Fungi in the genus Trichoderma have been known since at least the
1920s for their ability to act as biocontrol agents against plant pathogens.
Until recently, the principal mechanisms for control have been assumed to
be those primarily acting upon the pathogens and included mycoparasitism,
antibiosis, and competition for resources and space. Recent
advances demonstrate that the effects of Trichoderma on plants, including
induced systemic or localized resistance, are also very important. These
fungi colonize the root epidermis and outer cortical layers and release
bioactive molecules that cause walling off of the Trichoderma thallus. At
the same time, the transcriptome and the proteome of plants are sub
substantially
altered. As a consequence, in addition to induction of pathways
for resistance in plants, increased plant growth and nutrient uptake occur.
However, at least in maize, the increased growth response is genotype
specific, and some maize inbreds respond negatively to some strains.
Trichoderma spp. are beginning to be used in reasonably large quantities
in plant agriculture, both for disease control and yield increases. The
studies of mycoparasitism also have demonstrated that these fungi produce
a rich mixture of antifungal enzymes, including chitinases and β-1,3
glucanases. These enzymes are synergistic with each other, with other
antifungal enzymes, and with other materials. The genes encoding the enzymes
appear useful for producing transgenic plants resistant to diseases
and the enzymes themselves are beneficial for biological control and
other processes.