Commercial biocontrol formulations of
Trichoderma
Trichodermaspecies are easily grown in culture media
and have been marketed in many formulations, with
varying degrees of success. One example, among
many, is the product Trichodex™(T. harzianum) for
control of Botrytis cinerea(gray mould) on grapes.
Although it was reported not to be as effective as com-
mercial fungicides it can be used as an alternating treat-
ment with fungicides (O’Neill et al. 1996), halving the
total fungicide input, which is environmentally desir-
able. Trichodermais also impregnated into dowels,
which are hammered into drill-holes in trees to help
control wood-rot fungi, and similarly can be inoculated
into plum trees to help control silver leaf disease,
caused by toxins of the fungus Chondrostereum purpureum
(Basidiomycota) growing in the wood. A commercial
product of this type, called Trichodowels™, is marketed
through garden centers in New Zealand.
However, one role of Trichodermaspp. in biological
control exceeds all others – the inoculation of soil-
less rooting media in commercial glasshouses where
seedlings are raised. Soil-less rooting media composed
of peat-based or similar materials have a low resident
microbial population, and so have little biological
“buffering” capacity. If any seedling pathogens
become established in these conditions they can
spread rapidly and cause major damage. So, various
formulations of Trichoderma, with wheat bran or other
organic food bases, are incorporated into the rooting
medium, to help establish an antagonistic microflora.
One of the most successful commercial biocontrol
strains, Trichoderma harzianumstrain T-22, was developed
by fusing the protoplasts of two “wild” strains, then
allowing the hybrid strain to regenerate a wall and to
revert to a stable phenotype. The resulting T-22 strain
exhibits very strong “rhizosphere competence” – it
colonizes the whole root system and persists through-
out the life of a crop. This strain is marketed under the
name Bio-Trek 22G™ for golf course turf, and under
other names for field crops or greenhouse potting
mixes. Novel strains generated by protoplast fusion do
not involve genetic engineering, so they do not fall
under the regulatory requirements for GM (genetically
modified) products.Hyphal interferenceHyphal interferenceis a specific term describing the
behavior of several Basidiomycota that antagonize
other fungi at points of contact (Fig. 12.7). This
antagonism can be between different species of
Basidiomycota, or between Basidiomycota and other
fungi. It was discovered during in vitrostudies on theFUNGAL INTERACTIONS 241
Fig. 12.6Structures of some antibiotics
produced by species of Trichoderma.