<P> Teleomorphs of Trichoderma are species of the ascomycete genus Hypocrea . These are characterized by the formation of fleshy, stromata in shades of light or dark brown, yellow or orange . Typically the stroma is discoidal to pulvinate and limited in extent but stromata of some species are effused, sometimes covering extensive areas . Stromata of some species (Podostroma) are clavate or turbinate . Perithecia are completely immersed . Ascospores are bicellular but disarticulate at the septum early in development into 16 part - ascospores so that the ascus appears to contain 16 ascospores . Ascospores are hyaline or green and typically spinulose . More than 200 species of Hypocrea have been described but few have been grown in pure culture and even fewer have been described in modern terms . </P> <P> Trichoderma species are frequently isolated from forest or agricultural soils at all latitudes . Hypocrea species are most frequently found on bark or on decorticated wood but many species grow on bracket fungi (e.g. H. pulvinata), Exidia (H. sulphurea) or bird's nest fungi (H. latizonata) or agarics (H. avellanea). </P> <P> Several strains of Trichoderma have been developed as biocontrol agents against fungal diseases of plants . The various mechanisms include antibiosis, parasitism, inducing host - plant resistance, and competition . Most biocontrol agents are from the species T. harzianum, T. viride and T. hamatum . The biocontrol agent generally grows in its natural habitat on the root surface, and so affects root disease in particular, but can also be effective against foliar diseases . </P> <P> T. aggressivum (formerly T. harzianum biotype 4) is the causal agent of green mold, a disease of cultivated button mushrooms . Trichoderma viride is the causal agent of green mold rot of onion . A strain of Trichoderma viride is a known cause of dieback of Pinus nigra seedlings . </P>

Biocontrol mechanism of trichoderma harzianum is best described by
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