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United States Department of Agriculture

Agricultural Research Service

Title: Influence of Defoliation on Toxic Alkaloid Concentration and Alkaloid Pools in Tall Larkspur

Authors
item Ralphs, Michael
item Gardner, Dale

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 2000
Publication Date: January 1, 2001
Citation: Ralphs, M.H., Gardner, D.R. 2001. Influence of defoliation on toxic alkaloid concentration and alkaloid poolsin tall larkspur. Journal of Chemical Ecology.

Interpretive Summary: Early research suggested clipping Duncecap larkspur reduced total alkaloid concentration. The objective of this study was to determine if clipping would reduce toxic alkaloids in Tall larkspur. Clipping 1 inch above the soil reduced the size, vigor, and number of stalks the next year. Toxic and total alkaloid pools were reduced by 2/3 in clipped plants. This is contrary to the plant defense theory which predicts plants increase defens compounds to protect them from herbivory.

Technical Abstract: Early research suggested clipping Duncecap larkspur (Delphinium occidentale) reduced total alkaloid concentration. The objective of this study was to determine if clipping would reduce toxic alkaloids in tall larkspur (D. barbeyi). The study was replicated at two locations in the mountains of central Utah. In 1997 ten uniform plants in the bud elongation stage (40 cm in height) were selected at each site and clipped cm above the soil. The following year, one stalk from each plant was harvested on a weekly basis to evaluate the alkaloid response to clipping over the growing season. Toxic and total alkaloid concentration were measured and alkaloid pools in the entire stock were calculated. Clipping reduced stalk height to less than 50 cm (compared to over 100 cm in unclipped control plants), and some of the clipped plants were severely stunted (< 30 cm). The toxic alkaloid pools in the entire stalk of reduced-height and stunted plants were similar, but were only a third of those in undefoliated control plants. However, alkaloid concentration in stunted plants more than doubled, suggesting that a constant amount of alkaloid was concentrated in the smaller biomass of the stunted stalks. Clipping reduced subsequent vigor and the amount of toxic and total alkaloids in tall larkspur.

Last Modified: 9/10/2014
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