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Biology
of T-22 There
are many natural antagonists that keep disease organisms under suppression.
Members of the genus Trichoderma are filamentous fungi that can be
isolated from many soil types. They are part of a healthy soil environment
with numerous species found worldwide. A few select strains of T.
harzianum have been shown to suppress plant pathogens. However, they are
limited in the scope of plants they protect and the pathogens they control.
For example, one strain can control Pythium and grow
in cooler soils, while another can control Rhizoctonia and
colonizes the root system. To
overcome these limitations, researchers at Cornell University produced a
hybrid strain that had enhanced attributes of the parents. The researchers crossed various
unique strains of wild Trichoderma.
The 22nd hybrid strain showed incredible results. That strain is now known as T-22. T-22
attacks, parasitizes and gains nutrition from other fungi. T-22 has numerous
mechanisms for both attack of other fungi and for enhancing plant and root
growth. These include:
These
mechanisms allow T-22 to control various plant pathogens. The biofungicide
protects the plant by establishing itself on the outside of the root system
in the rhizosphere (root zone)(fig 2).
Because
it is a living organism, T-22 can grow along the entire length of the root
system where it establishes a barrier against pathogen attack. As long as the
root system remains active in its growth and development, T-22 will continue
to grow along with it by feeding on the waste products released. These waste
products can also serve as a meal for pathogens. Early applications of T-22
protects plant roots by removing secreted nutrients that pathogens might use.
Occupation of the roots by T-22 does not seem to interfere with the activity
of mycorrhizae or nitrogen-fixing Rhizobium. A
second line of defense by T-22 against root-rotting fungi is the release of
hydrolytic enzymes. Many plant pathogens contain chitin as a component of
their cell wall. T-22 releases chitinases that have been shown to disrupt the
cell wall of these pathogens. Electron micrographs illustrate how these
enzymes dissolve the cell wall and create holes in the pathogen (fig 3a and
3b). Once damaged, the pathogen itself becomes the prey of other soil
microflora.
These
enzymes work optimally in an acidic environment. Insects also contain chitin
as a constituent of their exoskeleton, but their pH is typically in the
alkaline range. Thus, the T-22 chitinases will not work on these nontarget
organisms; plants, birds, fish, humans and other organisms are also not
affected by T-22. T-22
can control some of the most common fungal pathogens. Because of squatter's
rights, it can also suppress other pathogens by displacing them from the
roots. This maintenance of the root system allows for a larger root biomass
to develop. Increased plant yields begin with a well-established root system.
Once the plant is harvested, T-22 levels in the soil drop. The levels
remaining after harvest will not be high enough for efficacious fungal
control on new plantings. T-22
has been granted an exemption from the need for a tolerance by the US-EPA and
is approved for use in certified organic production. Its effectiveness
against a range of pathogens on a diversity of plants allows it to be a part
of many integrated pest management programs. T-22 can protect plant parts
(roots) not previously protected by chemical fungicides. It can be used at
the time of planting as a seed treatment. The T-22 planter box formulation is
compatible with many standard chemical seed treatments (e.g. Captan) and is
applied directly over chemically treated seeds at the time of planting. The
chemical allows for stand establishment, but that's all. T-22 then kicks in
to protect the root system from fungal attack.
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