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Title:Examination of target-site-based mechanisms of glyphosate resistance in waterhemp (Amaranthus tuberculatus)
Author(s):Chatham, Laura
Advisor(s):Tranel, Patrick J.
Contributor(s):Juvik, John A.; Riechers, Dean E.
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):glyphosate resistance
5-enolpyruvylshikimate-3-phosphate (EPSPS) gene amplification
Abstract:Glyphosate is one of the most important and widely used herbicide in the world. While few weed species had evolved resistance in the two decades after glyphosate’s commercialization in 1974, an overreliance on glyphosate and lack of diversity in weed control methods following the introduction of glyphosate-resistant (GR) crops in 1996 has led to increased selection pressure on weeds to evolve resistance. In 2005, the first GR waterhemp (Amaranthus tuberculatus) population was identified. Waterhemp is perhaps the most economically threatening weed in the north central United States, with many populations evolving resistance to herbicides spanning multiple sites of action. Three potential mechanisms of resistance have been linked with GR waterhemp: EPSPS gene amplification, EPSPS target-site mutations, and reduced translocation. The objective of this research was to investigate the target-site-based mechanisms (EPSPS gene amplification and EPSPS mutations) of glyphosate resistance. Waterhemp populations were collected throughout Illinois and screened for glyphosate resistance and EPSPS gene amplification to address whether the mechanism could be used as a proxy for the resistance. The majority of the time, resistant populations had EPSPS gene amplification; however, populations without gene amplification were also found. In some populations, an EPSPS target-site mutation conferring a Pro106Ser substitution was associated with resistance, while in others neither of the target-site-based mechanisms was present. Further examination of the association between glyphosate resistance and EPSPS gene amplification was carried out via a multi-state study of GR waterhemp populations. Dose responses were performed at each location and survivors were tested for gene amplification. Four of five populations had EPSPS gene amplification, and one had no amplification but the Pro106Ser substitution instead. In populations with EPSPS gene amplification, copy number appeared to increase in plants surviving increasing glyphosate rates. Given the incidence of the Pro106Ser mutation in both of these studies, an investigation of this mechanism was carried out to determine the degree to which it confers resistance. A glyphosate dose response carried out on a segregating F2 population containing the Pro106Ser substitution revealed that a 2- to 4-fold level of resistance is conferred. Gene amplification appears to be the primary mechanism of resistance in the majority of waterhemp populations, with the Pro106Ser substitution present in fewer populations and conferring a lower level of resistance. Results from the studies herein also suggest that additional mechanisms of resistance exist, either separately or in conjunction with the target-site mechanisms studied.
Issue Date:2014-09-16
Rights Information:Copyright 2014 Laura Chatham
Date Available in IDEALS:2014-09-16
Date Deposited:2014-08

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