Seed Treatment Using Trichoderma Biofungicide

Trichoderma is one of the most common soil inhabitants and extensively studied biocontrol agents in the management of plant pathogens. Species of Trichoderma are being used for the management of fungal diseases of various crops. Trichoderma is a friendly fungus that offers biological resistance to underground enemy fungi, which spreads harmful diseases in crops. It prevents root, collar, stem rot, and wilt diseases in crops such as cotton, pulses, oilseeds, and vegetables. Trichoderma is a long-term efficient, beneficial, non-polluting, biologically safe fungicide for animals and humans.

Trichoderma are free-living fungi that are highly interactive in root, soil, and foliar environments and can parasitize other fungi. They have been gaining momentum as an important biocontrol agent in the control of plant diseases in recent times due to their eco-friendly nature, which minimizes the use of chemicals, giving a more cheap and efficient disease control method. The use of this biocontrol agent not only fights diseases but also enhances the growth of the plants.

The primary objective of seed treatment with Trichoderma is to suppress pathogens biologically using different isolates of Trichoderma spp. to avoid the harmful effects of chemicals. Trichoderma spp., as biocontrol agents, are used for foliar application, seed treatment, and soil treatment for the suppression of various disease-causing fungal pathogens. It can be used either dry or wet formulation or slurry.

2. Mechanisms of Action

Trichoderma controls plant pathogens through four primary mechanisms:

• Mycoparasitism: Trichoderma directly attacks, parasitizes, and otherwise gains nutrition from other fungi. It penetrates and destroys pathogen hyphae through the secretion of cell wall-degrading enzymes. This mechanism is a key mode of action for T. asperellum SKT-1.

• Production of antibiotics (Antibiosis): Trichoderma produces antibiotic substances and metabolites that inhibit the parasitical activity of pathogens, not allowing the development and reproduction of the pathogen.

• Induction of systemic resistance (ISR): Trichoderma induces systemic resistance via the salicylic acid signaling pathway. Selected isolates have been shown to enhance systemic resistance in tomato seedlings through the induction of growth hormones and defense enzymes. This activation of the plant's immune response helps the plant resist future pathogen attacks.

• Competitive antagonism: Trichoderma colonizes the rhizosphere rapidly, outcompeting pathogens for space and nutrients. It colonizes the root zone, starving the pathogenic competition of vital nutrients.

Seed coating with Trichoderma strains has been shown to promote plant growth and enhance systemic resistance against pathogens like Fusarium crown rot in durum wheat. Selected strains of Trichoderma spp. can be applied as seed treatments and have been shown to reliably increase crop yields over hundreds of trials.

3. Target Diseases and Suitable Crops

Trichoderma is effective against a wide range of soil-borne and seed-borne fungal pathogens across numerous crops.

3.1 Target Pathogens

Trichoderma species are effective against the following pathogens among many others:

• Fusarium spp. (causing wilt diseases) (especially F. oxysporum), including F. udum (pigeon pea wilt)

• Rhizoctonia solani (causing root rot and damping off)

• Pythium spp. (causing damping off and root rot)including P. aphanidermatum

• Sclerotium rolfsii (causing stem rot of groundnut, collar rot of tomato)

• Sclerotinia spp. (causing web blight, white mold)including S. minor

• Verticillium spp. (including V. dahliae)

• Alternaria spp.

• Phytophthora spp. (including P. infestans)

• Macrophomina phaseolina (causing charcoal rot)

• Cephalosporium spp.

• Meloidogyne incognita (root-knot nematodes)

• Botrytis cinerea

• Monilinia spp.

• Helminthosporium (Bipolaris) spp.

Trichoderma asperellum SKT-1, for example, has been shown to be effective against Gibberella fujikuroi, where mycoparasitism is the mode of action.

3.2 Suitable Crops

Trichoderma has a wide range of activity and is used in numerous crops:

• Cereals: Paddy, Maize, Rice, Sorghum, Wheat

• Pulses: Peas, Lentils, Red Gram, Chickpea, Mung Bean, including Pigeon Pea

• Oilseeds: Groundnut, Soybean, Sunflower, Mustard

• Vegetable Crops: Tomato, Brinjal (Eggplant), Chili, Capsicum, Okra (Bhendi), Cabbage, Cauliflower, Broccoli, Knol-Khol, Radish, Onion, Garlic, Ginger, Turmeric, Beans, Cucurbits, Leafy Greens

• Fruit Crops: Apple, Citrus, Grape, Pomegranate, Banana, Guava, Mango

• Other Crops: Cotton, Sugarcane, Tea, Coffee, Cardamom, Plantation Crops, Ornamental Plants

The efficacy of locally isolated Trichoderma species to control three soil-borne plant pathogens and one plant parasitic nematode was studied under in vitro and in vivo conditions.

Trichoderma is also used for the management of fungal diseases of tropical tuber crops. Species of Trichoderma are being used for the management of collar rot of elephant foot yam, tuber rot of cassava, yam anthracnose, and taro leaf blight.

4. Application Methods and Dosage Guidelines

Trichoderma can be applied through various methods, with seed treatment being one of the most effective. The table below provides a comprehensive guide to dosage recommendations per kilogram of seed across different crops. Note that dosages can vary based on product formulation and CFU count; always verify with the product label.

4.1 Step-by-Step Procedure for Seed Treatment

1. Selecting High-Quality Seeds: The foundation of successful seed treatment begins with selecting high-quality seeds that are genetically healthy, disease-free, and well-suited to your specific crop and growing conditions.

2. Procuring Trichoderma Products: Procure high-quality Trichoderma products from reputable suppliers or manufacturers.

3. Preparing Trichoderma Suspension: Trichoderma can be applied in various forms: dry, slurry, or liquid. To make a slurry, mix the recommended quantity of Trichoderma (e.g., 8-10 gm of 1.0% WP formulation) in 50 ml of water to treat 1 kg of seed, often with 5% organic jaggery or crude sugar, which acts as a food source for the fungus. Dry seeds can be mixed with 5g of TrichoShield™ per kg of seed and directly agitated. For root dipping of seedlings, 10-20 grams of trichoderma is mixed well in 1 litre of water. To treat one acre of land, mix 1 kg of Trichoderma culture in 25 kg of natural manure.

4. Mixing and Coating: Pour the Trichoderma slurry over the seeds and mix thoroughly with a mechanical mixer or by hand in a clean container until each seed is uniformly coated with the biocontrol agent ensuring a uniform coating all over the seeds.

5. Drying and Storage: After treatment, allow the seeds to dry thoroughly to promote adhesion of Trichoderma spores and prevent clumping or caking. Spread the treated seeds in a well-ventilated area away from direct sunlight and moisture, allowing them to air dry completely. Dry the seeds in shade for 30 minutes before sowing. Do not store treated/coated seeds more than 24 hours.

6. Sowing: Sow the treated seeds within 24 hours of treatment.

4.2 Nursery Bed and Seedling Treatment

Trichoderma is also used in nursery beds and for seedling treatment:

• Nursery Seedbed Treatment: Mix 500 gm formulation in 10 kg of well-decomposed Farm Yard Manure (FYM) / Compost / Vermicompost and broadcast in an acre. Alternatively, mix 10 to 15 g of Trichoderma powder per square meter area.

• Seedling Treatment: Dissolve 500 gm formulation in 50 liters of water, dip the seedling roots for about half an hour in the suspension, shade-dry for 15 minutes, and transplant immediately.

5. Compatibility and Tank Mixing

In the field, Trichoderma is often applied along with agrochemicals, making it essential to assess the compatibility of Trichoderma with these chemicals in order to tap the potential of them in the integrated management system.

5.1 Compatible Substances

Trichoderma is generally compatible with:

• Organic manures and bio-fertilizers, including Rhizobium spp.

• Organic amendments (FYM, compost, vermicompost) and oil cakes

• Bio-pesticides in some cases (test compatibility before mixing)

5.2 Incompatible Substances

• Chemical Fungicides: Fungicides containing carbendazim (e.g., Saaf, Bavistin, Sprint, Turf, Starbenz) are highly inhibitory to the mycelial growth of Trichoderma even at the lowest concentration tested (100 ppm). Other copper-based fungicides also kill Trichoderma.

• Antibiotics (e.g., streptocycline) are highly toxic to Trichoderma.

• Chemical Fertilizers: Generally low toxicity, but may cause slight growth inhibition: The growth inhibition by inorganic fertilizers was minimum (exhibiting <10% mycelial growth inhibition at 800 ppm). However, direct mixing is not recommended.

• High concentrations of synthetic pesticides: A large-scale, integrated pest management strategy is discordant with the direct mixing of a chemical pesticide with a biological product.

5.3 Key Compatibility Rules

1. Do NOT mix with chemical fungicides, bactericides, or high concentrations of other synthetic pesticides. Do not treat seed with chemicals before or after trichodermic treatment.

2. If chemical seed treatment is necessary, apply the chemical first, let the seeds dry completely, wait 7–10 days, and then treat with Trichoderma.

3. Do NOT use chlorinated water: Let tap water to stand for at least 2 hours to allow chlorine to evaporate before using it to prepare Trichoderma solutions.

6. Advantages of Trichoderma Seed Treatment

The use of Trichoderma in seed treatment offers several benefits:

• Disease suppression: Reduces the incidence of seed-borne and soil-borne fungal diseases.

• Plant growth promotion: Selected strains increase crop yields over hundreds of trials.

• Enhanced nutrient uptake: Trichoderma decomposes raw organic farm wastes, solubilizes soil phosphorus, and reclaims adverse soils.

• Induced systemic resistance: Builds resistance in plants to drought and diseases.

• Increased tolerance to abiotic stresses: Trichoderma atroviride TRS25 improved germination, enhanced vegetative plant growth, and reduced downy mildew infection in cucumber.

• Environmental safety: No MRL (Maximum Residue Limit), no pesticide residue in crops or fresh produce. 0 Day Preharvest Interval (PHI). Safe and environmentally friendly solution.

• Yield increase: Developed Trichoderma formulations improve soil fertility, increase microbial population in soil, and enhance crop yield (up to 10-12%).

7. Precautions and Limitations

To achieve success, avoid common mistakes:

• Avoid direct sunlight: Apply in the early morning or late evening.

• Storage: Shake the bottle before use and store in a cool and dry place away from direct sunlight.

• Shelf life: Use within the expiry date (typically 120 days to 24 months depending on formulation).

• Use Period: Use within 120 days of the date of formation.

• Moisture: Trichoderma growth in soil depends on moisture availability. More moisture allows better growth.

• Soil pH: If the soil (pH) is between 6.5 to 7.5, the result of Trichoderma biofertilizer is very good.

• Clean equipment: Spray tanks must be chemically free.

• Do not exceed recommended dosages.

8. Integration with Other Farming Practices

Trichoderma seed treatment is most effective when integrated with other supportive practices:

• Combine with organic manures (FYM, compost, vermicompost): Mixing Trichoderma powder with FYM or vermicompost helps in its establishment and activity. For example, in onion crops, mix 2 kg Trichoderma powder with 100 kg of farmyard manure per acre and broadcast before sowing for effective control of white rot and bulb rot.

• Maintain optimum moisture: Adequate soil moisture (50–70% of field capacity) after Trichoderma seed treatment is crucial for the fungus to colonize the rhizosphere effectively.

• Use soil solarization in combination: Soil solarization in integration with FYM amendment and seed treatment with T. harzianum potentially reduces the pre- and post-emergence damping-off incidence in solanaceous crops.

• Maintain proper soil pH (6.5–7.5): Trichoderma growth is optimum within this range.

9. Future Prospects and Innovations

Emerging research in Trichoderma biofungicides focuses on:

• High-concentration formulations: Products like VINTEC (WG formulation with 1×10¹⁰ CFU/g) are redefining biological control standards.

• Liquid formulations with longer shelf life: Liquid formulations (e.g., T Stanes Bio Cure F Liquid) offer extended shelf life up to 24 months and are easier to apply.

• Combination products (consortia): Formulations combining multiple beneficial microorganisms like Trichoderma spp., Pochonia chlamydosporia, and Pseudomonas fluorescens for controlling plant pathogenic bacteria, fungi, and nematodes.

• Strain-specific formulations: Development of multi-trait biocontrol formulations effective for the management of soilborne and root rot diseases and enhancing plant growth.

• Bio-priming: Integration of seed priming (soaking in water) with Trichoderma inoculation to improve both germination and microbial adherence