The Suppressive Effects of Trichoderma viride and Bacillus subtilis on Plant Fusarium Wilt

Plant fusarium wilt is a devastating disease that can cause significant losses in agricultural production. It affects a wide range of plants, including many economically important crops. In the pursuit of sustainable and eco – friendly solutions to combat this disease, the use of beneficial microorganisms such as Trichoderma viride and Bacillus subtilis has emerged as a promising approach.

Contents hide

1 Trichoderma viride: A Potent Biocontrol Agent

1.1 Antibiosis

1.2 Competition

1.3 Mycoparasitism

2 Bacillus subtilis: Another Key Player in Wilt Suppression

2.1 Production of Antimicrobial Compounds

2.2 Induced Systemic Resistance (ISR)

2.3 Improvement of Soil and Root Environment

3 Combined Effects of Trichoderma viride and Bacillus subtilis

3.1 Synergistic Antagonism

3.2 Complementary Mechanisms

Trichoderma viride: A Potent Biocontrol Agent

Trichoderma viride is a well – known fungus with remarkable biocontrol properties against plant pathogens, especially those causing fusarium wilt. It employs multiple mechanisms to suppress the growth and spread of the disease – causing Fusarium species.

Antibiosis

Trichoderma viride produces a variety of antifungal metabolites. These include antibiotics like trichodermin, gliotoxin, and viridin. These substances directly inhibit the growth of Fusarium fungi by interfering with their cell wall synthesis, membrane integrity, and metabolic processes. For example, trichodermin disrupts the fungal cell membrane, leading to leakage of cellular contents and ultimately the death of the pathogen. This antibiosis effect is crucial in reducing the population of Fusarium in the rhizosphere and on plant surfaces, thereby preventing the onset and progression of fusarium wilt.

Competition

In the plant rhizosphere, Trichoderma viride competes with Fusarium for essential resources such as nutrients and space. It has a high affinity for nutrients like nitrogen, phosphorus, and iron, which are also required by Fusarium. By out – competing the pathogen for these resources, Trichoderma viride restricts the growth and survival of Fusarium. Additionally, Trichoderma viride colonizes the root surface and root – associated soil more rapidly and efficiently than Fusarium. This physical occupation of space prevents Fusarium from establishing a foothold on the plant roots, reducing the likelihood of infection.

Mycoparasitism

Trichoderma viride is a mycoparasite, meaning it can directly attack and parasitize Fusarium fungi. It detects the presence of Fusarium through chemical signals and then grows towards it. Once in contact, Trichoderma viride penetrates the hyphae of Fusarium using specialized structures such as appressoria. Inside the host hyphae, Trichoderma viride secretes lytic enzymes like chitinases, glucanases, and proteases. These enzymes break down the cell walls of Fusarium, allowing Trichoderma viride to obtain nutrients from the host and ultimately kill it. This mycoparasitic behavior is a unique and effective way in which Trichoderma viride controls fusarium wilt.

Bacillus subtilis: Another Key Player in Wilt Suppression

Bacillus subtilis, a gram – positive bacterium, also plays a significant role in suppressing plant fusarium wilt.

Production of Antimicrobial Compounds

Bacillus subtilis synthesizes a wide array of antimicrobial substances, including lipopeptides, antibiotics, and bacteriocins. Lipopeptides such as surfactin, iturin, and fengycin have strong antifungal activities. Surfactin, for instance, has surfactant – like properties that can disrupt the cell membrane of Fusarium, leading to its lysis. These antimicrobial compounds are secreted into the rhizosphere, creating an environment that is hostile to the growth of Fusarium. They not only directly inhibit the growth of the pathogen but also act as a deterrent, preventing its spread in the soil and towards the plant roots.

Induced Systemic Resistance (ISR)

One of the unique features of Bacillus subtilis is its ability to induce systemic resistance in plants. When Bacillus subtilis colonizes the plant roots, it triggers a series of physiological and biochemical changes in the plant. It activates the plant’s defense mechanisms, making the plant more resistant to subsequent attacks by Fusarium. This is achieved through the production of signaling molecules that are recognized by the plant. These signals initiate a cascade of events in the plant, leading to the up – regulation of defense – related genes. As a result, the plant produces more antimicrobial compounds, strengthens its cell walls, and enhances its overall ability to withstand the infection by Fusarium.

Improvement of Soil and Root Environment

Bacillus subtilis can also improve the soil and root environment in ways that are beneficial for plant health and disease resistance. It helps in solubilizing nutrients in the soil, making them more available for plant uptake. For example, it can convert insoluble forms of phosphorus into soluble forms that plants can easily absorb. This enhanced nutrient availability promotes plant growth and vigor, making the plant more resilient to fusarium wilt. Additionally, Bacillus subtilis can modify the soil structure by producing extracellular polysaccharides. These polysaccharides help in aggregating soil particles, improving soil porosity and water – holding capacity. A healthier soil environment is less conducive to the growth and spread of Fusarium.

Combined Effects of Trichoderma viride and Bacillus subtilis

In many studies, the combined application of Trichoderma viride and Bacillus subtilis has shown even greater potential in suppressing plant fusarium wilt compared to their individual use.

Synergistic Antagonism

When used together, Trichoderma viride and Bacillus subtilis can act synergistically to inhibit Fusarium. The antifungal metabolites produced by Trichoderma viride and the antimicrobial compounds of Bacillus subtilis can work in tandem. For example, the antibiotics produced by Trichoderma viride may weaken the cell walls of Fusarium, making it more susceptible to the lipopeptides of Bacillus subtilis. This synergistic antagonism leads to a more effective reduction in the population of Fusarium, providing enhanced protection against fusarium wilt.

Complementary Mechanisms

The two microorganisms also have complementary mechanisms of action. Trichoderma viride’s mycoparasitism and competition for resources in the rhizosphere complement Bacillus subtilis’ ability to induce systemic resistance in plants. While Trichoderma viride directly attacks and out – competes Fusarium in the soil, Bacillus subtilis primes the plant’s internal defense system. This combination of external and internal defense strategies provides a more comprehensive and robust protection against fusarium wilt.