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Neal C Stewart - One of the best experts on this subject based on the ideXlab platform.

  • atmospheric pollen dispersion from herbicide resistant horseweed Conyza Canadensis l
    Aerobiologia, 2017
    Co-Authors: Junming Wang, Haiyan Huang, Neal C Stewart
    Abstract:

    Horseweed (Conyza Canadensis (L.) Cronq.) with evolved herbicide resistance has become an especially problematic weed in crop production across the USA and on four continents (North America, South America, Asia, and Europe). Spread of herbicide resistance can occur through pollen-mediated gene flow between resistant and susceptible horseweed populations. However, there are little knowledge, preventive guidelines, and mechanism modeling for pollen transport in this system. We need to better understand pollen dispersion and deposition in the context of atmospheric conditions, herbicide-resistant horseweed patch size, and buffer crop type, height, and field size. A mechanistic model is needed to account for these. A pollen dispersion and deposition model was calibrated and validated using 2013 experimental field data. The validated model was run for various combinations of atmospheric conditions, horseweed characteristics (source strength), and buffer species and size (pollen can be intercepted by crop plants). Large fields with crops with a high leaf area density and tall plants can effectively prevent pollen dispersion. The information will help provide guidelines for preventing herbicide resistance spread from herbicide-resistant weeds and genetically modified plants in general.

  • characterization of the horseweed Conyza Canadensis transcriptome using gs flx 454 pyrosequencing and its application for expression analysis of candidate non target herbicide resistance genes
    Pest Management Science, 2010
    Co-Authors: Yanhui Peng, Laura L G Abercrombie, Joshua S Yuan, Chance W Riggins, Douglas R Sammons, Patrick J Tranel, Neal C Stewart
    Abstract:

    BACKGROUND:Thedenovotranscriptomesequencingofaweedy plantusingGS-FLX454technologiesisreported.Horseweed (Conyza Canadensis L.) was the first broadleaf weed to evolve glyphosate resistance in agriculture, and also is the most widely distributedglyphosate-resistantweedintheUnitedStatesandtheworld.However,availablesequencedataforthisspeciesare scant.Thetranscriptomicsequenceshouldbeusefulforgenediscovery,andtohelpelucidatethenon-target-basedglyphosate resistance mechanismand the genomic basis of weediness. RESULTS: Sequencing experiments yielded 411962 raw reads, an average read length of 233 bp and a total dataset of 95.8 Mb (NCBI accession number SRA010952). After trimming and quality control, 379152 high-quality sequences were retained and assembled into contigs. The assembly resulted in 31783 unique transcripts, including 16102 contigs and 15681 singletons. The average coverage depth for each contig and each nucleotide position was 22-fold and 12-fold respectively. A total of 16306 unique sequences were annotated by searching a custom plant protein database. The utility of the transcriptome data was demonstratedby further explorationof ABC transporters,which were previously hypothesized to play a role in non-target glyphosate resistance. Real-time RT-PCR primers were designed from the transcriptome data, which made it possible to assess expression patterns of 17 ABC transporters from resistant and susceptible horseweed accessions from Tennessee, with and without glyphosate treatment. CONCLUSION:Theseresultsshow thatGS-FLX454sequencingisapowerful andcost-effective platform forthedevelopmentof functional genomic tools for a weed species. c � 2010 Society of Chemical Industry Supportinginformationmaybefoundintheonlineversionofthisarticle.

  • shikimate accumulates in both glyphosate sensitive and glyphosate resistant horseweed Conyza Canadensis l cronq
    Journal of Agricultural and Food Chemistry, 2003
    Co-Authors: Thomas C Mueller, Christopher L Main, Robert M Hayes, Joseph H Massey, Neal C Stewart
    Abstract:

    Horseweed (Conyza Canadensis) is a cosmopolitan weed that commonly grows throughout North America. Horseweed that is not completely controlled by normal applications of glyphosate has been reported...

Bradley D Hanson - One of the best experts on this subject based on the ideXlab platform.

  • Increased temperatures and elevated CO_2 levels reduce the sensitivity of Conyza Canadensis and Chenopodium album to glyphosate
    Scientific Reports, 2019
    Co-Authors: Maor Matzrafi, Caio Brunharo, Parsa Tehranchian, Bradley D Hanson, Marie Jasieniuk
    Abstract:

    Herbicides are the most commonly used means of controlling weeds. Recently, there has been growing concern over the potential impacts of global climate change, specifically, increasing temperatures and elevated carbon dioxide (CO_2) concentrations, on the sensitivity of weeds to herbicides. Here, glyphosate response of both Conyza Canadensis and Chenopodium album was evaluated under different environmental conditions. Reduced glyphosate sensitivity was observed in both species in response to increased temperature, elevated CO_2 level, and the combination of both factors. Increased temperature had greater effect on plant survival than elevated CO_2 level. In combination, high temperature and elevated CO_2 level resulted in loss of apical dominance and rapid necrosis in glyphosate-treated plants. To investigate the mechanistic basis of reduced glyphosate sensitivity, translocation was examined using ^14C-glyphosate. In plants that were subjected to high temperatures and elevated CO_2 level, glyphosate was more rapidly translocated out of the treated leaf to shoot meristems and roots than in plants grown under control conditions. These results suggest that altered glyphosate translocation and tissue-specific sequestration may be the basis of reduced plant sensitivity. Therefore, overreliance on glyphosate for weed control under changing climatic conditions may result in more weed control failures.

  • Increased temperatures and elevated CO2 levels reduce the sensitivity of Conyza Canadensis and Chenopodium album to glyphosate
    Nature Publishing Group, 2019
    Co-Authors: Maor Matzrafi, Caio Brunharo, Parsa Tehranchian, Bradley D Hanson, Marie Jasieniuk
    Abstract:

    Abstract Herbicides are the most commonly used means of controlling weeds. Recently, there has been growing concern over the potential impacts of global climate change, specifically, increasing temperatures and elevated carbon dioxide (CO2) concentrations, on the sensitivity of weeds to herbicides. Here, glyphosate response of both Conyza Canadensis and Chenopodium album was evaluated under different environmental conditions. Reduced glyphosate sensitivity was observed in both species in response to increased temperature, elevated CO2 level, and the combination of both factors. Increased temperature had greater effect on plant survival than elevated CO2 level. In combination, high temperature and elevated CO2 level resulted in loss of apical dominance and rapid necrosis in glyphosate-treated plants. To investigate the mechanistic basis of reduced glyphosate sensitivity, translocation was examined using 14C-glyphosate. In plants that were subjected to high temperatures and elevated CO2 level, glyphosate was more rapidly translocated out of the treated leaf to shoot meristems and roots than in plants grown under control conditions. These results suggest that altered glyphosate translocation and tissue-specific sequestration may be the basis of reduced plant sensitivity. Therefore, overreliance on glyphosate for weed control under changing climatic conditions may result in more weed control failures

  • transcription of putative tonoplast transporters in response to glyphosate and paraquat stress in Conyza bonariensis and Conyza Canadensis and selection of reference genes for qrt pcr
    PLOS ONE, 2017
    Co-Authors: Stephen Pearce, Marcelo L. Moretti, Sarah Morran, Rocio Alarconreverte, Bradley D Hanson
    Abstract:

    Herbicide resistance is a challenge for modern agriculture further complicated by cases of resistance to multiple herbicides. Conyza bonariensis and Conyza Canadensis are invasive weeds of field crops, orchards, and non-cropped areas in many parts of the world. In California, USA, Conyza populations resistant to the herbicides glyphosate and paraquat have recently been described. Although the mechanism conferring resistance to glyphosate and paraquat in these species was not elucidated, reduced translocation of these herbicides was observed under experimental conditions in both species. Glyphosate and paraquat resistance associated with reduced translocation are hypothesized to be a result of sequestration of herbicides into the vacuole, with the possible involvement of over-expression of genes encoding tonoplast transporters of ABC-transporter families in cases of glyphosate resistance or cationic amino acid transporters (CAT) in cases of paraquat resistance. However, gene expression in response to herbicide treatment has not been studied in glyphosate and paraquat resistant populations. In the current study, we evaluated the transcript levels of genes possibly involved in resistance using real-time PCR. First, we evaluated eight candidate reference genes following herbicide treatment and selected three genes that exhibited stable expression profiles; ACTIN, HEAT-SHOCK-PROTEIN-70, and CYCLOPHILIN. The reference genes identified here can be used for further studies related to plant-herbicide interactions. We used these reference genes to assay the transcript levels of EPSPS, ABC transporters, and CAT in response to herbicide treatment in susceptible and resistant Conyza spp. lines. No transcription changes were observed in EPSPS or CAT genes after glyphosate or paraquat treatment, suggesting that these genes are not involved in the resistance mechanism. Transcription of the two ABC transporter genes increased following glyphosate treatment in all Conyza spp. lines. Transcription of ABC transporters also increased after paraquat treatment in all three lines of C. bonariensis. However, in C. Canadensis, paraquat treatment increased transcription of only one ABC transporter gene in the susceptible line. The increase in transcription of ABC transporters after herbicide treatment is likely a stress response based on similar response observed across all Conyza lines regardless of resistance or sensitivity to glyphosate or paraquat, thus these genes do not appear to be directly involved in the mechanism of resistance in Conyza spp.

  • Transcription stability values and stability ranking of candidate reference genes calculated using the NormFinder algorithm.
    2017
    Co-Authors: Marcelo L. Moretti, Rocio Alárcon-reverte, Stephen Pearce, Sarah Morran, Bradley D Hanson
    Abstract:

    Transcription was evaluated on young leaves of Conyza bonariensis and Conyza Canadensis lines after glyphosate or paraquat treatments.

  • growth and development of fall and spring planted populations of Conyza Canadensis and c bonariensis
    International Journal of Pest Management, 2016
    Co-Authors: Anil Shrestha, Marie Jasieniuk, Bradley D Hanson, Kurt J Hembree, Katrina M Steinhauer, Steven D Wright
    Abstract:

    ABSTRACTThe growth and phenological development of spring- and fall-planted Conyza Canadensis and C. bonariensis were studied in Fresno, CA, USA. A glyphosate-resistant (GR) and a glyphosate-susceptible (GS) population of each species were used. Time taken by each plant to reach the rosette, bolting, appearance of first bud, appearance of first open flower, and initial seed set were converted to growing degree days (GDDs). The fall- and spring-planted C. Canadensis required similar GDDs to complete their life cycles but the GR type required fewer GDDs than the GS type. In C. bonariensis, the GDDs required to complete its life cycle differed between the fall- and spring-plantings but not between the GR and GS types. The total aboveground biomass of both fall- and spring-planted Conyzas at initial seed set was similar but the spring-planted GS C. Canadensis produced more biomass than the GR type, whereas the fall-planted GS C. bonariensis produced more biomass than the GR type. Plant development based on GD...

Allison A. Snow - One of the best experts on this subject based on the ideXlab platform.

  • target site epsps pro 106 ser mutation in Conyza Canadensis biotypes with extreme resistance to glyphosate in ohio and iowa usa
    Scientific Reports, 2020
    Co-Authors: Zachery T. Beres, Micheal D. K. Owen, Eric R Page, Laura Giese, David Mackey, Allison A. Snow
    Abstract:

    Documenting the diversity of mechanisms for herbicide resistance in agricultural weeds is helpful for understanding evolutionary processes that contribute to weed management problems. More than 40 species have evolved resistance to glyphosate, and at least 13 species have a target-site mutation at position 106 of EPSPS. In horseweed (Conyza Canadensis), this p106 mutation has only been reported in Canada. Here, we sampled seeds from one plant (= biotype) at 24 sites in Ohio and 20 in Iowa, screened these biotypes for levels of resistance, and sequenced their DNA to detect the p106 mutation. Resistance categories were based on 80% survival at five glyphosate doses: S (0×), R1 (1×), R2 (8×), R3 (20×), or R4 (40×). The p106 mutation was not found in the19 biotypes scored as S, R1, or R2, while all 25 biotypes scored as R3 or R4 had the same proline-to-serine substitution at p106. These findings represent the first documented case of target-site mediated glyphosate resistance in horseweed in the United States, and the first to show that this mutation was associated with very strong resistance. We hypothesize that the p106 mutation has occurred multiple times in horseweed and may be spreading rapidly, further complicating weed management efforts.

  • no evidence for early fitness penalty in glyphosate resistant biotypes of Conyza Canadensis common garden experiments in the absence of glyphosate
    Ecology and Evolution, 2019
    Co-Authors: Zachery T. Beres, Micheal D. K. Owen, Allison A. Snow
    Abstract:

    Strong selection from herbicides has led to the rapid evolution of herbicide-resistant weeds, greatly complicating weed management efforts worldwide. In particular, overreliance on glyphosate, the active ingredient in RoundUp®, has spurred the evolution of resistance to this herbicide in ≥40 species. Previously, we reported that Conyza Canadensis (horseweed) has evolved extreme resistance to glyphosate, surviving at 40× the original 1× effective dosage. Here, we tested for underlying fitness effects of glyphosate resistance to better understand whether resistance could persist indefinitely in this self-pollinating, annual weed. We sampled seeds from a single maternal plant ("biotype") at each of 26 horseweed populations in Iowa, representing nine susceptible biotypes (S), eight with low-level resistance (LR), and nine with extreme resistance (ER). In 2016 and 2017, we compared early growth rates and bolting dates of these biotypes in common garden experiments at two sites near Ames, Iowa. Nested ANOVAs showed that, as a group, ER biotypes attained similar or larger rosette size after 6 weeks compared to S or LR biotypes, which were similar to each other in size. Also, ER biotypes bolted 1-2 weeks earlier than S or LR biotypes. These fitness-related traits also varied among biotypes within the same resistance category, and time to bolting was inversely correlated with rosette size across all biotypes. Disease symptoms affected 40% of all plants in 2016 and 78% in 2017, so we did not attempt to measure lifetime fecundity. In both years, the frequency of disease symptoms was greatest in S biotypes and similar in LR versus ER biotypes. Overall, our findings indicate there are no early growth penalty and possibly no lifetime fitness penalty associated with glyphosate resistance, including extremely strong resistance. We conclude that glyphosate resistance is likely to persist in horseweed populations, with or without continued selection pressure from exposure to glyphosate.

  • High Levels of Glyphosate Resistance in Conyza Canadensis from Agricultural and Non-Agricultural Sites in Ohio and Iowa
    Scientific Reports, 2018
    Co-Authors: Zachery T. Beres, Emily E. Ernst, Bruce A. Ackley, Mark M. Loux, Micheal D. K. Owen, Allison A. Snow
    Abstract:

    Glyphosate is an important herbicide worldwide, but its efficacy has been compromised where weed species have evolved glyphosate resistance. To better understand evolutionary outcomes of continued and strong selection from glyphosate exposure, we characterized variation in resistance in self-pollinating Conyza Canadensis (horseweed) in Ohio and Iowa, where glyphosate resistance was first reported in 2002 and 2011, respectively. In 2015, we collected seeds from a total of 74 maternal plants (biotypes) from no-till soybean fields vs . non-agricultural sites in each state, using one representative plant per site. Young plants from each biotype were sprayed with glyphosate rates of 0x, 1x (840 g ae ha^−1), 8x, 20x, or 40x. Resistant biotypes with at least 80% survival at each dosage were designated as R1 (1x), R2 (8x), R3 (20x), or R4 (40x). Nearly all Ohio agricultural biotypes were R4, as were 62% of biotypes from the non-agricultural sites. In Iowa, R4 biotypes were clustered in the southeastern soybean fields, where no-till agriculture is more common, and 45% of non-agricultural biotypes were R1–R4. Our results show that resistance levels to glyphosate can be very high (at least 40x) in both states, and that non-agricultural sites likely serve as a refuge for glyphosate-resistant biotypes.

Mark J Vangessel - One of the best experts on this subject based on the ideXlab platform.

  • Conyza Canadensis seed ascent in the lower atmosphere
    Agricultural and Forest Meteorology, 2009
    Co-Authors: Joseph T Dauer, David A Mortensen, Edward C Luschei, Scott A Isard, Elson J Shields, Mark J Vangessel
    Abstract:

    Abstract Long-distance dispersal of wind dispersed plant seed is dependent on seeds ascending in the atmosphere's surface boundary layer (SL). However, seed dispersal research often focuses on the near-surface dynamics of abscission and deposition, with little attention paid to seed ascent and transport beyond the surface boundary layer. Our research sought to estimate the vertical seed density flux of Conyza Canadensis , a common agricultural weed, in the surface boundary layer. Using a 2.7 ha field infested with Conyza Canadensis , the vertical seed concentration profile was measured on 5 days, three times per day while simultaneously monitoring micrometeorological conditions to connect the mechanisms of release with the process of ascent. Vertical seed sampling was conducted from two to six meters above ground level using removable screen frames. Remotely piloted airplanes were used to quantify seed concentration at 68 and 120 m above ground level and provide a connection between near surface dynamics and dynamics higher in the SL. Seed flux density (area under seed concentration curve) decreased with height and decreased from morning to afternoon. The seed flux density was significantly correlated with mean mechanical turbulence and the interaction of mean mechanical and mean thermal turbulence, supporting earlier research of meteorological effects on seed dispersal. While fewer total seeds were collected in the afternoon, more seeds were collected at 68 and 120 m during this period and may suggest more seeds were present in the upper SL where dispersal distance may be greater. Seeds collected above the SL will potentially be carried for hours before descending, depositing seeds in the range of 2–122 m, and influencing a much greater area than seeds unable to ascend through the lower SL. While this range is very wide, the dispersal distances reported herein are several orders of magnitude greater than previously reported for plants. These findings are all the more striking since the study species has evolved resistance to glyphosate herbicide, an herbicide now widely used in soybean, cotton, and corn crops in the US. Therefore, aerial transport of C. Canadensis seeds carrying genes coding for glyphosate resistance enables seed to move tens or hundreds of kilometers in a single dispersal event, a spread rate corroborated by number of cases of reported glyphosate resistance occurrences in North America.

  • Influence of Glyphosate-Resistant Horseweed (Conyza Canadensis) Growth Stage on Response to Glyphosate Applications
    Weed Technology, 2009
    Co-Authors: Mark J Vangessel, Barbara A. Scott, Quintin R. Johnson, Susan E. White-hansen
    Abstract:

    Infestations of glyphosate-resistant (GR) horseweed have become widespread in the eastern United States. This biotype is problematic in no-tillage production that relies extensively on glyphosate for weed control. Because horseweed is treated at various stages of growth, a greenhouse study explored rate response of glyphosate-resistant and -susceptible horseweed at three growth stages. GR horseweed was more responsive to glyphosate at the seedling stage than at the large rosette or bolting stages. A field study evaluated GR horseweed response when treated with glyphosate at soybean planting time, POST in-crop (about 45 d after planting), or both at planting and POST in-crop. There was a cumulative effect of the atplanting followed by POST in-crop glyphosate applications. When evaluating single glyphosate applications, the atplanting application was more effective at suppressing GR horseweed than a POST in-crop application. Because glyphosate cannot control GR horseweed, this biotype should be controlled with an herbicide with an alternate mode of action and applied at the most effective timing. Nomenclature: Glyphosate; horseweed, Conyza Canadensis (L.) Cronq.; soybean, Glycine max (L.) Merr.

  • temporal and spatial dynamics of long distance Conyza Canadensis seed dispersal
    Journal of Applied Ecology, 2006
    Co-Authors: Joseph T Dauer, David A Mortensen, Mark J Vangessel
    Abstract:

    Summary 1 Glyphosate-resistant Conyza Canadensis populations now infest more than 44 000 ha of arable land in eastern USA, only 5 years after the first resistant population was reported. Seed dispersal, the expansive use of glyphosate and the lack of tillage are all factors contributing to this high invasion speed. 2 Seed collected from deliberately established C. Canadensis source populations were found at the furthest seed traps in our empirical studies, providing one of the most complete dispersal kernels for studying long-distance dispersal. The results indicate that seed regularly disperses at least 500 m from source populations. While a relatively small number of seeds moves long distances, 99% of the seed was found within 100 m of the source. 3 Empirical and mechanistic models were fitted to the data to predict the dispersal in the prevailing wind direction. Both models underestimated seed deposition beyond 200 m but the mechanistic model provided a better fit to the data (lower Akaike information criterion). A two-dimensional analysis examined the correlation between angular directions of wind and seed movement. All trials were anisotropic but only the cumulative wind and seed direction were significantly correlated (P < 0·05). 4 The empirical model was used to explore the effect of increasing source strength, which would be expected as an infestation of glyphosate-resistant C. Canadensis expands on a producer's farm. At infestation levels consistent with a heavy infestation in a 5-ha field, seed dispersed further than 1·5 km, easily affecting 10s to 100s of surrounding farms. 5 Synthesis and applications. Emigration of C. Canadensis seed, from a source farm to adjacent farms, means that population dynamics and weed management are dependent on both intra- and interfield dispersal phenomena. Wind-dispersed plants challenge the common practice of single field management as a viable management option for herbicide-resistant weeds. Farms coupled by seed dispersal require proactive management practices by every producer to prevent and minimize the development of glyphosate-resistant infestations of undesirable and alien plants.

  • glyphosate resistant horseweed from delaware
    Weed Science, 2001
    Co-Authors: Mark J Vangessel
    Abstract:

    Abstract No-tillage corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production has been widely accepted in the mid-Atlantic region, favoring establishment of horseweed [Conyza Canadensis (L.) Cronq.]. Within 3 yr of using only glyphosate for weed control in continuous glyphosate-resistant soybeans, glyphosate failed to control horseweed in some fields. Seedlings originating from seed of one population collected in Delaware were grown in the greenhouse and exhibited 8- to 13-fold glyphosate resistance compared with a susceptible population. There were no differences between the isopropylamine or diammonium salts of glyphosate. Nomenclature: Corn; Zea mays L.; horseweed; Conyza Canadensis (L.) Cronq. ERICA; soybean; Glycine max (L.) Merr.; glyphosate.

Christopher L Main - One of the best experts on this subject based on the ideXlab platform.