Sparks, Crystal Devona, authorGaines, Todd, advisorDayan, Franck, committee memberBeffa, Roland, committee memberNishimura, Marc, committee memberWestra, Phil, committee member2024-05-272025-05-202024https://hdl.handle.net/10217/238492Glyphosate is one of the most widely used herbicides worldwide due to favorable chemical characteristics and availability of compatible transgenic biotechnology in crops. Resistance to glyphosate has evolved in many weed species capable of significant yield reduction in top production systems globally. One such species is Ambrosia trifida (giant ragweed), a monoecious broadleaf with imperfect flowers native to North America where it is highly competitive in corn, soybean, and cotton production. Some glyphosate resistant populations of A. trifida also display a rapid response with cell death in the mature leaves within 24-48 hours after treatment with glyphosate. Transcriptomic analysis revealed differential expression of multiple gene families associated with known glyphosate resistance mechanisms such as ATP-binding cassette (ABC) transporters and aldo-keto reductases. Gene ontology analysis showed an enrichment of many genes related to phytohormone response to biotic and abiotic stress in the differentially expressed genes. This could be related to a novel glyphosate resistance mechanism or a signaling cascade involved in the rapid cell death response. The A. trifida genome contains two loci of the glyphosate target site gene 5-enolpyruvylshikimate-3-phosphate-synthase (EPSPS), with a previously reported Pro106Ser mutation in EPSPS2. This locus showed up-regulation by three hours after treatment. Trait mapping revealed three genomic regions associated with glyphosate resistance and a single interval associated with the rapid response. Along with phenotypic segregation ratios, this indicates that resistance and rapid response traits are genetically independent and multiple genes likely contribute to resistance.born digitaldoctoral dissertationsengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.glyphosategiant ragweedrapid responseTextEmbargo expires: 05/20/2025.