Trichoderma: Ally or Enemy? Understanding its Role in Mushroom Cultiva

"In the shadow of the undergrowth, a discreet fungus,
The Trichoderma, by its secret strength,
It mingles with the roots, weaving its destiny,
Ally of life, or dark assassin?

It nourishes the soil and defends the seedlings,
But beware of its steps that are sometimes enemies.
In the heart of the crops, it keeps its place,
A living mystery that science embraces.

Let's dive into its world, between good and danger,
To better discover what it comes to share.."

Poem in Alexandrine written by our MycoGuide, on 08/31/24

The Trichoderma is a genus of microscopic fungi widely studied for its beneficial and harmful properties. While mushroom growers often fear its presence as an aggressive contaminant, organic farmers appreciate it for its ability to stimulate plant growth and fight diseases.

This article explores the dual role of Trichoderma: a major problem in mushroom cultivation and a valuable ally in organic and sustainable agriculture. We will discuss its nature, life cycle, ways to prevent its contamination in mushroom cultivation, and its effective use in agriculture.

1. What is Trichoderma?

Definition and Classification

The Trichoderma is a genus of filamentous fungi belonging to the family Hypocreaceae. This genus includes many species, among which Trichoderma harzianum, Trichoderma virens, and Trichoderma atroviride are the best known and studied.

Fungi of this genus are characterized by rapid growth and the production of green conidia when developing on a substrate. These fungi are widely present in various environments, including forest soils, wood debris, and decomposing organic matter.

Role in Nature

In nature, Trichoderma is mainly a saprophyte, meaning it decomposes dead organic matter, playing a crucial role in the nutrient cycle. Some Trichoderma species also exhibit symbiotic or parasitic behavior, colonizing plant roots or attacking other pathogenic fungi.

This ability to colonize different environments makes Trichoderma very adaptable and effective at controlling microbial populations.

Life Cycle of Trichoderma

The life cycle of Trichoderma includes several stages:

1. Spore Germination : Conidia, or asexual spores, germinate when temperature, humidity, and nutrient availability conditions are favorable.
2. Mycelial Growth : After germination, the mycelium rapidly develops by forming a dense network of filaments. This growth is particularly effective in environments rich in organic matter.
3. Production of Conidia : Once the mycelium is established, the fungus produces conidia to reproduce and disperse. These spores can survive in harsh conditions until they find a new favorable environment to germinate.
4. Dispersion and Colonization : Conidia are dispersed by wind, water, or animals, colonizing new substrates and restarting the cycle.

The ecological adaptations of Trichoderma, such as its ability to break down cellulose and other complex organic compounds, give it a competitive advantage in various environments.

2. Trichoderma in Mushroom Cultivation: A Feared Contaminant

Why is Trichoderma a problem?

In mushroom cultivation, Trichoderma, often also called "green mold," is often seen as a major contaminant. Its presence in edible or medicinal mushroom crops can cause significant economic losses.

Trichoderma grows rapidly and competes directly with the mycelium of cultivated mushrooms for nutrients and space, inhibiting their growth and often leading to the total destruction of the substrate.

How does Trichoderma contaminate mushroom crops?

Trichoderma can contaminate mushroom crops through several vectors:

• The air : Trichoderma spores can be carried by the air and settle on substrates or crops.

• The substrate : A poorly prepared or poorly pasteurized substrate may contain Trichoderma spores.

• The grower : The hands, clothing, or tools of the grower can transfer Trichoderma spores to the crops.

• Flies and other insects : These insects can carry spores and deposit them on the crops.

• Mobile contamination units : This includes any mobile equipment or material that comes into contact with the substrate or culture.

Prevention and Control of Trichoderma Contamination

Trichoderma is a common contaminant in mushroom cultivation, and its presence can severely affect mushroom production. Prevention and control of contamination are therefore essential to maintain a healthy growing environment.

A. Pasteurization and Sterilization of Substrates

Temperatures and Treatment Methods :

• Pasteurization : Pasteurization involves heating substrates to specific temperatures (generally between 60°C and 80°C) for 1 to 2 hours. This method eliminates most pathogens, including some Trichoderma spores, while preserving beneficial microorganisms that help mushroom growth.
• Sterilization : For complete elimination of contaminants, substrate sterilization is carried out at higher temperatures, generally at 121°C for at least 30 minutes under pressure (autoclave). This destroys all microorganisms, including Trichoderma spores. However, after sterilization, it is crucial to maintain strict aseptic practices to avoid any recontamination. Handling must be done in a sterile environment (laminar flow, use of gloves, masks, etc.) to prevent the introduction of Trichoderma spores or other contaminants.

Precautions after Pasteurization or Sterilization :

• Once substrates are pasteurized or sterilized, they must be handled carefully to avoid recontamination. The use of sterile tools and maintaining a clean and aseptic work environment are essential. Work surfaces must be regularly disinfected, and ambient air filtered to reduce microbial load.

B. Controlled Work Environments

Use of Clean Growing Rooms and Laminar Flow :

• Mycologists must work in controlled environments, such as clean and sterile growing rooms equipped with laminar flow systems to filter air and prevent airborne contaminants. Trichoderma spores can be carried by air, hence the importance of maintaining a positive pressure work environment with HEPA filters.

UVC as a Prevention Method :

• The use of ultraviolet (UVC) lamps in growing rooms can be helpful to reduce microbial load, including Trichoderma spores, on surfaces and in the air. However, it is important to note that direct exposure of fungi to UVC rays can also damage them. UVC should therefore be used in the absence of live cultures or in specific disinfection areas.

C. What to Do in Case of Green Mold Contamination during Fruiting?

If green molds, generally indicating a Trichoderma infestation, appear during the Fruiting phase of the Fruiting Blocks, several measures can be taken:

• Removal of Contaminated Parts : As soon as the first green spots appear, it is essential to immediately remove the contaminated parts of the Fruiting Blocks. Use a sterilized knife or scissors to carefully cut the affected area, taking care not to disperse spores.

• Use of Salt : Sprinkling salt on contaminated areas after removing infected parts can help limit mold spread. Salt dries out fungal cells and can prevent further Trichoderma growth.

• Isolation of Contaminated Fruiting Blocks : Contaminated Fruiting Blocks must be isolated from others to prevent the spread of spores. A well-ventilated space with good air circulation can also help reduce humidity, making the environment less favorable for Trichoderma growth.

• Improvement of Growing Conditions: Ensure that growing conditions (humidity, temperature, ventilation) are optimal for mushrooms and not favorable to Trichoderma growth. Maintain constant monitoring and adjust conditions if necessary.

• Regular cleaning of soil and surfaces will help limit spore accumulation.

By following these rigorous prevention and control practices, mushroom growers can minimize the risks of contamination by Trichoderma and ensure healthy, high-quality mushroom production.

Conidiophores of Trichoderma harzianum (src: wikipedia)

3. Trichoderma in Agriculture: A Powerful Tool for Sustainable Cultivation

Why Use Trichoderma in Agriculture?

Trichoderma is used in agriculture mainly for its biocontrol and plant growth stimulation properties. Trichoderma fungi can parasitize other pathogenic fungi and release natural antifungal compounds that protect crops. Additionally, they induce plant resistance by stimulating the production of defense compounds.

The Benefits of Trichoderma in Organic Farming

1. Soil Health Improvement: By decomposing organic matter, Trichoderma contributes to humus formation and the release of essential nutrients for plants.
2. Stimulation of the Root Microbiome: By colonizing the rhizosphere (area around the roots), Trichoderma promotes plant growth by improving nutrient absorption.
3. Pathogen Reduction: Its mycoparasitic action against pathogens like Fusarium and Pythium makes it a preferred choice for biocontrol.

How to Use Trichoderma?

• Seed Coating: Seeds can be treated with a Trichoderma suspension to protect young plants from germination.
• Foliar Spraying and Soil Application: A diluted Trichoderma solution can be sprayed on foliage to prevent fungal diseases, or applied to the soil to improve root health.

Practical Recipe for Individuals: Cultivating and Using Trichoderma

Step 1: Prepare a Bag of Sterilized Fruiting Blocks

To start, get a bag of sterilized Fruiting Blocks available in our online store: Sterilized Fruiting Blocks Bag - Mycosphere. You can inoculate it with a Trichoderma strain you already have, or simply follow one of the following methods to promote the natural growth of Trichoderma:

1. Controlled Inoculation: If you have a Trichoderma strain (purchased or cultivated), introduce it into the bag of sterilized Fruiting Blocks. This ensures a purer and more effective culture.

2. Natural Method: If you do not have a Trichoderma strain on hand, simply open the bag to the open air for about 5 minutes. Trichoderma spores, often present in the air, have a 90% chance of colonizing the substrate. To further increase the chances, you can add a small pinch of garden soil to the bag. This method is less reliable than direct inoculation with a selected strain, but it can still work in most cases.

Step 2: Let the Trichoderma Colonize the Bag

• After inoculation (controlled or natural), seal the bag tightly and place it in a dark place at room temperature (between 20°C and 25°C).
• Wait about 7 to 10 days. During this period, the Trichoderma should begin to colonize the Fruiting Blocks, forming a green and white mass. Once the majority of the Fruiting Blocks are colonized, they are ready to be used.

Step 3: Preparation of the Trichoderma Spore Solution

1. Cover the Fruiting Blocks with Water: Open the bag of colonized Fruiting Blocks and transfer them to a large clean container. Cover the Fruiting Blocks with pure water (preferably filtered or distilled).

2. Spore Separation: Let the Fruiting Blocks rest in the water for about 10 minutes, stirring gently and turning regularly to help release the Trichoderma spores into the water.

3. Filtering: After 10 minutes, filter the mixture using a fine sieve or strainer. Retain the Fruiting Blocks in the sieve and keep only the green liquid containing the suspended spores. This green liquid is now rich in Trichoderma spores.

4. Storage: Pour the filtered liquid into clean, airtight bottles. Close the bottles and store them in a cool place, away from light. Trichoderma spores can remain viable for several weeks when stored properly.

Step 4: Application of the Trichoderma Solution

• Dilution: Before use, dilute the Trichoderma spore liquid in water at a ratio of 1:20 (1 part spore solution to 20 parts water). For example, for 1 liter of spore solution, add 20 liters of water.
• Spraying: Use this diluted solution to spray directly on the plant foliage or on the soil around the roots. This application helps prevent and control fungal diseases while promoting healthy plant growth.

4. Trichoderma Species Used in Agriculture

Commonly Used Species

The most commonly used species is Trichoderma harzianum, known for its effectiveness against a wide range of soil pathogens. Other species, such as Trichoderma virens and Trichoderma atroviride, are also used depending on specific conditions and crop types.

How to Choose the Right Strain?

Selecting the appropriate strain depends on many factors, such as crop type, soil conditions, and present pathogens. For example, some strains of T. harzianum are more effective against plant diseases in neutral to slightly acidic soils.

5. The Untapped Potential of Trichoderma and Future Innovations

New Applications in Development

Beyond agriculture, Trichoderma has potential in bioremediation of soils contaminated by heavy metals or pesticides. Its use in urban agriculture systems and hydroponics is also being explored, where it can help manage diseases without chemicals.

Scientific Developments and Innovations

Recent research focuses on the genetic improvement of Trichoderma to increase its resistance and effectiveness. Projects also aim to combine multiple strains to achieve more robust results.

Conclusion

Trichoderma represents both a challenge and an opportunity depending on its use. In mushroom cultivation, it is essential to manage it to avoid losses, while in organic farming, it offers a natural and effective tool to stimulate crops and control diseases.

Thanks to better understanding and continuous innovations, Trichoderma could play a key role in the sustainable agriculture of tomorrow.

References and Sources

1. Harman, G. E., et al. (2004). "Trichoderma species—Opportunistic, avirulent plant symbionts." Nature Reviews Microbiology.
2. Vinale, F., et al. (2008). "Trichoderma–plant–pathogen interactions." Soil Biology and Biochemistry.
3. Kubicek, C. P., et al. (2011). "Trichoderma: Biology and Applications." Wiley-Blackwell.
4. https://www.researchgate.net/figure/Graphical-diagram-representing-the-beneficial-roles-of-Trichoderma-spp-in-cherry-tomato_fig5_365618382