Understanding Resistance Mechanisms to Trifluralin in an Arkansas Palmer Amaranth Population

Abstract

Amaranthus palmeri S. Watson (Palmer amaranth) is considered a problematic and troublesome weed species in many crops in the USA, partly because of its ability to evolve resistance to herbicides. In this study, we explored the mechanism of resistance in a trifluralin-resistant A. palmeri accession collected from Arkansas, USA. Dose-response assays using agar plates demonstrated an EC50 (effective concentration that reduces root length by 50%) of 1.02 µM trifluralin compared to 0.39 µM obtained in the susceptible accession. Thus, under these conditions, the resistant accession required 2.6 times more trifluralin to inhibit root length by 50%. Seeds in the presence or absence of the cytochrome P450-inhibitior malathion displayed a differential response with no significant influence on root length, suggesting that resistance is not P450-mediated. In addition, application of 4-chloro-7-nitrobenzofurazan (NBD-Cl), a glutathione S-transferase (GST) inhibitor, showed significant differences in root length, indicating that GSTs are most likely involved in the resistance mechanism. Sequencing of α- and β-tubulin genes revealed no single nucleotide polymorphisms (SNPs) previously described between accessions. In addition, relative gene copy number of α- and β-tubulin genes were estimated; however, both resistant and susceptible accessions displayed similar gene copy numbers. Overall, our results revealed that GST-mediated metabolism contributes to trifluralin resistance in this A. palmeri accession from Arkansas.

Molecular Mechanisms of Herbicide Resistance in Weeds

“…Among grasses, Echinochloa ssp. is reported in two articles [ 9 , 14 ] and L. multiflorum in one [ 8 ]; among dicots, two articles reported on the global invasive weed species A. palmeri [ 10 , 13 ]. All these weeds are acknowledged to be among the top 10 weed species resistant to most SoAs globally [ 19 ].…”

“…Interestingly, information on the resistance to auxins in Echinochloa ssp. [ 14 ], microtubule assembly [ 13 ], and PPO inhibitors [ 10 ], both in A. palmeri , are contributions of this Special Issue.…”

“…Among NTSR mechanisms, most articles cover an enhanced metabolism involving different enzyme families and degradation pathways. One contribution referred to P450 [ 12 ] and two to GST [ 12 , 13 ], the most important enzyme families involved in herbicide degradation, while two other contributions highlighted that stress-responsive genes were involved in herbicide metabolism [ 12 , 14 ].…”

“…In another study by González-Torralva and Norsworthy [ 13 ], the resistance mechanism in a trifluralin-resistant A. palmeri population from the USA was investigated. Results indicated that applying a GST inhibitor showed significant differences in root length between susceptible and resistant plants, indicating that GSTs are probably involved in the resistance mechanism.…”

Function of Cytochrome P450CYP72A1182in Metabolic Herbicide Resistance Evolution inAmaranthus palmeriPopulations

“…Its dioecious nature, with separate male and female plants, allows for efficient cross-pollination, leading to the exchange of genetic material and the emergence of novel traits, including herbicide resistance (Ward et al ., 2013). Populations have evolved resistance to herbicide spanning eight different modes of action, including synthetic auxins (Shyam et al ., 2022) and herbicide targeting acetolactate synthase (ALS) (Berger et al, 2016), 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) (Gaines et al ., 2010), protoporphyrinogen oxidase (PPO) (Montgomery et al, 2021), photosystem II (PSII) (Jhala et al, 2014), 4-hydroxyphenylpyruvate dioxygenase (HPPD) (Küpper et al, 2018), very long chain fatty acid elongase (VLCFAE) (Hwang et al ., 2023), and tubulin biosynthesis (González-Torralva & Norsworthy, 2021).…”