Explore the vast range of titles available.

Kochia [Bassia scoparia (L.) A.J. Scott] is an invasive species in the High Plains of the United States that poses formidable management challenges in agricultural systems, primarily due to its evolution of resistance to glyphosate. Resistance is due to a transposon-associated increase in 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS) gene copy number relative to the sensitive biotype. Factors behind the rapid spread of glyphosate-resistant biotypes are likely associated with certain aspects of B. scoparia biology, such as a protogynous flower morphology producing large amounts of pollen, that encourages outcrossing and favors high genetic diversity. Furthermore, its ability to tumble over long distances ensures a rapid spread of the resistance trait. Herein, we explore glyphosate resistance in B. scoparia in Colorado. There was no difference in EPSPS gene (Type I, Type II) and FAR1 copy numbers between parent and progeny B. scoparia populations across multiple years (2018, 2020, and 2022), suggesting stable inheritance of glyphosate resistance. Further, the inheritance of glyphosate resistance was investigated using three specific microsatellites or simple sequence repeat (SSR) markers viz. 2656, 2896, and 1792. SSR marker analysis revealed an outcrossing rate of 78% and a selfing rate of 22% in B. scoparia progeny. By investigating the complex interplay between B. scoparia’s biology and genetics, this study investigates the inheritance of glyphosate resistance in B. scoparia, estimates the outcrossing rate under field conditions, and underscores the importance of developing effective management strategies to mitigate its impact on agricultural ecosystems.

Diflufenican is a pre-emergent and early post-emergent herbicide that inhibits phytoene desaturase, an essential enzyme in the biosynthesis of carotenoids. It has been used effectively in overseas markets such as Europe and Australia, but it never has been registered for use in the United States. With the herbicide resistance issues in the United States continuing to increase each year, the necessity for developing effective options to combat herbicide-resistant weeds magnifies. Recently, Bayer CropScience has begun research into developing diflufenican as a tool to manage herbicide-resistant weeds, namely Palmer amaranth (Amaranthus palmeri), in United States’ corn and soybean systems. In this thesis, research is presented on the impacts soil type, soil moisture, and soil surface residue cover have on diflufenican efficacy. Broad-spectrum weed control with diflufenican was reduced when applied to soils with higher organic matter. This is a consequence of diflufenican having higher sorption coefficients in soils with higher organic matter. Control of Palmer amaranth with diflufenican was not impacted by soil moisture when applied to sandy soils. Under increasing levels of corn residue cover, control of redroot pigweed (Amaranthus retroflexus) was not impacted in the field or the greenhouse. In the greenhouse, control of Palmer amaranth with diflufenican was reduced when applied at a lower rate to the highest corn residue coverage in comparison to treatments with no residue cover. Indications are that when robust rates of diflufenican are applied to soil surfaces with high corn residue cover, necessary control can be expected of susceptible species.

Bacterial infections represent a rapidly growing challenge to human health. Aminoglycosides are widely used broad-spectrum antibiotics, but they inflict permanent hearing loss in up to ~50% of patients by causing selective sensory hair cell loss. Here, we hypothesized that reducing aminoglycoside entry into hair cells via mechanotransducer channels would reduce ototoxicity, and therefore we synthesized 9 aminoglycosides with modifications based on biophysical properties of the hair cell mechanotransducer channel and interactions between aminoglycosides and the bacterial ribosome. Compared with the parent aminoglycoside sisomicin, all 9 derivatives displayed no or reduced ototoxicity, with the lead compound N1MS 17 times less ototoxic and with reduced penetration of hair cell mechanotransducer channels in rat cochlear cultures. Both N1MS and sisomicin suppressed growth of E. coli and K. pneumoniae, with N1MS exhibiting superior activity against extended spectrum β lactamase producers, despite diminished activity against P. aeruginosa and S. aureus. Moreover, systemic sisomicin treatment of mice resulted in 75% to 85% hair cell loss and profound hearing loss, whereas N1MS treatment preserved both hair cells and hearing. Finally, in mice with E. coli-infected bladders, systemic N1MS treatment eliminated bacteria from urinary tract tissues and serially collected urine samples, without compromising auditory and kidney functions. Together, our findings establish N1MS as a nonototoxic aminoglycoside and support targeted modification as a promising approach to generating nonototoxic antibiotics.