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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

Madhav P. Nepal


Falcaria vulgaris Bernh. (sickleweed), native to Eurasia, occurs disjunctly in the Midwest and the East Coast of the United States. In parts of Iowa, Nebraska and South Dakota, it is an aggressive weed potentially turning to invasive. The main objectives of this study were (1) to reconstruct the introduction history and spread of the plant, (2) to develop and apply molecular markers to study the genetics of sickleweed populations in the United States. I used herbarium records and a suite of molecular markers to accomplish the project objectives. I surveyed 178 US herbaria, including those in the sixteen states where USDA has reported the sickleweed occurrence. Nuclear microsatellite markers developed for Daucus carota were screened for their transferability to sickleweed. I also sequenced the trnL intron, trnL-F intergenic spacer, and trnQ-rps16 intergenic spacer regions of chloroplast DNA and ITS region of nuclear ribisomal DNA to study the genetic diversity. Herbarium records indicated that sickleweed was first introduced no later than 1922, and independent introduction of this plant took place in the East Coast state and in the Midwest of the United States. The species has been documented in 37 counties of 15 states of the United States. No recent sickleweed records have been reported for the last 17 years in the U.S. except in Iowa, Nebraska and South Dakota. Nuclear microsatellite data revealed three distinct genetic races of sickleweed in the Midwest. Chloroplast sequence data revealed six chlorotypes nested into two main lineages suggesting at least two introductions of sickleweed in the Midwest. All data sets- herbarium records, nuclear microsatellites, nuclear and Chloroplast DNA sequences support the occurrence of multiple introductions. Presence of multiple alleles in individuals suggested polyploidy in sickleweed. High genetic diversity along with evidence of multiple introductions and polyploidy suggest that sickleweed, if not controlled in a timely fashion, can emerge as a serious invader.

Library of Congress Subject Headings

Noxious weeds--United States


Includes bibliographical references



Number of Pages



South Dakota State University


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