Let’s know about Trichoderma Harzianum. richoderma harzianum is a filamentous fungal antagonist of plant pathogens, used in the biological control of diseases caused by phytopathogenic diseases. It is widely used in agriculture because of its properties as biofuel, biofertilizer and biostimulant.
Indeed, the scientific interest generated by this species is related to the control mechanism against phytopathogenic fungi. Functions such as competition for nutrients and space, mycoparasitism and enterosis are biological control mechanisms.
Trichoderma harzianum It is a cosmopolitan fungus, as it is distributed worldwide in diverse ecosystems and natural environments, typically growing in places where organic plant material accumulates, such as in crops or humic soils. remain..
The plants’ high density roots and a suitable rhizome favor their colonization. In fact, its great ability to adapt to different agronomic conditions is Trichoderma a fungus with a wide spectrum of uses.
At the nutritional level, Trichoderma is able to degrade complex substrates such as starch, pectin and cellulose. It later uses these elements to enhance the properties of the abundant enzymatic complexes it possesses (amylase, pectinases, cellulases and chitinases).
Features
aquatic and terrestrial ecosystems
These fungi are characterized by dissemination in terrestrial ecosystems (agricultural soils, pastures, forests and deserts) and aquatic ecosystems. Some species are free-living in the soil, opportunistic, plant symbionts, and others are mycoparasites.
Because of their different fertility, they also have the ability to colonize different environments. They can adapt and survive in extreme conditions of temperature, salinity and pH.
reproduction and nutrition
In their vegetative state they present a mycelium or simple, haploid septa and its wall is composed of chitin and glucans. They are vocal anaerobes and reproduce asexually by conidia.
The nutritional requirements of this species are low, although its growth is adapted to organic matter and moisture. The optimum temperature range for its growth and development is 25º to 30. C is between
habitat
a t. harzianum , it can be located in various organic materials and soils, due to their great adaptability they have a wide distribution. Some species prefer dry and temperate sites and others moist and cool.
Specifically, these fungi, as endophytic organisms, compete with the plant’s rhizosphere, managing to colonize the root surface. In fact, they penetrate through the intercellular spaces, to the cells of the first or second layer.
importance
This fungal group is of great importance to plants, as they contribute to the control of phytopathogenic fungi. In fact, they are widely known for their ability to produce toxins and antibiotics that control various pathogens.
Isolates of the genus Trichoderma They are among the biological control agents used in agriculture. Research work has allowed to verify their effective control, as they act on a large number of soil pathogens.
tasks
One of the main functions of Trichoderma harzianum is its ability to develop symbiotic relationships with plants. The fungus appears and grows in the rhizosphere of the crop, providing more space for its growth to grow.
In addition, used as a biological control agent, it has the ability to produce enzymes that attack and inhibit phytopathogenic fungi, in fact, it is very beneficial to incorporate into the substrate or cultivation area before planting.
In this regard, its action as a competitive hyperparasite is based on the production of antifungal metabolites and hydrolytic enzymes. Structural changes at the cellular level on controlled organisms, such as vacuolization, granulation, disruption of the cytoplasm and cell lysis.
Studies at the elmasigo level have allowed to determine the growth of the root system when using Trichoderma harzianum in different doses. In this regard, it stimulates seed germination and favors the growth of new shoots.
It is appropriate to include T. harzianum in a disease control program to take advantage of its anticancer potential. It has been proven that the application of Trichoderma inhibits and controls the pathogens Fusarium, Pythium, Phytophthora, Rhizoctonia and Sclerotium .
classification
The genus Trichoderma spp ., was initially described by Persoon (1794) to classify four currently unrelated species. Among them: Trichoderma viroides, Xylophiga nigressus, Sporotrichum aureum, and Trichotrichum roseus.
Subsequently, a number of features were created, based on the microscopic features, size and presence of phialides. Then Rafai (1969) reviewed the genus and described 9 species Trichoderma spp ., where I included Trichoderma harzianum.
Species T. harzianum (Rafai, 1969), belongs to the genre Trichoderma , Family Hypocreaceae, Order Hypocreales, Class Sordariomycetes, Subdivision Pezizomycotina, Division Ascomycota, Kingdom Fungi.
Taxonomy studies of Trichoderma harzianum , using PCR techniques, have been supported in the variations of DNA polymorphisms. T within the style . harzianum (rifae), four biological forms have been differentiated: Th1, Th2, Th3 and Th4.
morphology
Gender Trichoderma includes a range of species without a clear sexual stage. It is characterized by a septate mycelium, usually oval conidia, non-whorled hyaline conidiophores, singular or grouped phialids, and unicellular conidia.
Colonies at the macroscopic level are easily recognized by their whitish-green or yellow-green coloration. In addition, concentric rings are observed in areas with conidia; And unlike the colonies, the color is yellow, amber or yellow-green.
At the microscopic level, conidiophores are erect, hyaline, branched and non-vertical, present in groups or solitary. Phialids are pear-shaped, singly or in clusters, swollen in the central region and thin at the apex.
The angle of insertion between the phialids and the conidiophores is straight. Unicellular conidia are oblong or sub-globose, smooth or equatorial. of green coloration or hyaline, and they appear in public in the apes of phaelids.
Reproduction
Penis Trichoderma It does not present an advanced sexual period, naturally they reproduce by asexual spores. The life cycle of T. harzianum , begins when the organism grows and branches off as fungal hyphae of 5-10 µm in diameter.
Asexual sporulation begins when spores are released in large amounts of 3-5 µm. Similarly, chlamydospores intersect individually, although sometimes two or more fused chlamydospores are observed.
mechanism of action
Control effect of the fungus Trichoderma It is verified by different mechanisms of action on the growth of phytopathogenic fungi. One of the main activities that exert direct action is competition for space and nutrients, mycoparasitism and enterosis.
Biocontrol action of Trichoderma harzianum It is enhanced by its ability to colonize the rhizome of plants. In addition, mechanisms such as the secretion of enzymes and the production of inhibitory compounds serve as biocontrolling effects.
On the other hand, mechanisms whose indirect functions contribute as a bioregulatory effect are presented. They have the ability to activate compounds related to resistance, detoxification of toxins and neutralize enzymes in the plant.
The ability of fungi to facilitate the solubilization of nutrients, not naturally available to plants, is a process that improves the nutritional conditions of the medium to supply nutrients to the crop.
Likewise, when it grows under favorable conditions, it is able to colonize the rhizosphere of plants abundantly, which allows to create an environment conducive to radical growth, improving plant tolerance.
competition
Competition is defined as the unequal behavior between two individuals to satisfy the same need, be it substrate or nutrients. The success of the competition helps to overcome the ability of one organism from the ability of the other.
Trichoderma harzianum They have a great anticancer ability because they have a rapid rate of growth. Its biocontrol effect is favored by its broad adaptive ecology and adaptability to adverse conditions.
In addition, it has great ability to mobilize and take advantage of soil nutrients, mainly nitrogen, carbohydrates and polysaccharides. In this way, it is able to quickly colonize the environment, preventing the spread of other microorganisms in the same habitat.
microparasitism
Mycoparatism is defined as an anti-symbiotic interaction between a fungus and a pathogen. In this mechanism, extracellular interference with the cell wall of parasitic fungi: chitinases and cellulases.
This action occurs in four phases: chemotrophic growth, recognition, adhesion and deposition, and lytic activity. During the final stage the fungus produces additional lysis enzymes, degrading the pathogen’s cell wall and facilitating the penetration of hyphae.
During Trichoderma harzianum mycoperitism it progresses pathogenically, it coaxes and penetrates the host’s daughters. Through the generation of specific enzymes and degradation of the cell wall of the pathogen, it causes a weakening of the pheoestrogens.
Mycoparasitism as a mechanism of antagonistic action in T. harzianum It depends on various factors. Each stage of development is caused by the pathogens involved, the biotrophic or necrotrophic action of the antagonist, and environmental conditions.
- Chemolytic Evolution: It refers to the positive direct development of an organism towards a chemical stimulus. Trichoderma detects the presence of pathogen and its growth occurs in the body due to chemical stimulation.
- Validation: Research studies have determined that A. Trichoderma is an antagonist of specific phytopathogens. Molecules such as lectins—carbohydrates present in the host, make it susceptible to being parasitized by the fungus Trichoderma .
- Adhesive and penetrating: are hyphae of Trichoderma They have the ability to adhere to the structures forming the host, similar to hooks and apressoria. This process involves enzymatic processes and the antagonistic association of a sugar from the wall of the fungus with a lecithin in the wall of the phytopathogen.
- Lithic activity: degradation of the cell wall of phytopathogens, facilitating the penetration of hyphae of Trichoderma . The lytic enzymes involved in this process are basically chitinases, glucanases and proteases.
Antibiosis
It is the direct action of volatile or non-volatile organic compounds produced by Trichoderma on susceptible hosts. Different strains of T. harzianum produces antibiotics or toxic metabolites that inhibit the growth of other microorganisms.
Applications
Trichoderma harzianum It is widely used as a biological controller because of its rapid growth and development. In addition, it promotes various enzymes that are capable of reducing other phytopathogenic fungi.
This fungus is a natural agent, not aggressive with plants or soil. Used as a biocontroller, it does not report toxicity to crops, it also minimizes environmental impact due to the absence of chemicals in the soil.
Biocontrol effect of T. harzianum This is done depending on the environments where phytopathogens occur. Control method and mode of application are carried out in the structure, area and space that you wish to protect.
Typically, seed control is carried out through controlled applications to direct seeds into the substrate or to the ground. The use of sprays on leaves, flowers and fruits is common; More recent studies have been conducted to prevent attacks by postharvest pathogens.
biological control in seeds
Treating seeds with T. harzianum is oriented to protect the seed against internal or soil pathogens. Also, provide timely protection to the underground parts of the new plant after it has germinated.
In fact, once the seed is infected with the fungus, it is able to expel the plant’s rhizosphere by its biocontrol action. In addition, the amount of fungus to be planted in seeds is low, if compared to cultivated land.
For the application of Trichoderma on seeds different methods are used: use of a dry powder, application of biopreparation in the form of paste, dissolution in dry soil or coverage by pellet.
biological control in soil
The predictive medium for the control of pathogens through soil is Trichoderma harzianum . In fact, the rhizome of the plant is the most favorable environment for its antagonistic action.
The application of fungicides on seeds is done to establish biocontrollers locally in the rhizosphere. Therefore, biological control in the soil is directly related to the application of the fungus to the seed.
Other methods include direct application for sowing or broadcasting, at the time of sowing or during plant cleaning and hilling. In this case, it is incorporated with powder, granular or organic modifications.
Foliage surface control
Through biological control of Trichoderma in leguminous areas, such as flowers, fruits and leaves, it is subject to environmental conditions. Low availability of nutrients, changes in temperature, solar radiation and wind are conditions that make it difficult for the fungus to establish itself.
In this regard, the formulations intended for applying the antagonist should contain adherens and nutrients that facilitate the colonization of Trichoderma . The moderate effectiveness of this method and its high cost have led to the study of new control strategies at the leaf level.
