Mention has already been made of the ability of root symbiotic
Trichoderma strains to increase plant growth. This effect has been
studied for some time in this lab with maize as the system. The
general concepts have been published several times and are sum-
marized below. Among the positive effects on maize that have
been noted over the past 5 to 10 years in work conducted by Ad-
vanced Biological Marketing, Cornell University and others include
the following (documented in Harman [20] and Harman et al. [23]):
• Control of root and foliar pathogens
Induced resistance
Biological control of diseases by direct attack of plant-
pathogenic fungi
• Changes in the microfloral composition on roots
• Enhanced nutrient uptake, including but not limited to nitrogen
• Enhanced solubilization of soil nutrients
• Enhanced root development
• Increased root hair formation
• Deeper rooting
For some time, the possibility that different plants respond differ-
ently to biocontrol agents or plant symbiotic fungi has been dis-
cussed. However, since Trichoderma spp. are broadly effective
across a range of plant species, we did not view strong genetic
interactions with plants as a major factor. However, in maize this
is not true, at least for the enhanced growth response.
There have been more than 500 documented field trials that
compared field corn grown from seed, treated or not treated with
T. harzianum strain T22, and the average yield increase is about
5 bu/acre. However, trial results have shown tremendous variabil-
ity, with ranges between +50% to actual yield decreases. This
clearly indicates that there are uncontrolled or poorly understood
variables that affect results. The greatest yield increases appeared
when the variety tested had some genetic weaknesses (e.g., Nutri-
dense varieties) or where there were biotic (e.g., anthracnose or
rust) or abiotic (e.g., soil compaction, drought, or nutrient insuf-
ficiency) stresses present.
The reasons for the occasionally observed yield decreases were
at first attributed to unusual field variations, but a large trial (160
hybrids +/– T22 in three different sites in the U.S. corn belt) con-
ducted by a commercial company, Advanced Biological Market-
ing, suggested that there was a maize genetic component to the
interaction of T22 as well.
A first priority for research at Cornell University was to
identify a genetically homozygous inbred that responded strongly
to T22. An initial screen resulted in the discovery that seedling
growth (measured 2 weeks after planting) of maize inbred Mo17
is strongly enhanced by T22 and that this increased growth re-
sponse continues for the life of the plant (23). The same treatment
also induces systemic resistance. Further, T22 on roots increased
levels of total proteins and activity of the putative PR proteins
chitinase and β-1,3 glucanase in both shoots and roots (23).
Field trials and lab experiments have confirmed the observation
that there is a maize genetic component to the T22 response. In
field trials in 2002, a hybrid, Sgi860 × Sgi861, was used that had
not been evaluated before. The experiment was a replicated block
design that compared +/– T22 over a range of organic (composted
chicken manure) or inorganic (ammonium nitrate) fertilizer con-
centrations to give different levels of added nitrogen ranging from
0 to 100 kg/ha. From the earliest growth of the maize, reduced
growth in the presence of T22 was observed regardless of treat-
ment, and the end of the season yields in the presence of T22
were reduced about 7% over a total of 14 fertilizer treatments.
This hybrid was tested in the 2-week seedling assay developed
previously for Mo17. There was a statistically significant reduc-
tion in growth in this assay as well. This finding was significant
for two reasons, as follows:
• T22 reduced growth of Sgi860 × Sgi861 both in the field
across a range of fertilizer levels and in our lab assay with
2-week-old seedlings.