Monday, August 2, 2010
Exhibit Hall A, David L Lawrence Convention Center
Background/Question/Methods Solidago altissima is a dominant perennial with the ability to form dense, almost monospecific stands; the plant’s success is facilitated by large below-ground rhizome systems that allow clonal spread and possible allelopathic suppression of competitors. Few below-ground herbivores have been identified on goldenrod; however, over 120 herbivorous insects are hosted above ground, including specialist Trirhabda virgata larvae that periodically defoliate entire clones. Adult T. virgata beetles may cause additional damage to existing leaves and regrowth. To test the hypothesis that above-ground herbivory affects levels of rhizome defensive and allelopathic chemicals, 64 plants were propagated from rhizome sections of 32 genotypes and grown in an open-air container garden. Ten local T. virgata larvae were placed on each of 32 individually mesh-enclosed plants and allowed to feed until pupation. Following emergence, 10 adult beetles were bagged onto 16 larvae-damaged plants and 16 virgin plants; 16 bagged T. virgata excluded plants served as controls. Beetles fed until September, after which individual rhizome samples were harvested and extracted into MeOH. Subsamples of root tissue were obtained from 20 plants to compare root/rhizome chemical levels. Allelochemicals from all plant tissues were separated using acetonitrile-acidified water reverse-phase HPLC with a diode array detector.
Results/Conclusions Eight phenolics, four polyacetylenes and three diterpene acids were confirmed from the HPLC UV-visible spectra and subsequent mass spectral analysis. To quantify, HPLC peak areas were grouped and summed for each chemical class. Overall, dehydromatricaria ester (DME) dominated the polyacetylene profile whereas solidagoic acid dominated the diterpene profile. End of season relative concentrations of rhizome phenolics, polyacetylenes and diterpene acids did not differ between control T. virgata-free plants and plants hosting larvae only, adult beetles only and larvae + adult herbivory (all p-values >.1). Phenolic and diterpene relative concentrations were correlated (r = .415, p<.001); however, no relationship was seen between polyacetylene and either phenolic or diterpene relative concentrations. Paired comparisons found that root polyacetylene concentrations are 3times greater than rhizome levels (p<.001), but that phenolic and diterpene relative concentrations are approximately 2 times lower than rhizome tissue levels (p<.001). Goldenrod leaf herbivory over one growing season by T. virgata was not found to influence the relative concentrations of fall rhizome chemicals thought to function in below-ground defense and allelopathy. Differences in rhizome versus root polyacetylene, phenolic and diterpene concentrations suggest that future studies of goldenrod allelopathy and polyacetylenes accumulation should focus on lateral root tissue.
Results/Conclusions Eight phenolics, four polyacetylenes and three diterpene acids were confirmed from the HPLC UV-visible spectra and subsequent mass spectral analysis. To quantify, HPLC peak areas were grouped and summed for each chemical class. Overall, dehydromatricaria ester (DME) dominated the polyacetylene profile whereas solidagoic acid dominated the diterpene profile. End of season relative concentrations of rhizome phenolics, polyacetylenes and diterpene acids did not differ between control T. virgata-free plants and plants hosting larvae only, adult beetles only and larvae + adult herbivory (all p-values >.1). Phenolic and diterpene relative concentrations were correlated (r = .415, p<.001); however, no relationship was seen between polyacetylene and either phenolic or diterpene relative concentrations. Paired comparisons found that root polyacetylene concentrations are 3times greater than rhizome levels (p<.001), but that phenolic and diterpene relative concentrations are approximately 2 times lower than rhizome tissue levels (p<.001). Goldenrod leaf herbivory over one growing season by T. virgata was not found to influence the relative concentrations of fall rhizome chemicals thought to function in below-ground defense and allelopathy. Differences in rhizome versus root polyacetylene, phenolic and diterpene concentrations suggest that future studies of goldenrod allelopathy and polyacetylenes accumulation should focus on lateral root tissue.
