Survey of glyphosate-, atrazine- and lactofen-resistance mechanisms in Ohio waterhemp (Amaranthus tuberculatus) populations

Abstract

Herbicide resistance within key driver weeds, such as common waterhemp [Amaranthus tuberculatus (Moq.) Sauer var. rudis (Sauer) Costea and Tardif ], constrains available management options for crop production. Routine surveillance for herbicide resistance provides a mechanism to monitor the development and spread of resistant populations over time. Furthermore, the identification and quantification of resistance mechanisms at the population level can provide information that helps growers develop effective management plans. Populations of Amaranthus spp., including A. tuberculatus, redroot pigweed (Amaranthus retroflexus L.), and Palmer amaranth (Amaranthus palmeri S. Watson), were collected from 51 fields in Ohio during the 2016 growing season. Twenty-four A. tuberculatus populations were screened for resistance to the herbicides lactofen, atrazine, and glyphosate. Phenotypically resistant plants were further investigated to determine the frequency of known resistance mechanisms. Resistance to lactofen was infrequently observed throughout the populations, with 8 of 22 populations exhibiting resistant plants. Within those eight resistant populations, the ΔG210 resistance mechanism was observed in 17 of 30 phenotypically resistant plants, and the remainder lacked all known resistance mechanisms. Resistance to atrazine was observed in 12 of 15 populations; however, a target-site resistance mechanism was not observed in these populations. Resistance to glyphosate was observed in all populations. Gene amplification was the predominant glyphosate-resistance mechanism (147 of 322 plants) in the evaluated populations. The Pro-106-Ser mutation was identified in 24 plants, half of which also possessed gene amplification. In this study, molecular screening generally underestimated the phenotypically observed resistance. Continued mechanism discovery and marker development is required for improved detection of herbicide resistance through molecular assays.

Herbicide drift exposure leads to reduced herbicide sensitivity in Amaranthus spp.

“…Both are obligate outcrossing dioecious weed species with a fast growth habitat, extended emergence window, and prolific seed production with high genetic plasticity which pose a challenge to their management 37-44 . Numerous Palmer amaranth and waterhemp populations have evolved resistance to herbicides that target 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), 4-hydroxyphenylpyruvate dioxygenase (HPPD), photosystem II, protoporphyrinogen oxidase (PPO), auxin receptors, microtubule assembly, and acetolacte synthase (ALS) in the US 15,17,[45][46][47][48][49][50][51][52][53][54] . Moreover, pollen mediated gene flow has been reported as a major contributor to herbicide resistance dissemination in Palmer amaranth and waterhemp in the US Midwest 55,56 .Although controlling weed populations on field margins and ditches is considered a best management practice to delay herbicide resistance evolution, these weed populations are often neglected in agricultural landscapes [15][16][17]29 .…”

Fitness cost associated with enhancedEPSPSgene copy number and glyphosate resistance in anAmaranthus tuberculatuspopulation

“…EPSPS gene amplification has been shown to be the main mechanism of glyphosate resistance found in A. tuberculatus populations (Murphy et al 2019). EPSPS gene amplification has also been confirmed as the mechanism of evolved glyphosate resistance in Kochia scoparia, Lolium multiflorum and Amaranthus spp.…”

Herbicide resistance in Amaranthus tuberculatus†

“…Unlike some cases of herbicide resistance, in which resistance does not become a widespread problem but rather is primarily an academic curiosity, most herbicide resistances in A. tuberculatus already are, or are becoming, widespread management challenges. Based on various surveys, 21,[23][24][25] the occurrence of resistance in A. tuberculatus populations to herbicides from different groups can be listed as follows: ALS inhibitors > glyphosate = D1 serine 264 binders > PPO inhibitors > HPPD inhibitors > auxins = VLCFAS inhibitors. Resistance to ALS inhibitors in A. tuberculatus has been the norm, rather than the exception, in recent decades, and is now present in essentially every field population of this species.…”