Induced resistance in the indeterminate growth of aspen (<Emphasis Type="Italic">Populus tremuloides</Emphasis>) |
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Authors: | Email author" target="_blank">Michael?T?StevensEmail author Richard?L?Lindroth |
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Institution: | (1) Department of Botany, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706, USA;(2) Department of Entomology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706, USA |
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Abstract: | Studies of induction in trees have examined rapid induced resistance (RIR) or delayed induced resistance (DIR), but have not
examined induction that occurs in leaves produced by indeterminately growing trees subsequent to, but in the same season as,
damage. We refer to induction that occurs during this time period as intermediate-delayed induced resistance (IDIR). We assessed
the influences of genetic and environmental factors, and their interactions, on temporal and spatial variation in induction
and on tradeoffs between induced and constitutive levels of resistance in indeterminately growing saplings of aspen (Populus tremuloides). We utilized a common garden of 12 aspen genotypes experiencing two levels of defoliation and two levels of soil nutrients.
We assessed concentrations of phenolic glycosides and condensed tannins in damaged leaf remnants collected 1 week after defoliation
to examine rapid and local induction, and in undamaged leaves produced 8 weeks after defoliation to assess intermediate-delayed
and systemic induction. In general, tannins showed RIR, while phenolic glycosides expressed IDIR. For both classes of allelochemicals,
we found high estimates of broad-sense heritability and genetic variation in both induced and constitutive levels. Genetic
variation may be maintained by both direct costs of allelochemicals and by costs of inducibility (phenotypic plasticity).
Such costs may drive the tradeoff exhibited between induced and constitutive levels of phenolic glycosides. IDIR may be important
in reducing total-season tissue loss by providing augmented resistance against late summer herbivores in trees that have experienced
damage earlier in the season. Herbivore-resistant compensatory growth is especially beneficial to young trees growing in competitive
environments. |
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Keywords: | Defoliation Genotype × environment interaction Herbivory Phenotypic plasticity Plant defense |
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