Neelam Geat1,Devendra Singh2 and Harshraj Kanwar3
1Ph.D Scholar, Division of Plant Pathology, IARI, New delhi,110012
2Ph.D. Scholar, Division of Microbiology, IARI, New delhi,110012
3Department of Plant Pathology, RCA, MPUAT, Udaipur-313001
Trichoderma spp. are free-living, asexually reproducing and filamentous fungi, common in soil and root ecosystems. They produce or release a variety of compounds that induce localized or systemic resistance responses in plants. It is an exceptionally good model of biocontrol agent as it is easy to isolate and culture, multiply rapidly on many substrates, act as mycoparasite, strong opportunistic invaders, avirulent plant symbionts, competes for food and site with pathogens, prolific producers of spores, powerful antibiotics, antifungal compounds, secondary metabolites as well as enzymes. These properties make them ecologically very successful and are the reasons for their ubiquitousness. This type of fungi is usually present in most soil types and generally known as being the most established of the culturable types of fungi; these are very fast growing fungi growths and are very active in the temperature range of 25-30°C but they do not thrive in temperatures above the 3°C mark. These colonies are very much opaque in nature and give off a coconut aroma or typically sweet odour. They are one of the most prevalent of all fungal species in the soil and do have some very useful properties and do colonize very readily and have a long effect on the root zone of the plant. As for other helpful species of fungi, Trichoderma is very prolific in the root zone and further enhancement of your crops is available by promoting the growth of these fungi. Trichoderma also has properties of assisting in the germination of seeds and has a natural ability to promote effectual germination and good sustainability in young seedlings.
Trichoderma promotes plant growth by solubilizing of phosphates and micronutrients and increasing ability of drought resistance. It also produces biochemical elicitors' compounds which induce ethylene production, hypersensitive responses and other defense related reactions in plant cultivars which induces disease resistance endochitinase gene from Trichoderma are introduced into plants to elevate resistance against phytopathogenic fungi. Trichoderma strains play an important role in the bioremediation of soil that are contaminated with pesticides and also the potential to degrade a wide range of insecticides viz., organochlorines, organophosphates and carbonates. Trichoderma plays a crucial role in biocontrol management of cereals, pulse, oilseed, fruit, vegetable and spices crops diseases by producing various type of antagonistic compound which reduces the growth and infection caused by pathogens by different mechanisms like competition, antibiosis, mycoparasitism, hyphal interactions, and enzyme secretion when employ through seed and soil treatments.
Modes of action of Trichoderma spp. in biological control
Antagonistic fungi, Trichoderma, reduce growth, survival or infections caused by pathogens by different mechanisms like competition, antibiosis, mycoparasitism, hyphal interactions, and enzyme secretion.
Competition: It is the phenomenon in which the pathogen and biocontrol agent (antagonist) compete for the availability of space and nutrients. During this process, the antagonist may suppress the growth of the pathogen population in the rhizosphere and thus reduce disease development.
Antibiosis: Trichoderma species releases antibiotics or other chemicals which are harmful to the pathogen and inhibits its growth. Trichoderma virens is an antagonist of a number of soil borne plant pathogens like Rhaizoctonia solini, Sclerotium rolfsii, S. sclerotiorum, and Pythium ultimum and was known to produce gliotoxins. Trichoderma strains are known to produce antibiotics and toxins. Examples of such chemicals are: trichodermin, trichodermol, harzianum A, gliovirin, heptelidic acid, viridin, gliotoxin.
Mycoparasitism: It is the phenomenon in which the antagonist fungi parasitize other fungi.
The mechanism covers different stages of interactions. The antagonist (Trichoderma) hyphae either grow along the host hyphae or coil around it and secrete different complexes of lytic enzymes such as chitinase, glucanase and pectinase which are key factors in pathogen cell wall lysis, leading to the process of mycoparasitism.
Competitive saprophytic ability - Trichoderma is capable of degrading the substrates within a short period of time as its having high competitive saprophytic ability. Hence, the plant pathogens could not able to compete with this BCA and ultimately results in less disease development. This study could help farmers for microbial disease management.
Induced resistance- Specific strains of fungus Trichoderma colonize and penetrate plant tissues and induce a series of morphological and biochemical changes in the plant, considered to be the plant's defense response, thereby subsequently leading to induced systemic response in the plant.
Inactivation of the pathogen's enzymes: This is another biocontrol mechanism of Trichoderma in which various enzymes of pathogens like pectinases, glucanases, and cutinases were suppressed through the action of secreted protease of Trichoderma on plant surfaces.
Method of application
a) Seed treatment: Mix 10g of Trichoderma formulation per litre of cow dung slurry for treatment of 1kg of seed before sowing, particularly for cereals, pulses and oilseeds.
b) Nursery treatment: Drench nursery beds with @ 5 Trichoderma formulation per litre of water before sowing.
c) Cutting and seedling root dip: Mix 10g of Trichoderma formulation per litre of water and dip the cuttings and seedlings for 10 minutes before planting.
d) Soil treatment: Mix 1kg of Trichoderma formulation in 100 kg of farmyard manure and cover it for 7 days with polythene. Turn the mixture in every 3-4 days interval and then broadcast in the field.
e) Trichoderma formulations: Important commercial formulations are available in the name of Sanjibani, Guard, Niprot and Bioderma. These formulations contain 3x106 cfu per 1 g of carrier material.
Benefits of Trichoderma
i. Disease Control: Trichoderma is a potent biocontrol agent and used extensively for post-harvest disease control. It has been used successfully against various pathogenic fungi belonging to various genera, viz. Fusarium, Phytopthara, Scelerotia
ii. Plant Growth Promoter: Trichoderma strains solubilize phosphates and micronutrients.
iii. Biochemical Elicitors of Disease Resistance: Trichoderma strains are known to induce resistance in plants. Three classes of compounds that are produced by Trichoderma and induce resistance in plants are now known. These compounds induce ethylene production, hypersensitive responses and other defence related reactions in plant cultivates.
iv. Transgenic Plants: Introduction of endochitinase gene from Trichoderma into plants such as tobacco and potato plants have increased their resistance to fungal growth. Selected transgenic lines are highly tolerant to foliar pathogens such as Alternaria alternata, A. solani, and Botrytis cirerea as well as to the soil-borne pathogen, Rhizoctonia spp.
v. Bioremediation: Trichoderma strains play an important role in the bioremediation of soil that are contaminated with pesticides and herbicides. They have the ability to degrade a wide range of insecticides: organochlorines, organophosphates and carbonates.
Plant disease control by different Trichoderma spp.:
|Crop||Name of disease||Pathogens||Trichoderma spp.|
|Tomato, chili, peanut, Potato, black pepper||Wilt||Fusarium spp||T. hamatum, T. harzianum, T. virde, T. Virens|
|Citrus, Tobacco, Pineapple, black pepper||Root rot||Phytophthora spp.||T. harzianum, T. virde|
|Chilli, peanut, Potato,Tomato, soybean, maize, Cabbage,||Damping off||Pythium spp., R. solani||T. hamatum, T. harzianum, T. virde, T. Virens|
|Tomato, chilli, peanut, Potato, soybean||Southern stem rot||Sclerotium rolfsii||T. hamatum, T. harzianum, T. virde, T. Virens|
|Rice, maize||Sheath blight||R. solani||T. harzianum, T. virde|
|Rice, maize, wheat , soybean, chickpea, beans, tomato, brinjal, chilli||Sheath blight, late blight, early blight, leaf spot, root rots, downy mildew||Soil-borne pathogens and few foliar pathogens||T. harzianum strainTh3|
Commercial products of Trichoderma spp.:
Trichoderma viride : Ecofit, Funginil, Trichogourd, Defense SF, Tricho-X, Biogourd, Biocon
Trichoderma harzianum: Pant biocontrol, Pusa Th3
Disadvantages of Trichoderma
1. Trichoderma formulations are having short shelf-life. So we can't able to store or use it for a long time.
2. Trichoderma spp. is having a short host range as it is mostly controlling the soil-borne fungal pathogens and very few foliar pathogens.
3. Some species of Trichoderma pose a threat to the horticultural industry. For example, reduction in mushroom yield by as much as 50 per cent has been attributed to Trichoderma infection and hence it is considered as a harmful parasite of mushroom.
About Author / Additional Info:
I am pursuing Ph.D in Plant Pathology from IARI, New Delhi