Prevalence and Mechanism of Atrazine Resistance in Waterhemp (Amaranthus tuberculatus) from Nebraska

Abstract Resistance to atrazine (a photosystem II [PSII] inhibitor) is prevalent in waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] across the U.S. Midwest. Previous research suggests that target-site mutation or rapid metabolism of atrazine mediated by glutathione S-transferase (GST) conjugation confers resistance in A. tuberculatus from Illinois. The distribution and mechanism of resistance to atrazine in A. tuberculatus populations from Nebraska (NE) are unknown. In this research we (1) evaluated the response and frequency of resistance in NE A. tuberculatus to soil-applied PSII (metribuzin and atrazine) and protoporphyrinogen oxidase (sulfentrazone) inhibitors, as well as POST-applied atrazine; and (2) determined the mechanism of atrazine resistance in NE A. tuberculatus. The chloroplastic psbA gene, coding for a D1 protein (the target site of atrazine) was sequenced in 85 plants representing 27 populations of A. tuberculatus. Furthermore, 24 plants selected randomly from four atrazine-resistan...