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The below mentioned article provides notes on trichoderma species.
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Fungal genus Trichoderma is the most widely used biocontrol agent in the world with success against soil borne diseases, seed borne diseases, diseases in the phyllosphere and against storage rots.
Trichoderma isolates can stimulate plant growth even in the apparent absence of pathogens. The high rate of success of Trichoderma spp. as a biocontrol against is due to its fast growth, great arsenal of inducible polysaccharide- degrading enzyme that stimulate the fungi to produce the type of biomass appropriate to intended application.
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The isolate was tolerant to chemicals either inherently or through mutation or adaptation. A strain of T. harzianum exhibited the greatest biocontrol potential as compared to other fungi. Soil application of 1 g T. harzianum, T. hamatum or T. viride decreased the incidence of root rot of egg plant caused by Macrophomina phaseolina and increased the yield by 31-36 per cent.
An application of 140/kg ha. of inoculum of T. harzianum was used successfully to control damage to peanuts caused by Corticum rolfsii over a three-year period. It was equivalent to that of using a conventional fungicide.
Khan and Akram (2000) reported significant decrease in the severity of wilt of tomato caused by F. oxysporum f. sp. lycopersici due to application of T. virens at the rate 2 g per kg soil. Mutants of T. virens tolerant to benomyl at a concentration of 10 µg/ml have been isolated from aqueous suspensions of conidia tested with both ultraviolet radiation and ethyl methane sulphonate.
Soil application of T. harzianum checked the root rot of chickpea caused by R. solani. T. virens has also been used in combination with soil solarization as an integrated method to control diseases caused by C. rolfsii in tomato. Survival of the sclerotia of S. sclerotiorum in the soil is reduced by the activity of T. virens.
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Trichoderma species can antagonise a pathogen through competition, antibiosis and/ or mycoparasitism. Trichoderma spp. possess a great capability of competing in rhizosphere mycoflora in soil. With this ability this bioagent can suppress a pathogen in its parasitic and saprophytic phase.
Competition occurs when two or more microorganisms demand more or less the same resource. Biological control by T. viride or chondrostereum purpureum, the silver leaf pathogen on plum trees, is the result of competition.
Competition also seems to be the most potent mechanism employed by a strain of T. harzianum in the control of F. oxysporum f.sp. vasinfectum and F. oxysporum f. sp. melonis in the rhizosphere of cotton and melon.
Antibiosis occurs when production of toxic metabolites or antibiotics by one organism has a direct effect on another organism. Schermbock (1994) has demonstrated the synergistic activity of parallel formation of pentabiol antibiotics and hydrolytic enzymes by T. harzianum.
The mycoparasite also produces some form of biologically active heat- stable metabolites like ethyl acetate responsible for decrease in disease incidence, or plant growth-stimulating effect. Apart from production of antibiotic, especially gliotoxin. Trichoderma speices may also produce cell wall degrading enzymes which are responsible for the control of fungal disease.
A positive correlation between the lytic activity of several strains of T. harzianum on cell walls of S. rolfsii, R. solani and P. aphanidermatum and the degree of biological control of these pathogens in vitro has been found.
Larito (1993) showed that purified endochitinase and chitobiosidase from a strain of T. harzianum were highly active against F. solani. The mycolytic property of Trichoderma probably constitutes an important part of the invasive armory of this destructive necrotrophic mycoparasite.
