Multiple regression models of the HPLC chromatogram peak areas and the results from lettuce seed bioassays were used to determine which combination of isobutylamides from E. angustifolia root extracts accounted for the allelopathic effects in the bioassay. Two fractions initially identified as peaks 3 and 6 and subsequently determined to be undeca-2E-ene-8, 10-diynoic acid isobutylamide and dodeca-2E, 4E, 8Z, 10E-tetraenoic acid isobutylamide, respectively, were identified as the compounds responsible for the allelopathic activity. The two compounds each accounted for slightly more than 6% of the total bioassay variability, but together accounted for about 73% of the variability based on the simplest non-linear model. Direct application of the purified compounds in the bioassay demonstrated that use of the genetic variability in the Echinacea samples allowed identification of synergistic effects without the traditional approach of fractionation and testing of all compounds and their possible combinations.
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Kim Piechowski, Duane P. Mathees, R. Neil Reese and Rita S.K. Majerle, 2006. Identification of Potentially Allelopathic Isobutylamides in Echinacea angustifolia D.C. Roots. Journal of Biological Sciences, 6: 978-984.
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