BIOCONTROL AGENT – Trichoderma sp.

BIOCONTROL AGENT – Trichoderma sp.

General Characteristics of Trichoderma sp.

• Trichoderma is a genus of fungi in the family Hypocreaceae, commonly one of the rhizosphere inhabitants.
• Trichoderma sp. is the avirulent plant symbiont fungus which acts as an antagonistic against many plant pathogenic fungi and offers protection from phytopathogenic plant diseases.
• The discovery of Trichoderma spp. as natural decomposition agent and biological agent of bioremediation has been reported by several studies.
• Trichoderma sp. is highly involved in the production of Transgenic plants.
• Trichoderma spp. have great potential against soil borne pathogens, and it may be able to replace chemical pesticides in the near future.
• The difficulties encountered during the identification of Trichoderma isolates at the species level become more significant because of the morphological differences are rare and hard to observe.
• Commonly, biological control agents may not affect non-target organisms. Unfortunately, Trichoderma spp. that characterized as antagonistic strains do not particularly target on pathogenic organisms, but also the other microorganisms.

History of Trichoderma sp.

• The first description of the genus Trichoderma was in 1794 by Persoon.
• In 1969, Rifai introduced the concept of “species aggregate” and categorized Trichoderma strains into nine aggregates based on morphological features. Unfortunately, some of the “species aggregate” consists of two or more morphology that was non-differentiable.
• In 1983, Cook and Baker described genus Trichoderma as a common soil inhabitant and the conidiophores are terminating in phialides.
• In 1991, Bissett reviewed Rifai's work and attempted to integrate similar forms within the species concept based on morphology, including the characteristics of the Conidiophore branching system. As a result, Trichoderma was classified into five sections: (i) Saturnisporum, (ii) Pachybasium, (iii) Longibrahiatum, (iv) Trichoderma and (v) Hypocreanum.

Habitat of Trichoderma sp.

• Trichoderma sp. are mainly asexual fungi that are present in all types of agricultural soils and also in decaying wood.

Mode of action of Trichoderma sp.

• Products that are commercially marketed commonly contain one or more Trichoderma species such as Trichoderma viride, Trichoderma virens and Trichoderma harzianum. The efficiency of products containing various species or strains may act differently within the similar field and climate conditions.
• Trichoderma spp. are being used most abundantly against plant pathogens. Several species of Trichoderma which produce volatile and non-volatile antibiotics and enzymes are antagonistic to phytopathogenic fungi and nematodes.
• Trichoderma spp. are the most commonly used biocontrol agents against a broad spectrum of root, shoot, and postharvest pathogens.
• Trichoderma spp. employ several antagonistic mechanisms against plant pathogens. These include antibiosis, mycoparasitism, competition for nutrients and space, promotion of plant growth, induced plant defense mechanisms, and modification of environmental conditions.
• Researchers have reported that Trichoderma spp. suppress the growth plant pathogenic organisms such as Pythium arrhenomanes, Rhizoctonia solani, Fusarium oxysporum, Alternaria tenuis and Botrytis cinerea.
• Trichoderma sp. can act Indirectly on phytopathogens by - a) Competing for nutrients and space; b) Modifying environmental conditions; c) Promoting plant growth and d) Antibiosis - An antagonistic association between two microorganisms (especially microorganisms), in which one is adversely affected.
• Trichoderma sp. can act Directly on phytopathogens by - a) Production of Toxins – Trichiothecin, Sesquiterpine and Trichodermin; b) Production of Antibiotics and c) Mycoparasitism.
• Trichoderma sp. is also playing a major role in Nitrogen fixation and Phosphate solubilization.

Mycoparasitism of Trichoderma sp.

• The Trichoderma sp. grow tropically toward hyphae of other fungi, coil about them in a lectin-mediated reaction, and degrade cell walls of the target fungi. This process is called Mycoparastitism. The process Mycoparastitism limits growth and activity of plant pathogenic fungi.
• Mycoparasites produce cell wall-degrading enzymes (Chitinase, Glucanase and Pectinase), which allow them to bore holes into other fungi and extract nutrients for their own growth.

Microscopic identification of Trichoderma sp.

• Conidiophores are repeatedly branched, irregularly arranged in whorls, appear as clusters of divergent, usually asymmetrical bent, flask-shaped/cylindrical to nearly sub-globose phialides.
• The ellipsoidal to globose conidia are generally green, sometimes hyaline to cluster in aggregates at the terminal of the phialides

Figure – 1: LPCB Staining of Trichoderma sp.

Cultural characteristics of Trichoderma sp.

• In the beginning, Trichoderma strains appeared white and cottonish, then developing into yellowish-green to deep green compact tufts especially at the centre of a growing spot or in concentric ring-like zones on the agar surface.

          Trichoderma viride        Trichoderma hamatum     Trichoderma harzianum

Figure – 2: Colony morphology of Trichoderma sp. in SDA

Crop Recommendation

• Brinjal, Potato, Chilli, Tomatoes, Cucumbers, Cut and Pot flowers, Orchards, Vineyards Ornamentals in greenhouses, lawns and nurseries

Target Disease

• Pythium sp., Ganoderma sp., Rhizoctonia solani, Fusarium sp., Botrytis cinerea, Sclerotium sp., Sclerotinia sp. and Ustilogo sp.

Formulation

• Trichoderma spp. products are formulated in a wettable powder or granules. In order to establish the fungus in and on the plant roots, Trichoderma is effectively applied during seeding.