Browsing by Author "Mason, Richard, committee member"

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Herbicide resistance in kochia and wheat: the loss and gain of weed control tools for wheat production
(Colorado State University. Libraries, 2024) Montgomery, Jacob S., author; Gaines, Todd, advisor; Dayan, Franck, committee member; Pearce, Stephen, committee member; Mason, Richard, committee member
Weeds are one of the main causes of yield loss across agricultural systems worldwide. Currently, weed control in crop production systems relies heavily on the use of chemical herbicides. While these herbicides are largely effective and very efficient, they are prone to herbicide resistance evolution in weeds. Herbicide resistance evolution is the most pressing issue facing weed scientists, currently. As researchers scramble to develop new weed control technologies, herbicide resistance traits enable the use of herbicides in new cropping systems. While this is not the long-term answer to issues facing weed managers, herbicide resistance traits offer a short-term solution to systems that may be desperate for answers. Kochia is a tumble weed that was introduced to North America in the 1800's. Since its introduction, kochia has invaded many settings of the American West. Its abiotic stress tolerance, tumble seed dispersion mechanism, and ability to outcross allow it to invade new areas and maintain genetic diversity for selection to act on. In a study reported here, I identify the genetic basis of resistance to the herbicide dicamba in a population of kochia collected from Colorado. I use linkage mapping to identify a region of the genome associated with resistance. Within this locus, I find a transposable element insertion within an exon of an AUXIN/INDOLE-3-ACETIC ACID gene. This insertion causes differential splicing that changes the amino acid sequence near the degron domain in resistant plants. I apply dicamba to Arabidopsis plants expressing wildtype ii and mutant alleles of this gene to demonstrate that this mutation is sufficient in causing dicamba resistance. Protein modeling suggests that while several amino acids are affected, a specific glycine-to-threonine substitution is likely the most important in causing resistance. Finally, the mutant allele of this gene segregates with reduced plant height and biomass, suggesting this resistance mechanism has a pleotropic effect of a fitness cost. This study demonstrates the diverse ways that adaptive alleles can be generated in weedy species and describes the genetic and physiological basis of dicamba resistance in kochia. These findings may be used to design new auxinic herbicides that are not affected by this resistance mechanism. With the loss of herbicide efficacy in the face of herbicide resistance evolution, as described above, wheat producers could benefit from the availability of more weed control options. In another study presented here, I utilize gene editing and traditional mutagenesis approaches to generate wheat plants that are deficient in sulfolipids. In rice, eliminating these sulfolipids clearly results in resistance to the herbicide oxyfluorfen. Liquid chromatography coupled with mass spectrometry (LC/MS) experiments confirmed that the edits I made to the gene UTP- GLUCOSE-1-PHOSPHATE URIDYLYLTRANSFERASE 3 indeed resulted in drastic reduction in sulfolipid content. Dose response experiments showed that mutant lines gained moderate resistance to oxyfluorfen, but not lactofen, a herbicide from the same chemical family. Finally, LC/MS experiments confirmed that mutant wheat plants accumulated less porphyrin following oxyfluorfen application. The wheat lines developed in this study provide germplasm for trait introgression or a framework to make similar edits in locally adapted varieties to reproduce this herbicide resistance trait. If stewarded correctly, the trait will extend the effective lifespan of currently used herbicides in wheat and improve weed control.