Trichoderma: Ally or Enemy? Understanding its Role in Myciculture and

"In the shadows of the undergrowth, a discreet mushroom,
The Trichoderma, by its secret strength,
Mixes with the roots, weaving its destiny,
Ally of life, or dark assassin?

It nourishes the earth and protects the seedlings,
But watch out for his steps which sometimes are enemies.
In the heart of cultures, it keeps its place,
A living mystery that science entwines.

Let's dive into his world, between good and danger,
To better discover what he is sharing.."

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

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

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

1. What is Trichoderma?

Definition and Classification

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 growing on a substrate. These fungi are widely present in various environments, including forest floors, wood debris, and decaying organic matter.

Role in Nature

In nature, Trichoderma is primarily saprophytic, meaning it decomposes dead organic matter, playing a crucial role in the cycle of nutrients. Some species of Trichoderma also have a symbiotic or parasitic behavior, colonizing the roots of plants or attacking other pathogenic fungi.

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

Life Cycle of Trichoderma

The life cycle of Trichoderma includes several stages:

1. Spore Germination: Conidia, or asexual spores, germinate when conditions of temperature, humidity, and nutrient availability 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. Conidia Production: 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. Dispersal and Colonization: Conidia are dispersed by wind, water, or animals, colonizing new substrates and starting the cycle again.

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

2. Trichoderma in Myciculture: A Feared Contaminant

Why is Trichoderma a problem?

In myciculture, Trichoderma, which is also often called "green mold", is often perceived 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 resulting in total destruction of the substrate.

How does Trichoderma contaminate mushroom crops?

Trichoderma can contaminate mushroom crops by several vectors:

• Air : Trichoderma spores can be transported by air and deposited 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 crops.

• Flies and other insects : These insects can carry spores and deposit them on 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 myciculture, and its presence can seriously affect mushroom production. Preventing and controlling contamination is therefore essential to maintaining 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 the majority of pathogens, including some Trichoderma spores, while preserving the beneficial microorganisms that help the fungus grow.
• Sterilization: For complete removal of contaminants, sterilization of substrates 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 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 have been pasteurized or sterilized, they must be handled with care to avoid recontamination. Using sterile tools and maintaining a clean and aseptic work environment are essential. Work surfaces should be disinfected regularly, and ambient air should be filtered to reduce microbial load.

B. Controlled Work Environments

Use of Clean Culture Rooms and Laminar Flow :

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

UVC as a Prevention Method :

• The use of ultraviolet (UVC) lights in grow rooms can be helpful in reducing microbial load, including Trichoderma spores, on surfaces and in the air. However, it is important to note that direct exposure of mushrooms to UVC rays can also damage them. UVC must therefore be used in the absence of live cultures or in specific disinfection zones.

C. What to do in the event of Contamination by Green Mold during Fruiting?

If green mold, usually indicating Trichoderma infestation, appears during the fruiting phase of the grow bales, 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 bales. Use a sterilized knife or scissors to carefully cut out the affected area, being careful not to scatter the spores.

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

• Isolation of Contaminated Bales: Contaminated culture bales 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 Cultivation Conditions: Ensure that the cultivation conditions (humidity, temperature, ventilation) are optimal for the fungi and not favorable for the growth of Trichoderma. Maintain constant monitoring and adjust conditions as necessary.

• Regular cleaning of the floor and surfaces will help limit the accumulation of spores.

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

Conidiophores de 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. In addition, they induce plant resistance by stimulating the production of defense compounds.

Graphical diagram representing the beneficial roles of Trichoderma spp. in cherry tomato nutrition and growth. (*4)

 

The Advantages of Trichoderma in Organic Agriculture

1. Improved Soil Health: By decomposing organic matter, Trichoderma contributes to the formation of humus 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. Reduction of Pathogens: Its mycoparasitic action against pathogens such as Fusarium and Pythium makes it a preferred choice for biocontrol.

 

How to Use Trichoderma?

• Seed Coating: Seeds can be treated with a suspension of Trichoderma to protect young plants upon germination.
• Foliar Spray 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: Growing and Using Trichoderma

Step 1: Prepare a Bag of Sterilized Grains

To get started, get yourself a bag of sterilized mycelium on grains available on our online store: Bag of Sterilized Grains - Mycosphere . You can inoculate it with a strain of Trichoderma that you already have on hand, or simply follow one of the following methods to encourage the natural growth of Trichoderma:

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

2. Natural Method: If you don't have a strain of Trichoderma on hand, simply open the bag in the open air for about 5 minutes. Trichoderma spores, often present in the air, will 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: Allow Trichoderma to Colonize the Sac

• After inoculation (controlled or natural), close the bag tightly and place it in a dark place at room temperature (between 20°C and 25°C).
• Wait about 7-10 days . During this time, the Trichoderma should begin to colonize the mycelium on grains , forming a green and white mass. Once the majority of the mycelium on grains are colonized, they are ready to use.

 

Step 3: Preparation of Trichoderma Spore Solution

1. Covering the Grains with Water : Open the bag of colonized mycelium on grains and transfer them to a large, clean container. Cover the mycelium on grains with pure water (preferably filtered or distilled).

2. Spore Separation : Let the mycelium on grains sit in the water for about 10 minutes , stirring gently and turning regularly to help release the Trichoderma spores into the water.

3. Straining : After 10 minutes, strain the mixture through a fine strainer or sieve. Retain the mycelium on grains in the strainer and keep only the green liquid that contains 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 Trichoderma Solution

• Dilution: Before using, dilute Trichoderma Spore Liquid in water at the rate 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 plant foliage or at soil level around roots. This application helps prevent and control fungal diseases, while promoting healthy plant growth.

 

---

4. Trichoderma Species Used in Agriculture

Common Species Used

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 the specific conditions and types of crops.

How to Choose the Right Strain?

Selection of the appropriate strain depends on many factors, such as crop type, soil conditions, and pathogens present. For example, some strains ofT. harzianumare most effective against plant diseases in soils with neutral to slightly acidic pH.

 

---

5. The Unexplored Potential of Trichoderma and Future Innovations

New Applications in Development

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

Scientific Developments and Innovations

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

 

---

Conclusion

Trichoderma represents both a challenge and an opportunity depending on its use. In myciculture, 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.

With better understanding and continued innovation, 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