Trichoderma is a genus of fungi that is commonly used in agriculture and horticulture as a biological control agent against plant pathogens. It belongs to the class of fungi called Ascomycetes and is known for its ability to protect plants from various soil-borne diseases.
Trichoderma species are naturally found in soils worldwide and have a symbiotic or parasitic relationship with plants. They colonize plant roots and the surrounding soil, forming a mutually beneficial association. Trichoderma species have the ability to produce enzymes that degrade the cell walls of other fungi, including pathogenic species. This antagonistic activity helps to suppress the growth and development of plant pathogens, such as Fusarium, Rhizoctonia, and Pythium.
Role of Trichoderma:
By means of a variety of mechanisms, including mycoparasitism, competition, hyphal contacts, and enzyme release, they participate in growth, survival, or infections brought on by pathogens.
Trichoderma as Biological Agent
Numerous fungal plant diseases can have their growth slowed down by Trichoderma. It is used as a biological control agent against several ailments in the soil that are caused by fungi. Trichoderma species, which are nonparasitic fungi, are present in almost all soils and other natural environments. They are conveniently separable from earth and rotting organic waste. Numerous fungal strains in the genus Trichoderma function as biological control agents and their antagonistic traits are based on the activation of a number of pathways.
When employing conventional agricultural methods, an effective biocontrol system is one that is easy to build, manageable with regard to cost and secure with respect to safety. In a broader sense, “bio fungicides” refers to fungicides with a biological source, such as microbial and plant substances. As one of the key elements of IPM, the use of microbial fungicides is expanding. They are typically targeted, appear innocuous to beneficial insects, animals and humans therefore providing no residue issues or environmental risks.
Biological Control Mechanism
Microbes like environmentally friendly fungi are used to make microbial fungicides. By vying for resources and space, modifying the environment, or encouraging plant development, plant defence systems, and antibiosis. Trichoderma strains can regulate fungal phytopathogens either indirectly, directly or directly through mycoparasitism.
Depending on the Trichoderma strain, the antagonistic fungus, the crop plant, and environmental factors including nutrient availability, pH, temperature, and iron concentration, these indirect and direct processes’ relevance in the biocontrol process varies. In order to create new formulations for use in more effective plant disease management and postharvest applications, these metabolites can either be overproduced or coupled with relevant biocontrol strains.
Biocontrol in Relation to Chemical Control
In general, biocontrol methods do not compete with chemical fungicides successfully enough in the field. The sporulation or growth rates of the transgenic strain were barely different from those of the wild type. As soon as the plant pathogen came in touch with the host, GoxA expression began, and the glucose oxidase that was produced was secreted. Endo-chitinase and N-acetyl glycosaminidase are significantly lower in SJ3-4 activity than its non-transformed parent.
Spores of Botrytis cinerea did not germinate. much more inhibited by culture filtrates that included glucose oxidase. Additionally, Rhizoctonia solani and Pythium ultimum, two plant pathogens, were more quickly overgrown and lysed by the transgenic strain. SJ3-4 had no discernible enhanced effect in plants against these pathogens at low inoculum doses. Beans treated with conidia of the transgenic Trichoderma strain flourished in highly contaminated soil, while beans treated with wild-type spores did not.
Additionally, SJ3-4 was more successful at causing plants to develop systemic resistance. A significant level of resistance to the foliar pathogen B. cinerea’s ability to generate leaf lesions was shown by beans with SJ3-4 root protection. This study shows how heterologous genes with pathogen-inducible promoters can enhance the biocontrol and systemic resistance-inducing capacities of fungal biocontrol agents like Trichoderma spp. In addition, these microorganisms can act as carriers of helpful chemicals like glucose oxidase, which can increase plants’ disease resistance.
Mode of Action of Trichoderma atroviride
Several commercially relevant airborne and soilborne plant diseases are controlled by a filamentous soil fungus known as Trichoderma atroviride. This organism’s ability to microparasites is linked to an effective nutritional competition strategy, the creation of enzymes that break down cell walls, and antibiosis.
As alternatives to chemical fungicides, Research is being done on a number of Trichoderma strains. However, Trichoderma has not been applied frequently or extensively to biologically control plant diseases. In terms of molecular genetics, Trichoderma has concentrated on boosting the activity of chitinases or proteinases by either increasing the number of copies of the required genes or by fusing them with powerful promoters
Biochemistry of Biological Control Agents
A possible plant biocontrol agent diseases Rhizoctonia solani, Sclerotinia sclerotiorum, and Verticillium dahlia is called Talaromyces flavus and employs a distinct method of biocontrol. Studies carried out in vitro with T. flavus culture filtrates revealed that the majority of glucose oxidase is the cause of the microsclerotia and hypha of V. dahliae’s growth suppression. In trials conducted in greenhouses, a strain of T. flavus with a deficiency in glucose oxidase was unable to combat the Verticillium wilt of eggplant.
The oxygen-dependent oxidation of D-glucose to D-glucono-1,5-lactone and H2O2 is catalysed by the enzyme glucose oxidase. The development of R. solani, Pythium aphanidermatum, Pythium ultimum, and V. dahliae is not considerably slowed down when glucose oxidase, glucose, and gluconate are employed independently. Gluconate naturally forms D-glucono-1,5-lactone in aqueous solutions. Hence, higher quantities of H2O2 are what cause the glucose oxidase system to have an antifungal impact.
Resistivity of Trichoderma species
Compared to the aforementioned plant diseases, some Trichoderma species are more resilient to the effects of glucose oxidase activity, despite the fact that Trichoderma lacks an ortholog of glucose oxidase. The possibility that the disease-controlling ability of this biocontrol agent could be improved was raised by the availability of a versatile expression system for T. atroviride based on the use of previously characterized promoters linked to biocontrol.
The transgenic offspring of T. atroviride strain P1, which has 12 to 14 copies of the Aspergillus niger goxA (glucose oxidase) gene under the nag1 (N-acetyl-D-glycosaminidase) promoter, was employed in the study, to show in vivo a novel technique for enhancing this fungus’ capacity to inhibit phytopathogens directly and to cause systemic bacterial resistance in plants.
Dr. Kamran Saleem1, Hafiz Muhammad Rizwan Mazhar2, Shahid Ali Chand3, Dr. Muhammad Atiq4, Muhammad Ehetisham Ul Haq5
- 1,2NIAB, 5AARI, Faisalabad
- 3,4Dept of Plant Pathology, University of Agriculture Faisalabad
