iron uptake is essential for viability, and under iron starvation, most fungi excrete low molecular-weight ferric-iron specific chelators, termed siderophores, to mobilize environmental iron [62]. Certain *Trichoderma* strains can produce siderophores by trapping the ferric ions from the shared niche inhibiting the growth and activity of soil-borne fungal pathogens such *Botrytis cinerea* [63].

#### **3.4 Priming of resistance mechanism in host plants**

During plant–pathogen interactions, plants have evolved a wide range of defense mechanisms to cope with the constant attack by invading pathogens. However, plant defense can also be triggered by biocontrol agents [2, 54]. The rhizocompetent nature of *Trichoderma* species allows it to colonize roots, triggering the plant immune system (induced systemic resistance; ISR), and preactivation (priming) of the molecular mechanisms of defense against several


#### **Table 4.**

*Examples of Trichoderma antagonists used for successful control of fungal diseases and possible mode of action.*

potent phytopathogens and the stress challenged conditions [64–67]. Furthermore, colonization of this beneficial fungi promotes plant growth and also upgrades the host plants against various abiotic and biotic stresses [7, 68]. It balances different phytohormone-dependent pathways among which salicylic acid (SA), jasmonates (JA), ethylene (ET), abscisic acid (ABA), auxin (indole-3-acetic acid: IAA), and gibberellins (GA) are the most relevant—and modulating the levels of growth and defense regulatory proteins [2, 11, 54, 69–71]. Priming facilitates a faster and stronger reaction if the stress recurs. Reinforced responses to pathogen attacks come under the category of induced defense, while responses to abiotic are referred to as acclimation or hardening, even though these responses are similar at the beginning. They can also be enhanced by priming treatments [72, 73]. An accurate definition of how *Trichoderma* exerts its beneficial action on plants is of particular relevance to the way in which commercial products based on the abilities of *Trichoderma* are registered (**Table 4**) [15, 79, 80].
