Target Site–Based and Non–Target Site Based Resistance to ALS Inhibitors in Palmer Amaranth (Amaranthus palmeri)

Resistance to acetolactate synthase (ALS)-inhibitor herbicides due to continuous and repeated selection is widespread in many troublesome weed species, including Palmer amaranth, throughout the United States. The objective of this research was to investigate the physiological and molecular basis of resistance to ALS inhibitors in a chlorsulfuron-resistant Palmer amaranth population (KSR). Our results indicate that the KSR population exhibits a high level of resistance to chlorsulfuron compared with two known susceptible populations, MSS and KSS from Mississippi and Kansas, respectively. MSS is highly susceptible to chlorsulfuron, whereas KSS is moderately sensitive. Dose–response analysis revealed that KSR was more than 275-fold more resistant compared with KSS. Nucleotide sequence analysis of theALSgene from the plants that survived chlorsulfuron treatment revealed the possibility of evolution of both target site–based and non–target site based resistance to ALS inhibitors in the KSR population. The most common mutation (Pro-197-Ser) in theALSgene associated with resistance to the sulfonylureas in many weed species was found only in 30% of the KSR population. A preliminary malathion study showed that the remaining 70% of resistant plants might have cytochrome P450–mediated non–target site resistance. This is the first report elucidating the mechanism of resistance to ALS inhibitors in Palmer amaranth from Kansas. Presence of both target site– and non–target site based mechanisms of resistance limits the herbicide options to manage Palmer amaranth in cropping systems.

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Differentiation of Life-History Traits among Palmer Amaranth Populations (Amaranthus palmeri) and Its Relation to Cropping Systems and Glyphosate Sensitivity

Weed Science ◽

10.1017/wsc.2017.14 ◽

2017 ◽

Vol 65 (3) ◽

pp. 339-349 ◽

Cited By ~ 19

Author(s):

Washington Bravo ◽

Ramon G. Leon ◽

Jason A. Ferrell ◽

Michael J. Mulvaney ◽

C. Wesley Wood

Keyword(s):

Life History ◽

Crop Rotation ◽

Life History Traits ◽

Cropping Systems ◽

Glyphosate Resistance ◽

The United States ◽

Organic Production ◽

Palmer Amaranth ◽

Flowering Plant ◽

Weed Species

Palmer amaranth’s ability to evolve resistance to different herbicides has been studied extensively, but there is little information about how this weed species might be evolving other life-history traits that could potentially make it more aggressive and difficult to control. We characterized growth and morphological variation among 10 Palmer amaranth populations collected in Florida and Georgia from fields with different cropping histories, ranging from continuous short-statured crops (vegetables and peanut) to tall crops (corn and cotton) and from intensive herbicide use history to organic production. Palmer amaranth populations differed in multiple traits such as fresh and dry weight, days to flowering, plant height, and leaf and canopy shape. Differences between populations for these traits ranged from 36% up to 87%. Although glyphosate-resistant (GR) populations collected from cropping systems including GR crops exhibited higher values of the aforementioned variables than glyphosate-susceptible (GS) populations, variation in traits was not explained by glyphosate resistance or distance between populations. Cropping system components such as crop rotation and crop canopy structure better explained the differences among populations. The higher growth of GR populations compared with GS populations was likely the result of multiple selection forces present in the cropping systems in which they grow rather than a pleiotropic effect of the glyphosate resistance trait. Results suggest that Palmer amaranth can evolve life-history traits increasing its growth and reproduction potential in cropping systems, which explains its rapid spread throughout the United States. Furthermore, our findings highlight the need to consider the evolutionary consequences of crop rotation structure and the use of more competitive crops, which might promote the selection of more aggressive biotypes in weed species with high genetic variability.

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Palmer Amaranth (Amaranthus palmeri) Identification and Documentation of ALS-Resistance in Argentina

Weed Science ◽

10.1614/ws-d-15-00125.1 ◽

2016 ◽

Vol 64 (2) ◽

pp. 312-320 ◽

Cited By ~ 7

Author(s):

Sarah Berger ◽

Paul T. Madeira ◽

Jason Ferrell ◽

Lyn Gettys ◽

Sergio Morichetti ◽

...

Keyword(s):

Herbicide Resistance ◽

Rapid Evolution ◽

Agricultural Practices ◽

Acetolactate Synthase ◽

The United States ◽

Palmer Amaranth ◽

Sequencing Data ◽

Weed Species ◽

Plant Populations ◽

Amaranth Species

Palmer amaranth has greatly disrupted agricultural practices in the United States with its rapid growth and rapid evolution of herbicide resistance. This weed species is now suspected in Argentina. To document whether the suspected plant populations are indeed Palmer amaranth, molecular comparisons to known standards were conducted. Additionally, these same plant populations were screened for possible herbicide resistance to several acetolactate synthase (ALS)-inhibiting herbicides. Sequencing data confirmed that suspected populations (A2, A3, A4) were indeed Palmer amaranth. Another population (A1) was tested to determine whether hybridization had occurred between Palmer amaranth and mucronate amaranth the native amaranth species of the region. Tests confirmed that no hybridization had occurred and that A1 was simply a unique phenotype of mucronate amaranth. Each population was screened for resistance to imazapic, nicosulfuron, and diclosulam. All Palmer amaranth populations from Argentina were shown to be resistant to at least one ALS-inhibiting herbicide. The populations were then subjected to further testing to identify the mutation responsible for the observed ALS resistance. All mucronate amaranth populations exhibited a mutation previously documented to confer ALS resistance (S653N). No known resistance-conferring mutations were found in Palmer amaranth.

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Mechanism of atrazine resistance in atrazine- and HPPD inhibitor-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) from Nebraska

Canadian Journal of Plant Science ◽

10.1139/cjps-2018-0268 ◽

2019 ◽

Vol 99 (6) ◽

pp. 815-823 ◽

Cited By ~ 1

Author(s):

Parminder S. Chahal ◽

Mithila Jugulam ◽

Amit J. Jhala

Keyword(s):

The United States ◽

Palmer Amaranth ◽

Target Site ◽

Cytochrome P450 Monooxygenases ◽

Amaranthus Palmeri ◽

Weed Species ◽

Corn Production ◽

Agronomic Crops ◽

P450 Monooxygenases ◽

Atrazine Resistance

Palmer amaranth (Amaranthus palmeri S. Wats.) is one of the most problematic weed species in agronomic crops in the United States. A Palmer amaranth biotype multiple-resistant to atrazine and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors was reported in a seed corn production field in Nebraska. Rapid detoxification mediated by cytochrome P450 monooxygenases and increased HPPD gene expression were reported as the mechanisms of mesotrione resistance in atrazine- and HPPD inhibitor-resistant Palmer amaranth biotype from Nebraska; however, the mechanism of atrazine resistance is unknown. The objectives of this study were to investigate target site or non-target site based mechanisms conferring atrazine resistance in Palmer amaranth from Nebraska. 14C-atrazine absorption and translocation studies revealed that reduced atrazine absorption or translocation were not involved as one of the mechanisms of atrazine resistance. Instead, greater 14C-atrazine absorption and recovery in treated leaves were observed in resistant compared with susceptible Palmer amaranth. No known mutations including Ser264Gly substitution in the psbA gene causing target site based atrazine resistance were observed. However, the parent 14C-atrazine was metabolized rapidly <4 h after treatment in resistant plants, conferring enhanced atrazine metabolism as the mechanism of resistance.

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Multiple herbicide-resistant Palmer amaranth (Amaranthus palmeri) in Connecticut: confirmation and response to POST herbicides

Weed Technology ◽

10.1017/wet.2021.6 ◽

2021 ◽

pp. 1-7

Author(s):

Jatinder S. Aulakh ◽

Parminder S. Chahal ◽

Vipan Kumar ◽

Andrew J. Price ◽

Karl Guillard

Keyword(s):

Cropping Systems ◽

Acetolactate Synthase ◽

Palmer Amaranth ◽

Effective Control ◽

Herbicide Resistant ◽

First Case ◽

Whole Plant ◽

Chlorimuron Ethyl ◽

Als Inhibitors ◽

Als Inhibitor

Abstract Palmer amaranth is the latest pigweed species documented in Connecticut; it was identified there in 2019. In a single-dose experiment, the Connecticut Palmer amaranth biotype survived the field-use rates of glyphosate (840 g ae ha−1) and imazaquin (137 g ai ha−1) herbicides applied separately. Additional experiments were conducted to (1) determine the level of resistance to glyphosate and acetolactate synthase (ALS) inhibitors in the Connecticut-resistant (CT-Res) biotype using whole-plant dose-response bioassays, and (2) evaluate the response of the CT-Res biotype to POST herbicides commonly used in Connecticut cropping systems. Based on the effective dose required for 90% control (ED90), the CT-Res biotype was 10-fold resistant to glyphosate when compared with the Kansas-susceptible (KS-Sus) biotype. Furthermore, the CT-Res biotype was highly resistant to ALS-inhibitor herbicides; only 18% control was achieved with 2,196 g ai ha−1 imazaquin. The CT-Res biotype was also cross-resistant to other ALS-inhibitor herbicides, including chlorimuron-ethyl (13.1 g ai ha−1), halosulfuron-methyl (70 g ai ha−1), and sulfometuron-methyl (392 g ai ha−1). The CT-Res Palmer amaranth was controlled 75% to 100% at 21 d after treatment (DAT) with POST applications of 2,4-D (386 g ae ha−1), carfentrazone-ethyl (34 g ai ha−1), clopyralid (280 g ae ha−1), dicamba (280 g ae ha−1), glufosinate (595 g ai ha−1), lactofen (220 g ai ha−1), oxyfluorfen (1,121g ai ha−1), and mesotrione (105 g ai ha−1) herbicides. Atrazine (2,240 g ai ha−1) controlled the CT-Res biotype only 52%, suggesting the biotype is resistant to this herbicide as well. Here we report the first case of Palmer amaranth from Connecticut with multiple resistance to glyphosate and ALS inhibitors. Growers should proactively use all available weed control tactics, including the use of effective PRE and alternative POST herbicides (tested in this study), for effective control of the CT-Res biotype.

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Transfer and Expression of ALS Inhibitor Resistance from Palmer Amaranth (Amaranthus palmeri) to anA. spinosus×A. palmeriHybrid

Weed Science ◽

10.1614/ws-d-15-00172.1 ◽

2016 ◽

Vol 64 (2) ◽

pp. 240-247 ◽

Cited By ~ 17

Author(s):

William T. Molin ◽

Vijay K. Nandula ◽

Alice A. Wright ◽

Jason A. Bond

Keyword(s):

Field Experiments ◽

Acetolactate Synthase ◽

Palmer Amaranth ◽

Enzyme Assays ◽

Amaranthus Palmeri ◽

Weed Species ◽

Als Inhibitors ◽

Inhibitor Resistance ◽

Als Inhibitor ◽

Interspecific Transfer

Transfer of herbicide resistance among closely related weed species is a topic of growing concern. A spiny amaranth × Palmer amaranth hybrid was confirmed resistant to several acetolactate synthase (ALS) inhibitors including imazethapyr, nicosulfuron, pyrithiobac, and trifloxysulfuron. Enzyme assays indicated that the ALS enzyme was insensitive to pyrithiobac and sequencing revealed the presence of a known resistance conferring point mutation, Trp574Leu. Alignment of the ALS gene for Palmer amaranth, spiny amaranth, and putative hybrids revealed the presence of Palmer amaranth ALS sequence in the hybrids rather than spiny amaranth ALS sequences. In addition, sequence upstream of the ALS in the hybrids matched Palmer amaranth and not spiny amaranth. The potential for transfer of ALS inhibitor resistance by hybridization has been demonstrated in the greenhouse and in field experiments. This is the first report of gene transfer for ALS inhibitor resistance documented to occur in the field without artificial/human intervention. These results highlight the need to control related species in both field and surrounding noncrop areas to avoid interspecific transfer of resistance genes.

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A Statewide Survey of PPO-Inhibitor Resistance and the Prevalent Target-Site Mechanisms in Palmer amaranth (Amaranthus palmeri) Accessions from Arkansas

Weed Science ◽

10.1017/wsc.2017.68 ◽

2017 ◽

Vol 66 (2) ◽

pp. 149-158 ◽

Cited By ~ 24

Author(s):

Vijay K. Varanasi ◽

Chad Brabham ◽

Jason K. Norsworthy ◽

Haozhen Nie ◽

Bryan G. Young ◽

...

Keyword(s):

Resistance Mechanism ◽

Acetolactate Synthase ◽

Resistance Mechanisms ◽

Palmer Amaranth ◽

Target Site ◽

Evolution Of Resistance ◽

Target Site Resistance ◽

Novel Target ◽

Als Inhibitors ◽

Inhibitor Resistance

Palmer amaranth is one of the most problematic weeds in the midsouthern United States, and the evolution of resistance to protoporphyrinogen oxidase (PPO) inhibitors in biotypes already resistant to glyphosate and acetolactate synthase (ALS) inhibitors is a major cause of concern to soybean and cotton growers in these states. A late-season weed-escape survey was conducted in the major row crop–producing counties (29 counties) to determine the severity of PPO-inhibitor resistance in Arkansas. A total of 227 Palmer amaranth accessions were sprayed with fomesafen at 395 g ha−1to identify putative resistant plants. A TaqMan qPCR assay was used to confirm the presence of the ΔG210 codon deletion or the R128G/M (homologous to R98 mutation in common ragweed) target-site resistance mechanisms in thePPX2gene. Out of the 227 accessions screened, 44 were completely controlled with fomesafen, and 16 had only one or two severely injured plants (≥98% mortality) when compared with the 1986 susceptible check (100% mortality). The remaining 167 accessions were genotypically screened, and 82 (49%) accessions were found to harbor the ΔG210 deletion in thePPX2gene. The R128G was observed in 47 (28%) out of the 167 accessions screened. The mutation R128M, on the other hand was rare, found in only three accessions. About 13% of the accessions were segregating for both the ΔG210 and R128G mutations. Sixteen percent of the tested accessions had mortality ratings <90% and did not test positive for the ΔG210 or the R128G/M resistance mechanisms, indicating that a novel target or non–target site resistance mechanism is likely. Overall, PPO inhibitor–resistant Palmer amaranth is widespread in Arkansas, and the ΔG210 resistance mechanism is especially dominant in the northeast corridor, while the R128G mutation is more prevalent in counties near Memphis, TN.

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Control of acetolactate synthase inhibitor/glyphosate-resistant Palmer amaranth (Amaranthus palmeri) in isoxaflutole/glufosinate/glyphosate-resistant soybean

Weed Technology ◽

10.1017/wet.2021.49 ◽

2021 ◽

pp. 1-23

Author(s):

Jasmine Mausbach ◽

Suat Irmak ◽

Debalin Sarangi ◽

John Lindquist ◽

Amit J. Jhala

Keyword(s):

Field Experiments ◽

Cropping Systems ◽

Acetolactate Synthase ◽

The United States ◽

Palmer Amaranth ◽

Effective Control ◽

Synthase Inhibitor ◽

Density And Biomass ◽

Als Inhibitor ◽

Herbicide Programs

Abstract Palmer amaranth is the most problematic and troublesome weed in agronomic cropping systems in the United States. Acetolactate synthase (ALS) inhibitor- and glyphosate-resistant (GR) Palmer amaranth has been confirmed in Nebraska and it is widespread in several counties. Soybean resistant to isoxaflutole/glufosinate/glyphosate has been developed that provides additional herbicide site of action for control of herbicide-resistant weeds. The objectives of this study were to evaluate herbicide programs for control of ALS inhibitor/GR Palmer amaranth and their effect on Palmer amaranth density and biomass, as well as soybean injury and yield in isoxaflutole/glufosinate/glyphosate-resistant soybean. Field experiments were conducted in a grower’s field infested with ALS inhibitor- and GR Palmer amaranth near Carleton, Nebraska, in 2018 and 2019. Isoxaflutole applied alone or mixed with sulfentrazone/pyroxasulfone, flumioxazin/pyroxasulfone, or imazethapyr/saflufenacil/pyroxasulfone provided similar control (86%-99%) of Palmer amaranth 21 d after PRE (DAPRE). At 14 d after early-POST (DAEPOST), isoxaflutole applied PRE and PRE followed by (fb) POST controlled Palmer amaranth 10% to 63% compared to 75% to 96% control with glufosinate applied EPOST in both years. A PRE herbicide fb glufosinate controlled Palmer amaranth 80% to 99% 21 d after late-POST (DALPOST) in 2018 and reduced density 89% to 100% in 2018 and 58% to 100% in 2019 at 14 DAEPOST. No soybean injury was observed from any of the herbicide programs tested in this study. Soybean yield in 2019 was relatively higher due to higher precipitation compared with 2018 with generally no differences between herbicide programs. This research indicates that herbicide programs are available for effective control of ALS inhibitor/GR Palmer amaranth in isoxaflutole/glufosinate/glyphosate-resistant soybean.

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Controlling Herbicide-Resistant Annual Bluegrass (Poa annua) Phenotypes with Methiozolin

Weed Technology ◽

10.1017/wet.2017.13 ◽

2017 ◽

Vol 31 (3) ◽

pp. 470-476 ◽

Cited By ~ 3

Author(s):

James T. Brosnan ◽

Jose J. Vargas ◽

Gregory K. Breeden ◽

Sarah L. Boggess ◽

Margaret A. Staton ◽

...

Keyword(s):

Acetolactate Synthase ◽

Target Site ◽

Multiple Resistance ◽

Herbicide Resistant ◽

Annual Bluegrass ◽

Microtubule Inhibitors ◽

Effective Option ◽

Target Site Resistance ◽

Susceptible Control ◽

Als Inhibitors

Methiozolin is an isoxazoline herbicide being investigated for selective POST annual bluegrass control in managed turfgrass. Research was conducted to evaluate methiozolin efficacy for controlling two annual bluegrass phenotypes with target-site resistance to photosystem II (PSII) or enolpyruvylshikimate-3-phosphate synthase (EPSPS)-inhibiting herbicides (i.e., glyphosate), as well as phenotypes with multiple resistance to microtubule and EPSPS or PSII and acetolactate synthase (ALS)-inhibiting herbicides. All resistant phenotypes were established in glasshouse culture along with a known herbicide-susceptible control and treated with methiozolin at 0, 125, 250, 500, 1000, 2000, 4000, or 8000 g ai ha−1. Methiozolin effectively controlled annual bluegrass with target-site resistance to inhibitors of EPSPS, PSII, as well as multiple resistance to EPSPS and microtubule inhibitors. Methiozolin rates required to reduce aboveground biomass of these resistant phenotypes 50% (GR50 values) were not significantly different from the susceptible control, ranging from 159 to 421 g ha−1. A phenotype with target-site resistance to PSII and ALS inhibitors was less sensitive to methiozolin (GR50=862 g ha−1) than a susceptible phenotype (GR50=423 g ha−1). Our findings indicate that methiozolin is an effective option for controlling select annual bluegrass phenotypes with target-site resistance to several herbicides.

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Target-Site Mutations and Expression of ALS Gene Copies Vary According to Echinochloa Species

Genes ◽

10.3390/genes12111841 ◽

2021 ◽

Vol 12 (11) ◽

pp. 1841

Author(s):

Silvia Panozzo ◽

Elisa Mascanzoni ◽

Laura Scarabel ◽

Andrea Milani ◽

Giliardi Dalazen ◽

...

Keyword(s):

Cropping Systems ◽

Point Mutations ◽

Common Species ◽

Target Site ◽

The Other ◽

Gene Copy ◽

Resistance Level ◽

Resistance Evolution ◽

Gene Copies ◽

Als Inhibitors

The sustainability of rice cropping systems is jeopardized by the large number and variety of populations of polyploid Echinochloa spp. resistant to ALS inhibitors. Better knowledge of the Echinochloa species present in Italian rice fields and the study of ALS genes involved in target-site resistance could significantly contribute to a better understanding of resistance evolution and management. Using a CAPS-rbcL molecular marker, two species, E. crus-galli (L.) P. Beauv. and E. oryzicola (Vasinger) Vasing., were identified as the most common species in rice in Italy. Mutations involved in ALS inhibitor resistance in the different species were identified and associated with the ALS homoeologs. The relative expression of the ALS gene copies was evaluated. Molecular characterization led to the identification of three ALS genes in E. crus-galli and two in E. oryzicola. The two species also carried different point mutations conferring resistance: Ala122Asn in E. crus-galli and Trp574Leu in E. oryzicola. Mutations were carried in the same gene copy (ALS1), which was significantly more expressed than the other copies (ALS2 and ALS3) in both species. These results explain the high resistance level of these populations and why mutations in the other ALS copies are not involved in herbicide resistance.

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Palmer Amaranth (Amaranthus palmeri) Control by Glufosinate plus Fluometuron Applied Postemergence to WideStrike®Cotton

Weed Technology ◽

10.1614/wt-d-12-00158.1 ◽

2013 ◽

Vol 27 (2) ◽

pp. 291-297 ◽

Cited By ~ 14

Author(s):

Kelly A. Barnett ◽

A. Stanley Culpepper ◽

Alan C. York ◽

Lawrence E. Steckel

Keyword(s):

United States ◽

Weed Control ◽

Acetolactate Synthase ◽

The United States ◽

Palmer Amaranth ◽

Effective Control ◽

Yield Response ◽

Amaranthus Palmeri ◽

Cotton Yield ◽

Cotton Cultivar

Glyphosate-resistant (GR) weeds, especially GR Palmer amaranth, are very problematic for cotton growers in the Southeast and Midsouth regions of the United States. Glufosinate can control GR Palmer amaranth, and growers are transitioning to glufosinate-based systems. Palmer amaranth must be small for consistently effective control by glufosinate. Because this weed grows rapidly, growers are not always timely with applications. With widespread resistance to acetolactate synthase-inhibiting herbicides, growers have few herbicide options to mix with glufosinate to improve control of larger weeds. In a field study using a WideStrike®cotton cultivar, we evaluated fluometuron at 140 to 1,120 g ai ha−1mixed with the ammonium salt of glufosinate at 485 g ae ha−1for control of GR Palmer amaranth 13 and 26 cm tall. Standard PRE- and POST-directed herbicides were included in the systems. Glufosinate alone injured the WideStrike® cotton less than 10%. Fluometuron increased injury up to 25% but did not adversely affect yield. Glufosinate controlled 13-cm Palmer amaranth at least 90%, and there was no improvement in weed control nor a cotton yield response to fluometuron mixed with glufosinate. Palmer amaranth 26 cm tall was controlled only 59% by glufosinate. Fluometuron mixed with glufosinate increased control of the larger weeds up to 28% and there was a trend for greater yields. However, delaying applications until weeds were 26 cm reduced yield 22% relative to timely application. Our results suggest fluometuron mixed with glufosinate may be of some benefit when attempting to control large Palmer amaranth. However, mixing fluometuron with glufosinate is not a substitute for a timely glufosinate application.

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