ROOT DEVELOPMENT IN SWEET-CORN INOCULATED WITH THE
BIOCONTROL FUNGUS TRICHODERMA HARZIANUM
Thomas Björkman, Gary E. Harman, and Lisa Blanchard.
Department of Horticultural Sciences, NYSAES, Cornell
University, Geneva, NY 14456
Production of shrunken-2 sweet corn is often limited
by poor establishment. Good root development is necessary
for establishment, and it can be limited by stress
or disease. Trichoderma harzianum strain 1295-22 was
developed as a biocontrol fungus with particularly
strong root colonizing ability. In addition to acting
as a biocontrol agent, it stimulates root growth.
In greenhouse experiments using field soil, root dry
weight 21 days after planting was 500 mg, greater compared
with 320 mg in uninoculated controls, an average increase
of over 50%. The thoroughness of soil exploration
more than doubled, from 31% (control) to 70% (Trichoderma)
of the soil being within 1 cm of a root. The difference
in performance was not attributable to disease: no
disease symptoms were evident, the occurrence of disease
organisms was low, it was the same in both treatments,
and it was not associated with smaller plants. Furthermore,
the greatest differences were noted in steam-sterilized
soil. Colonization of the roots by Trichoderma was
related to the age of the root. The oldest part of
the radicle had 106 cfu/g root DW. Branched seminal
roots had 105.5 cfu/g. Even the rapidly-growing tips
of the first-whorl roots were well-colonized (104.7
cfu/g). The mechanism of increased root growth has
not been identified, but colonized roots acidify about
0.1 pH units more than control roots, which could cause
both faster acid-growth and increased ion uptake.
Ion leakage into distilled water is about 25% lower
in colonized roots.
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