Author ORCID Identifier:

https://orcid.org/0000-0002-4832-9062

Date of Graduation

9-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Norsworthy, Jason

Committee Member

Alejandro Rojas

Second Committee Member

L Barber

Third Committee Member

Matthew Bertucci

Fourth Committee Member

Trenton Roberts

Keywords

Gene amplification; Glufosinate; Multiple herbicide resistance; Palmer amaranth; Resistant weed; Weed management

Abstract

The aim of this dissertation was to: 1) provide an in-depth review about the potential use of natural and synthetic glutathione S-transferase (GST) inhibitors to enhance herbicidal activity or induce crop safety; 2) determine if the addition of metabolic inhibitors to glufosinate is an effective approach to enhance weed control; 3) investigate the mechanism conferring resistance to glufosinate in a highly-resistant Palmer amaranth accession; 4) characterize the genomic rearrangement involved in glutamine synthetase 2 amplification in a Palmer amaranth accession resistant to both glufosinate and glyphosate; 5) quantify the distribution of glufosinate resistance among Palmer amaranth accessions within a 15-km radius surrounding the glufosinate-resistant Palmer amaranth accession initially collected in 2020; 6) determine the postemergence resistance profile of glufosinate-resistant Palmer amaranth accession and identify effective herbicides to control it under field conditions; and 7) evaluate different herbicide programs and the presence of residual herbicides in soybean to control seven-way herbicide-resistant Palmer amaranth accession. Several GST inhibitors have the potential to increase efficacy when mixed with herbicides. However, further research is needed, particularly in vivo experiments. A formulated premixture of glufosinate with the plant-derived flavonoid baicalin enhanced weed control. The amplification and overexpression of the chloroplastic glutamine synthetase (GS2; enzyme targeted by glufosinate) was characterized as one of the resistance mechanisms conferring glufosinate resistance in Palmer amaranth. Extrachromosomal circular DNAs (eccDNAs) were identified as the cause of this increase in GS2. The eccDNA structure co-duplicated 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), which is the enzyme targeted by glyphosate, along with the increase in GS2. Palmer amaranth accessions collected in 2023 were capable of surviving glufosinate applications, and the presence of GS2 amplification was observed in crop fields near the location where the 2020 sample was originally collected, suggesting that glufosinate resistance is present in more areas than initially detected. This result is alarming due to the resistance profile also observed in this accession. Additional investigations with the initial glufosinate-resistant accession revealed the presence of seven-way resistance to postemergence herbicides from groups 2, 4, 5, 9, 10, 14, and 27 (Weed Science Society of America/Herbicide Resistance Action Committee). Field experiments showed that this accession was more likely controlled by preemergence than postemergence herbicide chemistries. A high level of control of the seven-way resistant accession was achievable when residual herbicides were applied sequentially with 2,4-D or dicamba. However, not all plants were controlled, and a zero-tolerance approach should be employed to avoid seed deposition into soil seedbank.

Download

Share

COinS