Trichoderma: A Biofertilizer and a Bio-Fungicide for Sustainable Crop Production

Abstract

Trichoderma has been studied widely. It has been found to play a major role in agricultural production. Around the world scientists and farmers have taken advantage of this knowledge. It is reported to improve plant growth of many crops such as tomato, lettuce, maize, beans, cabbage sugarcane and many more crops. There are two broad categories where Trichoderma plays a major role which is its use as a biofertilizer as well as a biofungicide. Its use as a biofertilizer has been aggravated by its ability to produce volatile compounds, ability to solubilize phosphates making them available to the plant. Moreover, farmers use it as a biofertilizer because it improves the uptake of macro and micro nutrients by the plant. As a biofungicide, Trichoderma is not to control many pathogens from various crops. This includes the control of pathogens such as Rhizoctonia, Phytophthora, Rhizoctonia, Sclerotinia, Phythium, Fusarium, Sclerotinia species and Galumannomyces. The mechanisms used by Trichoderma as a biofungicide includes, antibiosis, mycoparasitism, competitive advantage in the rhizosphere as well as priming of the crop self-defense mechanisms. The purpose of this book chapter is to highlight the importance of Trichoderma in agriculture as a biofertilizer and biofungicide.

1. Introduction

The increase in the human population around the world has pushed farmers to produce more food. This pressure forced some farmers to use more chemicals in their operations, which led to concerns raised by environmentalists and health officials as some chemicals were damaging the environment and people’s health. This has raised a necessity of exploring alternative methods to improve fertilization, and manage pests and diseases.

Biofertilizer became an option as it is friendlier to the environment as well as on human health. Trichoderma is one of the fungal cultures that has been studied for this purpose [1]. It has been found that Trichoderma can produce various plant growth-promoting compounds such as enzymes and phytohormones [2]. Some enzymes produced, helps the plant to access nutrients that are not accessible by the plant due to their form. For example acid soils tend to bind phosphorus forming toxic complexes rendering the phosphorus unavailable to the crop. This results in the crop not getting the nutrients that were meant for it, thus reducing the crop yields. Some enzymes produced by Trichoderma solubilize phosphates making the phosphorus available again to the crop [3].

Phytohormones on the other hand are compounds that are responsible for the growth and development of the plant. Some are responsible for plant elongation, shoot and root developments, others are involved in plant pests and disease control [4]. Trichoderma has been reported to produce some of the plant growth hormones such as indole-3-acetic acid (IAA), Auxins, gibberellic acid [5, 6, 7]. Scientists and farmers exploit these properties by developing biofertilizers, in this case using Trichoderma as the organism that can produce multiple phytohormones [8].

Biofungicides also became an alternative to chemical or synthetic fungicides to minimize the damage caused by chemical fungicides to the environment, animals and human beings. Trichoderma is one of the fungi that is also used as biofungicides by farmers as it has various mechanisms for controlling growth and development of several plant pathogens. Trichoderma is reported to produce antibiotics [9, 10], volatile compounds [11, 12], induce or prime plant resistance [13]. Moreover, it is reported to compete better than other microorganisms in the rhizosphere and has mycoparasitism behavior [14].

The objective of this book chapter is to prove that Trichoderma may be used as both a biofertilizer and biofungicide providing a sustainable alternative to chemical methods of fertilization and controlling plant pathogens.

2. Trichoderma as a biofertilizer

Trichoderma has been reported to promote plant growth in various ways. Some people have used it as a biofertilizer because of its ability to stimulate plant growth of many crops. It comes as an alternative to chemical fertilizer or as an amendment to improve crop production. Many attributes qualifies it to be used as an alternative or amendment to improve fertilization sustainably. Some of them are the following facts:

• It produces plant growth hormones and volatile compounds;

• It contributes to solubilizing phosphates that are unavailable to the crop

• It also takes part in promoting the uptake of macro and micro nutrients needed by the crop

2.1 Production of plant growth hormones and volatile compounds

Plant growth hormones are also called phytohormones. They are involved in many processes in the plant including communication, biotic and abiotic stress management, and many more processes. They have been reported for many years to play a vital role in the growth and development of a crop. Root and shoot elongation needs phyto-hormones to happen properly at the correct speed that supports high productivity. It has been reported that the presence of Trichoderma increases the production of some growth hormones such as indole-3-acetic acid (IAA) and gibberellic acid [15]. These two hormones are important in promoting plant growth, they are responsible for plant elongation [7]. As stated in Table 1, Trichoderma also improves germination rate and improves seedling vigor, which is an advantage for the crop. This is also associated with balanced phytohormones.

Trichoderma strain	Intended use	Target crop	Mode of application	Benefits/comments	Ref. (s)
Trichoderma azevedoi	Growth promotion and inhibition of phytopathogen development	Lettuce	Expose plants to T. azevedoi	Increased chlorophyll content, and carotenoids.; Decreased the severity of white mold by up to 78.83%	[16]
Trichoderma afroharzianum	Growth promotion	Tomato	Seed treatment	Phytohormone homeostasis, antioxidant activity, phenylpropanoid biosynthesis and glutathione metabolism	[17]
Trichoderma harzianum, Trichoderma asperellum, Trichoderma hamatum, and Trichoderma atroviride	Biofertilizer	Chinese cabbage	Through irrigation	Increased yield by 37%; Increased enzyme activity in the soils (urease by 25.1%, phosphatase by 13.1%, and catalase by 14.0%, Providing more inorganic nitrogen and phosphorus to the soil	[18]
T. asperellum strain GDFS1009	Soil conditioner	Maize	On soil as granules	Increased yields	[19]
Trichoderma brevicompactum, Trichoderma gamsii and T. harzianum	Biofertilizer	Tomato	Seedling drenching	Produces indole-3 acetic acid and	[15]

Table 1.

Production of plant growth hormones and volatile compounds by Trichoderma to improve plant growth.

2.2 Solubilization of phosphates

Phosphorus is one of the critical nutrients that plants need for their growth and development. It is found in the soil but due to depletion farmers have to apply fertilizers. However, the availability of phosphorus to the crop depends on the form it is in. Acidic soils bind phosphorus and make it unavailable to the crop, which is an undesired outcome [20]. Due to this, the accuracy of the amount required by the crop may not be achieved resulting in challenges associated with lack or insufficient phosphorus in the soil [3]. Some microorganisms mediate this process by solubilizing phosphates, converting them back to be in the available form for crop utilization. Trichoderma species have been reported to be one of those organisms. Species such as Trichoderma harzianum [21], Trichoderma reesei [22], solubilize phosphates through the production of enzymes called phytase. The phytase activity is induced by the presence of insoluble tricalcium phosphate [5]. Other Trichoderma species such as Trichoderma koningiopsis solubilize phosphates by producing alkaline phosphatase enzymes (Table 2) [6].

Trichoderma strain	Intended use	Target crop	Mode of application	Benefits/comments	Ref. (s)
T. harzianum, T. asperellum, T. hamatum, and T. atroviride	Biofertilizer	Chinese cabbage	Through irrigation	Increased yield by 37%; Increased enzyme activity in the soils (urease by 25.1%, phosphatase by 13.1%, and catalase by 14.0%, Providing more inorganic nitrogen and phosphorus to the soil	[18]
T. harzianum Rifai; T. asperellum T42	Biofertilizer	Tomato	Seed treatment	Increase Phosphorus uptake	[23]
T. brevicompactum,; T. gamsii and T. harzianum	Biofertilizer	Tomato	Seedling drenching	Phosphorus solubilization	[15]

Table 2.

Solubilization of phosphates by Trichoderma to promote plant growth.

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]. 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].

Trichoderma strain	Intended use	Target crop	Mode of application	Benefits/comments	Ref. (s)
T. azevedoi	Growth promotion and inhibition of phytopathogen development	Lettuce	Expose plants to T. azevedoi	Increased the content of chlorophyll, and carotenoids.; Decreased the severity of white mold by up to 78.83%	[16]
Trichoderma erinaceum	Biofertilizer and biofungicide	Rice	Seed treatment	Improved germination rate and enhanced vigor. Increased yields	[27]
T. harzianum T22	Biofertilizer	Tomato	Seed treatment	Improved soil fertility, nutrient uptake, increased yields, antioxidants and minerals	[28]
T. harzianum, T. asperellum, T. hamatum, and T. atroviride	Biofertilizer	Chinese cabbage	Through irrigation	Increased yield by 37%; Increased enzyme activity in the soils (urease by 25.1%, phosphatase by 13.1%, and catalase by 4.0%, Providing more inorganic nitrogen and phosphorus to the soil	[18]
T. harzianum Rifai; T. asperellum T42	Biofertilizer	Tomato	Seed treatment	Improves nutrient uptake (enhance nitrogen utilization efficiency, increase Phosphorus uptake	[23]
T. harzianum T22	BioF/compost	Tomato	Soil amendment compost	Provided 12.9% yield increase compared to recommended fertilization	[29]
T. asperellum strain GDFS1009	Soil conditioner	Maize	On soil as granules	Increased yields	[19]
T. viride	Biofertilizer	Sugar cane	Powder broadcasted with fertilizer	Improve nutrient uptake NPK	[25]
T. asperellum T34	Biofertilizer -micronutrient	Cucumber	Seedling drenching	Enhance Fe and Cu uptake by plants	[30]
T. harzianum	Compost	Most crops	Compost	Improves the rate of Residue decomposition resulting in greater availability of soil nutrients	[31]
Trichoderma simmonsii	Biofertilizer	Bell pepper	Seedling drenching	Bell pepper yield increase up to 67%.; Enhance tolerance to abiotic stresses	[32]
T.brevicompactum, T. gamsii and T.harzianum	Biofertilizer	Tomato	Seedling drenching	Improve nutrient uptake	[15]
Trichoderma harzianum T22	Biofertilizer; BioF/compost	Tomato	Seed treatment	Improved soil fertility, nutrient uptake, increased yields, antioxidants and minerals (P, K, Ca, Mg, Cu, Fe, Mn and Zn)	[28, 29]
T. asperellum T34	Biofertilizer -micronutrient	Cucumber	Seedling drenching	Enhance Fe and Cu uptake by plants	[30]
T. harzianum	Compost	Most crops	Compost	Improves the rate of Residue decomposition resulting in greater availability of soil nutrients	[31]
T. reesei	Plant growth promoter	Chickpea	Seed treatment	mineral mobilization and their uptake	[33]

Table 3.

Trichoderma improving macro and micro nutrient uptake by crops.

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 non-chemical 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, 37, 38, 39, 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, 42, 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, 44, 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 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, 48, 49, 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, 52, 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 pre-activation (priming) of the molecular mechanisms of defense against several potent phytopathogens and the stress challenged conditions [64, 65, 66, 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, 70, 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].

Trichoderma strain	Disease	Mode of action	Ref. (s)
Trichoderma pseudokoningii	Fusarium oxysporum	Antibiosis metacaspase-independent; Apoptotic cell death.	[74, 75]
T. harzianum	B. cinerea; F. oxysporum Sclerotium rolfsii	Endo-chitinase, chitobiosidase	[63, 76, 77]
Trichoderma virens	Rhizoctonia solani	Colonization and antibiosis	[10, 48, 78]
T. brevicrasum	R. solani	Mycoparasitism	[14]
T. harzianum	B. cinerea	Competition for space	[45]
T. asperellum	Pseudomonas syringae	Induced resistance	[69]

Table 4.

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

4. Conclusions

Trichoderma is one of the most important fungi in agriculture. It has demonstrated many capabilities to be used as biofertilizers as well as biofungicides. It has also shown its sustainability and various mechanisms of providing the crop with nutrients. Moreover, it has various control mechanisms for various plant pathogens, which gives it an advantage when compared to other phytopathogen control mechanisms. It is therefore an option for farmers to use for sustainable cropping and increase in yields and quality of the produce.

Acknowledgments

Authors would like to acknowledge Dr. Kwasi Sackey Yobo, Bongi Kubheka, Nolitha Skenjana and Sinegugu Shude for their support during the writing of this chapter. We would also like to acknowledge our families for moral support and understanding.

Conflict of interest

The authors declare no conflict of interest.