Inheritance of glyphosate resistance and cross-pollination rates under field conditions in kochia (<i>Bassia scoparia</i>)

Abstract 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.