HortScience 33:525 (1998)
The effect of rhizosphere competence on coloniztion of sweet corn roots
by biocontrol fungi in differing soils.
Thomas Björkman, Lisa M. Blanchard and Gary E. Harman
Department of Horticultural Sciences, New York State Agricultural Experiment
Station, Cornell University, Geneva, NY 14456-0462
ABSTRACT To be effective biocontrol agents, fungi need to colonize
roots under a wide range of conditions. The ability do so is called rhizosphere
competence. A common beneficial fungus, Trichoderma harzianum, has
been bred to produce a new strain, T-22, that has exceptionally high rhizosphere
competence. In field experiments, we have demonstrated that T-22 was resistant
to edaphic conditions that reduce colonization by indigenous Trichoderma
species, so that it can provide protection against root pathogens. Well-drained
sand, stone or gravel soils supported lower populations of wild Trichoderma
than did loams (100.5 vs 10 3.3 cfu/g), but populations
of T-22 were high in all soils (>104 cfu/g). In a multivariate
analysis of soil characteristics affecting colonization, only soils with
low Ca and low pH had reduced populations. No other measured soil characteristics
were correlated with colonization. When sown in the field at different
initial soil temperatures ranging from 10 to 27°C, T-22 populations
were unaffected by temperature, having a population from 104.6
to 105.4 cfu/g. Indigenous strains were 103 in cold
soils, peaked at 104 at 15°C, declining in later sowings
due to higher biological competition. Differences in microbial competition
had little effect. Roots were equally colonized in the differing soil microflora
in three management systems at the Rodale Farming Systems Trial. Invading
an existing soil microbial community is the most difficult thing to achieve
with a biocontrol organism. These data show that T-22 is the first to consistently
do so.
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