Herbicide Resistance and Reproductive Biology in Dioecious Weedy Amaranths

Lopez, Alexander

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https://hdl.handle.net/2142/133345 Copy

Description

Title

Herbicide Resistance and Reproductive Biology in Dioecious Weedy Amaranths

Author(s)

Lopez, Alexander

Issue Date

2026-06-09

Doctoral Committee Chair(s)

Tranel, Patrick

Committee Member(s)

• Lipka, Alexander
• Studer, Anthony
• Jamann, Tiffany

Department of Study

Crop Science

Discipline

Weed Science

Degree Granting Institution

University of Illinois

Degree Name

Ph.D. (doctoral)

Degree Level

Dissertation

Date of Ingest

2026-06-09T17:37:24-05:00

Keyword(s)

• Amaranthus palmeri
• Amaranthus tuberculatus
• Dioecy
• Herbicide resistance
• Genomics
• Molecular biology

Language

eng

Abstract

In recent decades, Palmer amaranth (Amaranthus palmeri S. Watson) and waterhemp [A. tuberculatus (Moq.) Sauer] have become two of the most challenging weeds to manage in row-crop production systems throughout the much of the United States. Both species possess several life-history traits considered to be advantageous to opportunistic weedy species that make them highly competitive. However, the growing difficulty in managing them arises from the extraordinary rate at which they continue to evolve resistance to different herbicides, which increasingly limits the effectiveness of chemical control options. As such, it is increasingly imperative that we continue to optimize existing chemical management strategies and explore innovative integrated weed management approaches to sustain long-term control of these weeds. To that end, this dissertation explores how knowledge of herbicide resistance mechanisms can be leveraged to improve control of resistant populations, as well as how knowledge of the reproductive biology in these species can inform the development of novel control strategies exploiting vulnerabilities in their dioecious sexual systems. To explore how resistance mechanistic knowledge can inform management strategies, I evaluated the efficacy of different herbicide chemistries targeting photosystem II (PSII) in A. tuberculatus populations exhibiting either target-site (TS) or non-target-site (NTS) PSII resistance. While TS resistance affecting inhibitor binding to PSII conferred cross-resistance to unrelated PSII inhibitor chemistries, NTS metabolic resistance exhibited selectivity toward triazine PSII chemistries due to the specific detoxification mechanism involved. These results indicate the importance of understanding resistance mechanisms to identify opportunities to optimize herbicide selection and improve management of resistant weed populations. To explore the potential for exploiting the reproductive biology of these two species as a novel management strategy, I investigated the genetic regulation of flowering and sex differentiation, as well as the stability of their current dioecious sexual system. I identified a suite of sRNAs and genes with sex-biased expression in both species that represent promising candidates to target for designing future genetic control strategies aimed at disrupting their mating systems through sex-ratio manipulation. In addition, I also demonstrated that dioecy in these species is not as stable as previously considered and showed that mate limitation can act as a selective pressure to bring about the breakdown of dioecy. These results together provide new insights into the reproductive biology of two of the most problematic agricultural weeds and build upon an established foundation for the development of innovative management strategies that exploit vulnerabilities in their mating systems.

Type of Resource

dataset

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