Plant Growth Regulation 43: 89-92. 2004.
Effect of Trichoderma
colonization on auxin-mediated regulation of root elongation.
Thomas Björkman
Department of Horticultural Sciences, New York State
Agricultural Experiment
Station, Cornell University, Geneva, NY 14456
ABSTRACT The biocontrol fungus Trichoderma harzianum 1295-22 increases root growth in addition to roles in
suppressing disease. Its agricultural use could be expanded if the
mechanism of growth enhancement were
known. Among the proposed mechanisms of growth enhancement is that the
fungus counteracts auxin
inhibition of root-cell elongation. We tested whether there was
evidence for a secreted auxin inhibitor, for
enhanced auxin degradation, or for altered auxin sensitivity. Our
results provide no support for any of these
mechanisms. Trichoderma secretions inhibited growth, whereas an auxin
inhibitor would increase growth.
Auxin inhibited growth to the same extent in colonized and uncolonized
roots, indicating no change in auxin
sensitivity. Endogenous auxin levels maintained growth closer to the
maximum in uncolonized roots,
indicating stronger auxin limitation of growth in colonized roots.
These tests indicated that Trichoderma-colonized roots had a faster maximum growth rate, but an unchanged
response to auxin.
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