ORCID Profile
0000-0001-8488-8833
Current Organisation
Colorado State University
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Publisher: Elsevier BV
Date: 02-2013
Publisher: Cambridge University Press (CUP)
Date: 12-05-2020
DOI: 10.1017/WSC.2020.39
Abstract: Glufosinate inhibits glutamine synthetase (GS), a key enzyme for amino acid metabolism and photorespiration. Protoporphyrinogen oxidase (PPO) inhibitors block chlorophyll biosynthesis and cause protoporphyrin accumulation, a highly photodynamic intermediate. Both herbicides ultimately lead to plant death by a massive accumulation of reactive oxygen species (ROS) through different mechanisms. We investigated a potential synergistic effect by the mixture of the two herbicide mechanisms of action (MoAs). The tank mix between a low rate of glufosinate (280 g ai ha −1 ) with an ultra-low dose of saflufenacil (1 g ha −1 ) provided enhanced herbicidal activity compared with the products applied in idually on Palmer amaranth ( Amaranthus palmeri S. Watson). The synergism between the two herbicides was also confirmed by isobole analysis and field trials. The herbicide combination provided high levels of efficacy when applied at low temperature and low humidity. Mechanistically, glufosinate caused a transient accumulation of glutamate, the building block for chlorophyll biosynthesis. Consequently, inhibition of both GS and PPO resulted in greater accumulation of protoporphyrin and ROS, forming the physiological basis for the synergism between glufosinate and PPO inhibitors. While the synergy between the two herbicide MoAs provided excellent efficacy on weeds, it caused low injury to PPO-resistant waterhemp [ Amaranthus tuberculatus (Moq.) Sauer] and high injury to both glufosinate-resistant and glufosinate-susceptible soybean [ Glycine max (L.) Merr.]. Glufosinate enhances the activity of PPO inhibitors through glutamate and protoporphyrin accumulation, leading to increased levels of ROS and lipid peroxidation. The synergism between the two herbicide MoAs can help to overcome environmental effects limiting the efficacy of glufosinate. Future research is needed to optimize the uses for this herbicidal composition across different cropping systems.
Publisher: Springer Science and Business Media LLC
Date: 05-05-2020
Publisher: Springer Science and Business Media LLC
Date: 08-03-2019
DOI: 10.1007/S00425-019-03124-3
Abstract: Glufosinate is primarily toxic to plants due to a massive light-dependent generation of reactive oxygen species rather than ammonia accumulation or carbon assimilation inhibition. Glutamine synthetase (GS) plays a key role in plant nitrogen metabolism and photorespiration. Glufosinate (C
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: 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: 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: 02-2009
DOI: 10.1614/WS-08-098.1
Abstract: The inheritance of resistance to the auxinic herbicide dicamba was examined in a kochia population from Nebraska. An inbred, resistant line was developed by selection and selfing over seven generations to ensure any resistance alleles would be homozygous in the parents. An inbred, susceptible line was similarly developed, but without selection. Dose–response experiments with dicamba determined a glyphosate-resistant concentration required to inhibit dry weight accumulation by 50% (GR 50 ) of 45 and 1,331 g ae ha −1 for the susceptible and resistant populations, respectively. F 1 crosses were made between resistant and susceptible inbred in iduals by hand-pollination, and the F 1 plants were selfed to produce F 2 plants. The F 2 population was screened with 280 g ha −1 dicamba, a rate that could discriminate between susceptible and resistant plants. A total of eight F 2 families were screened twice. In the first screen, seven F 2 families segregated in a 3:1 ratio, consistent with a single dominant allele controlling resistance, and in the second screen six F 2 families segregated in a 3:1 ratio. F 2 in iduals were selfed, the F 3 progeny were tested with 280 g ha −1 dicamba, and the genotype of each F 2 parent was determined based on F 3 progeny segregation. F 3 family segregation was consistent with the F 2 parents having a 1:2:1 homozygous-susceptible:heterozygote:homozygous-resistant pattern, confirming that resistance to dicamba in kochia is likely conferred by a single allele with a high degree of dominance.
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: 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: Public Library of Science (PLoS)
Date: 10-06-2013
No related grants have been discovered for Philip Westra.