Shikimic Acid Accumulation Research Articles

Adenosine triphosphate alleviates high temperature-enhanced glyphosate toxicity in maize seedlings

Extracellular ATP plays a key role in regulating plants stress responses. Here, we aimed to determine whether ATP can alleviate the glyphosate toxicity in maize seedlings under high temperature by regulating antioxidant responses. Foliar spraying with 100 μM glyphosate inhibited the growth of maize seedlings at room temperature (25 °C), leading to an increase in shikimic acid accumulation and oxidative stress (evaluated via lipid peroxidation, free proline, and H2O2 content) in the leaves, all of which were further exacerbated by high temperature (35 °C). The growth inhibition and oxidative stress caused by glyphosate were both alleviated by exogenous ATP. Moreover, the glyphosate-induced antioxidant enzyme activity and antioxidant accumulation were attenuated by high temperature, while ATP treatment reversed this inhibitory effect. Similarly, qPCR data showed that the relative expression levels of antioxidant enzyme-related genes (CAT1, GR1, and γ-ECS) in maize leaves were upregulated by ATP before exposure to GLY. Moreover, high temperature-enhanced GLY residue accumulation in maize leaves was reduced by ATP. ATP-induced detoxification was attenuated through NADPH oxidase (NOX) inhibition. Higher NOX activities and O2•− production were noted in ATP-treated maize leaves compared to controls prior to GLY treatment, indicating that the extracellular ATP-induced alleviation of GLY toxicity was closely associated with NOX-dependent reactive oxygen species signalling. The current findings present a new approach for reducing herbicide toxicity in crops exposed to high temperatures.

Occurrence of Multiple Glyphosate-Resistant Weeds in Brazilian Citrus Orchards

Glyphosate is the most widely used herbicide for weed control in citrus orchards in Brazil; therefore, it is likely that several species have gained resistance to this herbicide and that more than one resistant species can be found in the same orchard. The objective was to identify weeds resistant to glyphosate in citrus orchards from different regions of the São Paulo State (SP) and determine how many resistant species are present within the same orchard. Seeds of Amaranthus deflexus, A. hybridus, Bidens pilosa, Chloris elata, Conyza bonariensis, Digitaria insularis, Solanum Americanum, and Tridax procumbens, which, as reported by growers, are suspected to be resistant to glyphosate, were collected from plants that survived the last application of this herbicide (>720 g of acid equivalent [ae] ha–1) in sweet orange and Tahiti acid lime orchards. Based on dose–response and shikimic acid accumulation assays, all populations of A. deflexus, A. hybridus, B. pilosa, and T. procumbens were sensitive to glyphosate. However, populations of B. pilosa from the Olimpia region (R-NS, R-PT and R-OdA) showed signs of resistance based on plant mortality rates by 50% within a population (LD50 = 355–460 g ae ha−1). All populations of C. bonariensis, C. elata, and D. insularis were resistant to glyphosate, presenting resistance ratios from 1.9 to 27.6 and low shikimate accumulation rates. Solanum americanum also showed resistance, with resistance ratios ranging from 4.3 to 25.4. Most of the citrus orchards sampled presented the occurrence of more than one species resistant to glyphosate: Nossa Senhora—one species; Olhos D’agua and Passatempo—two species; Araras—four species; and Cordeiropolis and Mogi-Mirim—up to five species. The results reported in this paper provide evidence of multiple species in citrus orchards from São Paulo that have exhibited resistance to glyphosate. This underscores the difficulties in managing glyphosate-resistant weeds which are prevalent throughout the country, such as C. bonariensis and D. insularis. The presence of these resistant species further complicates the control of susceptible species that may also develop resistance. In addition, the glyphosate resistance of S. americanum was identified for the first time.

Temperature influences glyphosate efficacy on glyphosate-resistant and -susceptible goosegrass (Eleusine indica).

Glyphosate has been widely used to control Eleusine indica and other weeds in South China for many years. Among the most troublesome weeds in South China, E. indica can remain alive all year round. However, the influence of temperature on glyphosate efficacy on E. indica, especially under days with fluctuating temperature, is unknown. This study evaluated the influence of two temperature regimes on glyphosate efficacy on glyphosate-resistant (R) and -susceptible (S) E. indica biotypes. Plants of the R and S biotypes were cultivated under two temperature regimes (high: 30°C/20°C day/night; low: 20°C/15°C day/night). Dose-response experiments showed improved efficacy of glyphosate at the low temperature compared with that at the high temperature for both biotypes. Based on the LD50 values, the R biotype was 8.9 times more resistant to glyphosate than the S biotype at the high temperature; however, the resistance index (R/S) decreased to 3.1 at the low temperature. At 4 days after glyphosate application, shikimic acid accumulation was greater at the low temperature than at the high temperature in plants of both biotypes, and the increase was higher in plants of the R biotype than in the S biotype. At a sublethal glyphosate dose (R: 400 g ai ha-1; S: 200 g ai ha-1), plants grown at the low temperature showed a strong decrease in leaf chlorophyll content and Fv/Fm value compared with those of plants grown at the high temperature and the untreated control. At 3 days after treatment, glyphosate absorption was similar between biotypes at the high temperature, but absorption decreased to 64.9% and 53.1% at the low temperature for the R and S biotypes, respectively. For both biotypes, glyphosate translocation from the leaf to the remainder of the plant was reduced at the low temperature compared with that at the high temperature. No differences in glyphosate translocation were observed between biotypes within each temperature regime. This is the first report on the effect of temperature on glyphosate efficacy on E. indica, and provides important insights for glyphosate application and resistance management.

Different Non-Target Site Mechanisms Endow Different Glyphosate Susceptibility in Avena Species from Spain

In recent decades, cereal agriculture across main producing areas in Spain has progressively adopted direct sowing, associated with an increased use of herbicides in pre-sowing. Weedy species from genus Avena have been observed after the application of glyphosate in wheat. Here, Avena fatua (two accessions), Avena byzantina and Avena sterilis subsp. sterilis, one accession each, were taxonomically characterized by a biometric study. Dose-response trials confirmed that one A. fatua accession evolved to resistance, because it was four times more resistant (R) than the others, ascribed as susceptible (S). In addition, based on LD50, A. byzantina and A. sterilis had low susceptibility to glyphosate, with 604 and 458 g ae ha−1. Shikimic acid accumulation was able to discriminate between high susceptible (A. fatua (S)), low susceptible (A. byzantina and A. sterilis), and low resistant (A. fatua (R)) populations. On the other hand, the study revealed that A. fatua (R), A. byzantina and A. sterilis had low foliar uptake and decreased movement of glyphosate. In addition, the metabolism study showed less metabolite accumulation in A. byzantina and A. fatua (S). However, at 96 h after glyphosate application, A. fatua (R) and A. sterilis were able to convert more than 30% of glyphosate to aminomethylphosphonic acid (AMPA) and sarcosine. Enzyme basal activity and I50 values predicted high affinity between the herbicide and the target enzyme for all accessions, thus indicating that a target-site (TS) mechanism is probably not involved in the differences in glyphosate susceptibility. In closing, non-target site (NTS) mechanisms could participate both in A. fatua R to glyphosate, and low susceptibility in A. byzantina and A. sterilis from Spain.

First report of a wide distribution of glyphosate-resistant compact brome (Bromus madritensis) in the Iberian Peninsula: confirmation and field management

AbstractGlyphosate resistance is spreading in Spain and Portugal due to excessive herbicide use, in both annual and perennial crops. Compact brome (Bromus madritensis L.) is increasing in frequency in these different cropping systems when under conservation agriculture, particularly when glyphosate fails to control it. Fourteen populations from different areas in the Iberian Peninsula were confirmed as being B. madritensis using simple sequence repeat markers and clearly separated from the closely related species red brome (Bromus rubens L.) and ripgut brome (Bromus diandrus Roth). Six B. madritensis populations were classified as resistant, according to both their shikimic acid accumulation levels and their resistance factors based on LD50 or GR50 (values between 4 and 8). Populations with higher resistance factors also showed lower shikimic acid concentrations. Moreover, these resistant populations were able to survive the minimum registered dose for glyphosate in Spain in perennial crops (1,080 g ae ha−1, five populations) or in arable crops before seeding for annual weeds (540 g ae ha−1, one population), under both greenhouse and field conditions. The trials carried out in a glyphosate-resistant field during 2 consecutive years showed that acceptable control (≥90%) was only consistently achieved 90 d after application for preemergence treatment with flazasulfuron in a tank mix with glyphosate, while control with postemergence treatments, such as propaquizafop plus glyphosate, was below 80%. This research describes the first herbicide-resistance report for the weed species B. madritensis, confirming the presence of glyphosate-resistant populations mainly in perennial cropping systems but also in winter cereals from Spain. Due to the limited chemical tools to manage these populations, there is an urgent need for farmers to implement integrated weed management strategies.

Stacking herbicide detoxification and resistant genes improves glyphosate tolerance and reduces phytotoxicity in tobacco (Nicotiana tabacum L.) and rice (Oryza sativa L.)

Glyphosate residues retained in the growing meristematic tissues or in grains of glyphosate-resistant crops affect the plants physiological functions and crop yield. Removing glyphosate residues in the plants is desirable with no penalty on crop yield and quality. We report a new combination of scientific strategy to detoxify glyphosate that reduces the residual levels and improve crop resistance. The glyphosate detoxifying enzymes Aldo-keto reductase (AKR1) and mutated glycine oxidase (mGO) with different modes of action were co-expressed with modified EPSPS, which is insensitive to glyphosate in tobacco (Nicotiana tabacum L.) and rice (Oryza sativa L.). The transgenic tobacco plants expressing individual PsAKR1, mGO, CP4-EPSPS, combinations of PsAKR1:CP4EPSPS, PsAKR1:mGO, and multigene with PsAKR1: mGO: CP4EPSPS genes were developed. The bio-efficacy studies of in-vitro leaf regeneration on different concentrations of glyphosate, seedling bioassay, and spray on transgenic tobacco plants demonstrate that glyphosate detoxification with enhanced resistance. Comparative analysis of the transgenic tobacco plants reveals that double and multigene expressing transgenics had reduced accumulation of shikimic acid, glyphosate, and its primary residue AMPA, and increased levels of sarcosine were observed in all PsAKR1 expressing transgenics. The multigene expressing rice transgenics showed improved glyphosate resistance with yield maintenance. In summary, results suggest that stacking genes with two different detoxification mechanisms and insensitive EPSPS is a potential approach for developing glyphosate-resistant plants with less residual content.

Asexually propagated Agave tequilana var. azul exhibits variation in genetic markers and defence responses to Fusarium solani.

Agave (Agave tequilana var. azul) is considered a crop with low genetic diversity because it has been propagated vegetatively for centuries for commercial purposes, and consequently, it could be equally susceptible to pests and diseases. However, the present study employs plant material derived from field-grown plants exhibiting phenotypic variability in susceptibility to agave wilt. The offshoots from rhizomes of these plants were reproduced in vitro and classified as potentially resistant or susceptible. Amplified fragment length polymorphism analysis confirmed wide genetic differences among individuals, but these differences were not correlated with the observed phenotypic variability in resistance. Propagated plantlets were inoculated with Fusarium solani in two time-lapse confrontations for 72 h and 30 days. The early biochemical response showed statistically superior levels in the accumulation of shikimic acid, phenolic compounds, and chitinase activity in potentially resistant plantlets. There was an inverse correlation of these early biochemical responses and salicylic acid and the incidence of diseased root cells in isogenic plantlets in the 30-day confrontation with F. solani, suggesting that these activities and accumulation of molecules were primordial in the defence against this pathogen.

Inheritance and mechanism of glyphosate resistance in annual bluegrass (Poa annua L.).

In initial screening, glyphosate was ineffective in controlling five Poa annua populations. These populations were tested for resistance, and studies undertaken to determine resistance mechanisms and inheritance pattern. Dose-response studies conducted at 16/12°C and 27/20°C on the five putative resistant populations showed low-level resistance (1.4- to 2.5-fold) to glyphosate. Shikimic acid accumulation in response to glyphosate confirmed differences among the populations, with greater shikimic acid accumulation in the susceptible population. The EPSPS gene copy number was 0.5- to 5.2-fold greater in one resistant population (HT) than in the susceptible (S) population, but not in the others. EPSPS gene expression was five- to tenfold higher in HT compared with the susceptible population. Target site mutations, differences in glyphosate absorption or translocation or altered expression of aldo-keto reductase (AKR) were not identified in any of the resistant populations. Crosses were successful between one resistant population and the susceptible population (P262-16♂ ✕ S♀) and inheritance of glyphosate resistance appears to be controlled by a single, nuclear dominant gene in this population. Our study identified EPSPS gene amplification in a South Australian glyphosate-resistant P. annua population (HT). This mechanism of resistance was not identified in the other four glyphosate-resistant populations, and other common mechanisms were excluded. Although the resistance mechanism in some P. annua populations remains unknown, inheritance studies with one population suggest the involvement of a single dominant gene. © 2021 Society of Chemical Industry.

Glyphosate hormesis attenuates water deficit stress in safflower (Carthamus tinctorius L.) by modulating physiological and biochemical mediators

Changes in photosynthetic machinery can induce physiological and biochemical damage in plants. Low doses of glyphosate have been shown to exert a positive effect in mitigating the deleterious effects of water deficit in plants. Here, the physiological and biochemical mechanisms of safflower plants (Carthamus tinctorius L.) were studied under conditions of water deficit mediated by the attenuating effect of low-dose glyphosate. The plants were divided into two groups of water regimes in soil, without water deficit (−10 kPa) and with water deficit (−70 kPa), and were exposed to different concentrations of glyphosate (0, 1.8, 3.6, 7.2, 18, 36, 72, 180, 360, and 720 g a.e. ha−1). Evident protective responses at the physiological and biochemical levels were obtained after applying low doses of glyphosate to plants under water deficit, with a limiting dose for the occurrence of hormesis (LDS) = 72 g a.e. ha−1. The water deficit in plants resulted in hydrogen peroxide (H2O2) accumulation and consequently lipid peroxidation (LPO) associated with the accumulation of shikimic acid and glyphosate in plants, which triggered an increase in the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) that act by dismuting the levels of reactive oxygen species (ROS), maintaining, and/or increasing the maximum quantum efficiency of photosystem II (Fv/Fm), effective quantum yield of photosystem II (ΦPSII), electron transport rate (ETR), photochemical extinction coefficient (qP), and non-photochemical extinction coefficient (NPQ). APX appears to be the main enzyme involved in eliminating H2O2. Low doses of glyphosate act as water deficit ameliorators, allowing the plant to maintain/increase metabolism at physiological and biochemical levels by activating antioxidant enzymes in the dismutation of ROS in safflower plants.

Increased Activity of 5-Enolpyruvylshikimate-3-phosphate Synthase (EPSPS) Enzyme Describe the Natural Tolerance of Vulpia myuros to Glyphosate in Comparison with Apera spica-venti

Rattail fescue (Vulpia myuros (L.) C.C. Gmel.) is a self-pollinating winter annual grassy weed of winter annual crops. The problems with V. myuros are mostly associated with no-till cropping systems where glyphosate application before sowing or emergence of the crop is the most important control measure. Ineffective V. myuros control has been reported following glyphosate applications. Experiments were performed to study the effectiveness of glyphosate on V. myuros, and determine the causes of the lower performance of glyphosate on V. myuros compared to other grass weeds. Estimated GR50 values demonstrated that V. myuros was less susceptible to glyphosate than Apera spica-venti regardless of the growth stage. Within each species, glyphosate efficacy at different growth stages was closely related to spray retention. However, the low susceptibility to glyphosate in V. myuros was not caused by lower retention as previously suggested. A significantly lower shikimic acid accumulation in V. myuros compared to A. spica-venti was associated with a higher activity of the EPSPS enzyme in V. myuros. Nevertheless, the relative responses in EPSPS activity to different glyphosate concentrations were similar in the two grass species, which indicate that EPSPS from V. myuros is as susceptible to glyphosate as EPSPS from A. spica-venti suggesting no alternation in the binding site of EPSPS. The results from the current study indicate that V. myuros is less susceptible to glyphosate compared to A. spica-venti, and the low susceptibility of V. myuros is caused by an increased EPSPS enzyme activity.

Investigating glyphosate resistance in Amaranthus palmeri biotypes from Turkey

Amaranthus palmeri is a troublesome weed which is growing in importance worldwide. It causes serious competition in many crops. A. palmeri was introduced into Turkey 4–5 years ago and appears to adapt to different environmental conditions. Monoculture cropping systems and repeated use of the same herbicides have led to development of herbicide resistance in A. palmeri to several active ingredients including glyphosate, in USA and in South America. This study was conducted to investigate the evolution of glyphosate resistance in A. palmeri in Turkey. Seeds of 21 A. palmeri populations were collected in Turkish citrus fields where control problems with glyphosate were reported. A potentially glyphosate susceptible A. palmeri population was collected from a maize field (GS1 biotype). Seeds of putatively resistant and potentially susceptible (GS) biotypes were germinated and transplanted into large pots, and then allowed to grow in separate greenhouse chambers to obtain F2 generations. After carrying out a preliminary test experiment to exclude the most susceptible populations, a dose-response experiment was conducted in which glyphosate was applied at the 3–4 true leaf stage at 0, 332.5, 665, 1330, 2660, 5320, 10,640 and 21,280 g a.i. ha−1. Plants were harvested 21 days after treatment and dry weight was determined. Glyphosate applied at the recommended rate (1330 g a.i ha−1) controlled GS A. palmeri biotypes by more than 95% while controlling the GR biotypes at about 45%. Among those biotypes, GR1 and GR2 biotypes were confirmed to have an incipient resistance to glyphosate. The effect of glyphosate on shikimic acid accumulation was determined. Results showed that the GS2 biotype accumulated 3.1 and 1.56 times more shikimic acid than GR2 and GR1 biotypes which demonstrates that there is a lower accumulation of shikimic acid in the alleged resistant biotypes than in GS1. These findings demonstrate some increased tolerance of A. palmeri biotypes to glyphosate, which reinforces the need to implement integrated weed management to control this invasive plant in Turkey.

Glyphosate Resistance Confirmation and Field Management of Red Brome (Bromus rubens L.) in Perennial Crops Grown in Southern Spain

The excessive use of the herbicide glyphosate on annual and perennial crops grown in Southern Spain has caused an increase in resistant weed populations. Bromus rubens has begun to spread through olive and almond cultivars due to low glyphosate control over these species, whereas previously it had been well controlled with field dose (1080 g ae ha−1). Characterization using Simple Sequence Repeat (SSR) markers confirmed the presence of B. rubens collected in Andalusia. A rapid shikimic acid accumulation screening showed 17 resistant (R) populations with values between 300 and 700 µg shikimate g−1 fresh weight and three susceptible (S) populations with values between 1200 and 1700 µg shikimate g−1 fresh weight. In dose–response experiments the GR50 values agreed with previous results and the resistance factors (RFs: GR50 R/GR50 S (Br1)) were between 4.35 (Br9) and 7.61 (Br19). Foliar retention assays shown no differences in glyphosate retention in both R and S populations. The tests carried out in a resistant field (Br10) demonstrated the control efficacy of pre-emergence herbicides since flazasulfuron in the tank mix with glyphosate had up to 80% control 15 to 120 days after application (DAA) and grass weed postemergence herbicides, such as propaquizafop + glyphosate and quizalofop + glyphosate, had up to 90% control 15 to 90 DAA. Results confirm the first scientific report of glyphosate-resistant B. rubens worldwide; however, the use of herbicides with another mode of action (MOA) is the best tool for integrated weed management.

Confirmation of Multiple Resistant Chloris radiata Population, Harvested in Colombian Rice Fields

This paper reports the first C. radiata population with resistance to glyphosate and multiple resistance to the acetolactate synthase (ALS) inhibitor, imazamox. Two populations, one putative resistant (R) and one susceptible (S), were used in the studies. Dose–response experiments were performed to evaluate the resistance factor (RF). Shikimic acid accumulation, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and ALS enzyme activities were studied together with chemical integrated weed management (adjuvants and alternative herbicides). The resistance to glyphosate and imazamox was confirmed based on the dry weight reduction, visual evaluation and survival. The results of dose–response curve assays showed for the R population intermedium RF for glyphosate (5.1 and 9.7 for amount of herbicide needed to reduce the dry weight by 50% GR50 and lethal dose of 50% LD50, respectively) and high RF for imazamox (34.9 and 37.4, respectively). The low shikimic acid accumulation in R population confirmed the glyphosate resistance. The glyphosate concentration which inhibited the EPSPS enzyme in 50% (I50) was approximately 20 times higher for R population than the S population, while the imazamox I50 in ALS enzyme for the R plants was 89 times greater than the S plants. In the chemical integrated weed management, the foliar retention and effectivity assays showed that the use of adjuvants improves the retention of glyphosate and imazamox, and the reduction in dry weight of weeds. The alternative herbicides study showed that the acetyl-CoA carboxylase (ACCase) inhibitors, paraquat and glufosinate, had better results for control in this species. However, poor control was observed with bispyribac-sodium, metsulfuron-methyl and quinclorac, indicating possible cross-resistance for ALS-inhibitors and also multiple resistance for auxinic herbicides (quinclorac). Nevertheless dose–response experiments are required to confirm this assumption.

Physiological and morphoanatomical effects of glyphosate in Eugenia uniflora, a Brazilian plant species native to the Atlantic Forest biome.

The herbicide glyphosate can cause severe ecotoxicological effects on non-target organisms. Eugenia uniflora L. (Myrtaceae) is very important for in situ environmental biomonitoring due to its wide distribution in the Atlantic Forest biome. Thus, this study aimed to evaluate the response of E. uniflora leaves to glyphosate. Eight-month-old plants were exposed to an aerial application of the herbicide at concentrations of 0, 144, 432, 864, and 1440 g a. e. ha-1 (grams of acid equivalent per hectare). Evaluations were performed on the 12th day after the glyphosate application (DAA). An accumulation of shikimic acid in the leaves of E. uniflora was observed. Glyphosate altered the photosynthetic parameters of the treated plants, with a drastic decrease in the photosynthetic rate, stomatal conductance, transpiration, and pigment content. There was an increase in Ci/Ca, lipid peroxidation, and electrolyte extravasation levels. Glyphosate also promoted ultrastructural, anatomical and visible damage to the E. uniflora leaves. Our findings indicate that glyphosate is phytotoxic to the native species E. uniflora at the tested doses. The presence of visible damage suggests that E. uniflora has remarkable potential as a bioindicator of glyphosate in the environment, making it a possible species for future biomonitoring projects.

Use of Shotgun Metagenomics and Metabolomics to Evaluate the Impact of Glyphosate or Roundup MON 52276 on the Gut Microbiota and Serum Metabolome of Sprague-Dawley Rats.

Background:There is intense debate on whether glyphosate can inhibit the shikimate pathway of gastrointestinal microorganisms, with potential health implications.Objectives:We tested whether glyphosate or its representative EU herbicide formulation Roundup MON 52276 affects the rat gut microbiome.Methods:We combined cecal microbiome shotgun metagenomics with serum and cecum metabolomics to assess the effects of glyphosate [0.5, 50, ] or MON 52276 at the same glyphosate-equivalent doses, in a 90-d toxicity test in rats.Results:Glyphosate and MON 52276 treatment resulted in ceca accumulation of shikimic acid and 3-dehydroshikimic acid, suggesting inhibition of 5-enolpyruvylshikimate-3-phosphate synthase of the shikimate pathway in the gut microbiome. Cysteinylglycine, , and valylglycine levels were elevated in the cecal microbiome following glyphosate and MON 52276 treatments. Altered cecum metabolites were not differentially expressed in serum, suggesting that the glyphosate and MON 52276 impact on gut microbial metabolism had limited consequences on physiological biochemistry. Serum metabolites differentially expressed with glyphosate treatment were associated with nicotinamide, branched-chain amino acid, methionine, cysteine, and taurine metabolism, indicative of a response to oxidative stress. MON 52276 had similar, but more pronounced, effects than glyphosate on the serum metabolome. Shotgun metagenomics of the cecum showed that treatment with glyphosate and MON 52276 resulted in higher levels of Eggerthella spp., Shinella zoogleoides, Acinetobacter johnsonii, and Akkermansia muciniphila. Shinella zoogleoides was higher only with MON 52276 exposure. In vitro culture assays with Lacticaseibacillus rhamnosus strains showed that Roundup GT plus inhibited growth at concentrations at which MON 52276 and glyphosate had no effect.Discussion:Our study highlights the power of multi-omics approaches to investigate the toxic effects of pesticides. Multi-omics revealed that glyphosate and MON 52276 inhibited the shikimate pathway in the rat gut microbiome. Our findings could be used to develop biomarkers for epidemiological studies aimed at evaluating the effects of glyphosate herbicides on humans. https://doi.org/10.1289/EHP6990

Resistance Evolution to EPSPS Inhibiting Herbicides in False Barley (Hordeum murinum) Harvested in Southern Spain

A failure of the EPSPS-inhibiting herbicide glyphosate to control several populations of Hordeum murinum subsp. leporinum (or H. murinum) occurred in southern Spain after more than fifteen applications in both crop (olive, orchards, and citrus) and non-crop (dry areas, roadsides and ditches) areas. Eight out of 18 populations studied were resistant (R) to glyphosate with R factors higher than four based on GR50. These populations also had the highest values of LD50 and the lowest levels of shikimic acid accumulation. Two adjuvants tested increased glyphosate efficacy in both susceptible (S) and R populations thanks to better spray foliar retention. Moreover, PS I-, PS II-, and ACCase-inhibiting herbicides, in pre- or post-emergence, proved to be the best chemical alternatives with different sites of action (SoA) to control both S and glyphosate-R populations. This study represents the first report worldwide of glyphosate resistance in H. murinum found in very different crop and non-crop areas from southern Spain. To design chemical strategies to implement integrated weed management programs for glyphosate-R H. murinum, both adjuvants and herbicides with alternative SoA as well as application timings should be considered.

Effects of pre-harvest glyphosate use on protein composition and shikimic acid accumulation in spring wheat.

During wheat cultivation, glyphosate-based herbicides are recommended to be applied a week prior to harvest during the ripe stage of physiological maturity. However, some grains may not be at this physiological stage due to non-uniform maturation within the field. The goal of this study was to determine the effect of glyphosate-based herbicide timing on the chemistry of wheat gluten proteins and shikimic acid accumulation. The results of the study indicate that pre-harvest glyphosate application does not impact the amino acid composition, protein secondary structure or gluten protein composition. However, pre-harvest glyphosate application decreased the molecular weight of SDS extractable and unextractable proteins, and significantly increased the amount of shikimic acid accumulation, especially when applied early. Thus, this study indicates that pre-harvest use of glyphosate-based herbicides can cause significant differences in wheat protein chemistry and shikimic acid levels, especially when applied earlier than recommended, emphasizing the importance of timely application.

Prospecting alternative source of shikimic acid from clusiaceae of Western Ghats, India and evaluating discrepancies with reference to seasonal variation, developmental stage and sex of Mammea suriga

Clusiaceae is renowned for producing a wide range of phytochemicals like isoprenylated xanthones, biflavonoids and anthraquinones. Recently, focus on Shikimic Acid (SA) has increased since its appearance as a key precursor for the synthesis of drug against H5N1 virus. Present work quantifies shikimic acid from, different parts of clusiaceae species. RP-HPLC analysis showed M. suriga collected form Siddhapur with higher content of shikimic acid (47.19 mg/g). Similarly, leaves of all species showed highest content of SA than stem and fruits of species analyzed. Results revealed that the seasons had important role in accumulation of SA in M. suriga. While, young leaves showed highest accumulation of SA compared to old and different growth stages and sexuality of M. suriga does not affect SA content. Similarly, various method had less role in extraction of SA. The present investigation is the first comprehensive report on clusiaceae species with respect to shikimic acid and the findings are of considerable interest to design new bioproducts in pharmaceutical point of view and to provide suitable alternative source of SA to star anise.

New Case of False-Star-Grass (Chloris distichophylla) Population Evolving Glyphosate Resistance

Chloris distichophylla, suspected of glyphosate resistance (GR), was collected from areas of soybean cultivation in Rio Grande do Sul, Brazil. A comparison was made with a susceptible population (GS) to evaluate the resistance level, mechanisms involved, and control alternatives. Glyphosate doses required to reduce the dry weight (GR50) or cause a mortality rate of 50% (LD50) were around 5.1–3 times greater in the GR population than in the GS population. The shikimic acid accumulation was around 6.2-fold greater in GS plants than in GR plants. No metabolized glyphosate was found in either GR or GS plants. Both populations did not differ in the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) basal activity or in vitro inhibition of EPSPS activity by glyphosate (I50). The maximum glyphosate absorption was observed at 96 hours after treatment (HAT), which was twofold higher in the GS plants than in the GR plants. This confirms the first case of glyphosate resistance in C. distichophylla. In addition, at 96 HAT, the GS plants translocated more 14C-glyphosate than the GR ones. The best options for the chemical control of both C. distichophylla populations were clethodim, quizalofop, paraquat, glufosinate, tembotrione, diuron, and atrazine. The first case of glyphosate resistance in C. distichophylla was due to impaired uptake and translocation. Chemical control using multiple herbicides with different modes of action (MOA) could be a tool used for integrated weed management (IWM) programs.

Metabolic profiling of glyphosate-resistant sourgrass (Digitaria insularis)

AbstractPutative glyphosate-resistant sourgrass was collected to determine its resistance level and to evaluate its metabolic profile after resistance. Although accumulation of shikimic acid is known to occur in glyphosate-susceptible populations, differences in the ability of resistant (R) and susceptible (S) biotypes to accumulate quinic acid, salicylic acid, and aminomethylphosphonic acid (AMPA) have been studied to a lesser extent. Our objective was to confirm glyphosate resistance in sourgrass and to understand the metabolic profile of these plants in response to the herbicide. Greenhouse experiments were carried out from January 2016 to June 2018. There were no significant differences in glyphosate translocation in the plants. No metabolism of glyphosate to AMPA was observed; therefore, metabolism of glyphosate to AMPA is not a mechanism in R biotypes. S biotypes showed higher concentrations of shikimic acid and quinic acid before glyphosate and accumulated less of both secondary acids in treated leaves 72 h after glyphosate application. Resistant biotypes showed higher concentrations of salicylic acid before glyphosate application.