ORCID Profile
0000-0003-1485-7665
Current Organisations
University of Western Australia
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Colorado State University
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Publisher: Cambridge University Press (CUP)
Date: 21-02-2022
DOI: 10.1017/WSC.2022.10
Abstract: In this work, we evaluated the short time-induced oxidative stress–mediated rapid metabolic and physiological responses of resistant and susceptible Sumatran fleabane [ Conyza sumatrensis (Retz.) E. Walker syn.: Erigeron sumatrensis Retz.] to 2,4-D herbicide. Under fixed conditions (25 C and 65 ± 5% relative humidity), we assayed injury symptoms, chlorophyll a fluorescence, and antioxidative systems of biotypes both resistant and susceptible to 2,4-D (1,005 g ae ha −1 ). Under 15 versus 25 C temperatures and light and dark conditions, oxidative stress–mediated damage was assayed on plants that received 2,4-D herbicide applications. The injury symptoms observed in the 2,4-D–resistant biotype were rapid necrosis in leaves within 30 min, with the reestablishment of normal growth within 1 to 2 wk after 2,4-D treatment. The basal antioxidant enzyme activities of superoxide dismutase, catalase, and ascorbate peroxidase were greater in the resistant than in the susceptible biotype, although the activities of all enzymes generally did not differ between untreated and treated in the resistant biotype. The resistant biotype showed great reduction (at 1 and 4 h after application) in the photosynthetic electron transport chain performance index, while these metabolic changes were only detected after 4 h in the susceptible biotype. The resistant biotype recovered from the foliar damage 1 to 2 wk after 2,4-D application, while the susceptible biotype was controlled. The production of H 2 O 2 was responsive to temperature and increased more rapidly in the 2,4-D–resistant biotype than in the susceptible one at both 15 and 25 C however, there was a greater increase at 25 C in the resistant biotype. H 2 O 2 production was not light dependent in 2,4-D–resistant C. sumatrensis , with increases even under dark conditions. The 2,4-D–resistant biotype showed rapid photosynthetic damage, possibly due to the rapid necrosis and leaf disruption, and increased H 2 O 2 content compared with the susceptible biotype.
Publisher: Wiley
Date: 17-05-2019
Publisher: Cambridge University Press (CUP)
Date: 2017
DOI: 10.1017/WET.2016.4
Abstract: Field and greenhouse experiments were conducted in Nebraska to (1) confirm the 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting resistant-waterhemp biotype (HPPD-RW) by quantifying the resistance levels in dose-response studies, and (2) to evaluate efficacy of PRE-only, POST-only, and PRE followed by POST herbicide programs for control of HPPD-RW in corn. Greenhouse dose-response studies confirmed that the suspected waterhemp biotype in Nebraska has evolved resistance to HPPD-inhibiting herbicides with a 2- to 18-fold resistance depending upon the type of HPPD-inhibiting herbicide being sprayed. Under field conditions, at 56 d after treatment, ≥90% control of the HPPD-RW was achieved with PRE-applied mesotrione/atrazine/ S- metolachlor+acetochlor, pyroxasulfone (180 and 270 g ai ha −1 ), pyroxasulfone/fluthiacet-methyl/atrazine, and pyroxasulfone+saflufenacil+atrazine. Among POST-only herbicide programs, glyphosate, a premix of mesotrione/atrazine tank-mixed with diflufenzopyr/dicamba, or metribuzin, or glufosinate provided ≥92% HPPD-RW control. Herbicide combinations of different effective sites of action in mixtures provided ≥86% HPPD-RW control in PRE followed by POST herbicide programs. It is concluded that the suspected waterhemp biotype is resistant to HPPD-inhibiting herbicides and alternative herbicide programs are available for effective control in corn. The occurrence of HPPD-RW in Nebraska is significant because it limits the effectiveness of HPPD-inhibiting herbicides.
Publisher: Public Library of Science (PLoS)
Date: 10-06-2013
Publisher: Springer Science and Business Media LLC
Date: 27-04-2017
Publisher: Frontiers Media SA
Date: 11-01-2022
DOI: 10.3389/FAGRO.2021.800731
Abstract: Quizalofop-resistant wheat is the core component of the recently commercialized CoAXium™ Wheat Production System. As with other herbicides, quizalofop provides better weed control at early growth stages and under optimum temperature. However, in regions with winter wheat production, quizalofop application may be affected by unpredictable, rapid temperature decreases. Temperature shifts can cause crop injury or impact weed control efficacy. In the following study, we examine the effect of reduced temperature on quizalofop content and metabolism in CoAXium™ winter wheat and three winter weed species: downy brome ( Bromus tectorum L.), feral rye ( Secale cereale L.), and jointed goatgrass ( Aegilops cylindrica Host). Temperature conditions include either 19 or 4.5°C daytime temperatures with tissue s ling over 5 timepoints (1–16 or 18 days after treatment, DAT). Analysis features liquid chromatography coupled to tandem mass spectrometry detection of the active form of quizalofop, quizalofop acid. Quizalofop content trends reveal delayed metabolism under cooler conditions for wheat and weeds. Quizalofop content peaks within 1–2 DAT in the warmer temperatures for all species and decreases thereafter. In contrast, content peaks between 8 and 9 DAT at cooler temperatures except for downy brome. Minimal decreases in content over time generally follow cooler temperature peaks. Further, the absence of differences in maximum quizalofop content in all species suggests absorption and/or de-esterification of quizalofop proherbicide to the active form is not reduced at cooler temperatures. Final dry shoot tissue biomass does not necessarily correspond to differences in metabolism, as biomass of wheat treated with a field rate of quizalofop does not differ between temperatures. Weeds were treated with sublethal doses of quizalofop in order to monitor herbicide metabolism without causing plant death. Under this condition, weed biomass only differs for jointed goatgrass, which has a greater biomass in the cooler temperature.
Publisher: Cambridge University Press (CUP)
Date: 23-12-2020
DOI: 10.1017/WET.2020.141
Abstract: Kochia accessions (designated as KS-4A and KS-4H) collected from a corn field near Garden City, KS, have previously shown multiple resistance to glyphosate, dicamba, and fluroxypyr. These accessions were also suspected as being resistant to photosystem II (PS II) inhibitors. The main objectives of this research were to 1) confirm the coexistence of cross-resistance to PS II inhibitors (atrazine and metribuzin) applied PRE and POST, 2) investigate the underlying mechanism of PS II-inhibitor resistance, and 3) determine the effectiveness of alternative POST herbicides for control of these multiple herbicide–resistant (MHR) kochia accessions. Results from dose-response experiments revealed that the KS-4A and KS-4H kochia accessions were 23-fold to 48-fold resistant to PRE- and POST-applied atrazine and 13-fold to 18-fold resistant to POST-applied metribuzin compared to a known susceptible kochia accession (KS-SUS). Both accessions also showed putative resistance to PRE-applied metribuzin that needs to be confirmed. Sequence analyses of the psb A gene further revealed that all s les from the KS-4A and KS-4H kochia accessions had a Ser 264 Gly point mutation. A pretreatment with malathion followed by a POST application of atrazine at 1,120 g ha −1 or metribuzin at 630 g ha −1 did not reverse the resistance phenotypes of these MHR accessions. In a separate greenhouse study, alternative POST herbicides, including bicyclopyrone + bromoxynil bromoxynil + pyrasulfotole paraquat alone or in combination with atrazine, metribuzin, 2,4-D, or saflufenacil and saflufenacil alone or in combination with 2,4-D effectively controlled the KS-4H accession (≥97% injury). To our knowledge, this research reports the first case of kochia accessions with cross-resistance to PRE-applied atrazine and POST-applied metribuzin. Growers should adopt ersified weed control strategies, including the use of competitive crops, cover crops, targeted tillage, and harvest weed seed control along with effective alternative PRE and POST herbicides with multiple sites of action to control MHR kochia seedbanks on their production fields.
Publisher: Frontiers Media SA
Date: 08-05-2017
Publisher: Wiley
Date: 31-05-2023
DOI: 10.1002/PS.7541
Abstract: Resistance to 2,4‐Dichlorophenoxyacetic acid (2,4‐D) has been reported in several weed species since the 1950s however, a biotype of Conyza sumatrensis showing a novel physiology of the rapid response minutes after herbicide application was reported in 2017. The objective of this research was to investigate the mechanisms of resistance and identify transcripts associated with the rapid physiological response of C. sumatrensis to 2,4‐D herbicide. Differences were found in 2,4‐D absorption between the resistant and susceptible biotypes. Herbicide translocation was reduced in the resistant biotype compared to the susceptible. In resistant plants 98.8% of [ 14 C] 2,4‐D was found in the treated leaf, whereas ≈13% translocated to other plant parts in the susceptible biotype at 96 h after treatment. Resistant plants did not metabolize [ 14 C] 2,4‐D and had only intact [ 14 C] 2,4‐D at 96 h after application, whereas susceptible plants metabolized [ 14 C] 2,4‐D into four detected metabolites, consistent with reversible conjugation metabolites found in other 2,4‐D sensitive plant species. Pre‐treatment with the cytochrome P450 inhibitor malathion did not enhance 2,4‐D sensitivity in either biotype. Following treatment with 2,4‐D, resistant plants showed increased expression of transcripts within plant defense response and hypersensitivity pathways, whereas both sensitive and resistant plants showed increased expression of auxin‐response transcripts. Our results demonstrate that reduced 2,4‐D translocation contributes to resistance in the C. sumatrensis biotype. The reduction in 2,4‐D transport is likely to be a consequence of the rapid physiological response to 2,4‐D in resistant C. sumatrensis . Resistant plants had increased expression of auxin‐responsive transcripts, indicating that a target‐site mechanism is unlikely. © 2023 Society of Chemical Industry.
Publisher: Elsevier BV
Date: 11-2020
Publisher: Cambridge University Press (CUP)
Date: 19-02-2018
DOI: 10.1017/WET.2017.111
Abstract: Palmer amaranth, a dioecious summer annual weed species, is the most troublesome weed in agronomic crop production systems in the United States. Palmer amaranth resistant to photosystem (PS) II- and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors is of particular concern in south central Nebraska. The objectives of this study were to determine the effect of PRE followed by POST herbicide programs on PS II- and HPPD-inhibitor-resistant Palmer amaranth control, crop yield, and net economic return in conventional corn. A field study was conducted in 2014, 2015, and 2016 in a grower’s field infested with PS II- and HPPD-inhibitor-resistant Palmer amaranth near Shickley in Fillmore County, Nebraska. A contrast analysis suggested that mesotrione+ S -metolachlor+atrazine applied PRE provided 83% Palmer amaranth control at 21 d after application compared to 78 and 72% control with pyroxasulfone+fluthiacet-ethyl+atrazine and saflufenacil+dimethenamid-P, respectively. Most of the PRE followed by POST herbicide programs provided ≥85% Palmer amaranth control. Based on contrast analysis, POST application of dicamba+diflufenzopyr provided 93% Palmer amaranth control compared to 87, 79, and 42% control with dicamba, dicamba+halosulfuron, and acetochlor, respectively, at 28 d after POST. All PRE followed by POST herbicide programs, aside from mesotrione+ S -metolachlor+atrazine followed by acetochlor (2,530 to 7,809 kg ha −1 ), provided 9,550 to 10,500 kg ha −1 corn yield compared with 2,713 to 6,110 kg ha −1 from nontreated control. Similarly, PRE followed by POST herbicide programs, except for mesotrione+ S -metolachlor+atrazine followed by acetochlor ($191 and $897 ha −1 ), provided similar net return of $427 to $707 ha −1 and $1,127 to $1,727 ha −1 in 2014 and 2015-16, respectively. It is concluded that herbicide programs based on multiple sites of action are available for control of PS II- and HPPD-inhibitor-resistant Palmer amaranth in conventional corn.
Publisher: Wiley
Date: 11-09-2018
DOI: 10.1002/PS.5128
Publisher: Elsevier
Date: 2016
Publisher: Authorea, Inc.
Date: 03-11-2020
Publisher: Frontiers Media SA
Date: 08-07-1970
Publisher: American Chemical Society (ACS)
Date: 30-07-2014
DOI: 10.1021/JF501040X
Abstract: The evolution of glyphosate-resistant weeds has recently increased dramatically. Six suspected glyphosate-resistant Amaranthus tuberculatus populations were studied to confirm resistance and determine the resistance mechanism. Resistance was confirmed in greenhouse for all six populations with glyphosate resistance factors (R/S) between 5.2 and 7.5. No difference in glyphosate absorption or translocation was observed between resistant and susceptible in iduals. No mutation at amino acid positions G101, T102, or P106 was detected in the EPSPS gene coding sequence, the target enzyme of glyphosate. Analysis of EPSPS gene copy number revealed that all glyphosate-resistant populations possessed increased EPSPS gene copy number, and this correlated with increased expression at both RNA and protein levels. EPSPS Vmax and Kcat values were more than doubled in resistant plants, indicating higher levels of catalytically active expressed EPSPS protein. EPSPS gene lification is the main mechanism contributing to glyphosate resistance in the A. tuberculatus populations analyzed.
Publisher: Wiley
Date: 12-03-2014
DOI: 10.1002/PS.3743
Publisher: Wiley
Date: 23-08-2012
Publisher: Wiley
Date: 10-2012
Publisher: Wiley
Date: 20-05-2021
DOI: 10.1002/PS.6457
Abstract: While herbicides are the most effective and widely adopted weed management approach, the evolution of multiple herbicide resistance in damaging weed species threatens the yield and profitability of many crops. Weeds accumulate multiple resistance mechanisms through sequential selection and/or gene flow, with long‐range and international transport of herbicide‐resistant weeds proving to be a serious issue. Metabolic resistance mechanisms can confer resistance across multiple sites of action and even to herbicides not yet discovered. When a new site of action herbicide is introduced to control a key driver weed, it likely will be one of very few effective available herbicide options for that weed in a specific crop due to the continuous use of herbicides over the years and the resulting accumulation of resistance mechanisms, placing it at even higher risk to be rapidly lost to resistance due to the high selection pressure it will experience. The number of available, effective herbicides for certain driver weeds is decreasing over time because the rate of resistance evolution is faster than the rate of new herbicide discovery. Effective monitoring for species movement and diagnostics for resistance should be deployed to rapidly identify emerging resistance to any new site of action. While innovation in herbicide discovery is urgently needed to combat the pressing issue of resistance in weeds, the rate of selection for herbicide resistance in weeds must be slowed through changes in the patterns of how herbicides are used. © 2021 Society of Chemical Industry. © 2021 Society of Chemical Industry.
Publisher: Wiley
Date: 16-02-2018
DOI: 10.1002/PS.4822
Abstract: Transcriptomic profiling, specifically via RNA sequencing (RNA-seq), is becoming one of the more commonly used methods for investigating non-target site resistance (NTSR) to herbicides due to its high throughput capabilities and utility in organisms with little to no previous sequence information. A review of the weed science RNA-seq literature revealed some basic principles behind generating quality data from these types of studies. First, studies that included more replicates per biotype and took steps to control for genetic background had significantly better control of false positives and, consequently, shorter lists of potential resistance genes to sift through. Pooling of biological replicates prior to sequencing was successful in some cases, but likely contributed to an overall increase in the false discovery rate. Although the inclusion of herbicide-treated s les was common across most of the studies, it ultimately introduced difficulties in interpretation of the final results due to challenges in capturing the right s ling window after treatment and to the induction of stress responses in the injured herbicide-sensitive plants. RNA-seq is an effective tool for NTSR gene discovery, but careful consideration should be given to finding the most powerful and cost-effective balance between replicate number, sequencing depth and treatment number. © 2017 Society of Chemical Industry.
Publisher: Advances in Weed Science
Date: 2022
Publisher: Public Library of Science (PLoS)
Date: 18-07-2019
Publisher: Elsevier BV
Date: 09-2019
DOI: 10.1016/J.PESTBP.2019.05.009
Abstract: Herbicide efficacy depends on herbicides crossing cell and organelle membranes. We evaluated an artificial membrane system to understand how herbicides cross biological membranes. This understanding aids in predicting herbicide behavior in planta and, consequently, efficacy, mode of action, and whether active transporter-based herbicide resistance mechanisms may be possible. Five herbicides with different log K
Publisher: Cold Spring Harbor Laboratory
Date: 05-04-2019
DOI: 10.1101/600072
Abstract: Increased copy number of the 5-enolpyruvylshikimate-3-phosphate synthase ( EPSPS ) gene confers resistance to glyphosate, the world’s most-used herbicide. There are typically three to eight EPSPS copies arranged in tandem in glyphosate-resistant populations of the weed kochia ( Kochia scoparia ). Here, we report a draft genome assembly from a glyphosate-susceptible kochia in idual. Additionally, we assembled the EPSPS locus from a glyphosate-resistant kochia plant by sequencing a kochia bacterial artificial chromosome library. These resources helped reconstruct the history of duplication in the structurally complex EPSPS locus and uncover the genes that are co-duplicated with EPSPS , several of which have a corresponding change in transcription. The comparison between the susceptible and resistant assemblies revealed two dominant repeat types. We discovered a FHY3/FAR1-like mobile genetic element that is associated with the duplicated EPSPS gene copies in the resistant line. We present a hypothetical model based on unequal crossing over that implicates this mobile element as responsible for the origin of the EPSPS gene duplication event and the evolution of herbicide resistance in this system. These findings add to our understanding of stress resistance evolution and provide an ex le of rapid resistance evolution to high levels of environmental stress.
Publisher: Cambridge University Press (CUP)
Date: 08-2018
DOI: 10.1017/WET.2018.49
Abstract: Herbicide resistance is ‘wicked’ in nature therefore, results of the many educational efforts to encourage ersification of weed control practices in the United States have been mixed. It is clear that we do not sufficiently understand the totality of the grassroots obstacles, concerns, challenges, and specific solutions needed for varied crop production systems. Weed management issues and solutions vary with such variables as management styles, regions, cropping systems, and available or affordable technologies. Therefore, to help the weed science community better understand the needs and ideas of those directly dealing with herbicide resistance, seven half-day regional listening sessions were held across the United States between December 2016 and April 2017 with groups of erse stakeholders on the issues and potential solutions for herbicide resistance management. The major goals of the sessions were to gain an understanding of stakeholders and their goals and concerns related to herbicide resistance management, to become familiar with regional differences, and to identify decision maker needs to address herbicide resistance. The messages shared by listening-session participants could be summarized by six themes: we need new herbicides there is no need for more regulation there is a need for more education, especially for others who were not present ersity is hard the agricultural economy makes it difficult to make changes and we are aware of herbicide resistance but are managing it. The authors concluded that more work is needed to bring a community-wide, interdisciplinary approach to understanding the complexity of managing weeds within the context of the whole farm operation and for communicating the need to address herbicide resistance.
Publisher: Research Information Ltd.
Date: 08-2020
DOI: 10.1564/V31_AUG_04
Abstract: Evolution of resistance to pesticides is a problem challenging the sustainability of global food production. Resistance to herbicides is driven by the intense selection pressure imparted by synthetic herbicides on which we rely to manage weeds. Target-site resistance (TSR) mechanisms involve changes to the herbicide target protein and provide resistance only to herbicides within a single mechanism of action. Non-target site resistance (NTSR) mechanisms reduce the quantity of herbicide reaching the target site and/or modify the herbicide. NTSR mechanisms include reduced absorption and/or translocation, increased sequestration, and enhanced metabolic degradation. Of these erse mechanisms contributing to NTSR, metabolism-based herbicide resistance represents a major threat because it can impart resistance to herbicides from varied chemical classes across any number of mechanisms of action.
Publisher: Springer Science and Business Media LLC
Date: 03-01-2014
DOI: 10.1007/S00425-013-2022-X
Abstract: Amplification of the EPSPS gene has been previously identified as the glyphosate resistance mechanism in many populations of Amaranthus palmeri, a major weed pest in US agriculture. Here, we evaluate the effects of EPSPS gene lification on both the level of glyphosate resistance and fitness cost of resistance. A. palmeri in iduals resistant to glyphosate by expressing a wide range of EPSPS gene copy numbers were evaluated under competitive conditions in the presence or absence of glyphosate. Survival rates to glyphosate and fitness traits of plants under intra-specific competition were assessed. Plants with higher lification of the EPSPS gene (53-fold) showed high levels of glyphosate resistance, whereas less lification of the EPSPS gene (21-fold) endowed a lower level of glyphosate resistance. Without glyphosate but under competitive conditions, plants exhibiting up to 76-fold EPSPS gene lification exhibited similar height, and biomass allocation to vegetative and reproductive organs, compared to glyphosate susceptible A. palmeri plants with no lification of the EPSPS gene. Both the additive effects of EPSPS gene lification on the level of glyphosate resistance and the lack of associated fitness costs are key factors contributing to EPSPS gene lification as a widespread and important glyphosate resistance mechanism likely to become much more evident in weed plant species.
Publisher: Frontiers Media SA
Date: 16-11-2017
Publisher: No publisher found
Date: 2018
DOI: 10.1002/PS.4781
Abstract: Palmer amaranth (Amaranthus palmeri S. Wats.), common waterhemp (Amaranthus tuberculatus var. rudis), and redroot pigweed (Amaranthus retroflexus L.) are major weeds occurring in fields throughout Nebraska with recurrent grower complaints regarding control with glyphosate. The objective of this study was to investigate the frequency and distribution of glyphosate-resistant Palmer amaranth, common waterhemp, and redroot pigweed populations in Nebraska. The study also aimed to investigate how agronomic practices influence the occurrence of glyphosate resistance in the three Amaranthus species. Glyphosate resistance was widespread in common waterhemp (81% of the screened populations), few Palmer amaranth populations were glyphosate-resistant (6% of the screened populations), whereas no glyphosate-resistant redroot pigweed populations were identified in Nebraska. Weed species, geographic region within the state, and current crop were the most important factors predicting the occurrence of glyphosate resistance in fields infested with Amaranthus species in Nebraska. The intensive glyphosate selection pressure exerted in soybean (Glycine max) fields in eastern Nebraska is one of the major factors causing widespread occurrence of glyphosate resistance in common waterhemp in the state. The relatively low frequency of glyphosate-resistant Palmer amaranth in the state highlights the importance of the application timing and the adoption of multiple modes of action in weed management practices to delay the evolution of glyphosate resistance. © 2017 Society of Chemical Industry.
Publisher: Cambridge University Press (CUP)
Date: 30-08-2018
DOI: 10.1017/WSC.2018.33
Abstract: Modern high-throughput molecular and analytical tools offer exciting opportunities to gain a mechanistic understanding of unique traits of weeds. During the past decade, tremendous progress has been made within the weed science discipline using genomic techniques to gain deeper insights into weedy traits such as invasiveness, hybridization, and herbicide resistance. Though the adoption of newer “omics” techniques such as proteomics, metabolomics, and physionomics has been slow, applications of these omics platforms to study plants, especially agriculturally important crops and weeds, have been increasing over the years. In weed science, these platforms are now used more frequently to understand mechanisms of herbicide resistance, weed resistance evolution, and crop–weed interactions. Use of these techniques could help weed scientists to further reduce the knowledge gaps in understanding weedy traits. Although these techniques can provide robust insights about the molecular functioning of plants, employing a single omics platform can rarely elucidate the gene-level regulation and the associated real-time expression of weedy traits due to the complex and overlapping nature of biological interactions. Therefore, it is desirable to integrate the different omics technologies to give a better understanding of molecular functioning of biological systems. This multidimensional integrated approach can therefore offer new avenues for better understanding of questions of interest to weed scientists. This review offers a retrospective and prospective examination of omics platforms employed to investigate weed physiology and novel approaches and new technologies that can provide holistic and knowledge-based weed management strategies for future.
Publisher: Wiley
Date: 05-01-2018
DOI: 10.1002/PS.4786
Abstract: Resistance to the 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide tembotrione in an Amaranthus palmeri population from Nebraska (NER) has previously been confirmed to be attributable to enhanced metabolism. The objective of this study was to identify and quantify the metabolites formed in Nebraska susceptible (NES) and resistant (NER) biotypes. NER and NES formed the same metabolites. Tembotrione metabolism in NER differed from that in NES in that resistant plants showed faster 4-hydroxylation followed by glycosylation. The T Further research with the aim of identifying the gene or genes responsible for conferring metabolic resistance to HPPD inhibitors should focus on cytochrome P450s. Such research is important because non-target-site-based resistance (NTSR) poses the threat of cross resistance to other chemical classes of HPPD inhibitors, other herbicide modes of action, or even unknown herbicides. © 2017 Society of Chemical Industry.
Publisher: Cambridge University Press (CUP)
Date: 12-2016
Abstract: Halosulfuron-methyl, a sulfonylurea herbicide, was registered for broadleaf weed control in dry bean. This herbicide has an adequate margin of crop safety in white bean, but causes unacceptable injury to adzuki bean. Halosulfuron-methyl absorption, translocation, and metabolism were evaluated in white and adzuki bean using radiolabeled herbicide to determine if differences in these parameters could explain the difference in crop safety between these two species. Adzuki bean had more rapid halosulfuron-methyl absorption than white bean. Adzuki bean reached 90% absorption ( t 90 ) 26.2 h after treatment (HAT), whereas white bean required 40.1 HAT to reach t 90 . The maximum halosulfuron-methyl absorption was higher in adzuki bean (75.7%) than in white bean (65.3%). More 14 C-halosulfuron was translocated to the apex, first trifoliate, stem above the treated leaf, and roots in aduzki bean than in white bean. The maximum radioactivity translocated out of treated leaf was higher in adzuki bean (17.7%) than in white bean (12.1%). Halosulfuron-methyl was broken down to the same metabolites in white and adzuki bean. The half-life of halosulfuron-methyl in adzuki bean was 16 HAT, compared with less than 6 HAT in white bean. More herbicide remained as the free acid in adzuki bean compared with white bean over the entire 48-h time course. The differential tolerance of white and adzuki bean to halosulfuron can be attributed to greater absorption and translocation and decreased metabolism in adzuki bean.
Publisher: Wiley
Date: 20-02-2018
DOI: 10.1111/WRE.12294
Publisher: Cambridge University Press (CUP)
Date: 04-09-2023
DOI: 10.1017/WET.2023.55
Publisher: Research Information Ltd.
Date: 12-2018
DOI: 10.1564/V29_DEC_05
Publisher: Advances in Weed Science
Date: 2022
Publisher: Wiley
Date: 03-2022
DOI: 10.1002/AGJ2.20998
Abstract: Winter annual grass species such as jointed goatgrass ( Aegilops cylindrica Host), downy brome ( Bromus tectorum L.), and feral rye ( Secale cereale L.) negatively affect winter wheat ( Triticum aestivum L.) yields. To generate a novel in‐crop selective herbicide trait for winter annual grass control, mutagenesis was used to generate multiple winter wheat lines resistant to the acetyl co‐A carboxylase (ACCase) inhibitor quizalofop p‐ethyl (QPE). Field trials were performed to assess crop safety for wheat lines with one or two homoeologous mutations and to assess winter annual grass control with QPE treatments. Crop safety parameters including visual injury rating, plant height, grain yield, and kernel weight were evaluated following QPE treatment at multiple growth stages. The susceptible winter wheat cultivar Hatcher displayed 100% crop injury when treated at tillering in early spring or at jointing in late spring. Single‐gene lines generally had crop injury and yield loss, especially at the jointing application timing. The two‐mutation cultivars Incline AX and LCS Fusion AX had low to no injury or yield loss from QPE applications at all timings and no injury from high rate QPE applications (93 and 185 g ha −1 ) in either the fall or the spring. Control of downy brome and feral rye was highest (92–99%), while jointed goatgrass control ranged from a low of 73% at 93 g a.i. ha −1 to a high of 98% at 109 a.i. ha −1 QPE. Our data indicate that the targeted winter annual grass weeds are controlled by QPE at rates that have acceptable crop safety for two‐mutation QPE‐resistant wheat cultivars.
Publisher: Wiley
Date: 27-09-2017
DOI: 10.1002/PS.4697
Abstract: A population of Amaranthus tuberculatus (var. rudis) was confirmed resistant to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitor herbicides (mesotrione, tembotrione, and topramezone) in a seed corn/soybean rotation in Nebraska. Further investigation confirmed a non-target-site resistance mechanism in this population. The main objective of this study was to explore the role of cytochrome P450 inhibitors in restoring the efficacy of HPPD-inhibitor herbicides on the HPPD-inhibitor resistant A. tuberculatus population from Nebraska, USA (HPPD-R). Enhanced metabolism via cytochrome P450 enzymes is the mechanism of resistance in HPPD-R. Amitrole partially restored the activity of mesotrione, whereas malathion, amitrole, and piperonyl butoxide restored the activity of tembotrione and topramezone in HPPD-R. Although corn was injured through malathion followed by mesotrione application a week after treatment, the injury was transient, and the crop recovered. The use of cytochrome P450 inhibitors with tembotrione may provide a new way of controlling HPPD-inhibitor resistant A. tuberculatus, but further research is needed to identify the cytochrome P450 candidate gene(s) conferring metabolism-based resistance. The results presented here aid to gain an insight into non-target-site resistance weed management strategies. © 2017 Society of Chemical Industry.
Publisher: Springer Science and Business Media LLC
Date: 07-02-2020
DOI: 10.1038/S41598-020-59126-9
Abstract: While the introduction of herbicide tolerant crops provided growers new options to manage weeds, the widespread adoption of these herbicides increased the risk for herbicide spray drift to surrounding vegetation. The impact of herbicide drift in sensitive crops is extensively investigated, whereas scarce information is available on the consequences of herbicide drift in non-target plants. Weeds are often abundant in field margins and ditches surrounding agricultural landscapes. Repeated herbicide drift exposure to weeds could be detrimental to long-term management as numerous weeds evolved herbicide resistance following recurrent-selection with low herbicide rates. The objective of this study was to evaluate if glyphosate, 2,4-D, and dicamba spray drift could select Amaranthus spp. biotypes with reduced herbicide sensitivity. Palmer amaranth and waterhemp populations were recurrently exposed to herbicide drift in a wind tunnel study over two generations. Seeds from survival plants were used for the subsequent rounds of herbicide drift exposure. Progenies were subjected to herbicide dose-response studies following drift selection. Herbicide drift exposure rapidly selected for Amaranthus spp. biotypes with reduced herbicide sensitivity over two generations. Weed management programs should consider strategies to mitigate near-field spray drift and suppress the establishment of resistance-prone weeds on field borders and ditches in agricultural landscapes.
Publisher: Cambridge University Press (CUP)
Date: 03-2019
DOI: 10.1017/WSC.2018.88
Abstract: Several grass and broadleaf weed species around the world have evolved multiple-herbicide resistance at alarmingly increasing rates. Research on the biochemical and molecular resistance mechanisms of multiple-resistant weed populations indicate a prevalence of herbicide metabolism catalyzed by enzyme systems such as cytochrome P450 monooxygenases and glutathione S -transferases and, to a lesser extent, by glucosyl transferases. A symposium was conducted to gain an understanding of the current state of research on metabolic resistance mechanisms in weed species that pose major management problems around the world. These topics, as well as future directions of investigations that were identified in the symposium, are summarized herein. In addition, the latest information on selected topics such as the role of safeners in inducing crop tolerance to herbicides, selectivity to clomazone, glyphosate metabolism in crops and weeds, and bioactivation of natural molecules is reviewed.
Publisher: Wiley
Date: 02-05-2018
DOI: 10.1002/PS.4569
Abstract: The glyphosate-resistant rapid response (GR RR) resistance mechanism in Ambrosia trifida is not due to target-site resistance (TSR) mechanisms. This study explores the physiology of the rapid response and the possibility of reduced translocation and vacuolar sequestration as non-target-site resistance (NTSR) mechanisms. GR RR leaf discs accumulated hydrogen peroxide within minutes of glyphosate exposure, but only in mature leaf tissue. The rapid response required energy either as light or exogenous sucrose. The combination of phenylalanine and tyrosine inhibited the rapid response in a dose-dependent manner. Reduced glyphosate translocation was observed in GR RR, but only when associated with tissue death caused by the rapid response. Nuclear magnetic resonance studies indicated that glyphosate enters the cytoplasm and reaches chloroplasts, and it is not moved into the vacuole of GR RR, GR non-rapid response or glyphosate-susceptible A. trifida. The GR RR mechanism of resistance is not associated with vacuole sequestration of glyphosate, and the observed reduced translocation is likely a consequence of rapid tissue death. Rapid cell death was inhibited by exogenous application of aromatic amino acids phenylalanine and tyrosine. The mechanism by which these amino acids inhibit rapid cell death in the GR RR phenotype remains unknown, and it could involve glyphosate phytotoxicity or other agents generating reactive oxygen species. Implications of these findings are discussed. The GR RR mechanism is distinct from the currently described glyphosate TSR or NTSR mechanisms in other species. © 2017 Society of Chemical Industry.
Publisher: Wiley
Date: 31-12-2020
DOI: 10.1002/AGJ2.20484
Abstract: Feral rye ( Secale cereale L.) is one of the most troublesome winter annual grass weed species in semi‐arid winter wheat ( Triticum aestivum L.) production systems across the central Great Plains (CGP). Lack of effective herbicide options further complicates the selective control of feral rye in winter wheat. The main objectives of this research were: (a) determine the sensitivity response of 10 feral rye populations collected from Kansas wheat fields to quizalofop‐p‐ethyl in a dose‐response assay, and (b) to determine the effectiveness of various rates and application timings (fall or spring) of quizalofop‐p‐ethyl for feral rye control in quizalofop‐resistant winter wheat in the CGP. Dose‐response assays indicated that all tested feral rye populations were highly sensitive to quizalofop‐p‐ethyl with GR 90 values (doses of quizalofop‐p‐ethyl needed for 90% reductions in shoot biomass at 3 wk after treatment) ranging from 33 to 72 g a.i. ha −1 . A field study conducted in Colorado, Kansas, and Oklahoma for a total of 5 site‐years indicated that quizalofop‐p‐ethyl applied at ≥77 g a.i. ha −1 in the fall or spring provided season‐long feral rye control at 92–100% in quizalofop‐resistant winter wheat. Irrespective of tested rates and application timings, a quizalofop‐p‐ethyl treatment protected winter wheat yield loss of 17–27% due to reduced feral rye competition compared to the nontreated weedy check in Colorado and Oklahoma. Results suggested that quizalofop‐p‐ethyl at labelled use rates (77–92 g a.i. ha −1 ) applied in fall or spring can provide effective feral rye control in quizalofop‐resistant winter wheat.
Publisher: Cambridge University Press (CUP)
Date: 20-01-2022
DOI: 10.1017/WSC.2022.2
Abstract: Glyphosate’s efficacy is influenced by the amount absorbed and translocated throughout the plant to inhibit 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS). Glyphosate resistance can be due to target-site (TS) or non–target site (NTS) resistance mechanisms. TS resistance includes an altered target site and gene overexpression, while NTS resistance includes reduced absorption, reduced translocation, enhanced metabolism, and exclusion/sequestration. The goal of this research was to elucidate the mechanism(s) of glyphosate resistance in common ragweed ( Ambrosia artemisiifolia L.) from Ontario, Canada. The resistance factor for this glyphosate-resistant (GR) A. artemisiifolia biotype is 5.1. No amino acid substitutions were found at positions 102 or 106 of the EPSPS enzyme in this A. artemisiifolia biotype. Based on [ 14 C]glyphosate studies, there was no difference in glyphosate absorption or translocation between glyphosate-susceptible (GS) and GR A. artemisiifolia biotypes. Radio-labeled glyphosate metabolites were similar for GS and GR A. artemisiifolia 96 h after application. Glyphosate resistance in this A. artemisiifolia biotype is not due to an altered target site due to amino acid substitutions at positions 102 and 106 in the EPSPS and is not due to the NTS mechanisms of reduced absorption, reduced translocation, or enhanced metabolism.
Publisher: Elsevier BV
Date: 06-2018
DOI: 10.1016/J.PESTBP.2018.03.017
Abstract: The evolution of resistant weed populations in response to intensive herbicide selection pressure is a global issue. Resistance to post-emergence herbicides is widespread, whereas soil-applied pre-emergence herbicides can often remain effective. For ex le, in Australia pyroxasulfone is a new pre-emergence soil-applied herbicide which provides control of Lolium rigidum populations resistant to multiple post-emergence herbicide modes of action. A fundamental knowledge of the genetic basis of metabolic resistance in weeds is important for understanding plant evolution pathways under herbicide selection and sustaining long-term weed resistance management. In this study we define the mechanistic basis of resistance to pyroxasulfone in a L. rigidum population. TLC provides evidence that pyroxasulfone resistance is metabolism-based with approximately 88% of parental [
Publisher: Proceedings of the National Academy of Sciences
Date: 25-02-2022
Abstract: Synthetic auxin herbicides intersect basic plant developmental biology and applied weed management. We investigated resistance to 2,4-D in the Australian weed Sisymbrium orientale (Indian hedge mustard). We identified a mechanism involving an in-frame 27-bp deletion in the degron tail of auxin coreceptor IAA2, one member of the gene family of Aux/IAA auxin co-receptors. We show that this deletion in IAA2 is a gain-of-function mutation that confers synthetic auxin resistance. This field-evolved mechanism of resistance to synthetic auxin herbicides confirms previous biochemical studies showing the role of the Aux/IAA degron tail in regulating Aux/IAA protein degradation upon auxin perception. The deletion mutation could be generated in crops using gene-editing approaches for cross-resistance to multiple synthetic auxin herbicides.
Publisher: Cambridge University Press (CUP)
Date: 02-06-2020
DOI: 10.1017/WSC.2020.42
Abstract: Wild poinsettia ( Euphorbia heterophylla L.) is a troublesome broadleaf weed in grain production areas in South America. Herbicide resistance to multiple sites of action has been documented in this species, including protoporphyrinogen oxidase (PPO) inhibitors. We investigated the physiological and molecular bases for PPO-inhibitor resistance in a E. heterophylla population (R PPO ) from Southern Brazil. Whole-plant dose–response experiments revealed a cross-resistance profile to three different chemical groups of PPO inhibitors. Based on dose–response parameters, R PPO was resistant to lactofen (47.7-fold), saflufenacil (8.6-fold), and pyraflufen-ethyl (3.5-fold). Twenty-four hours after lactofen treatment (120 g ha −1 ) POST, R PPO accumulated 27 times less protoporphyrin than the susceptible population (S PPO ). In addition, R PPO generated 5 and 4.5 times less hydrogen peroxide and superoxide than S PPO , respectively. The chloroplast PPO ( PPO1 ) sequences were identical between the two populations, whereas 35 single-nucleotide polymorphisms were found for the mitochondrial PPO ( PPO2 ). Based on protein homology modeling, the Arg-128-Leu (homologous to Arg-98-Leu in common ragweed [ Ambrosia artemisiifolia L.] was the only one located near the catalytic site, also in a conserved region of PPO2 . The cytochrome P450 monooxygenase inhibitor malathion did not reverse resistance to lactofen in R PPO , and both populations showed similar levels of PPO1 and PPO2 expression, suggesting that metabolic resistance and PPO overexpression are unlikely. This is the first report of an Arg-128-Leu mutation in PPO2 conferring cross-resistance to PPO inhibitors in E. heterophylla .
Publisher: CRC Press
Date: 12-07-2017
Publisher: American Chemical Society (ACS)
Date: 27-04-2023
Publisher: Wiley
Date: 17-09-2022
DOI: 10.1002/PS.7154
Abstract: Early detection of herbicide resistance in weeds is crucial for successful implementation of integrated weed management. We conducted a herbicide resistance survey of the winter annual grasses feral rye (Secale cereale), downy brome (Bromus tectorum), and jointed goatgrass (Aegilops cylindrica) from Colorado winter wheat production areas for resistance to imazamox and quizalofop. All s les were susceptible to quizalofop. All downy brome and jointed goatgrass s les were susceptible to imazamox. Out of 314 field collected s les, we identified three feral rye populations (named A, B, and C) that were imazamox resistant. Populations B and C had a target-site mechanism with mutations in the Ser653 residue of the acetolactate synthase (ALS) gene to Asn in B and to Thr in C. Both populations B and C had greatly reduced ALS in vitro enzyme inhibition by imazamox. ALS feral rye protein modeling showed that steric interactions induced by the amino acid substitutions at Ser653 impaired imazamox binding. In iduals from population A had no mutations in the ALS gene. The ALS enzyme from population A was equally sensitive to imazamox as to known susceptible feral rye populations. Imazamox was degraded two times faster in population A compared with a susceptible control. An oxidized imazamox metabolite formed faster in population A and this detoxification reaction was inhibited by malathion. Population A has a nontarget-site mechanism of enhanced imazamox metabolism that may be conferred by cytochrome P450 enzymes. This is the first report of both target-site and metabolism-based imazamox resistance in feral rye. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
Publisher: MDPI AG
Date: 14-12-2019
Abstract: The rapid development of omics technologies has drastically altered the way biologists conduct research. Basic plant biology and genomics have incorporated these technologies, while some challenges remain for use in applied biology. Weed science, on the whole, is still learning how to integrate omics technologies into the discipline however, omics techniques are more frequently being implemented in new and creative ways to address basic questions in weed biology as well as the more practical questions of improving weed management. This has been especially true in the subdiscipline of herbicide resistance where important questions are the evolution and genetic basis of herbicide resistance. This review examines the advantages, challenges, potential solutions, and outlook for omics technologies in the discipline of weed science, with ex les of how omics technologies will impact herbicide resistance studies and ultimately improve management of herbicide-resistant populations.
Publisher: Cambridge University Press (CUP)
Date: 09-2016
Abstract: An overreliance on herbicides in several important grain- and cotton-producing regions of the world has led to the widespread evolution of herbicide-resistant weed populations. Of particular concern are weed populations that exhibit simultaneous resistance to multiple herbicides (MHR). Too often, herbicides are the only tool used for weed control. We use the term herbicide-only syndrome (HOS) for this quasi-addiction to herbicides. Growers and their advisers focus on herbicide technology, unaware of or ignoring basic evolutionary principles or the necessary ersity provided by other methods of weed control. Diversity in weed control practices disrupts resistance evolution. Significant challenges exist to implementing ersity, including how to address information so that producers choose to alter existing behaviors (HOS) and take calculated risks by attempting new and more complex strategies. Herbicide resistance management in the long term will require creativity in many sectors, including roles for growers, industry, researchers, consultants, retailers, and regulators. There can be creativity in herbicide registration and regulation, as exemplified by the recent U.S. Environmental Protection Agency program that encourages herbicide registrants to register products in minor crops. We propose one idea for a regulatory incentive to enable herbicide registrants in jurisdictions such as the United States to receive an extended data exclusivity period in exchange for not developing one new herbicide in multiple crops used together in rotation, or for implementing stewardship practices such as robust mixtures or limitations on application frequency. This incentive would provide a mechanism to register herbicides in ways that help to ensure herbicide longevity. Approaches based only on market or financial incentives have contributed to the current situation of widespread MHR. Our suggestion for regulatory creativity is one way to provide both financial and biological benefits to the registering company and to the overall stakeholder community by incentivizing good resistance management.
Publisher: Wiley
Date: 17-11-2016
DOI: 10.1002/PS.4441
Abstract: Organophosphate insecticides can inhibit specific cytochrome P450 enzymes involved in metabolic herbicide resistance mechanisms, leading to synergistic interactions between the insecticide and the herbicide. In this study we report synergistic versus antagonistic interactions between the organophosphate insecticide phorate and five different herbicides observed in a population of multiple herbicide-resistant Lolium rigidum. Phorate synergised with three different herbicide modes of action, enhancing the activity of the ALS inhibitor chlorsulfuron (60% LD We report the selective reversal of P450-mediated metabolic multiple resistance to chlorsulfuron and trifluralin in the grass weed L. rigidum by synergistic interaction with the insecticide phorate, and discuss the putative mechanistic basis. This research should encourage ersity in herbicide use patterns for weed control as part of a long-term integrated management effort to reduce the risk of selection of metabolism-based multiple herbicide resistance in L. rigidum. © 2016 Society of Chemical Industry.
Publisher: Elsevier BV
Date: 03-2014
DOI: 10.1016/J.PLANTSCI.2013.12.005
Abstract: Agricultural weeds have rapidly adapted to intensive herbicide selection and resistance to herbicides has evolved within ecological timescales. Yet, the genetic basis of broad-spectrum generalist herbicide resistance is largely unknown. This study aims to determine the genetic control of non-target-site herbicide resistance trait(s) that rapidly evolved under recurrent selection of the novel lipid biosynthesis inhibitor pyroxasulfone in Lolium rigidum. The phenotypic segregation of pyroxasulfone resistance in parental, F1 and back-cross (BC) families was assessed in plants exposed to a gradient of pyroxasulfone doses. The inheritance of resistance to chemically dissimilar herbicides (cross-resistance) was also evaluated. Evolved resistance to the novel selective agent (pyroxasulfone) is explained by Mendelian segregation of one semi-dominant allele incrementally herbicide-selected at higher frequency in the progeny. In BC families, cross-resistance is conferred by an incompletely dominant single major locus. This study confirms that herbicide resistance can rapidly evolve to any novel selective herbicide agents by continuous and repeated herbicide use. The results imply that the combination of herbicide options (rotation, mixtures or combinations) to exploit incomplete dominance can provide acceptable control of broad-spectrum generalist resistance-endowing monogenic traits. Herbicide ersity within a set of integrated management tactics can be one important component to reduce the herbicide selection intensity.
Publisher: Wiley
Date: 12-04-2018
DOI: 10.1002/PS.4567
Abstract: Glyphosate-resistant (GR) Ambrosia trifida is now present in the midwestern United States and in southwestern Ontario, Canada. Two distinct GR phenotypes are known, including a rapid response (GR RR) phenotype, which exhibits cell death within hours after treatment, and a non-rapid response (GR NRR) phenotype. The mechanisms of resistance in both GR RR and GR NRR remain unknown. Here, we present a description of the RR phenotype and an investigation of target-site mechanisms on multiple A. trifida accessions. Glyphosate resistance was confirmed in several accessions, and whole-plant levels of resistance ranged from 2.3- to 7.5-fold compared with glyphosate-susceptible (GS) accessions. The two GR phenotypes displayed similar levels of resistance, despite having dramatically different phenotypic responses to glyphosate. Glyphosate resistance was not associated with mutations in EPSPS sequence, increased EPSPS copy number, EPSPS quantity, or EPSPS activity. These encompassing results suggest that resistance to glyphosate in these GR RR A. trifida accessions is not conferred by a target-site resistance mechanism. © 2017 Society of Chemical Industry.
Publisher: Wiley
Date: 12-08-2020
DOI: 10.1002/PS.5535
Abstract: Bidens subalternans (greater beggarticks) is a tetraploid and troublesome weed infesting annual crops in most tropical regions of the world. A glyphosate-resistant (GR) B. subalternans biotype was detected in a soybean field from Paraguay. A series of physiological and molecular analyses were conducted to elucidate its resistance mechanisms. The GR biotype had a high level of resistance (> 15-fold LD This is the first report of a TIPT double mutation conferring high levels of glyphosate resistance in a weed species. The presence of both wild-type and TIPT mutant EPSPS on the polyploid genome of GR B. subalternans may offset a potential fitness cost, requiring additional research to confirm the absence of deleterious effects. © 2019 Society of Chemical Industry.
Publisher: Wiley
Date: 04-02-2016
DOI: 10.1002/PS.4205
Abstract: Overreliance on glyphosate as a single tool for weed management in agricultural systems in Brazil has selected glyphosate-resistant populations of tall windmill grass (Chloris elata Desv.). Two C. elata populations, one glyphosate resistant (GR) and one glyphosate susceptible (GS), were studied in detail for a dose-response experiment and for resistance mechanism. The dose causing 50% reduction in dry weight was 620 g a.e. ha(-1) for GR and 114 g ha(-1) for GS, resulting in an R/S ratio of 5.4. GS had significantly higher maximum (14) C-glyphosate absorption into the treated leaf (51.3%) than GR (39.5%), a difference of 11.8% in maximum absorption. GR also retained more (14) C-glyphosate in the treated leaf (74%) than GS (51%), and GR translocated less glyphosate (27%) to other plant parts (stems, roots and root exudation) than GS (36%). There were no mutations at the Pro106 codon in the gene encoding 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). There was no difference in EPSPS genomic copy number or EPSPS transcription between GS and GR populations. Based on these data, reduced glyphosate absorption and increased glyphosate retention in the treated leaf contribute to glyphosate resistance in this C. elata population from Brazil. © 2015 Society of Chemical Industry.
Publisher: FapUNIFESP (SciELO)
Date: 08-2015
Publisher: Cambridge University Press (CUP)
Date: 09-2012
Abstract: The objective of this study was to determine whether a junglerice population from the tropical Ord River region of northwest Australia was glyphosate resistant, and whether alternative herbicides labeled for junglerice control were still effective. Seed s les collected from the field site were initially screened with glyphosate in the glasshouse, and surviving in iduals were self-pollinated for subsequent glyphosate dose-response studies. Glyphosate resistance was confirmed, as the suspected resistant population was found to be 8.6-fold more resistant to glyphosate than a susceptible population based on survival (LD 50 of 3.72 kg ha −1 ), and 5.6-fold more resistant based on biomass reduction (GR 50 of 1.16 kg ha −1 ). The glyphosate-resistant population was susceptible to label-recommended doses of all other herbicides assessed, including three acetyl-CoA carboxylase (ACC) –inhibiting herbicides (fluazifop-P, haloxyfop, and sethoxydim), two acetolactate synthase (ALS) –inhibiting herbicides (imazamox and sulfometuron), paraquat, and glufosinate. Glyphosate resistance has previously evolved in numerous species found in glyphosate-resistant cropping systems, no-till chemical fallow, fence line, and perennial crop situations. Here we report the evolution of glyphosate resistance in a cropping system that included annual tillage. The evolution of glyphosate resistance in junglerice from a tropical cropping system further demonstrates the need for improved glyphosate stewardship practices globally.
Publisher: Wiley
Date: 23-10-2018
DOI: 10.1111/TPJ.14089
Abstract: Pollen-mediated gene flow (PMGF) might play an important role in dispersing herbicide resistance alleles in dioecious weedy Amaranthus species. Field experiments in a concentric donor-receptor design were conducted to quantify two sets of PMGF studies, an interspecific (Amaranthus tuberculatus × Amaranthus palmeri) and an intraspecific (A. tuberculatus × A. tuberculatus). In both studies, PMGF was evaluated using a resistant A. tuberculatus phenotype with enhanced mesotrione detoxification via P450 enzymes as a source of resistance alleles. For interspecific hybridization, more than 104 000 putative hybrid seedlings were screened with three markers, one phenotypic and two molecular. The two molecular markers used, including 2-bp polymorphisms in the internal transcribed spacer region, distinguished A. palmeri, A. tuberculatus and their hybrids. Results showed that 0.1% hybridization between A. tuberculatus × A. palmeri occurred under field research conditions. For intraspecific hybridization, 22 582 seedlings were screened to assess the frequency of gene flow. The frequency of gene flow (F
Publisher: Wiley
Date: 07-10-2021
DOI: 10.1002/PS.6097
Publisher: Public Library of Science (PLoS)
Date: 10-09-2020
Publisher: Elsevier BV
Date: 11-2023
Publisher: Wiley
Date: 12-06-2018
DOI: 10.1002/PS.5048
Abstract: There have been previous calls for, and efforts focused on, realizing the power and potential of weed genomics for better understanding of weeds. Sustained advances in genome sequencing and assembly technologies now make it possible for in idual research groups to generate reference genomes for multiple weed species at reasonable costs. Here, we present the outcomes from several meetings, discussions, and workshops focused on establishing an International Weed Genomics Consortium (IWGC) for a coordinated international effort in weed genomics. We review the 'state of the art' in genomics and weed genomics, including technologies, applications, and on-going weed genome projects. We also report the outcomes from a workshop and a global survey of the weed science community to identify priority species, key biological questions, and weed management applications that can be addressed through greater availability of, and access to, genomic resources. Major focus areas include the evolution of herbicide resistance and weedy traits, the development of molecular diagnostics, and the identification of novel targets and approaches for weed management. There is increasing interest in, and need for, weed genomics, and the establishment of the IWGC will provide the necessary global platform for communication and coordination of weed genomics research. © 2018 Society of Chemical Industry.
Publisher: Wiley
Date: 10-09-2013
DOI: 10.1111/EVA.12098
Publisher: MDPI AG
Date: 22-07-2020
Abstract: Wild poinsettia (Euphorbia heterophylla L.) is an important weed species in southern Brazil, especially due to the evolution of multiple herbicide resistance (e.g., acetolactate synthase (ALS)- inhibitors, protoporphyrinogen oxidase inhibitors, and glyphosate). The mechanism of resistance to imazamox was investigated in two wild poinsettia populations (R1 and R2) from southern Brazil and compared to a known susceptible (S) population. Imazamox dose-response experiments revealed high levels of resistance: 45-fold and 224.5-fold based on dry biomass reduction, for R1 and R2, respectively. Extremely high concentrations of imazamox (20,000 µM) were not sufficient to provide 50% inhibition of ALS enzyme activity (I50) for R1 or R2. Hence, resistance levels were estimated to be greater than 123-fold for both populations based on in vitro ALS assays. The ALS gene from all R1 and R2 plants had a Trp574Leu mutation. A genotyping assay was developed to discriminate resistant and susceptible alleles based on the Trp574Leu mutation.
Publisher: Cold Spring Harbor Laboratory
Date: 20-07-2023
DOI: 10.1101/2023.07.19.549613
Abstract: The International Weed Genomics Consortium is a collaborative group of researchers focused on developing genomic resources for the study of weedy plants. Weeds are attractive systems for basic and applied research due to their impacts on agricultural systems and capacity to swiftly adapt in response to anthropogenic selection pressures. Our goal is to use genomic information to develop sustainable and effective weed control methods and to provide insights about biotic and abiotic stress tolerance to assist crop breeding. Here, we outline resources under development by the consortium and highlight areas of research that will be impacted by these enabling resources.
Publisher: Cold Spring Harbor Laboratory
Date: 13-03-2017
DOI: 10.1101/116269
Abstract: RB and AP designed and performed the experiments. RB, AP, TG, SP wrote the manuscript. This study provides novel insight into herbicide resistance conferred by GST-based detoxification to allow proactive intervention to minimize weed resistance evolution. The evolution of herbicide-resistant weed populations in response to synthetic herbicide selective pressure is threatening safe weed control practices achieved by these molecules. In Australia multiple-resistant populations of annual ryegrass ( Lolium rigidum ) are effectively controlled by soil-applied herbicides which provide adequate weed control. In this study we define the mechanistic basis of the experimentally-evolved resistance to the soil-applied herbicide pyroxasulfone in a L. rigidum population. TLC and HPLC-MS provide biochemical confirmation that pyroxasulfone resistance is metabolism-based with identification and quantification of pyroxasulfone metabolites formed via a glutathione conjugation pathway in pyroxasulfone-resistant L. rigidum plants. The observed over-expression of two putative resistance-endowing GST genes is consistent with pyroxasulfone-resistance in parental plants (P6) and positively correlated to pyroxasulfone resistance in F 1 pair-cross progenies. Thus, a major detoxification mechanism involves glutathione conjugation to pyroxasulfone and GST over-expression in pyroxasulfone-resistant L. rigidum plants. The definition of the genetic basis of metabolic resistance in weeds can be a first crucial step towards chemical means to reverse resistance and improve long-term weed resistance management.
Publisher: Oxford University Press (OUP)
Date: 11-09-2020
DOI: 10.1093/GBE/EVAA191
Abstract: In the last decade, Amaranthus tuberculatus has evolved resistance to 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-hydroxyphenylpyruvate dioxygenase inhibitors in multiple states across the midwestern United States. Two populations resistant to both mode-of-action groups, one from Nebraska (NEB) and one from Illinois (CHR), were studied using an RNA-seq approach on F2 mapping populations to identify the genes responsible for resistance. Using both an A. tuberculatus transcriptome assembly and a high-quality grain amaranth (A. hypochondriacus) genome as references, differential transcript and gene expression analyses were conducted to identify genes that were significantly over- or underexpressed in resistant plants. When these differentially expressed genes (DEGs) were mapped on the A. hypochondriacus genome, physical clustering of the DEGs was apparent along several of the 16 A. hypochondriacus scaffolds. Furthermore, single-nucleotide polymorphism calling to look for resistant-specific (R) variants, and subsequent mapping of these variants, also found similar patterns of clustering. Specifically, regions biased toward R alleles overlapped with the DEG clusters. Within one of these clusters, allele-specific expression of cytochrome P450 81E8 was observed for 2,4-D resistance in both the CHR and NEB populations, and phylogenetic analysis indicated a common evolutionary origin of this R allele in the two populations.
Publisher: Oxford University Press (OUP)
Date: 13-09-2019
DOI: 10.1093/GBE/EVZ198
Abstract: Increased copy number of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene confers resistance to glyphosate, the world’s most-used herbicide. There are typically three to eight EPSPS copies arranged in tandem in glyphosate-resistant populations of the weed kochia (Kochia scoparia). Here, we report a draft genome assembly from a glyphosate-susceptible kochia in idual. Additionally, we assembled the EPSPS locus from a glyphosate-resistant kochia plant by sequencing select bacterial artificial chromosomes from a kochia bacterial artificial chromosome library. Comparing the resistant and susceptible EPSPS locus allowed us to reconstruct the history of duplication in the structurally complex EPSPS locus and uncover the genes that are coduplicated with EPSPS, several of which have a corresponding change in transcription. The comparison between the susceptible and resistant assemblies revealed two dominant repeat types. Additionally, we discovered a mobile genetic element with a FHY3/FAR1-like gene predicted in its sequence that is associated with the duplicated EPSPS gene copies in the resistant line. We present a hypothetical model based on unequal crossing over that implicates this mobile element as responsible for the origin of the EPSPS gene duplication event and the evolution of herbicide resistance in this system. These findings add to our understanding of stress resistance evolution and provide an ex le of rapid resistance evolution to high levels of environmental stress.
Publisher: Springer Science and Business Media LLC
Date: 05-11-2014
DOI: 10.1007/S00425-014-2197-9
Abstract: Field-evolved resistance to the herbicide glyphosate is due to lification of one of two EPSPS alleles, increasing transcription and protein with no splice variants or effects on other pathway genes. The widely used herbicide glyphosate inhibits the shikimate pathway enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Globally, the intensive use of glyphosate for weed control has selected for glyphosate resistance in 31 weed species. Populations of suspected glyphosate-resistant Kochia scoparia were collected from fields located in the US central Great Plains. Glyphosate dose response verified glyphosate resistance in nine populations. The mechanism of resistance to glyphosate was investigated using targeted sequencing, quantitative PCR, immunoblotting, and whole transcriptome de novo sequencing to characterize the sequence and expression of EPSPS. Sequence analysis showed no mutation of the EPSPS Pro106 codon in glyphosate-resistant K. scoparia, whereas EPSPS genomic copy number and transcript abundance were elevated three- to ten-fold in resistant in iduals relative to susceptible in iduals. Glyphosate-resistant in iduals with increased relative EPSPS copy numbers had consistently lower shikimate accumulation in leaf disks treated with 100 μM glyphosate and EPSPS protein levels were higher in glyphosate-resistant in iduals with increased gene copy number compared to glyphosate-susceptible in iduals. RNA sequence analysis revealed seven nucleotide positions with two different expressed alleles in glyphosate-susceptible reads. However, one nucleotide at the seven positions was predominant in glyphosate-resistant sequences, suggesting that only one of two EPSPS alleles was lified in glyphosate-resistant in iduals. No alternatively spliced EPSPS transcripts were detected. Expression of five other genes in the chorismate pathway was unaffected in glyphosate-resistant in iduals with increased EPSPS expression. These results indicate increased EPSPS expression is a mechanism for glyphosate resistance in these K. scoparia populations.
Publisher: Cambridge University Press (CUP)
Date: 02-11-2021
DOI: 10.1017/WSC.2021.70
Abstract: Herbicide-resistant weed management is one of the greatest agricultural challenges in crop production. Thus, the quick identification of herbicide-resistant weeds is extremely important for management. This study aimed to evaluate resistance to PSI-inhibiting herbicides (diquat) and physiological response to paraquat application in Sumatran fleabane [ Conyza sumatrensis (Retz.) E. Walker syn.: Erigeron sumatrensis Retz.]. The research was conducted with two C. sumatrensis biotypes, one susceptible and the other with multiple resistance to herbicides from five different modes of action (glyphosate, paraquat, diuron, saflufenacil, and 2,4-D). A dose–response assay was carried out to evaluate herbicide resistance to diquat in the paraquat-resistant C. sumatrensis biotype. The enzymatic activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), hydrogen peroxide (H 2 O 2 ) content, and chlorophyll a (Chl a ) fluorescence were measured in both biotypes after paraquat (400 g ai ha −1 ) application. The dose–response assay confirmed resistance of C. sumatrensis to diquat with resistance factor levels of 26-fold and 6-fold for LD 50 and GR 50 values, respectively, compared with the susceptible biotype. Accumulation of H 2 O 2 occurred more rapidly in the paraquat-susceptible biotype than in the resistant one. Paraquat treatment caused an increase in SOD and APX activity in the susceptible biotype, but antioxidant enzyme activities were unaffected by paraquat in the resistant one at 5 h after application (HAA). Chl a fluorescence increased across the first 4 HAA in both resistant and susceptible biotypes. However, at 24 HAA, the resistant biotype showed a decline in fluorescence close to untreated plants, while the susceptible biotype died, confirming resistance to diquat in the paraquat-resistant C. sumatrensis biotype. The paraquat-resistant biotype does not induce antioxidative enzymes, as a possible mechanism of resistance to paraquat, but shows rapid recovery of photosynthesis and continuous growth when subjected to paraquat, while the paraquat-susceptible biotype does not survive.
Publisher: Frontiers Media SA
Date: 25-01-2018
Publisher: Wiley
Date: 11-2021
DOI: 10.1111/MEC.16221
Abstract: The global invasion, and subsequent spread and evolution of weeds provides unique opportunities to address fundamental questions in evolutionary and invasion ecology. Amaranthus palmeri is a widespread glyphosate‐resistant (GR) weed in the USA. Since 2015, GR populations of A . palmeri have been confirmed in South America, raising questions about introduction pathways and the importance of pre‐ vs. post‐invasion evolution of GR traits. We used RAD‐sequencing genotyping to characterize genetic structure of populations from Brazil, Argentina, Uruguay and the USA. We also quantified gene copy number of the glyphosate target, 5‐enolpyruvyl‐3‐shikimate phosphate synthase ( EPSPS ), and the presence of an extrachromosomal circular DNA (eccDNA) replicon known to confer glyphosate resistance in USA populations. Populations in Brazil, Argentina and Uruguay were only weakly differentiated (pairwise F ST ≤0.043) in comparison to USA populations (mean pairwise F ST =0.161, range =0.068–0.258), suggesting a single major invasion event. However, elevated EPSPS copy number and the EPSPS replicon were identified in all populations from Brazil and Uruguay, but only in a single Argentinean population. These observations are consistent with independent in situ evolution of glyphosate resistance in Argentina, followed by some limited recent migration of the eccDNA‐based mechanism from Brazil to Argentina. Taken together, our results are consistent with an initial introduction of A . palmeri into South America sometime before the 1980s, and local evolution of GR in Argentina, followed by a secondary invasion of GR A . palmeri with the unique eccDNA‐based mechanism from the USA into Brazil and Uruguay during the 2010s.
Publisher: Public Library of Science (PLoS)
Date: 16-12-2016
Publisher: Cold Spring Harbor Laboratory
Date: 27-05-2023
DOI: 10.1101/2023.05.26.542497
Abstract: Transposable element activity has greatly impacted the evolution of Kochia scoparia syn. Bassia scoparia (kochia), an important agricultural weed. In this study, an improved kochia genome assembly of the glyphosate-susceptible line 7710 was analyzed in comparison to a glyphosate-resistant line, M32. A near complete genome assembly consisting of 14 super-scaffolds with a total length of 969.6 Mb, and N50 scaffold length of 99.88 Mb, was generated with hybrid short-read (Illumina), and singlemolecule (PacBio/Bionano genomics) data, in addition to chromatin interaction mapping (Hi-C). The 9 largest scaffolds corresponded to the 9 chromosomes of a close relative, Beta vulgaris . From this assembly, 54,387 protein-coding gene loci were annotated. After gene annotation it was revealed that 58% of the whole-genome consisted of transposable elements. We identified that gene families containing FHY3 (FAR-Red Elongated Hypocotyl 3) and FAR1 (FAR-Red Impaired Response 1) functional domains have undergone a massive Bassia -lineage specific expansion. FHY3 and FAR1 domains were first described as a “domesticated” (non-active) sub-type of Mutator Don-Robertson transposase (MuDR) that function as transcription factors however, the domains may still function as transposases in the correct genomic context, but this has yet to be observed. Mutator elements are associated with large DNA segmental transposition within the genome including gene duplication events, which can greatly influence plant phenotypes and evolution. We discovered in our work that putative MuDR elements with detectable FHY3 / FAR1 domains were tightly associated with segmental duplications of 5-enolpyruvylshikimate-3-phosphate synthase ( EPSPS ) that confer resistance to the herbicide glyphosate. Further, in a case study of MuDR activity, we characterized a new MuDR subtype, named here as “Muntjac”, which contributes to the evolution of herbicide resistance in kochia through the process of transduplication. Collectively, our study provides insights into the de-domestication of a FHY3/FAR1 transposon and provides new perspectives on the evolution of glyphosate resistance in kochia.
Publisher: Springer Science and Business Media LLC
Date: 22-03-2017
DOI: 10.1038/SREP44913
Abstract: Gene flow is an important component in evolutionary biology however, the role of gene flow in dispersal of herbicide-resistant alleles among weed populations is poorly understood. Field experiments were conducted at the University of Nebraska-Lincoln to quantify pollen-mediated gene flow (PMGF) from glyphosate-resistant (GR) to -susceptible (GS) common waterhemp using a concentric donor-receptor design. More than 130,000 common waterhemp plants were screened and 26,199 plants were confirmed resistant to glyphosate. Frequency of gene flow from all distances, directions, and years was estimated with a double exponential decay model using Generalized Nonlinear Model (package gnm ) in R. PMGF declined by 50% at m distance from the pollen source, whereas 90% reduction was found at 88 m (maximum) depending on the direction of the pollen-receptor blocks. Amplification of the target site gene, 5-enolpyruvylshikimate-3-phosphate synthase ( EPSPS ), was identified as the mechanism of glyphosate resistance in parent biotype. The EPSPS gene lification was heritable in common waterhemp and can be transferred via PMGF, and also correlated with glyphosate resistance in pseudo-F 2 progeny. This is the first report of PMGF in GR common waterhemp and the results are critical in explaining the rapid dispersal of GR common waterhemp in Midwestern United States.
Publisher: Cambridge University Press (CUP)
Date: 18-12-2018
DOI: 10.1017/WSC.2018.71
Abstract: Glyphosate-resistant (GR) goosegrass [ Eleusine indica (L.) Gaertn.] was recently identified in Brazil, but its resistance mechanism was unknown. This study elucidated the resistance mechanism in this species and developed a molecular marker for rapid detection of this target-site resistance trait. The resistance factor for the resistant biotype was 4.4-fold compared with the glyphosate-susceptible (GS) in greenhouse dose–response experiments. This was accompanied by a similar (4-fold) difference in the levels of in vitro and in planta shikimate accumulation in these biotypes. However, there was no difference in uptake, translocation, or metabolism of glyphosate between the GS and GR biotypes. Moreover, both biotypes showed similar values for 5-enolpyruvylshikimate-3-phosphate synthase ( EPSPS ) copy number and transcription. Sequencing of a 330-bp fragment of the EPSPS gene identified a single-nucleotide polymorphism that led to a Pro-106-Ser amino acid substitution in the enzyme from the GR biotype. This mutation imparted a 3.8-fold increase in the amount of glyphosate required to inhibit 50% of EPSPS activity, confirming the role of this amino acid substitution in resistance to glyphosate. A quantitative PCR–based genotyping assay was developed for the rapid detection of resistant plants containing this Pro-106-Ser mutation.
Publisher: Cambridge University Press (CUP)
Date: 08-2019
DOI: 10.1017/WET.2019.54
Abstract: Glyphosate-resistant (GR) kochia has been reported across the western and midwestern United States. From 2011 to 2014, kochia seed was collected from agronomic regions across Colorado to evaluate the frequency and distribution of glyphosate-, dicamba-, and fluroxypyr-resistant kochia, and to assess the frequency of multiple resistance. Here we report resistance frequency as percent resistance within a population, and resistance distribution as the percentage and locations of accessions classified as resistant to a discriminating herbicide dose. In 2011, kochia accessions were screened with glyphosate only, whereas from 2012 to 2014 kochia accessions were screened with glyphosate, dicamba, and fluroxypyr. From 2011 to 2014, the percentages of GR kochia accessions were 60%, 45%, 39%, and 52%, respectively. The percentages of dicamba-resistant kochia accessions from 2012 to 2014 were 33%, 45%, and 28%, respectively. No fluroxypyr-resistant accessions were identified. Multiple-resistant accessions (low resistance or resistant to both glyphosate and dicamba) from 2012 to 2014 were identified in 14%, 15%, and 20% of total s led accessions, respectively. This confirmation of multiple glyphosate and dicamba resistance in kochia accessions emphasizes the importance of ersity in herbicide site of action as critical to extend the usefulness of remaining effective herbicides such as fluroxypyr for management of this weed.
Publisher: Wiley
Date: 05-2008
Publisher: Wiley
Date: 03-2007
Publisher: Wiley
Date: 29-12-2017
DOI: 10.1002/PS.4778
Abstract: Resistance to the synthetic auxin herbicide dicamba is increasingly problematic in Kochia scoparia. The resistance mechanism in an inbred dicamba-resistant K. scoparia line (9425R) was investigated using physiological and transcriptomics (RNA-Seq) approaches. No differences were found in dicamba absorption or metabolism between 9425R and a dicamba-susceptible line, but 9425R was found to have significantly reduced dicamba translocation. Known auxin-responsive genes ACC synthase (ACS) and indole-3-acetic acid amino synthetase (GH3) were transcriptionally induced following dicamba treatment in dicamba-susceptible K. scoparia but not in 9425R. Chalcone synthase (CHS), the gene regulating synthesis of the flavonols quertecin and kaemperfol, was found to have twofold higher transcription in 9425R both without and 12 h after dicamba treatment. Increased CHS transcription co-segregated with dicamba resistance in a forward genetics screen using an F Prior work has shown that the flavonols quertecin and kaemperfol compete with auxin for intercellular movement and vascular loading via ATP-binding cassette subfamily B (ABCB) membrane transporters. The results of this study support a model in which constitutively increased CHS expression in the meristem produces more flavonols that would compete with dicamba for intercellular transport by ABCB transporters, resulting in reduced dicamba translocation. © 2017 Society of Chemical Industry.
Publisher: Wiley
Date: 06-02-2018
DOI: 10.1002/PS.4811
Abstract: Synthetic auxins such as 2,4-dichlorophenoxyacetic acid (2,4-D) have been widely used for selective control of broadleaf weeds since the mid-1940s. In 2009, an Amaranthus tuberculatus (common waterhemp) population with 10-fold resistance to 2,4-D was found in Nebraska, USA. The 2,4-D resistance mechanism was examined by conducting [ No differences were found in 2,4-D absorption or translocation between resistant and susceptible A. tuberculatus plants. Resistant plants metabolized [ Our results demonstrate that rapid 2,4-D metabolism is a contributing factor to resistance in A. tuberculatus, potentially mediated by cytochrome P450. Metabolism-based resistance to 2,4-D could pose a serious challenge for A. tuberculatus control because of the potential for cross-resistance to other herbicides. © 2017 Society of Chemical Industry.
Publisher: Cambridge University Press (CUP)
Date: 05-2017
DOI: 10.1017/WSC.2017.1
Abstract: Palmer amaranth is native to the United States, but was discovered in 2015 in Brazil. Palmer amaranth populations in Brazil were very difficult to control using glyphosate, which resulted in many changes to standard weed management practices. A genotyping assay was used to confirm that the population detected in Mato Grosso State, Brazil, was correctly identified as Palmer amaranth and that it was not tall waterhemp. Greenhouse dose–response curves and shikimate accumulation assays showed that the Brazilian population was highly resistant to glyphosate, with an LD50 value (3,982 g glyphosate ha −1 ) more than twice the typical use rates and very little shikimate accumulation at 1 mM glyphosate concentrations in a leaf-disk assay. The Brazilian population was also resistant to sulfonylurea and imidazolinone acetolactate synthase (ALS) inhibitor herbicides. The resistance mechanisms in the Brazilian population were identified as increased EPSPS gene copy number for glyphosate resistance (between 50- and 179-fold relative EPSPS gene copy number increase) and two different alleles for target-site mutations in the ALS gene (W574L and S653N). These results confirm the introduction of Palmer amaranth to Brazil using a genetic marker for species identification, as well as resistance to glyphosate and ALS inhibitors.
Publisher: Wiley
Date: 17-05-2019
Publisher: Wiley
Date: 17-05-2019
Publisher: Wiley
Date: 21-10-2021
DOI: 10.1111/MEC.16215
Abstract: Genomic‐based epidemiology can provide insight into the origins and spread of herbicide resistance mechanisms in weeds. We used kochia ( Bassia scoparia ) populations resistant to the herbicide glyphosate from across western North America to test the alternative hypotheses that (i) a single EPSPS gene duplication event occurred initially in the Central Great Plains and then subsequently spread to all other geographical areas now exhibiting glyphosate‐resistant kochia populations or that (ii) gene duplication occurred multiple times in independent events in a case of parallel evolution. We used qPCR markers previously developed for measuring the structure of the EPSPS tandem duplication to investigate whether all glyphosate‐resistant in iduals had the same EPSPS repeat structure. We also investigated population structure using simple sequence repeat markers to determine the relatedness of kochia populations from across the Central Great Plains, Northern Plains and the Pacific Northwest. We found that the original EPSPS duplication genotype was predominant in the Central Great Plains where glyphosate resistance was first reported. We identified two additional EPSPS duplication genotypes, one having geographical associations with the Northern Plains and the other with the Pacific Northwest. The EPSPS duplication genotype from the Pacific Northwest seems likely to represent a second, independent evolutionary origin of a resistance allele. We found evidence of gene flow across populations and a general lack of population structure. The results support at least two independent evolutionary origins of glyphosate resistance in kochia, followed by substantial and mostly geographically localized gene flow to spread the resistance alleles into erse genetic backgrounds.
Publisher: Cambridge University Press (CUP)
Date: 24-10-2019
DOI: 10.1017/WET.2019.108
Abstract: Downy brome, feral rye, and jointed goatgrass are problematic winter annual grasses in central Great Plains winter wheat production. Integrated control strategies are needed to manage winter annual grasses and reduce selection pressure exerted on these weed populations by the limited herbicide options currently available. Harvest weed-seed control (HWSC) methods aim to remove or destroy weed seeds, thereby reducing seed-bank enrichment at crop harvest. An added advantage is the potential to reduce herbicide-resistant weed seeds that are more likely to be present at harvest, thereby providing a nonchemical resistance-management strategy. Our objective was to assess the potential for HWSC of winter annual grass weeds in winter wheat by measuring seed retention at harvest and destruction percentage in an impact mill. During 2015 and 2016, 40 wheat fields in eastern Colorado were s led. Seed retention was quantified and compared per weed species by counting seed retained above the harvested fraction of the wheat upper canopy (15 cm and above), seed retained below 15 cm, and shattered seed on the soil surface at wheat harvest. A stand-mounted impact mill device was used to determine the percent seed destruction of grass weed species in processed wheat chaff. Averaged across both years, seed retention (±SE) was 75% ± 2.9%, 90% ± 1.7%, and 76% ± 4.3% for downy brome, feral rye, and jointed goatgrass, respectively. Seed retention was most variable for downy brome, because 59% of the s les had at least 75% seed retention, whereas the proportions for feral rye and jointed goatgrass s les with at least 75% seed retention were 93% and 70%, respectively. Weed seed destruction percentages were at least 98% for all three species. These results suggest HWSC could be implemented as an integrated strategy for winter annual grass management in central Great Plains winter wheat cropping systems.
Publisher: Oxford University Press (OUP)
Date: 12-06-2018
DOI: 10.1093/JXB/ERY215
Abstract: Seeds exist in the vulnerable state of being unable to repair the chemical degradation all organisms suffer, which slowly ages seeds and eventually results in death. Proposed seed aging mechanisms involve all classes of biological molecules, and degradation of total RNA has been detected contemporaneously with viability loss in dry-stored seeds. To identify changes specific to mRNA, we examined the soybean (Glycine max) seed transcriptome, using new, whole-molecule sequencing technology. We detected strong evidence of transcript fragmentation in 23-year-old, compared with 2-year-old, seeds. Transcripts were broken non-specifically, and greater fragmentation occurred in longer transcripts, consistent with the proposed mechanism of molecular fission by free radical attack at random bases. Seeds died despite high integrity of short transcripts, indicating that functions encoded by short transcripts are not sufficient to maintain viability. This study provides an approach to probe the asymptomatic phase of seed aging, namely by quantifying transcript degradation as a function of storage time.
Publisher: Wiley
Date: 11-09-2018
DOI: 10.1002/PS.5187
Publisher: Elsevier BV
Date: 07-2020
Publisher: Cambridge University Press (CUP)
Date: 08-2018
DOI: 10.1017/WET.2018.53
Abstract: Seven half-day regional listening sessions were held between December 2016 and April 2017 with groups of erse stakeholders on the issues and potential solutions for herbicide-resistance management. The objective of the listening sessions was to connect with stakeholders and hear their challenges and recommendations for addressing herbicide resistance. The coordinating team hired Strategic Conservation Solutions, LLC, to facilitate all the sessions. They and the coordinating team used in-person meetings, teleconferences, and email to communicate and coordinate the activities leading up to each regional listening session. The agenda was the same across all sessions and included small-group discussions followed by reporting to the full group for discussion. The planning process was the same across all the sessions, although the selection of venue, time of day, and stakeholder participants differed to accommodate the differences among regions. The listening-session format required a great deal of work and flexibility on the part of the coordinating team and regional coordinators. Overall, the participant evaluations from the sessions were positive, with participants expressing appreciation that they were asked for their thoughts on the subject of herbicide resistance. This paper details the methods and processes used to conduct these regional listening sessions and provides an assessment of the strengths and limitations of those processes.
Publisher: Wiley
Date: 02-02-2021
DOI: 10.1002/PS.6278
Publisher: Cold Spring Harbor Laboratory
Date: 31-08-2023
DOI: 10.1101/2023.08.29.554743
Abstract: Auxin-mimic herbicides chemically mimic the phytohormone indole-3-acetic-acid (IAA). Within the auxin-mimic herbicide class, the herbicide fluroxypyr has been extensively used to control an agronomically problematic Great Plains tumbleweed, kochia (Bassia scoparia). A 2014 field survey for herbicide resistance in kochia populations across Colorado identified a putative fluroxypyr resistant population that was assessed for response to five different herbicides representing four different herbicide modes of action. These included fluroxypyr and dicamba (auxin-mimics), atrazine (photosystem II inhibitor), glyphosate (EPSPS inhibitor), and chlorsulfuron (acetolactate synthase inhibitor). The greenhouse screen identified that this kochia population was resistant to fluroxypyr and chlorsulfuron, but sensitive to glyphosate, atrazine, and dicamba. This population was designated Flur-R. Subsequent dose response studies determined that 75% of the Flur-R population survived 628 g ae ha-1 of fluroxypyr (4x the label application rate in wheat fallow, which is 157 g ae ha-1 at 1x). Flur-R was 40 times more resistant to fluroxypyr than a susceptible population (J01-S) collected from the same field survey (LD50 720 and 20 g ae ha-1, respectively). Auxin-responsive gene expression increased following fluroxypyr treatment in Flur-R, J01-S, and in a dicamba-resistant, fluroxypyr-susceptible line 9425 in an RNA-sequencing experiment. In Flur-R, several transcripts with molecular functions for conjugation and transport were constitutively higher expressed, such as glutathione S-transferases (GSTs), UDP-glucosyl transferase (GT), and ATP binding cassette transporters (ABC transporters). After analyzing metabolic profiles over time, both Flur-R and J01-S rapidly converted [14C]-fluroxypyr ester, the herbicide formulation applied to plants, to [14C]-fluroxypyr acid, the biologically active form of the herbicide, and three unknown metabolites. Formation and flux of these metabolites was faster in Flur-R than J01-S, reducing the concentration of phytotoxic fluroxypyr acid. One unique metabolite was present in Flur-R that was not present in the J01-S metabolic profile. Gene sequence variant analysis specifically for auxin receptor and signaling proteins revealed the absence of non-synonymous mutations affecting auxin signaling and binding in candidate auxin target site genes, further supporting our hypothesis that non-target site metabolic degradation is contributing to fluroxypyr resistance in Flur-R.
Publisher: Cold Spring Harbor Laboratory
Date: 05-03-2021
DOI: 10.1101/2021.03.04.433944
Abstract: The natural auxin indole-3-acetic acid (IAA) is a key regulator of many aspects of plant growth and development. Synthetic auxin herbicides mimic the effects of IAA by inducing strong auxinic signaling responses in plants. Synthetic auxins are crucial herbicides in agriculture, made more important by the recent introduction of transgenic synthetic auxin resistant soybean and cotton. Currently, 41 weed species have evolved resistance to synthetic auxin herbicides and, in all but one case, the molecular basis of these resistance mechanisms is unknown. To determine the mechanism of 2,4-D resistance in a Sisymbrium orientale (Indian hedge mustard) weed population, we performed a transcriptome analysis of 2,4-D-resistant (R) and-susceptible (S) genotypes that revealed an in-frame 27-nucleotide deletion removing 9 amino acids in the degron tail (DT) of the auxin co-receptor Aux/IAA2 (SoIAA2). The deletion allele co-segregated with 2,4-D resistance in recombinant inbred lines. Further, this deletion was also detected in several 2,4-D resistant field populations of this species. Arabidopsis transgenic lines expressing the SoIAA2 mutant allele were resistant to 2,4-D and dicamba. The IAA2-DT deletion reduced binding to TIR1 in vitro with both natural and synthetic auxins, causing reduced association and increased dissociation rates. This novel mechanism of synthetic auxin herbicide resistance assigns a new in planta function to the DT region of this Aux/IAA co-receptor for its role in synthetic auxin binding kinetics and reveals a potential biotechnological approach to produce synthetic auxin resistant crops using gene editing.
Publisher: American Chemical Society (ACS)
Date: 12-2022
Abstract: A 2,4-dichlorophenoxyactic acid (2,4-D)-resistant population of
Publisher: Oxford University Press (OUP)
Date: 10-10-2017
Abstract: One of the increasingly widespread mechanisms of resistance to the herbicide glyphosate is copy number variation (CNV) of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene. EPSPS gene duplication has been reported in 8 weed species, ranging from 3 to 5 extra copies to more than 150 extra copies. In the case of Palmer amaranth (Amaranthus palmeri), a section of >300 kb containing EPSPS and many other genes has been replicated and inserted at new loci throughout the genome, resulting in significant increase in total genome size. The replicated sequence contains several classes of mobile genetic elements including helitrons, raising the intriguing possibility of extra-chromosomal replication of the EPSPS-containing sequence. In kochia (Kochia scoparia), from 3 to more than 10 extra EPSPS copies are arranged as a tandem gene duplication at one locus. In the remaining 6 weed species that exhibit EPSPS gene duplication, little is known about the underlying mechanisms of gene duplication or their entire sequence. There is mounting evidence that adaptive gene lification is an important mode of evolution in the face of intense human-mediated selection pressure. The convergent evolution of CNVs for glyphosate resistance in weeds, through at least 2 different mechanisms, may be indicative of a more general importance for this mechanism of adaptation in plants. CNVs warrant further investigation across plant functional genomics for adaptation to biotic and abiotic stresses, particularly for adaptive evolution on rapid time scales.
Publisher: Wiley
Date: 08-05-2014
DOI: 10.1111/TPJ.12514
Abstract: Weed control failures due to herbicide resistance are an increasing and worldwide problem that significantly affect crop yields. Metabolism-based herbicide resistance (referred to as metabolic resistance) in weeds is not well characterized at the genetic level. An RNA-Seq transcriptome analysis was used to find candidate genes that conferred metabolic resistance to the herbicide diclofop in a diclofop-resistant population (R) of the major global weed Lolium rigidum. A reference cDNA transcriptome (19 623 contigs) was assembled and assigned putative annotations. Global gene expression was measured using Illumina reads from untreated control, adjuvant-only control, and diclofop treatment of R and susceptible (S). Contigs that showed constitutive expression differences between untreated R and untreated S were selected for further validation analysis, including 11 contigs putatively annotated as cytochrome P450 (CytP450), glutathione transferase (GST), or glucosyltransferase (GT), and 17 additional contigs with annotations related to metabolism or signal transduction. In a forward genetics validation experiment, nine contigs had constitutive up-regulation in R in iduals from a segregating F2 population, including three CytP450, one nitronate monooxygenase (NMO), three GST, and one GT. Principal component analysis using these nine contigs differentiated F2 -R from F2 -S in iduals. In a physiological validation experiment in which 2,4-D pre-treatment induced diclofop protection in S in iduals due to increased metabolism, seven of the nine genetically validated contigs were induced significantly. Four contigs (two CytP450, NMO, and GT) were consistently highly expressed in nine field-evolved metabolic resistant L. rigidum populations. These four contigs were strongly associated with the resistance phenotype and are major candidates for contributing to metabolic diclofop resistance.
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 03-2020
Publisher: Cambridge University Press (CUP)
Date: 12-07-2019
DOI: 10.1017/WSC.2019.29
Abstract: A waterhemp [ Amaranthus tuberculatus (Moq.) J. D. Sauer] biotype (designated as “NER”) collected from a soybean [ Glycine max (L.) Merr.] production field in eastern Nebraska survived the POST application of fomesafen at the labeled rate. The objectives of this study were to (1) quantify the level of resistance to protoporphyrinogen oxidase (PPO) inhibitors (acifluorfen, fomesafen, and lactofen) applied POST, (2) determine the mechanism of PPO-inhibitor resistance in the NER biotype, (3) determine whether NER possessed multiple resistance to acetolactate synthase (ALS)-, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS)-, and photosystem II (PSII)-inhibiting herbicides, and (4) control NER with POST soybean herbicides. A whole-plant dose–response bioassay revealed that the NER biotype was 4- to 6-fold resistant to PPO-inhibiting herbicides depending on the known susceptible biotype (S1 or S2) used for comparison. A Kompetitive Allele Specific PCR (KASP™) assay was developed and performed for rapid and robust detection of the ΔG210 mutation (deletion of a codon) in the PPX2L gene. All s les of the NER biotype tested positive for the ΔG210 mutation. Dose–response bioassays confirmed that the NER biotype was resistant to three additional herbicide sites of action. Chlorimuron and imazethapyr, both ALS inhibitors, applied at 32X the labeled rate resulted in & % reduction in the aboveground biomass of the NER biotype. The same biotype was 3- and 7-fold resistant to glyphosate (EPSPS inhibitor) and atrazine (PSII inhibitor), respectively. Glufosinate, 2,4-D choline plus glyphosate, and dicamba were the only soybean POST herbicides that controlled NER effectively (≥92% aboveground biomass reduction). Amaranthus tuberculatus is the first confirmed weed species in Nebraska to evolve resistance to four distinct herbicide sites of action, leaving no POST herbicide choice for effective control in glyphosate-resistant and conventional (non-transgenic) soybean.
Publisher: Research Information Ltd.
Date: 08-2021
DOI: 10.1564/V32_AUG_04
Abstract: The authors discuss the importance of wheat as a global food source and describe a novel multi-institutional, public-private partnership between Colorado State University, the Colorado Wheat Research Foundation, and private chemical and seed companies that resulted in the development of a new herbicide-resistant wheat production system.
Publisher: Wiley
Date: 15-05-2019
DOI: 10.1111/NPH.15858
Abstract: The human-directed, global selection for glyphosate resistance in weeds has revealed a fascinating ersity of evolved resistance mechanisms, including herbicide sequestration in the vacuole, a rapid cell death response, nucleotide polymorphisms in the herbicide target (5-enolpyruvylshikimate-3-phosphate synthase, EPSPS) and increased gene copy number of EPSPS. For this latter mechanism, two distinct molecular genetic mechanisms have been observed, a tandem duplication mechanism and a large extrachromosomal circular DNA (eccDNA) that is tethered to the chromosomes and passed to gametes at meiosis. These ergent mechanisms have a range of consequences for the spread, fitness, and inheritance of resistance traits, and, particularly in the case of the eccDNA, demonstrate how evolved herbicide resistance can generate new insights into plant adaptation to contemporary environmental stress.
No related grants have been discovered for Todd Gaines.