Trichoderma species are free-living fungi that are highly interactive in root, soil and foliar environments and have been used successfully in field trials to control many crop pathogens. Structural and biological studies of the metabolites isolated from Trichoderma species are reviewed. This review, encompassing all the literature in this field up to the present and in which 269 references are cited, also includes a detailed study of the biological activity of the metabolites, especially the role of these metabolites in biological control mechanisms. Some aspects of the biosynthesis of these metabolites and related compounds are likewise discussed.

Secondary metabolites from species of the biocontrol agent Trichoderma

Tetramic and tetronic acids: an update on new derivatives and biological aspects.

Trichoderma species are soil-borne filamentous fungi widely utilized for their many plant health benefits, such as conferring improved growth, disease resistance and abiotic stress tolerance to their hosts. Many Trichoderma species are able to produce the auxin phytohormone indole-3-acetic acid (IAA), and its production has been suggested to promote root growth. Here we show that the production of IAA is strain dependent and diverse external stimuli are associated with its production. In in vitro assays, Arabidopsis primary root length was negatively affected by the interaction with some Trichoderma strains. In soil experiments, a continuum effect on plant growth was shown and this was also strain dependent. In plate assays, some strains of Trichoderma spp. inhibited the expression of the auxin reporter gene DR5 in Arabidopsis primary roots but not secondary roots. When Trichoderma spp. and A. thaliana were physically separated, enhancement of both shoot and root biomass, increased root production and chlorophyll content were observed, which strongly suggested that volatile production by the fungus influenced the parameters analyzed. Trichoderma strains T. virens Gv29.8, T. atroviride IMI206040, T. sp. "atroviride B" LU132, and T. asperellum LU1370 were demonstrated to promote plant growth through volatile production. However, contrasting differences were observed with LU1370 which had a negative effect on plant growth in soil but a positive effect in plate assays. Altogether our results suggest that the mechanisms and molecules involved in plant growth promotion by Trichoderma spp. are multivariable and are affected by the environmental conditions.

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Environmental growth conditions of Trichoderma spp. affects indole acetic acid derivatives, volatile organic compounds, and plant growth promotion

Fungal phytotoxins with potential herbicidal activity: chemical and biological characterization

Beneficial microbes typically produce bioactive molecules that can affect the interactions of plants with their pathogens. Many secondary metabolites may also have antibiotic properties, which enable the producing microbe to inhibit and/or kill other microorganisms i.e. competing for a nutritional niche. Indeed, some of these compounds have been found to play an important role in the biocontrol of plant diseases by various beneficial microbes used world-wide for crop protection and bio-fertilization. In addition to direct toxic activity against plant pathogens, biocontrol-related metabolites may also increase disease resistance by triggering systemic plant defence activity, and/or enhance root and shoot growth. Fungi belonging to the Trichoderma genus are well known producers of secondary metabolites with a direct activity against phytopathogens and compounds that substantially affect the metabolism of the plant. The widescale application of selected metabolites to induce host resistance and/or to promote crop yield may become a reality in the near future and represents a powerful tool for the implementation of IPM strategies.

Trichoderma Secondary Metabolites Active on Plants and FungalPathogens

Trichosetin, a tetramic acid-containing metabolite produced in the dual culture of Trichoderma harzianum and Catharanthus roseus (L.) G. Don callus, was subjected to phytotoxicity assays. In seedling growth assays, trichosetin inhibited root and shoot growth of all five plant species tested by damaging the cell membrane, as evidenced by the dose-dependent increase in electrolyte leakage and lipid peroxidation. Vital staining of trichosetin-treated Nicotiana tabacum BY-2 cells, with rhodamine 123, showed a weaker green fluorescence compared to controls indicating damaging effects on mitochondria. FDA-PI staining, to determine cell viability, indicated that cells of the trichosetin-treated roots were mostly dead.

E. C. Marfori

Papers

Phytotoxicity of the tetramic acid metabolite trichoetin