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Glyphosate: Uses Other Than in Glyphosate-Resistant Crops, Mode of Action, Degradation in Plants, and Effects on Non-target Plants and Agricultural Microbes
Abstract
Glyphosate is the most used herbicide globally. It is a unique non-selective herbicide with a mode of action that is ideal for vegetation management in both agricultural and non-agricultural settings. Its use was more than doubled by the introduction of transgenic, glyphosate-resistant (GR) crops. All of its phytotoxic effects are the result of inhibition of only 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), but inhibition of this single enzyme of the shikimate pathway results in multiple phytotoxicity effects, both upstream and downstream from EPSPS, including loss of plant defenses against pathogens. Degradation of glyphosate in plants and microbes is predominantly by a glyphosate oxidoreductase to produce aminomethylphosphonic acid and glyoxylate and to a lesser extent by a C-P lyase to produce sarcosine and phosphate. Its effects on non-target plant species are generally less than that of many other herbicides, as it is not volatile and is generally sprayed in larger droplet sizes with a relatively low propensity to drift and is inactivated by tight binding to most soils. Some microbes, including fungal plant pathogens, have glyphosate-sensitive EPSPS. Thus, glyphosate can benefit GR crops by its activity on some plant pathogens. On the other hand, glyphosate can adversely affect some microbes that are beneficial to agriculture, such as Bradyrhizobium species, although GR crop yield data indicate that such an effect has been minor. Effects of glyphosate on microbes of agricultural soils are generally minor and transient, with other agricultural practices having much stronger effects.
... Glyphosate (N-(phosphonomethyl) glycine, Gly) and glyphosate-based herbicides (GBHs) are the world's leading post-emergent, organophosphate, systemic, broad-spectrum, and nonselective herbicides for the control of both annual and perennial weeds [1]. As a systemic herbicide, Gly is readily translocated through the phloem to all parts of the plant, absorbed from the leaf surface into the cells, where it is translocated into the meristems of growing plants [1][2][3]. The effects of Gly are visible within two to seven days, depending on the type of weed; the primary mode of action is the blockade of the shikimate pathway, a pathway linking primary and secondary metabolism. ...
... The effects of Gly are visible within two to seven days, depending on the type of weed; the primary mode of action is the blockade of the shikimate pathway, a pathway linking primary and secondary metabolism. The target enzyme of glyphosate is 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), one of seven enzymes that catalyze a series of reactions, which begins with the reaction between shikimate-3-phosphate (S3P) and phosphoenolpyruvate (PEP) and leads to the formation of the chorismate, a precursor of the biosynthesis of the aromatic amino acids phenylalanine, tryptophan, and tyrosine [1][2][3]. By inhibiting the activity of EPSPS, Gly causes a deficiency in the production of essential substances necessary for organisms that contain EPSPS to survive and propagate [3]. ...
... The target enzyme of glyphosate is 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), one of seven enzymes that catalyze a series of reactions, which begins with the reaction between shikimate-3-phosphate (S3P) and phosphoenolpyruvate (PEP) and leads to the formation of the chorismate, a precursor of the biosynthesis of the aromatic amino acids phenylalanine, tryptophan, and tyrosine [1][2][3]. By inhibiting the activity of EPSPS, Gly causes a deficiency in the production of essential substances necessary for organisms that contain EPSPS to survive and propagate [3]. This pathway is absent in animals, and this explains the wide use of glyphosate in agriculture, which is considered safe for animals. ...
Simple Summary
The use of the herbicide glyphosate in agriculture exposes wildlife to this substance. In this review, data obtained using the lizard Podarcis siculus as an unconventional model organism were collected and analyzed. This is to answer the question of whether occasional exposure to glyphosate can endanger the reproductive health of terrestrial vertebrates, shifting the balance of agricultural ecosystems, in which these animals play an important role by feeding on phytopathogenic organisms. The results state that glyphosate affects the liver and gonads, inducing many morphological and molecular alterations and acting as an endocrine disruptor. The data also validate the common field lizard as a valuable model organism that can provide an assessment of the toxic effect of environmental contaminants. By sharing physiological processes and reproductive mechanisms with many other animals, both aquatic and terrestrial, the information gleaned from the lizard can be transferred to other vertebrates and can serve as a starting point for the recovery of endangered wildlife.
Abstract
Soil contaminants (herbicides, pesticides, and heavy metals) are among the main causes of change in terrestrial ecosystems. These substances lead to a general loss of biodiversity, both of flora and fauna and being able to biomagnify and pass through the food chain, they can endanger the survival of terrestrial vertebrates at the top of this chain. This review analyzes the risks associated with exposure to glyphosate, the active principle of many herbicide products, for the reproductive health of the field lizard (Podarcis siculus) potentially exposed to the substance in its natural habitat; therefore, introducing it as a possible model organism. Data demonstrate that glyphosate is toxic for this animal, affecting the health of the reproductive organs, both in males and females, and of the liver, the main detoxifying organ and closely involved in the female reproductive process. Sharing structural and functional characteristics of these organs with many other vertebrates, the information obtained with this reptile represents a wake-up call to consider when analyzing the cost/benefit ratio of glyphosate-based substances. The data clearly demonstrate that the P. siculus lizard can be considered a good target organism to study the reproductive risk assessment and hazards of exposure to soil contaminants on wild terrestrial vertebrates.
... This is not a well-researched claim, but a comprehensive study with effects of glyphosate on sudden death syndrome in GR soybeans [14] and another on the effects of glyphosate on Goss's wilt in GR maize [23] found no effects on the respective crop diseases. Several studies show that glyphosate can kill some plant pathogenic fungi in the GR crops that were reviewed in [24,25]. ...
... The content of glyphosate and aminomethylphosphonic acid (AMPA), the most common degradation product of glyphosate [25], in dried (65 • C for 7 days) grain was determined using a modification of a previously published method [27] and HPLC (Shimadzu, Kyoto, Japan) coupled to a triple quadrupole mass spectrometer (LS-MS/MS AB Sciex API 4500, Applied Biosystems, Foster City, CA, USA) with an electrospray ionization (ESI) source in the negative ionization mode to detect and quantify underivatized glyphosate and AMPA. One hundred mg of dried and powdered grain material was extracted for each sample. ...
... The content of glyphosate and aminomethylphosphonic acid (AMPA), the most common degradation product of glyphosate [25], in dried (65 °C for 7 days) grain was determined using a modification of a previously published method [27] and HPLC (Shimadzu, Kyoto, Japan) coupled to a triple quadrupole mass spectrometer (LS-MS/MS AB Sciex API 4500, Applied Biosystems, Foster City, CA, USA) with an electrospray ionization (ESI) source in the negative ionization mode to detect and quantify underivatized glyphosate and AMPA. One hundred mg of dried and powdered grain material was extracted for each sample. ...
Glyphosate-resistant (GR) maize is dominant in countries where it is grown. Significant, adverse effects of glyphosate application to GR maize have been reported, but few data from robust studies exist to determine if such effects are common. In this study, the effects of recommended application rates (single and sequential applications) were used on GR maize grown at two locations for one season and for two seasons in a third location. No significant effects of glyphosate on mineral content (N, P, K, Ca, Mg, S, Cu, Fe, Mn, and Zn) in leaves or grain, plant height, stem diameter, ear parameters, or yield were found at any location or in any growing season. Likewise, harvested grain quality, as determined by percent starch, protein, and total lipids, was unaffected by glyphosate treatment at any location. Neither glyphosate nor aminomethylphosphonic acid, the primary degradation product of glyphosate, were found in grain from any treatment at any location, except for 20 ng g−1 of glyphosate found in grain from one season at one location. These results support the view that recommended applications of glyphosate have no significant effects on growth, grain composition, mineral content, grain quality, nor yield of GR maize.
... Currently, bean breeding programs have developed early cycle cultivars; however, under ideal climatic conditions, early cycle cultivars produce less grains than normal cycle cultivars. [3] Normal cycle cultivars last from 90 to 100 days in field, while early cycle cultivars last from 60 to 75 days in field. Early cycle cultivars are dependent on cultural management to achieve high productive potential. ...
... Hormesis is defined as an adaptive response characterized by a biphasic dose response, consisting of a stimulatory effect with the use of low doses of a toxic compound and inhibition at high doses. [1,3,5] Glyphosate [C6H8NO5P; N-(phosphonomethyl)glycine] is an herbicide that acts by blocking the enzyme 5-enolpyruvyl chiquimate 3-phosphate synthase (EPSPs) and has a systemic and nonselective action. This blockade of the EPSPs leads to a reduction in aromatic amino acid production, which is essential to plants, causing an imbalance in carbon flow in the plant and can leads to death. ...
... It is the most widely used herbicide worldwide. [3] Glyphosate can be used in other ways besides herbicide, such as, weed control in nonagricultural situations, terminating cover crops, controlling weeds before cultivation, as a crop harvest aid, as sugarcane ripener and potential use as plant growth regulator. [3] The stimulatory effect of low glyphosate doses application was observed in dry weight of conventional soybean (Glycine max L.), maize (Zea mays), eucalyptus (Eucalptus sp.), pine (Pinus caribea L.) and Commelina benghalensis [5] , in the height and dry matter of sugarcane [6,7] , Brachiaria brizantha cv. ...
Glyphosate applied at low doses can stimulate photosynthesis and yield. The objective of this study was to evaluate the application of low doses of glyphosate and sowing seasons in physiological characteristics and grain yield of common bean of early cycle. Two experiments were conducted in the field, the first in winter season and the second in wet season. The experimental design was a randomized complete block design, consisting of five and seven low doses of glyphosate and one period of application, with four replications. Glyphosate low dose of 108.0 g a.e. ha-1 impaired net CO2 assimilation rate, stomatal conductance, transpiration rate, instantaneous carboxylation efficiency, number of pods per plant, number of grains per plant and number of grains per pod. Glyphosate dose of 7.2 g a.e. ha-1 provided a 23% increase in grain yield in winter season, and the dose of 36.0 g a.e. ha-1 provided a 109% increase in grain yield in wet season. To our knowledge, this is the first report on effect of glyphosate at low doses and sowing season to obtain yield increases in common bean of early cycle.
... A number of research studies have focussed on the potential accumulation of glyphosate residues, because the rapid increase in glyphosate use of over the past two decades (Benbrook, 2016) has led to concerns of 'pseudopersistence' as the frequency of use exceeds its rate of degradation in soil (Primost et al., 2017). There are also related concerns about the impact of glyphosate on soil organisms and functions Nguyen et al., 2016); the presence of glyphosate in harvested products (Bøhn et al., 2014); transport in spray drift (Cederlund, 2017) and wind-eroded dust (Bento et al., 2017) and other potential offsite impacts (as critically discussed in Duke, 2020). The occurrence and magnitude of glyphosate residues in soils have been reported in studies in the EU (Silva et al., 2018), the USA (Battaglin et al., 2014) and Argentina (Peruzzo et al., 2008;Aparicio et al., 2013;Primost et al., 2017). ...
... Thus, the low concentrations reported in the EU study from the 0-15/20 cm layer (Silva et al., 2018) would likely have been higher had the samples been sampled at 0-5 cm or 0-10 cm depth. Notably, in Australian grain cropping systems, the majority of glyphosate is applied as a summer fallow spray and presowing knockdown (Harries et al., 2020), rather than in-crop use on glyphosate-tolerant crops as occurs elsewhere in the world (Duke, 2020). Application to dry, microbiologically inactive soil, along with strong adsorption, would tend to enhance the known persistence of glyphosate and AMPA in agricultural soils (Vereecken, 2005;Borggaard and Gimsing, 2008). ...
... Despite the frequent detection of glyphosate and AMPA at concentrations greater than other herbicide residues, no reliable, objective assessment could be made regarding the potential effect of glyphosate and AMPA on crop growth due to insufficient dose-response data. This may be because glyphosate is assumed to strongly adsorb to soil and is widely considered to be 'inactivated' and unavailable to crops (Duke, 2020). Indeed, Blackshaw and Harker (2016) found that the minimum glyphosate concentration causing 20% biomass reduction of wheat, canola or field pea was 80 mg kg −1 in two different soils, and the minimum AMPA toxicity threshold concentration was 20 mg kg −1 . ...
Herbicides are used extensively in Australian grain cropping systems. Despite occasional observations of herbicide-induced phytotoxicity, there is little information on the persistence and carryover of multiple herbicide classes in cropping soils and the risk to subsequent crops. Two soil surveys were conducted in 2015 (n = 40) and 2016 (n = 42) across different Australian grain cropping fields prior to sowing of winter crops, and soil samples analysed for herbicide residues (16 analytes in 2015 and 22 analytes in 2016). Samples in 2015 were taken at two depth (0–10 cm and 10-30 cm), whilst samples in 2016 were taken in topsoil (0–10 cm) only, but from two discrete locations in each field. Our research in both years found at least one herbicide (or herbicide metabolite) residue at all sites, with a median of 6 analytes detected in 2015 and 7 analytes detected in 2016. The most frequently detected residues were glyphosate and its primary breakdown product aminomethylphosphonic acid (AMPA), in 87 and 100%, respectively, of topsoil (0–10 cm) samples in 2015, and 67 and 93% of samples in 2016. The median concentration of glyphosate in 2015 was 0.12 mg kg⁻¹, while AMPA was 0.41 mg kg⁻¹. In 2016, median concentrations of glyphosate and AMPA were 0.22 mg kg⁻¹ and 0.31 mg kg⁻¹. Residues of 2,4-dichlorophenoxyacetic acid, trifluralin and diflufenican were also detected in >40% of topsoil samples in both seasons, but with median concentrations of <0.05 mg kg⁻¹. A literature review found limited availability of phytotoxicity thresholds for major grain crops exposed to soilborne herbicide residues. A risk assessment using available thresholds suggested that although up to 29% of fields contained trifluralin residues that could constrain cereal crop growth, and 24% of fields contained residues of phenoxy or sulfonylureas that could affect dicotyledonous crops, the majority of these fields when planted with tolerant crops would be unlikely to be affected by herbicide residues. More work is required to ascertain the spatial distribution, bioavailability and phytotoxicity of residues and residue mixtures to enable a more accurate agronomic risk assessment.
... Hormesis occurred in more than 50% of the evaluated dose-response curves for acifluorfen and terbuthylazine and in over 70% of the curves for glyphosate and metsulfuron-methyl, suggesting the frequent occurrence of herbicideinduced hormesis in plants for the first time (Cedergreen et al., 2007). Glyphosate, the world's most used herbicide, widely induces hormesis in various plant species, with low doses increasing photosynthesis and stomatal conductance, inducing the accumulation of shikimic acid, enhancing growth and seed yields, 4 and shortening the life cycle (Brito et al., 2018), potentially playing a role in the evolution of plant resistance to herbicides (Duke, 2020;Duke, 2021;Belz and Duke, 2017). Paraquat but also 2,4dichlorophenoxyacetic acid (2,4-D) applied alone or in combination with other chemicals also induce hormesis in higher plants, algae, and macrophytes (Jalal et al., 2021;Agathokleous et al., 2019b). ...
... Conversely to the target of herbicide application to inhibit growth, sub-NOAEL doses of herbicides stimulate growth, and the sub-NOAEL stimulation is commonly in the range 20-30% and barely above 60% in the above mentioned studies. Another important suggestion of this abundant literature is that herbicide-resistant plants may exhibit hormesis at considerably higher doses than non-herbicide-resistant or herbicide-susceptible plants because the dose-response curves shift to larger doses (Fig. 7), e.g. by a factor of approximately 50 for glyphosate (Duke, 2021). ...
... This passing down of hormetic traits to the next generation suggests that agendas targeting to eliminate and control enhanced pathogenicity explosions due to low-dose exposure should target the multiple generations too. The current scientific base shows that hormetic responses start at much smaller doses in susceptible isolates/strains than in resistant ones (Agathokleous and Calabrese, 2021;Hu et al., 2021), which is in line with findings from herbicides-plants experiments (Duke, 2021;Anunciato et al., 2022). ...
Increasing amounts of silver iodide (AgI) in the environment are expected because of the recent massive expansion of weather modification programs. Concurrently, pharmaceuticals, microplastics, hydrocarbons, and pesticides in terrestrial ecosystems continue contaminating forests and agroforests. Our review supports that AgI induces hormesis, a biphasic dose response characterized by often beneficial low-dose responses and toxic high-dose effects, which adds to the evidence for pharmaceuticals, microplastics, hydrocarbons, and pesticides induced hormesis in numerous species. Doses smaller than the no-observed-adverse-effect-level (NOAEL) positively affect defense physiology, growth, biomass, yields, survival, lifespan, and reproduction. They also lead to negative or undesirable outcomes, including stimulation of pathogenic microbes, pest insects, and weeds with enhanced resistance to drugs and potential negative multi- or trans-generational effects. Such sub-NOAEL effects perplex terrestrial ecosystems managements and may compromise combating outbreaks of disease vectors that can threaten not only forest and agroforestry health but also sensitive human subpopulations living in remote forested areas.
... An active substance can act on one or more metabolic pathways which are characterized by phytotoxic effects. Conventional herbicides can affect multiple processes, such as photosynthesis, biosynthesis of amino acids or the intracellular redox potential of targeted plants [20,21]. ...
... This results in multiple phytotoxic effects of which the inhibition of the biosynthesis of aromatic amino acids (shikimate pathway) is the most important. Thereby, as only transgenic glyphosate-resistant crops are not affected, this is a non-selective effect [21]. Another molecule, metribuzin, is a preand post-emergent selective herbicide (against a range of di-and monocot weeds) which inhibits photosynthesis at the level of Hill's reaction, blocking electron transport, leading to lipid and chlorophyll photooxidation [23]. ...
... Another molecule, metribuzin, is a preand post-emergent selective herbicide (against a range of di-and monocot weeds) which inhibits photosynthesis at the level of Hill's reaction, blocking electron transport, leading to lipid and chlorophyll photooxidation [23]. Some sulfonylureas, including rimsulfuron, are selective herbicides that affect the biosynthesis of branched-chain amino acids by influencing the enzyme acetolactate synthase [21]. ...
In recent years, the development of new bio-based products for biocontrol has been gaining importance as it contributes to reducing the use of synthetic herbicides in agriculture. Conventional herbicides (i.e., the ones with synthetic molecules) can lead to adverse effects such as human diseases (cancers, neurodegenerative diseases, reproductive perturbations, etc.) but also to disturbing the environment because of their drift in the air, transport throughout aquatic systems and persistence across different environments. The use of natural molecules seems to be a very good alternative for maintaining productive agriculture but without the negative side effects of synthetic herb-icides. In this context, essential oils and their components are increasingly studied in order to produce several categories of biopesticides thanks to their well-known biocidal activities. However, these molecules can also be potentially hazardous to humans and the environment. This article reviews the state of the literature and regulations with regard to the potential risks related to the use of essential oils as bioherbicides in agricultural and horticultural applications.
... 22 It can be taken up by roots of different crop species, such as maize, beets, rapeseed, cotton, and barley, with 2-6% of the applied GLY being absorbed by roots within 6-24 h aer application. 11,23 The enzyme EPSPS, found in plant plastids, facilitates the transfer of the enolpyruvyl group from phosphoenolpyruvate (PEP) to 5-hydroxyl shikimate-3-phosphate, resulting in 5-enolpyruvylshikimate-3-phosphate (EPSP). Upon application to crops, it binds to the enzyme EPSPS and inhibits its functions, as shown in Fig. 2, resulting in hindered plant growth. ...
... Upon application to crops, it binds to the enzyme EPSPS and inhibits its functions, as shown in Fig. 2, resulting in hindered plant growth. 8,23 The manufacturing of GBHs involves mixing GLY with different formulations to stabilize the active ingredient and enhance its penetration into plant parts. 24 5. Examining the risks and consequences to health and the environment ...
Glyphosate (GLY), a versatile herbicide with several applications, has become quite popular for controlling weed growth in residential, commercial, and agricultural settings. Its widespread acceptance has been facilitated by its effectiveness and low cost. However, overuse and improper application of GLY have become an urgent concern, raising questions about potential harm to human health and environmental sustainability. Studies have revealed that GLY exhibits toxic properties that can lead to detrimental consequences for human well-being. These include the potential to induce cancer, contribute to birth defects, and disrupt reproductive functions. Moreover, when exposed to non-target organisms, GLY has been found to inflict adverse impacts on various forms of aquatic life, insects, and essential soil microorganisms. Because of its great solubility and low quantities in soil and water, GLY detection is a difficult process. In response to the concerns surrounding GLY, several detection techniques have been devised, encompassing chromatography, immunoassays, and mass spectrometry. These methods play a crucial role in investigating the ramifications associated with GLY application in agriculture and the environment. The study also emphasizes the need for continued research to fully understand the long-term effects of GLY exposure on human health and the environment.
... An overall decreasing trend was observed for leaf biomass (Table 1), which showed a 47.3 % decrease at 100 mg L −1 levofloxacin (2.21 g DW plant −1 ), compared to the control (4.19 g DW plant −1 ). It has been described that the stimulatory response in a single plant trait does not essentially correlate with the response in the other plant traits (Duke, 2020) and this seems to relate to the endpoints determined on roots and leaves in the present study. ...
... Plants treated with the mixture comprising 20 mg L −1 of each antibiotic exhibited a significant increase, with the highest values of root, shoot, leaves, and pods biomass and the number of pods compared to the control (Table 1). The lower doses of some herbicides and abiotic stressors may favour the hormetic effect by stimulating the morphology and growth of plants (Duke, 2020) which protects plants from stress by improving their tolerance to unfavorable conditions and helping them to survive as well as maintain biomass production (Agathokleous and Calabrese, 2020). The higher toxicity of antibiotic mixtures to plants at lower concentrations reported by Riaz et al. (2017) is probably due to one-time application, which probably overstated the effects observed in the field conditions. ...
Excessive use and release of antibiotics into the soil environment in the developing world have resulted in altered soil processes affecting terrestrial organisms and posing a serious threat to crop growth and productivity. The present study investigated the influence of exogenously applied oxytetracycline (OXY) and levofloxacin (LEV) on plant physiological responses, key enzymes involved in nitrogen metabolism (e.g., nitrate reductase, glutamine synthetase), nitrogen contents and oxidative stress response of mung bean (Vigna radiata). Plants were irrigated weekly with antibiotics containing water for exposing the plants to different concentrations i.e., 1, 10, 20, 50, and 100 mg L-1. Results showed a significant decrease in nitrate reductase activity in both antibiotic treatments and their mixtures and increased antioxidant enzymatic activities in plants. At lower concentrations of antibiotics (≤20 mg L-1), 53.9 % to 78.4 % increase in nitrogen content was observed in levofloxacin and mixtures compared to the control, resulting in an increase in the overall plant biomass. Higher antibiotic (≥50 mg L-1) concentration showed 58 % decrease in plant biomass content and an overall decrease in plant nitrogen content upon exposure to the mixtures. This was further complemented by 22 % to 42 % increase in glutamine synthetase activity observed in the plants treated with levofloxacin and mixtures. The application of low doses of antibiotics throughout the experiments resulted in lower toxicity symptoms in the plants. However, significantly higher malondialdehyde (MDA) concentrations at higher doses (20 mg L-1 and above) than the control showed that plants' tolerance against oxidative stress was conceded with increasing antibiotic concentrations. The toxicity trend was levofloxacin > mixture > oxytetracycline.
... however, when the details of low-dose effects in doseresponse curves for herbicides are properly determined, hormesis is often found [4,5]. The most used herbicide worldwide is glyphosate [6], and hormesis seems more common and of greater magnitude with this herbicide than most others [7,8]. Unlike other herbicides, every known mechanism of resistance has been reported for glyphosate [9,10]. ...
... Unlike other herbicides, every known mechanism of resistance has been reported for glyphosate [9,10]. Since the review by Duke [8] covering glyphosate hormesis, there have been more papers on this topic [e.g. [11]]. ...
Hormesis is a common response of both herbicide-susceptible and -resistant plants to herbicides. Herbicide resistance in weeds is rapidly evolving, and, although little studied, there is growing evidence that hormesis plays a role in the changes in sensitivity of weed populations to herbicides. This can occur in susceptible weed populations in which hormesis favors a subpopulation of more vigorous plants. At recommended application doses for weed control, a hormetic dose is likely to favorably influence a significant proportion of the herbicide-resistant weeds, enhancing their propagation and spread.
... The herbicide glyphosate, (CAS# 1071-83-6 [N-(phosphonomethyl)glycine] Fig. 1), has been on the market since the mid-1970s and is one of the most widely used pesticides in the world (Duke 2018(Duke , 2020. The widespread agricultural and "The data do not support IARC's conclusion that glyphosate is a 'probable human carcinogen' and, consistent with previous regulatory assessments, further concluded that glyphosate is unlikely to pose a carcinogenic risk to humans" (Williams et al. , 2018 and related papers in the same issue of the journal. ...
... Glyphosate is systemic and, after penetration into the leaf, it is translocated to other parts of the plant. This property allows GBHs to be used pre-plant for field preparation or for early post-plant weed control before the seedlings emerge in a large range of crops (Duke 2020). This sorption to soils and sediments results in rapid dissipation of glyphosate in natural waters such that exposures are usually short enough that much larger concentrations are required to elicit toxicity than in the absence of sediments (also see Sect. ...
The chemical and biological properties of glyphosate are key to understanding its fate in the environment and potential risks to non-target organisms. Glyphosate is polar and water soluble and therefore does not bioaccumulate, biomagnify, or accumulate to high levels in the environment. It sorbs strongly to particles in soil and sediments and this reduces bioavailability so that exposures to non-target organisms in the environment are acute and decrease with half-lives in the order of hours to a few days. The target site for glyphosate is not known to be expressed in animals, which reduces the probability of toxicity and small risks. Technical glyphosate (acid or salts) is of low to moderate toxicity; however, when mixed with some formulants such as polyoxyethylene amines (POEAs), toxicity to aquatic animals increases about 15-fold on average. However, glyphosate and the formulants have different fates in the environment and they do not necessarily co-occur. Therefore, toxicity tests on formulated products in scenarios where they would not be used are unrealistic and of limited use for assessment of risk. Concentrations of glyphosate in surface water are generally low with minimal risk to aquatic organisms, including plants. Toxicity and risks to non-target terrestrial organisms other than plants treated directly are low and risks to terrestrial invertebrates and microbial processes in soil are very small. Formulations containing POEAs are not labeled for use over water but, because POEA rapidly partitions into sediment, risks to aquatic organisms from accidental over-sprays are reduced in shallow water bodies. We conclude that use of formulations of glyphosate under good agricultural practices presents a de minimis risk of direct and indirect adverse effects in non-target organisms.
... Herbicides are considered essential to maintain agricultural production, but a number of issues related to their use can be mentioned. These can include the following problems: • Residues from the use of herbicides persist in the environment (van der Werf, 1996;Vassilev & Kambourova, 2006;Edwards, 2013;Mahmood et al., 2016;Carvalho, 2017;Bilal et al., 2019) and destroy non-target plants and beneficial insects (Serrão et al., 2022;Duke, 2021), • They cause health effects in animals and humans. There is overwhelming evidence of an association between pesticide exposure and an increased incidence of chronic diseases such as various types of cancer, diabetes, neurodegenerative diseases, birth defects, and reproductive disorders (Mostafalou & Abdollahi, 2013;Blair et al., 2015;Cocco, 2016;Özkara et al., 2016;Shah, 2020;Pathak et al., 2022;Singh et al., 2022). ...
The article aims to evaluate – from the point of view of selected socio-economic aspects – the implementation of an innovative weed control technology into agricultural practice using laser energy targeted at reducing pesticide use. The achievement of the stated objective required an analysis of the research output concerning the problem of pesticide sustainability in European Union agriculture and an analysis of EU policies in this field. The paper also utilises data obtained through research by conducting in-depth interviews with representatives of three stakeholder groups: farmers, society and business. The subject of the interviews was to assess the impact of large-scale dissemination of an innovative weed control technology on selected socio-economic aspects. The article is one of the first studies to assess the social impact of innovative technologies using artificial intelligence and laser technology for weed control in agriculture. The implementation of this technology can have a significant impact on running farms in a more sustainable way, but a prerequisite for its successful use is the inclusion of social and economic considerations.
... It was estimated recently that between 600 and 750 thousand tons of glyphosate were applied to crops globally in 2020, a figure that is projected to increase to up to 920 thousand tones by 2025 (Maggi et al., 2020). Glyphosate is a broad-spectrum, post-emergence, non-selective herbicide which acts by inhibiting 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), a key enzyme in the shikimate pathway needed by plants to synthesize aromatic amino acids essential for their growth and survival (Duke, 2021;Duke and Powles, 2008). ...
Glyphosate is the world's most widely applied herbicide. Despite its extensive and heavy use in agriculture and forestry, the microbial key players involved in glyphosate breakdown and the impact of this compound on the soil microbiota including fungi is not fully understood. Here, we used microcosm experiments to determine the impact of glyphosate application on the microbial community structure and abundance of four different agricultural soils from the Ammer valley, Germany, with a history of glyphosate application. We identified putative glyphosate degraders that could be active under in-situ conditions. Glyphosate was applied to the soils in a single dose of 15 mg⋅kg − 1 , which were incubated in the dark with 60 % water-filled pore space at 20 • C for 56 days. Soil samples were taken on the day of glyphosate addition (day 0) and after 7, 28 and 56 days. Capillary electrophoresis-mass spectrometry was used to quantify glyphosate and its major transformation product ami-nomethylphosphonic acid. Changes in the microbial community structure and abundance were evaluated using 16S rRNA gene or internal transcribed spacer region amplicon sequencing and qPCR. Our findings demonstrate that glyphosate was rapidly degraded in the four soils, with 60-85 % of the applied glyphosate disappearing within 7 days. However, the observed impact of glyphosate application on the microbial community composition was minimal and, notably, there was no significant time-dependent glyphosate effect at 7 days across all four soils. This suggests that glyphosate degradation in soil might be a concerted effort by a wide microbial network or it might be occurring co-metabolically. In addition, the sorption/desorption dynamics of glyphosate with the soil matrix can heavily influence its bioavailability, further reasoning the subtle effects observed on the microbial community structure.
... While non-chemical methods like mowing between rows are employed (Zaidan et al., 2022), herbicides, mainly glyphosate, are the primary choice for in-row weed management (Ronchi, Silva, 2018). Glyphosate, a non-selective systemic herbicide, stands out for its ability to control both broadleaf and narrowleaf species, its relatively low toxicity, and favorable cost-effectiveness (Costa et al., 2021;Duke, 2021). To maintain sustainable practices, the Global Coffee Platform of Brazil (GCP-Brazil) established a limit of three glyphosate applications annually: the first after the onset of the rainy season in October, the second in November-December, and the third in March (Global Coffee Platform Brazil, 2020). ...
Farmers often use glyphosate for cost-effective land clearance to streamline coffee harvest processes despite recommendations against its application near the harvest period. However, as set by national and international regulatory authorities, this practice poses a high risk of exceeding the maximum residue limit (MRL) for glyphosate in coffee beans. In this study, glyphosate residues in green coffee beans were assessed, considering different herbicide application methods (mechanical or manual), nozzles (hooded or unhooded), application volumes, and ripening stages. Coffee beans were collected between 15 to 60 days before harvest, and glyphosate residues were determined by high efficiency liquid chromatography and mass spectrometry (LC-MS/MS). Mechanical and manual applications using a protective spray bar device, avoiding the lower third of the coffee trees, maintained glyphosate residue levels within the MRLs established by Brazilian (1.0 mg kg–1) and European (0.1 mg kg–1) regulatory authorities. In contrast, applying glyphosate with the TK-VS-02 nozzle (high-flow impact) without a protective device resulted in levels below the Brazilian MRL but exceeded importing countries’ requirements. These residue levels persisted even when applications occurred outside the recommended rainy season but within the 15-day minimum safe re-entry interval. Applications using TK-VS-02 or AI11002 (low-flow air-induced) nozzles targeting the lower third of trees resulted in high glyphosate residue levels, surpassing national and international MRLs, even when applications were conducted 60 days before coffee harvest. These findings emphasize the importance of employing the right application technology to produce coffee that complies with the MRLs of any regulatory authority.
... 14 The NPQ reaction has been proposed to play a key role in plant hormesis, yet the detailed mechanism remains unclear. 15,16 Glyphosate [N-(phosphonomethyl)glycine; chemical structure shown in Fig. S1] is a slow-acting, systemic, nonselective, postemergence herbicide that targets the enzyme 5-enolpryuvylchiquime-3-phosphate synthase (EPSPS) of the shikimate pathway, 17,18 inducing high levels of shikimate acid accumulation and inhibiting the biosynthesis of essential aromatic amino acids for plant growth and development. 19 In addition to herbicidal applications, low doses of glyphosate that stimulate plant growth have become a considerable research topic. ...
Background
Glyphosate is the most widely applied herbicide in the world. Hormesis caused by low glyphosate doses has been widely documented in many plant species. However, the specific adaptative mechanism of plants responding to glyphosate hormesis stimulation remains unclear. This study focused on the biphasic relationship between glyphosate dose and tomato plant growth, and how glyphosate hormesis stimulates plant growth and enhances tolerance to environmental stress.
Results
We constructed a hormesis model to describe the biphasic relationship with a maximal stimulation (MAX) of 162% above control by glyphosate at 0.063 g ha⁻¹. Low‐dose glyphosate increased photosynthetic pigment contents and improve photosynthetic efficiency, leading to plant growth stimulation. We also found that glyphosate hormesis enhanced plant tolerance to diuron (DCMU; a representative photosynthesis inhibitor) by triggering the nonphotochemical chlorophyll fluorescence quenching (NPQ) reaction to dissipate excess energy stress from photosystem II (PSII). Transcriptomic analysis and quantitative real‐time polymerase chain reaction results revealed that the photosynthesis–antenna proteins pathway was the most sensitive to glyphosate hormesis, and PsbS (encoding photosystem II subunit S), ZEP (encoding zeaxanthin epoxidase) and VDE (encoding violaxanthin de‐epoxidase) involved in NPQ played crucial roles in the plant response to glyphosate hormesis.
Conclusion
These results provide novel insights into the mechanisms of plant hormesis and is meaningful to the application of glyphosate hormesis in agriculture. © 2024 Society of Chemical Industry.
... Glyphosate inhibits EPSPS in the shikimic acid pathway, preventing the production of aromatic amino acids and their derivatives such as flavonoids, lignin, indole acetic acid, and plastoquinone (Maeda and Dudareva, 2012). In addition, glyphosate deregulates carbon flow of other essential metabolic pathways (Orcaray et al., 2012;Duke, 2021). Due to the complexity of the effects of EPSPS inhibition by glyphosate, it is important to study all of the biochemical, physiological, and morphological effects caused by this herbicide in plants, such as hormesis (Velini et al., 2008;Brito et al., 2018). ...
Low glyphosate doses that produce hormesis may alter the susceptibility to herbicides of weeds or enhance their propagation and dispersal. The objective of this work was to evaluate the hormetic effects of glyphosate on the vegetative, phenological and reproductive development in resistant (R) and susceptible (S) Conyza sumatrensis biotypes. The glyphosate resistance level of biotype R was 11.2-fold compared to the S biotype. Glyphosate doses <11.25 g ae ha −1 induced temporary and permanent hormetic effects for the number of leaves, plant height and dry mass accumulation up to 28 d after application in both R and S biotypes. The S biotype required 15-19% fewer thermal units at 1.4 and 2.8 g ae ha −1 glyphosate than untreated plants to reach the bolting stage. Also, this biotype had less thermal units associated with the appearance (1225 vs 1408 units) and opening (1520 vs 1765 units) of the first capitulum than the R biotype. In addition, glyphosate affected reproductive traits of both bio-types compared to their controls, increasing the number of capitulum's and seeds per plant up to 37 and 41% (at 2.8 and 0.7 g ae h −1 , respectively) in the S biotype, and by 48 and 114% (both at 5.6 g ae ha −1) in the R biotype. Depending on environmental parameters, glyphosate may or may not cause hormetic effects on the vegetative and phenological development of C. sumatrenis biotypes; however, this herbicide increases the speed and fecun-dity of reproduction, regardless of the glyphosate susceptibility level, which can alter the population dynamics and glyphosate susceptibility of future generations.
... Brazil has attained global leadership in grain production, primarily attributed to the swift adoption and expansion of areas cultivated with genetic modified (GM) crops resistant to herbicides, notably glyphosate (Alcántara-de la Cruz et al., 2020). Glyphosate, a broad-spectrum herbicide, functions by inhibiting 5-enolpyruvylshikimate-3-phosphate synthetase (EPSPS) in the metabolic pathway of shikimic acid, disrupting the biosynthesis of tryptophan, phenylalanine and tyrosineessential precursors of products such as lignin, alkaloids, flavonoids and benzoic acids (Duke, 2018(Duke, , 2021. In GM cultivars of glyphosateresistant (GR) crops, resistance is conferred by the cp4epsps, 2mepsps or mepsps genes from Agrobacterium spp., that produce insensitive isoforms of the EPSPS (Green, 2009(Green, , 2018. ...
Glyphosate hormesis, identified as a potential means to enhance crop yields, encounters practical constraints because it is typically assessed through foliar applications. The expression and extend of hormesis in this approach are influenced by unpredictable environmental conditions, highlighting the need to explore alternative glyphosate application methods, such as seed treatment. This study aimed to assess glyphosate hormesis on growth rates and biomass accumulation in seedlings soybean cultivars. Two dose-response experiments [doses from 0 to 2880 g acid equivalent (ae) ha−1], one via foliar and one via seed, were conducted on three soybean cultivars [one non-glyphosate-resistant (NGR) and two glyphosate-resistant (GR, one RR and one RR2)]. In a subsequent experiment, three safe glyphosate doses (0, 90 and 180 g ae ha−1) applied via seed were evaluated on four soybean cultivars (two RR and two RR2). For foliar applications, the range of glyphosate doses increasing growth rates and dry biomass by 12–28 % were 5.6–45 g ae ha−1 for the NGR cultivar, of 45–720 g ae ha−1 for RR and of 11.25–180 g ae ha−1 for RR2. In the seed treatment, biomass increases of 16–60 % occurred at 45–180 g ae ha−1 for the NGR and RR cultivars, and 90–360 g ae ha−1 for RR2. Glyphosate doses of 90 and 180 g ae ha−1, applied via seeds, provided greater growth and biomass accumulation for the RR and RR2 soybean cultivars. Both foliar and seed applications of glyphosate increased growth and biomass accumulation in soybean cultivars, with seed treatments showing greater and more consistent enhancements. These findings propose practical and viable alternative for harnessing glyphosate hormesis to facilitate the early development of soybeans and potentially enhance crop yield.
... The main advantages are the lower cost of glyphosate compared to other herbicides and the broad-spectrum, killing most types of plants (Kanissery et al., 2019). Glyphosate blocks the activity of the enzyme 5-enolpyruvylshikimate-3phosphate synthase (EPSPS), interfering with the biosynthesis of important amino acids in susceptible plants (Duke, 2021). However, symbiont bacteria, which possess the EPSPS enzyme can be affected by glyphosate (De María et al., 2006). ...
O glifosato é o principal herbicida aplicado em pós-emergência na soja GM. Pesquisas anteriores mostraram que o glifosato pode afetar o número e a massa de nódulos que afetam o rendimento. No entanto, com o uso de técnicas para aumentar a nodulação, o efeito do glifosato na produtividade da soja GM pode ser diminuído. O objetivo foi avaliar a nodulação e a produtividade da soja GM em função das aplicações de glifosato e coinoculação. Quatro experimentos foram realizados em uma área com histórico de coinoculação. Os tratamentos com glifosato incluíram: dessecação 10 dias antes da semeadura mais uma aplicação em pós-emergência, dessecação 10 dias antes da semeadura mais duas aplicações em pós-emergência, uma aplicação em pós-emergência, duas aplicações em pós-emergência e controle realizado mecanicamente. Os tratamentos de inoculação envolveram três tipos: coinoculação, inoculação e sem inoculação. As aplicações de glifosato reduziram a nodulação em apenas um dos quatro experimentos. A coinoculação aumentou o número de nódulos e o peso seco em 105 e 168, respectivamente, em um experimento da safra 2018/19, em comparação ao sem inoculação. Neste estudo, as aplicações de glifosato alteraram a nodulação, mas não influenciaram na produtividade de grãos.
... [110][111][112] Nevertheless, the agriculture system is a complex of multiple biotic and abiotic factors and some agricultural practices may have strong effects on the microbes of agricultural soils. 113 Thus, it is essential to evaluate the comprehensive control efficacy on late blight when combining the biological control with other pest management strategies. ...
Phytophthora infestans causes late blight on potatoes and tomatoes, which has a significant economic impact on agriculture. The management of late blight has been largely dependent on the application of synthetic fungicides, which is not an ultimate solution for sustainable agriculture and environmental safety. Biocontrol strategies are expected to be alternative methods to the conventional chemicals in controlling plant diseases in the integrated pest management (IPM) programs. Well‐studied biocontrol agents against Phytophthora infestans include fungi, oomycetes, bacteria, and compounds produced by these antagonists, in addition to certain bioactive metabolites produced by plants. Laboratory and glasshouse experiments suggest a potential for using biocontrol in practical late blight disease management. However, the transition of biocontrol to field applications is problematic for the moment, due to low and variable efficacies. In this review, we provide a comprehensive summary on these biocontrol strategies and the underlying corresponding mechanisms. To give a more intuitive understanding of the promising biocontrol agents against Phytophthora infestans in agricultural systems, we discuss the utilizations, modes of action and future potentials of these antagonists based on their taxonomic classifications. To achieve a goal of best possible results produced by biocontrol agents, it is suggested to work on field trials, strain modifications, formulations, regulations, and optimizations of application. Combined biocontrol agents having different modes of action or biological adaptation traits may be used to strengthen the biocontrol efficacy. More importantly, biological control agents should be applied in the coordination of other existing and forthcoming methods in the IPM programs. © 2023 Society of Chemical Industry.
... Usually, its effects on non-target plants are smaller in comparison to those of many other herbicides, owing to its composition, application methods and strong binding to most soils, which ultimately inactivate it. Still, there may be varied actions on pathogens, e.g., promoting disease control or even changing virulence [34]. ...
The seed yield of guarana (Paullinia cupana H.B.K. var. sorbilis) is affected by weeds. Management is difficult for Amazon farmers and ranchers, owing to the hot and humid climate prevailing in the region, which makes mechanical control inefficient and leads farmers to the decision to use herbicides. Herbicide damage to this species is unknown. The objective of this study was to evaluate glyphosate damage to the development and quality of guarana seedlings. The treatments consisted of glyphosate doses at concentrations of 0, 126, 252, 540, 1080, 2160 and 3240 g a.e. ha-1 and were evaluated for 60 days, in two applications. Analyses were performed for biometrics, seedling development, anthracnose and Injury characteristics. Glyphosate caused symptoms of Injury in all doses applied, but lower doses did not interfere with seedling growth and development. There was a correlation between anthracnose severity and increased glyphosate dose. When applied correctly, glyphosate can be an integrated weed management tool for use in guarana crops.
... [1,2] The use of low doses of compounds, that are toxic at high doses, such as glyphosate, to achieve a stimulatory effect is known as hormesis, which consists of an adaptive response characterized by a biphasic dose response. [7][8][9] Crop production is reduced due to environmental changes, such as drought and high temperatures, and at the same time, population growth increases the demand for food, so it is necessary to search for resources that increase crop productivity in different environments. [8] One of this resources may be hormesis. ...
Glyphosate application, even in low doses, changes the metabolism of crops. This research aimed to evaluate the effects of glyphosate low doses and sowing season on metabolic changes of early-cycle common beans. Two experiments were conducted in the field, one in the winter season and one in the wet season. The experimental design was a randomized complete block design consisting of the application of glyphosate low doses [0.0, 1.8, 7.2, 12.0, 36.0, 54.0, and 108.0 g acid equivalent (a.e.) ha-1] in the phenological stage V4 with four replications. In the winter season, glyphosate and shikimic acid were increased five days after the application of treatments. In contrast, the same compounds increased only at doses of 36 g a.e. ha-1 and above in the wet season. The dose of 7.2 g a.e. ha-1 increased phenylalanine ammonia-lyase and benzoic acid in the winter season. The doses of 54 and 108 g a.e. ha-1 increased benzoic acid, caffeic acid, and salicylic acid. Our study indicated that glyphosate low doses increase the concentration of shikimic, benzoic, salicylic and caffeic acid, PAL and tyrosine. There was no reduction in aromatic amino acids and in secondary compounds from the shikimic acid pathway.
... 23 This effect was attributed to a decrease in leaf concentration caused by the dilution or rapid metabolism and breakdown of molecules in the growing plant tissues, which then reached a non-inhibitory level. 23,[33][34][35] This may also be the case for the commercial Gly + 2,4-D mixture. For ASR in previously conducted work, glyphosate showed control activity for up to 14 days after application (DAA), 22 for between 21 and 35 DAA with wheat rust, 33 and for up to 10 DAA for alfalfa rust, when applied at the recommended dose. ...
BACKGROUND
Transgenic event DAS44406‐6 (E3) makes soybeans that are herbicide [glyphosate (Gly), 2,4‐dichlorophenoxyacetic acid (2,4‐D) and glufosinate] and caterpillar resistant. The E3 soybean was commercially released for the 2021/2022 harvest in Brazil. We conducted this study to test whether Gly and 2,4‐D applied alone and in a commercial mixture affect Asian soybean rust (ASR). Assays were conducted in detached leaves and in vivo, in a controlled environment using the herbicides Gly, 2,4‐D and Gly + 2,4‐D, and pathogen inoculation. Disease severity and spore production were evaluated.
RESULTS
Only the herbicides Gly and Gly + 2,4‐D inhibited ASR in detached leaves and in vivo. When applied preventively and curatively in vivo, these herbicides reduced the disease severity and spore production of the fungus. In vivo, inhibition of disease severity reached 87% for Gly + 2,4‐D and 42% for Gly. A synergistic effect was observed with the commercial Gly + 2,4‐D mixture. Application of 2,4‐D alone in the in vivo assays did not reduce or increase disease severity. Gly and Gly + 2,4‐D act residually in inhibiting the disease. Growing E3 soybeans may combine weed and caterpillar management benefits with ASR inhibition.
CONCLUSION
Application of Gly and Gly + 2,4‐D herbicides in resistant E3 soybean shows inhibitory activity for ASR. © 2023 Society of Chemical Industry.
... The most remarkable absolute differences in N concentration observed between the treatments at 30 DAA can be explained by the mode of action of these chemical products on the leaves, mainly in the case of sulfometuron-methyl and glyphosate that have an herbicidal origin and, thus, maintained the N levels below those observed in natural ripening. Glyphosate acts by inhibiting the activity of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) of the shikimic acid metabolic pathway, blocking the biosynthesis of amino acids, phenolic compounds, indoleacetic acid (IAA), and secondary nitrogen compounds (Rizzardi, Karam, and Michelle 2004;Velini et al. 2009;Duke 2020). ...
... While AMPA exposure in the present study amounted to approximately 1% of the total exposure (GLY + AMPA) in GLY groups (0.99% GLY HC , 0.86% GLY LC ), urinary concentrations of AMPA reached 6.33% (GLY LC ) and 7.01% (GLY HC ) of the total concentrations (GLY + AMPA), indicating putative ruminal GLY metabolization to AMPA [5]. Since a GLY formulation was applied to feedstuff in the present study and therefore cattle were also exposed to other formulation ingredients besides GLY, AMPA concentrations could additionally result from the degradation of other formulation detergents as reviewed [48]. ...
Glyphosate (GLY), the active substance in non-selective herbicides, is often found in ruminant feed. The present feeding study aimed to investigate the effects of GLY-contaminated rations and different concentrate feed proportions (CFP) on the health of fattening German Holstein bulls. Bulls were grouped by low (LC) or high (HC) CFP with (GLYLC, GLYHC) or without GLY-contaminations (CONLC, CONHC) in their rations. Intakes (dry matter, water) and body weight were documented continuously lasting over an average range from 392.2 ± 60.4 kg to 541.2 ± 67.4 kg (mean ± SD). Blood samples collected at the trial’s beginning, and after 7 and 15 weeks, were analyzed for hematological and clinical-chemical traits, functional properties of leukocytes, redox parameters and DNA damage. The average GLY exposures of 128.6 (GLYHC), 213.7 (GLYLC), 1.3 (CONHC) and 2.0 µg/kg body weight/d (CONLC) did not lead to GLY effects for most of the assessed parameters relating to animal health and performance. CFP and time displayed marked influences on most of the experimental parameters such as higher dry matter intake and average daily gain in HC compared with the LC groups. GLY effects were rather weak. However, the observed interactive effects between GLY and CFP and/or time occurring in an inconsistent manner are likely not reproducible. Finally, all animals remained clinically inconspicuous, which brings into question the physiological relevance of putative GLY effects.
... The persistence of Bradyrhizobium may be explained by the ability of bacteria belonging to this genus to degrade glyphosate and atrazine (Hernández-Guijarro et al. 2021;Vercellino and Gómez 2013). Although it has been reported that formulated products based on glyphosate were toxic to the strain Bradyrhizobium sp BR 3901 (Madureira- Barroso et al. 2020), it has been proposed that the effects of glyphosate on microbes of agricultural soils are minor and transient (Duke 2021). It is also interesting to note that most of the Bradyrhizobium strains recently isolated from peanutnodules were denitrifiers, according to the genomic analysis, but only one third of this population could reduce N 2 O and had strong preference for N 2 O over NO − 3 as electron acceptor . ...
Sustainable agriculture relies on the use of herbicides to preserve soil carbon and minimize disturbance to the soil structure. Glyphosate and atrazine, widespread and frequently used herbicides in South America, can affect soil microbial populations involved in nutrient recycling. In this work, the effect of commercial glyphosate and atrazine on denitrifying and diazotrophic populations has been compared. A soil without a history of previous herbicide application was incubated with one or several doses of herbicide, which was monitored along the experiment, and the microbial rate of denitrification and N2 fixation, the abundance of specific genes nirS, nirK, nosZ, nifH and the community structure of diazotrophs were analyzed. One dose of glyphosate or atrazine increased by 55% and 54%, respectively, the rate of N2 fixation and significantly reduced the rate of N2O production by incomplete denitrifiers. Long time exposure to glyphosate increased the abundance of nirK, nosZ, and nifH genes, but atrazine significantly reduced the nosZ gene density. Remarkably, diazotrophs belonging to the Bradyrhizobium genus, predominant in this soil, constituted a resilient population that became enriched after incubation with glyphosate or atrazine. Therefore, short and long-exposure to glyphosate and atrazine modifies the performance and survival of diazotrophs and denitrifiers in soil impacting the N biogeochemical cycle and the soil quality.
... Glyphosate is another herbicide that can cause significant damage to tomato crops, even at low doses. According to Duke [22], glyphosate is a systemic herbicide that has a total action and is moderately absorbed by the cuticle, requiring approximately 6 h without rain after application. Symptoms of glyphosate drift on tomato plants include meristem yellowing and necrosis, and plant death may occur 7-30 days after application. ...
Tomatoes are often grown in proximity to other crops such as grain, which can increase their susceptibility to herbicide drift and subsequent crop. Therefore, the objective of this study was to evaluate the effect of simulated herbicide drift on tomato plants. Treatments were established in a 10 × 3 + 1 factorial scheme using a completely randomized design with four replications. The first factor consisted of ten herbicides, while the second was composed by three subdoses (1/4, 1/16, and 1/32) along with an additional treatment without herbicide application. The herbicides 2,4-D, dicamba, glyphosate, saflufenacil, oxyfluorfen, and isoxaflutole caused injury levels greater than 20% or reductions in plant biomass greater than 30% at the lowest subdose. Increasing the subdose resulted in a corresponding increase in injury level and a reduction in biomass. Tomato exposed to hexazinone, diuron, nicosulfuron, and diquat at a subdose of 1/64 exhibited low injury levels and biomass reductions. However, at other subdoses, these herbicides caused significant plant damage. Among the herbicides tested, the auxinic herbicides, particularly dicamba, presented a higher risk for the tomato crop. The documentation and description of the visual symptoms caused by each herbicide applied to tomatoes will aid producers to identify drift problems in the field.
... And this management has increased yields from the most productive agricultural areas of the world [3]. Nevertheless, it implies the use of large quantities of GBH [4,5]. The half-life of GLY in soil depends on soil composition and climatic conditions, and varies from 7 to 28 days [6][7][8], to several months [6]. ...
Most productive lands worldwide base their crop production on the use of glyphosate (GLY)-resistant plants, and consequently, widespread use of this herbicide has led to environmental issues that need to be solved. Soil bioremediation technologies based on degradation of GLY by microorganisms are strategies that have been considered useful to solve this environmental problem. Recently, a further step has been taken considering the use of bacteria that interact with plants, either alone or both bacteria and plant together, for the removal of GLY herbicide. Plant-interacting microorganisms with plant growth-promoting traits can also enhance plant growth and contribute to successful bioremediation strategies.
... Another point that is mandatory is to evaluate low concentrations, long time exposure and adults to verify what is the possible GBH effects on development. Glyphosate is already known to widely induce hormesis in several plant species, demonstrating that lower doses increase photosynthesis, growth, stomatal conductance, and induce shikimic acid accumulation (Duke, 2020;Duke, 2021;Belz and Duke, 2017). In addition, it has already been found that hormesis occurs in aquatic and terrestrial organisms, being characterized as a generalizable biological phenomenon (Agathokleous and Calabrese, 2020;Lopes et al., 2020;Erofeeva, 2022;Sun et al., 2021;Calabrese, 2021). ...
Glyphosate-Based Herbicides (GBH) show risks to the environment and also to aquatic organisms, such as fish. The present work aimed to evaluate the effects of GBH and Pure Glyphosate (PG) exposure on Danio rerio embryos at drinking water concentrations. Zebrafish embryos were exposed to 250, 500, and 1000 μg L⁻¹ of Roundup Original DI® and pure glyphosate for 96 h. Glyphosate concentration in water, parameters physicochemical water, survival, hatching rate, heart rate, malformations, behavior, and biomarkers were evaluated. We verified that at 6 h post-fertilization (hpf), animals exposed to GBH 500 showed decreased survival as compared to the control. The hatching rate increased in all groups exposed to GBH at 48 hpf as compared to the control group. The embryos exposed did not present changes in the spontaneous movement and touch response. Exposed groups to GBH demonstrated a higher number of malformations in fish embryos as compared to the control. Most malformations were: pericardial edema, yolk sac edema, body malformations, and curvature of the spine. In heart rate, bradycardia occurred in groups exposed, as predicted due to cardiac abnormalities. As biochemical endpoints, we observed a decrease in Glutathione S-transferase (GBH 250, GBH 500 and PG 250) and Acetylcholinesterase (GBH 250 and PG 250) activity. No differences were found between the groups in the concentration of protein, Total Antioxidant Capacity Against Peroxyl Radicals, Lipid peroxidation, Reactive Oxygen Species, Non-protein thiols, and Catalase. In conclusion, the damage in all evaluated stages of development was aggravated by survival and malformations. Therefore, the large-scale use of GBHs, coupled with the permissiveness of its presence could be the cause damage to the aquatic environment affecting the embryonic development of non-target organisms.
... As for microbes, glyphosate degradation in plants is predominantly by a glyphosate oxidoreductase to produce AMPA and glyoxylate, although evidence of metabolism by a C-P lyase has been reported in a few species of high plants (Duke 2011). AMPA, in turns, requires a C-P lyase enzyme to be degraded in a relative longer process compared to glyphosate metabolism (Duke 2021). Therefore, when both compounds were applied together, the plant's AMPA phytoremediation capacity may be overestimated due to glyphosate metabolism in plants. ...
We evaluated the individual and combined effects of different environmentally representative concentrations of glyphosate (0, 25, 50, 75, and 100 µg l⁻¹) and aminomethylphosphonic acid (AMPA; 0, 12.5, 25, 37.5, and 50 µg l⁻¹) on the physiology of Aedes aegypti larvae, as well as the capacity of the aquatic macrophyte Salvinia molesta to attenuate those compounds’ toxicological effects. Larvae of Ae. aegypti (between the third and fourth larval stages) were exposed for 48 h to glyphosate and/or AMPA in the presence or absence of S. molesta. Glyphosate and AMPA induced sublethal responses in Ae. aegypti larvae during acute exposures. Plants removed up to 49% of the glyphosate and 25% of AMPA from the water, resulting in the exposure of larvae to lower concentration of those compounds in relation to media without plants. As a result, lesser effects of glyphosate and/or AMPA were observed on larval acetylcholinesterase, P450 reductase, superoxide dismutase, mitochondrial electron transport chain enzymes, respiration rates, and lipid peroxidation. In addition to evidence of deleterious effects by media contamination with glyphosate and AMPA on aquatic invertebrates, our results attest to the ability of S. molesta plants to mitigate the toxicological impacts of those contaminants.
Graphical abstract
... The latter, in particular, restrain the growth of weeds and favor the drying of crops such as wheat, making these crops easier and cheaper to produce [1,2]. In recent years, glyphosate (Gly) has been widely used; this chemical is a non-selective herbicide that is absorbed by the stem and leaves and then transported throughout the plant, blocking enolpyruvylshikimate-3-phosphate synthase (EPSPS), a key enzyme involved in the synthesis of aromatic amino acids essential for plant growth [3]. This inhibitory mechanism towards a missing enzyme in animal tissues and its rapid degradation made glyphosate the herbicide of choice for many years. ...
The expansion of agriculture produces a steady increase in habitat fragmentation and degradation due to the increased use of pesticides and herbicides. Habitat loss and alteration associated with crop production play an important role in reptile decline, among which lizards are particularly endangered. In this study, we evaluated testicular structure, steroidogenesis, and estrogen receptor expression/localization after three weeks of oral exposure to glyphosate at 0.05 and 0.5 μg/kg body weight every other day in the field lizard Podarcis siculus. Our results show that glyphosate affected testicular morphology, reduced spermatogenesis, altered gap junctions and changed the localization of estrogen receptors in germ cells, increasing their expression; the effects were mostly dose-dependent. The result also demonstrates that glyphosate, at least at these concentrations, did not influence steroidogenesis. Overall, the data indicate that this herbicide can disturb the morphophysiology of the male lizard’s reproductive system, with obviously detrimental effects on their reproductive fitness. The effects of glyphosate must be considered biologically relevant and could endanger the reproductive capacity not only of lizards but also of other vertebrates, including humans; a more controlled and less intensive use of glyphosate in areas devoted to crop production would therefore be advisable.
... The EU's proposed replacement of glyphosate with natural herbicides may be an ineffective solution because natural pesticides do not differ from synthetic pesticides in their dose-response behaviour Calabrese 2020, 2021;Agathokleous et al. 2022a). The general occurrence of hormesis ( Fig. 1) across pesticides, allelochemicals, and other types of chemicals with significant subtoxic responses, suggests that all pesticides would affect sensitive or resistant targeted and non-targeted organisms depending on concentration and time (Duke et al. 2006;Belz and Duke 2017;Carvalho et al. 2020;Shahid et al. 2020;Duke 2021;Erofeeva 2021Erofeeva , 2022Jalal et al. 2021;Agathokleous et al. 2022a;Cutler et al. 2022;Rix and Cutler 2022). Hence, pesticide effects cannot be prevented by simply turning them into natural ones. ...
The European Federation of Food, Agriculture, and Tourism Trade Unions (EFFAT) called for the immediate ban on glyphosate in the 2022 renewal process, promoting the use of natural herbicides and recommending against the use of other harmful or hazardous chemicals. The new chemical testing and selection research agendas should consider the hormetic effects of individual natural herbicides, and their potential mixtures, on targeted and non-targeted organisms to avoid stimulation of pests and negative effects on non-targeted organisms. New scientific research programs are needed to study the effects of mixtures of natural pesticides on soils, plants, animals, and microorganisms within the context of agroforestry.
[this is an open-access paper]
... Glyphosate is the most used pesticide in the world, 1 used in both agricultural (for weed control and preharvest desiccation) and nonagricultural settings. 1,2,3 Studies have detected glyphosate in the air, soil, drinking water, and food. 4 Use of glyphosate-based herbicides has increased dramatically since their introduction, 1 largely due to the growing use of genetically modified glyphosateresistant crops starting in the late 1990s. ...
Background:
Glyphosate is the most commonly used herbicide in the world and is purported to have a variety of health effects, including endocrine disruption and an elevated risk of several types of cancer. Blood DNA methylation has been shown to be associated with many other environmental exposures, but to our knowledge, no studies to date have examined the association between blood DNA methylation and glyphosate exposure.
Objective:
We conducted an epigenome-wide association study to identify DNA methylation loci associated with urinary glyphosate and its metabolite aminomethylphosphonic acid (AMPA) levels. Secondary goals were to determine the association of epigenetic age acceleration with glyphosate and AMPA and develop blood DNA methylation indices to predict urinary glyphosate and AMPA levels.
Methods:
For 392 postmenopausal women, white blood cell DNA methylation was measured using the Illumina Infinium MethylationEPIC BeadChip array. Glyphosate and AMPA were measured in two urine samples per participant using liquid chromatography-tandem mass spectrometry. Methylation differences at the probe and regional level associated with glyphosate and AMPA levels were assessed using a resampling-based approach. Probes and regions that had an false discovery rate q<0.1 in ≥90% of 1,000 subsamples of the study population were considered differentially methylated. Differentially methylated sites from the probe-specific analysis were combined into a methylation index. Epigenetic age acceleration from three epigenetic clocks and an epigenetic measure of pace of aging were examined for associations with glyphosate and AMPA.
Results:
We identified 24 CpG sites whose methylation level was associated with urinary glyphosate concentration and two associated with AMPA. Four regions, within the promoters of the MSH4, KCNA6, ABAT, and NDUFAF2/ERCC8 genes, were associated with glyphosate levels, along with an association between ESR1 promoter hypomethylation and AMPA. The methylation index accurately predicted glyphosate levels in an internal validation cohort. AMPA, but not glyphosate, was associated with greater epigenetic age acceleration.
Discussion:
Glyphosate and AMPA exposure were associated with DNA methylation differences that could promote the development of cancer and other diseases. Further studies are warranted to replicate our results, determine the functional impact of glyphosate- and AMPA-associated differential DNA methylation, and further explore whether DNA methylation could serve as a biomarker of glyphosate exposure. https://doi.org/10.1289/EHP10174.
... However, microbes have enzymes to readily break glyphosate down, the main reason for its relatively short half-life in soil and water. For years, whether glyphosate was metabolized in plants was controversial, but now it is clear that it is significantly metabolized to aminomethylphosponic acid (AMPA) and glyoxylate in many plant species, especially some legumes (Duke, 2011(Duke, , 2019(Duke, , 2021. Even though some plants apparently have an enzyme to break down glyphosate, there were no rigorously proven examples of GR weeds using enhanced enzymatic degradation as a resistance mechanism. ...
Weeding has been the bane of humanity since the dawn of agriculture. For about 70 years, synthetic herbicides have removed much of the drudgery of this onerous task. Glyphosate was introduced as a non-selective herbicide in 1974. Its ideal properties made it a very popular herbicide, and the introduction of glyphosate-resistant (GR) crops allowed its use as a selective herbicide, greatly expanding its use to become the most used herbicide on earth. For farmers who used glyphosate in GR crops, it was the golden age of weed management, as this technology significantly improved the efficacy and reduced the cost of weed management. Weed management was also simplified, an asset that was particularly valuable to part-time farmers. Furthermore, this technology provided the environmental benefits (reduced soil loss and fossil fuel use) of significantly reducing tillage. Farmers saved billions of US$, and weed management became more effective and simple. Indeed, to many farmers, glyphosate with GR crops became the goose that laid the golden egg. After more than 20 years of use, the first cases of GR weeds were reported in the latter 1990s. After a lag period of less than 10 years after the first GR weed was reported, the number of species reported to have evolved glyphosate resistance began to increase in a linear fashion, reaching 53 species in 2021, third only to atrazine (66 species), a much older herbicide and to ALS inhibitors (168 species), which include several different herbicides used in numerous crops since the 1980s. The long lag phase before any resistance was detected led some to believe by the mid-1990s that evolution of resistance was improbable. By this time, glyphosate use was greatly increasing, especially in GR crops, an ideal situation for the evolution of resistance. After this, the number of glyphosate-resistance cases exploded, and the mechanisms of resistance to many of these cases of resistance were determined. A recent, short commentary detailed these mechanisms after a new mechanism of resistance was reported. The number of mechanisms for resistance to no other herbicide comes close to those of glyphosate. In the present paper, we briefly describe the many evolved mechanisms by which weeds have evolved resistance to glyphosate.
... Abbreviations: AMPA, aminomethylphosphonic acid; GOX, glyphosate oxidoreductase. Adapted from Duke (2021) and Giesy et al. (2000) in plants. Because these amino acids are needed for synthesis of proteins and lignin in all eukaryotic plants (Tzin & Galili, 2010), glyphosate is a broad spectrum herbicide. ...
Glyphosate is the active ingredient in Roundup® brand nonselective herbicides, and residue testing for food has been conducted as part of the normal regulatory processes. Additional testing has been conducted by university researchers and nongovernmental agencies. Presence of residues needs to be put into the context of safety standards. Furthermore, to appropriately interpret residue data, analytical assays must be validated for each food sample matrix. Regulatory agency surveys indicate that 99% of glyphosate residues in food are below the European maximum residue limits (MRLs) or U.S. Environmental Protection Agency tolerances. These data support the conclusion that overall residues are not elevated above MRLs/tolerances due to agricultural practices or usage on genetically modified (GM) crops. However, it is important to understand that MRLs and tolerances are limits for legal pesticide usage. MRLs only provide health information when the sum of MRLs of all foods is compared to limits established by toxicology studies, such as the acceptable daily intake (ADI). Conclusions from dietary modeling that use actual food residues, or MRLs themselves, combined with consumption data indicate that dietary exposures to glyphosate are within established safe limits. Measurements of glyphosate in urine can also be used to estimate ingested glyphosate exposure, and studies indicate that exposure is <3% of the current European ADI for glyphosate, which is 0.5 mg glyphosate/kg body weight. Conclusions of risk assessments, based on dietary modeling or urine data, are that exposures to glyphosate from food are well below the amount that can be ingested daily over a lifetime with a reasonable certainty of no harm.
... Sometimes, reversion studies give only a weak effect, but their results can accurately indicate the biosynthetic pathway affected. For example, some reversion studies using aromatic amino acids to reverse the effects of glyphosate gave weak results, but later in vitro enzymology and genetics research proved unequivocally that this very successful herbicide inhibits only one enzyme, EPSPS, an essential enzyme for the shikimate pathway that produces aromatic amino acids [54]. ...
Knowledge of the mode of action of an allelochemical can be valuable for several reasons, such as proving and elucidating the role of the compound in nature and evaluating its potential utility as a pesticide. However, discovery of the molecular target site of a natural phytotoxin can be challenging. Because of this, we know little about the molecular targets of relatively few allelochemicals. It is much simpler to describe the secondary effects of these compounds, and, as a result, there is much information about these effects, which usually tell us little about the mode of action. This review describes the many approaches to molecular target site discovery, with an attempt to point out the pitfalls of each approach. Clues from molecular structure, phenotypic effects, physiological effects, omics studies, genetic approaches, and use of artificial intelligence are discussed. All these approaches can be confounded if the phytotoxin has more than one molecular target at similar concentrations or is a prophytotoxin, requiring structural alteration to create an active compound. Unequivocal determination of the molecular target site requires proof of activity on the function of the target protein and proof that a resistant form of the target protein confers resistance to the target organism
The occurrence and chemistry of glyphosate in the environment, its impact on living beings, and its detection in the environment system is central themes of this review article. Glyphosate, a herbicide, has become a matter of environmental and public health concern in recent times. While it is effective in weed control, its excessive use has negative effects on ecosystems, biodiversity, and precious soil. The overuse of glyphosate has prompted the search for alternatives, which is a topic of discussion in both the scientific community and civil societies. Numerous chromatographic and immunoassay-based detection techniques, as well as precision-era sensitive detection techniques, have been developed and utilized for monitoring and regulating glyphosate. Glyphosate (GLY), a versatile herbicide with several applications, has become quite popular for controlling weed growth in residential, commercial, and agricultural settings. Its widespread acceptance has been facilitated by its effectiveness and cost. However, the overuse and improper application of GLY have become an urgent concern, raising questions about potential harm to human health and environmental sustainability. Studies have revealed that GLY exhibits toxic properties that can lead to detrimental consequences for human well-being. These include the potential to induce cancer, contribute to birth defects, and disrupt reproductive functions. Moreover, when exposed to non-target organisms, GLY has been found to inflict adverse impacts on various forms of aquatic life, insects, and essential soil microorganisms. Because of its great solubility and low quantities in soil and water, GLY detection is a difficult process. In response to the concerns surrounding GLY, several detection techniques have been devised, encompassing chromatography, immunoassays, and mass spectrometry. These methods play a crucial role in investigating the ramifications associated with glyphosate application in agriculture and the environment. The study also emphasizes the need for continued research to fully understand the long-term effects of GLY exposure on human health and the environment.
Rampant use of fertilizers and pesticides for boosting agricultural crop productivity has proven detrimental impact on land, water, and air quality globally. Although fertilizers and pesticides ensure greater food security, their unscientific management negatively impacts soil fertility, structure of soil microbiome and ultimately human health and hygiene. Pesticides exert varying impacts on soil properties and microbial community functions, contingent on factors such as their chemical structure, mode of action, toxicity, and dose-response characteristics. The diversity of bacterial responses to different pesticides presents a valuable opportunity for pesticide remediation. In this context, OMICS technologies are currently under development, and notable advancements in gene editing, including CRISPR technologies, have facilitated bacterial engineering, opening promising avenues for reducing toxicity and enhancing biological remediation. This paper provides a holistic overview of pesticide dynamics, with a specific focus on organophosphate, organochlorine, and pyrethroids. It covers their occurrence, activity, and potential mitigation strategies, with an emphasis on the microbial degradation route. Subsequently, the pesticide degradation pathways, associated genes and regulatory mechanisms, associated OMICS approaches in soil microbes with a special emphasis on CRISPR/Cas9 are also being discussed. Here, we analyze key environmental factors that significantly impact pesticide degradation mechanisms and underscore the urgency of developing alternative strategies to diminish our reliance on synthetic chemicals.
Phosphonate structures in phosphonate compounds are biologically active organic synthetic materials derived from natural products. Due to their unique carbon-phosphorus (C–P) bonds, phosphonate compounds are highly biologically active and less susceptible to resistance and have the advantages of high efficacy, fast efficacy, low dosage, and wide use. With the increasing prevalence of drug resistance of pathogens, there is growing concern regarding the development of new environmentally friendly and non-drug resistant pesticides. In this review, we focused on phosphonate compounds with herbicidal, bactericidal, fungicidal, insecticidal, antiviral, and plant growth regulation functions, providing a basis for the development of new phosphonate compound pesticides.
New fungicide modes of action are needed for fungicide resistance management strategies. Several commercial herbicide targets found in fungi that are not utilized by commercial fungicides are discussed as possible fungicide molecular targets. These are acetyl CoA carboxylase, acetolactate synthase, 5-enolpyruvylshikimate-3-phosphate synthase, glutamine synthase, phytoene desaturase, protoporphyrinogen oxidase, long-chain fatty acid synthase, dihydropteroate synthase, hydroxyphenyl pyruvate dioxygenase, and Ser/Thr protein phosphatase. Some of the inhibitors of these herbicide targets appear to be either good fungicides or good leads for new fungicides. For example, some acetolactate synthase and dihydropteroate inhibitors are excellent fungicides. There is evidence that some herbicides have indirect benefits to certain crops due to their effects on fungal crop pathogens. Using a pesticide with both herbicide and fungicide activities based on the same molecular target could reduce the total amount of pesticide used. The limitations of such a product are discussed.
Pesticides are chemicals that are required to be implemented in agricultural setups in order to maintain crop production and eliminate the insect pests which are adversely impacting crop yields. These chemical toxicants are generally classified as insecticides, herbicides, fungicides, bactericides, etc. The uncontrolled and unchecked applications of these toxicants are drastically impacting the global environment as well as the associated ecosystems. Their entry into the soil and water ecosystems will lead to their residual entities getting incorporated inside the plant tissues and leads to their entry into the human through food chains. In plants, these pesticides get their entry through absorption via roots, through leaf surfaces, and further gets accumulated in the plant tissues, whereas plants have developed certain mechanisms to cope with these toxic chemicals through enzymatic and nonenzymatic antioxidants. Whereas humans get exposed mainly through toxic food chains as well as through contaminated water resources which further gets accumulated inside the tissues and leads to adverse impact on the kidneys, brain, lungs, liver, gastrointestinal, and skin, and severely leads to mutations, certain diseases as well act cancerous in multiple cases. Pesticides are also prevalent to cause toxicity in honeybees which further compromises the pollination process, also they are known to impair the functions of aquatic animals, and birds and invariably affect the soil microbial populations which are potential growth regulators to plants in the soils. In this chapter, a confined mechanism of entry of pesticides into different organism have been elaborated. Also, a precise mechanism for their detoxification in plants has been provided.
Climate change is one of the most pressing challenges facing agriculture today, with its adverse effects on crop productivity and global food security. To combat the impacts of climate change, the development of climate-resilient crop species is crucial. Plant‒microbe interactions play a significant role in enhancing plant resilience to various stressors, including drought, heat, salinity, and pathogen attacks. This chapter explores the intricate relationship between plants and microbes and their potential role in developing climate-resilient crop species. It delves into the various mechanisms involved, highlighting the importance of harnessing these interactions for sustainable agriculture in the face of a changing climate.
Weeds are a significant threat to the production of agronomic, horticultural, and ornamental crops, as direct competition for resources can result in substantial yield shortfalls (WSSA 2023). A review of research data generated across the United States and Canada indicated that unmanaged weeds have the potential to reduce corn and soybean production by approximately 50%, even when other best management practices are applied (Soltani et al. 2016, 2017). The associated economic losses, which were estimated at 26.7 and 17.2 billion USD for corn and soybeans, respectively, would be catastrophic. Weeds can also interfere with crops, indirectly. For example, weeds may impede or delay harvest operations (Smith et al. 2000), reduce crop quality because of contamination (Moore et al. 2004), and serve as alternate hosts for pests and pathogens (Chen et al. 2011; Wisler and Norris 2005). Other habitats, such as rangelands, wetlands, and other natural and urban areas, are also affected by weedy and invasive plant species. Impacts of unwanted vegetation can include damage to infrastructure, damage to recreational space, altered water flow, degraded natural resources, reduced biodiversity and species displacement, and a loss of ecosystem services, among other effects (DiTomaso 2000; Jetter et al. 2021; Neal 2023; Vilà et al. 2011).
Glyphosate (Glp) was encapsulated onto the dopamine-modified attapulgite to develop an attapulgite-based nano-enabled Glp (DGlp) in this study with comparable weed control effects to pure Glp and commercial Glp solutions. Within 24 h, the active Glp molecule was slowly released from DGlp at a maximum remaining rate of over 90%, and then degraded similarly to Glp solution in soil. The addition of DGlp improved soil available phosphorus (P) contents, phosphatase activity, and enzyme extractable P fraction. However, compared to Glp solution, DGlp addition had no effect on the transformation of soil inorganic P fractions. The 16S rRNA sequencing and co-occurrence network results revealed that DGlp had no significant effect on the soil bacterial diversity but diminished the complexity of soil bacterial network. According to the Mantel test, DGlp addition stimulated soil phosphatase activity and proliferation of dominant bacterial taxa (Proteobacteria and Firmicutes) capable of degrading Glp. Proteobacteria and Firmicutes that had been extensively recruited and enriched for their phosphatase activities may have mobilized reactive enzyme-P, significantly enhancing the transformation of reactive organic P and P-pool in soil. These results contributed to our understanding of the ecotoxicity and environmental impacts of nano-enabled Glp prior to its successful and sustainable application in agriculture.
Unsustainable agriculture is producing a great socio-ecological transformation in Latin America because it has expanded into areas occupied by native forests. Glyphosate is the most widely used herbicide, with severe ecotoxicological effects on non-target organisms. The aim of this study was to determine the effects of glyphosate on seedlings of 24 non-target herbaceous and non-herbaceous plant species present in forest relicts of Argentine Chaco. The effects of a gradient of glyphosate doses (525, 1050, 2100, 4200, and 8400 g ai/ha) were measured in seedlings of each species under greenhouse conditions. Seedlings were grown from seeds collected from native forest fragments of different sizes (assuming three different degrees of historical exposure to glyphosate in the landscape). Doses were applied at different stages of seedling development (five- and ten-weeks after emergence), and phytotoxicity, growth reduction, and sensitivity were measured. Glyphosate produced lethal or sublethal effects in all 24 species, some of which were very sensitive (>60 % of the species presented strong to severe growth reduction with ¼ of the dose used on crops). The greatest toxicological effects were related to early stage of development, herbaceous species, and low historical exposure to glyphosate. According to the species sensitivity distribution, the drift-dose to protect 95 % of the plant species that occur in larger forest fragments should not exceed 5 % of the dose commonly used on crops. These results suggest that the current weed management linked to glyphosate-resistant crops could lead to a gradual loss of biodiversity in the landscape. Concurrently, selection of glyphosate-tolerant biotypes in some non-target species could represent a very problematic cycle for the current model of industrial agriculture. Some alternatives for weed control are proposed.
A widespread increase in intense phytoplankton blooms has been noted in lakes worldwide since the 1980s, with the summertime peak intensity amplifying in most lakes. Such blooms cause annual economic losses of multibillion USD and present a major challenge, affecting 11 out of the 17 United Nations Sustainable Development Goals. Here, we evaluate recent scientific evidence for hormetic effects of emerging contaminants and regulated pollutants on Microcystis sp., the most notorious cyanobacteria forming harmful algal blooms and releasing phycotoxins in eutrophic freshwater systems. This new evidence leads to the conclusion that pollution is linked to algal bloom intensification. Concentrations of contaminants that are considerably smaller than the threshold for toxicity enhance the formation of harmful colonies, increase the production of phycotoxins and their release into the environment, and lower the efficacy of algaecides to control algal blooms. The low-dose enhancement of microcystins is attributed to the up-regulation of a protein controlling microcystin release (McyH) and various microcystin synthetases in tandem with the global nitrogen regulator Ycf28, nonribosomal peptide synthetases, and several ATP-binding cassette transport proteins. Given that colony formation and phycotoxin production and release are enhanced by contaminant concentrations smaller than the toxicological threshold and are widely occurring in the environment, the effect of contaminants on harmful algal blooms is more prevalent than previously thought. Climate change and nutrient enrichment, known mechanisms underpinning algal blooms, are thus joined by low-level pollutants as another causal mechanism.
Hormesis drives biological modifications from cells to higher levels of biological organization and emerges as a general basic principle of biology, integrating evolution, ecology, medicine, physiology, toxicology, and public health.
Glyphosate-resistant (GR) crops, commercially referred to as glyphosate-tolerant (GT), started the revolution in crop biotechnology in 1996. Growers rapidly accepted GR crops whenever they became available and made them the most rapidly adopted technology in agriculture history. Adoption usually meant sole reliance on glyphosate [N-(phosphonomethyl)glycine, CAS No. 1071-83-6] for weed control. Not surprisingly, weeds eventually evolved resistance and are forcing growers to change their weed management practices. Today, the widespread dissemination of GR weeds that are also resistant to other herbicide modes-of-action (MoA) has greatly reduced the value of the GR crop weed management systems. However, growers continue to use the technology widely in six major crops throughout North and South America. Integrated chemistry and seed providers seek to sustain glyphosate efficacy by promoting glyphosate combinations with other herbicides and stacking the traits necessary to enable the use of partner herbicides. These include glufosinate {4-[hydroxy(methyl)phosphinoyl]-DL-homoalanine, CAS No. 51276-47-2}, dicamba (3,6-dichloro-2-methoxybenzoic acid, CAS No. 1918-00-9), 2,4-D [2-(2,4-dichlorophenoxy)acetic acid, CAS No. 94-75-7], 4-hydroxyphenyl pyruvate dioxygenase inhibitors, acetyl coenzyme A carboxylase (ACCase) inhibitors, and other herbicides. Unfortunately, herbicide companies have not commercialized a new MoA for over 30 years and have nearly exhausted the useful herbicide trait possibilities. Today, glyphosate-based crop systems are still mainstays of weed management, but they cannot keep up with the capacity of weeds to evolve resistance. Growers desperately need new technologies, but no technology with the impact of glyphosate and GR crops is on the horizon. Although the expansion of GR crop traits is possible into new geographic areas and crops such as wheat and sugarcane and could have high value, the Roundup Ready® revolution is over. Its future is at a nexus and dependent on a variety of issues.
Widespread adoption of glyphosate-resistant crops and concomitant reliance on glyphosate for weed control set an unprecedented stage for the evolution of herbicide-resistant weeds. There are now 48 weed species that have evolved glyphosate resistance. Diverse glyphosate-resistance mechanisms have evolved, including single, double, and triple amino acid substitutions in the target-site gene, duplication of the gene encoding the target site, and others that are rare or nonexistent for evolved resistance to other herbicides. This review summarizes these resistance mechanisms, discusses what is known about their evolution, and concludes with some of the impacts glyphosate-resistant weeds have had on weed management.
BACKGROUND
The current climate change scenario may affect water availability in the soil, impacting the agricultural sector. Planting of safflower (Carthamus tinctorius L.) has increased because of its potential for cultivation under drought conditions during the off‐season in Brazil and its high potential for use in biofuel production. There are several reports about the potential of low doses of glyphosate to promote plant growth and development (hormesis). Despite the concept of glyphosate hormesis being well established, little is known about any mitigating effect on plants under water deficit conditions. The hypothesis raised is that low doses of glyphosate promote water stress tolerance during the growth and reproductive phases of C. tinctorius exposed to different water regimes.
RESULTS
In regimes with and without water deficiency, growth of plants treated with low doses of glyphosate increased, reaching a maximum stimulus amplitude of ~ 131% of control. However, plants under water deficit required lower doses to achieve maximum growth and development. They maintained photosynthetic rates at the level of well‐watered plants because they had reduced stomatal conductance and transpiration. Gains in plant height and leaf area were the same as for controls.
CONCLUSIONS
Low doses of glyphosate can act as mitigators of water deficit in C. tinctorius, allowing plants to maintain their metabolism, reaching levels close to those of plants without water stress, as observed for plant height and leaf area. Our findings indicate that there are even greater implications for understanding glyphosate hormesis in plants under drought conditions, given the current climate change scenario. © 2020 Society of Chemical Industry
Quinate (1,3,4,5-tetrahydroxycyclohexanecarboxylate) is a compound synthesized in plants through a side-branch of the shikimate biosynthesis pathway, which is accumulated after glyphosate and acetolactate synthase inhibiting herbicides (ALS-inhibitors) and has phytotoxic potential. The objective of this study was to evaluate the phytotoxicity of quinate on several weed species. Among the species evaluated, Cynodon dactylon, Bromus diandrus, Lolium rigidum, Sinapis alba, and Papaver rhoeas, P. rhoeas was the most sensitive, and its growth was controlled with quinate concentrations above 100 mM at the phenological stage of 6-8 true leaves. A physiological study, including the shikimate pathway and the physiological markers of ALS-inhibitors (carbohydrates and amino acids), was performed in the sensitive and resistant plants treated with sulfonylureas or quinate. The typical physiological effects of ALS-inhibitors were detected in the sensitive population (free amino acid and carbohydrate accumulation) and not detected in the resistant population. The mode of action of quinate appeared to be related to general perturbations in their carbon/nitrogen metabolism rather than to specific changes in the shikimate pathway. These results suggest the possibility of using quinate in the weed control management of P. rhoeas.
In this paper, several experiments were carried out to study the environmental behavior and influencing factors of glyphosate (PMG) in peach orchard ecosystem. The results of field experiments showed that PMG and its metabolite aminomethylphosphonic acid (AMPA) were detected in peach tree leaves and peach tree fruits, although PMG was only sprayed on the soil. The residues of PMG and AMPA in peach tree leaves were ~0.1 mg/kg and ~0.5 mg/kg and in peach tree fruits were ~0.01 mg/kg and 0.07-0.11 mg/kg, respectively. By conducting a series of laboratory simulation experiments, the environmental factors affecting the degradation of PMG were screened and evaluated. The results showed that PMG metabolized much faster in loess soil than red soil and black soil (with the DT50 of 11.6 days, 62.4 days, and 34.1 days, respectively). By analyzing the basic properties of the soil, we investigated the effects of pH, moisture content, organic matter (exogenous biochar) and ambient temperature using orthogonal experiments, and the results were further confirmed by microbial experiment. The results showed that alkaline conditions (pH = 7.8/9), high water content (25%) and microorganisms could promote the degradation of PMG. Sterile soil environment had a negative impact on the metabolic behavior of PMG to AMPA.
In 2019, the ENDURE network launched a survey on the agricultural use of glyphosate in European countries. This report presents the results obtained through the survey and proposes a framework for
understanding and monitoring glyphosate uses.
The share of herbicides among all pesticide sales varies from one country to another. It is particularly high in Sweden (where herbicides represented 85% of the total volume of pesticides sold in 2017),
Norway (83%), Denmark (82%), Estonia (76%), Ireland (73%), Latvia (73%), Lithuania (63%), United Kingdom (62%) and Poland (61%) and is particularly low in Malta (2%), Cyprus (13%) and Italy (17%).
When reported by hectare of agricultural area, the countries with the highest average use of herbicides are Belgium, Netherlands, Cyprus, France, Germany, Denmark and Poland. The average use of
herbicides in the agricultural sector at the EU 28+3 level can be estimated at 0.62 kg of a.i. per hectare.
The total volume of herbicides sold in all EU 28+3 countries remained rather stable from 2011 to 2017, while at the national level, herbicide sales numbers showed a high degree of fluctuation.
The ENDURE survey made it possible to collect data on glyphosate sales in 25 countries. In addition, an estimation was calculated for the other seven countries for which no data could be obtained. The
total sales of glyphosate are estimated at 46,527 tonnes of a.i. in 2017 across the EU 28+3 (47,452 tonnes of a.i. across the EU 28+4). Overall, sales of glyphosate represent 33% of total herbicide sales
in the EU 28+3. Therefore, glyphosate is one of the most widely used herbicides in European agriculture.
Similar to overall herbicide sales, glyphosate sales (in volume of active ingredients) appear to be the highest in France (20% of the EU 28+4 total glyphosate sales volume in 2017), Poland (14%), Germany
(10%), Italy (8%) and Spain (8%). Glyphosate represents 15% to 78% of total herbicide active ingredient sales in the countries surveyed. According to the survey, glyphosate is mainly used in the agricultural
sector. Across the 13 countries for which the share of glyphosate sales to the agricultural sector was available, the agricultural sector consumes on average 90% of total national glyphosate sales (by
volume). When reported by hectare of agricultural area, the average use of glyphosate at the EU 28+3 level is 0.20 kg a.i. per hectare. The five countries with the highest use of glyphosate in 2017 were
Denmark, Poland, Netherlands, Portugal and France (≥0.32 kg of a.i. per ha). The five countries with the lowest use of glyphosate were Turkey, Lithuania, Latvia, UK and Switzerland (≤0.12 kg of a.i. per
ha).
This report offers a framework for understanding and monitoring glyphosate uses in the agricultural sector, based on the identification of the cropping systems in which glyphosate is used, the agronomic
purposes for which it is used and the nature of this use (from occasional to systematic). Glyphosate is widely used in annual cropping systems, perennial crops and grasslands. In annual cropping systems, it is mostly used prior to sowing, shortly after sowing of the crop (at the pre-emergence stage) or at the post-harvest stage for controlling weeds and volunteers. Annual cropping systems in which glyphosate is used include a large variety of crops (such as maize, oilseed rape, cereals, legume crops, sugar and fodder beet etc.). It is also used for the destruction of cover crops, and for ensuring the desiccation of certain annual crops at the pre-harvest stage. In perennial crops (such as vineyards, fruit orchards,
olives groves etc.), glyphosate is used for controlling weeds within or between crop rows. Finally, glyphosate is used for the destruction of temporary grassland, for local control of perennial weeds in
permanent grassland and for grassland renewal. Overall, the survey shows that the herbicide is used for at least eight agronomic purposes.
Statistical data regarding glyphosate use in annual cropping systems is limited. In addition, the allocation of glyphosate treatments that are applied in the intercropping period may vary across countries. Four
different allocation rules were identified through the survey: allocation from harvest to harvest, allocation from field preparation to post-harvest treatments, allocation to the intercrop period and allocation to the cropping system. In some countries, several allocation rules may apply depending on the statistical dataset. As a consequence, comparisons of glyphosate uses in annual cropping systems between
countries or crops must be considered as a preliminary indication.
Within the scope for which data could be obtained through the survey, 32% of the wheat acreage, 25% of the maize acreage and 52% of the oilseed rape acreage were treated with glyphosate in any single
year. The treated acreage varies greatly from one country to another: the use of glyphosate in maize fields was almost inexistent in some countries, while it reached up to 40% of the crop area in other
countries. In oilseed rape fields, the share of the crop area treated with glyphosate varied from less than 10% to more than 70%. Similarly, in winter wheat fields, the share of the crop area on which glyphosate
is used varied from less than 10% to 90%. Those percentages include: treatments for controlling weeds applied before cultivation (at the pre-sowing or pre-emergence stage) that may occur for each new
sowing in the crop rotation; treatments for controlling weeds that are applied only once in the crop rotation (at a post-harvest stage or during an intercropping period); and desiccation/harvest aid for some
of the crops (in countries in which this is allowed). As the percentages are for any single year, the area treated with glyphosate in any region over a full crop rotation period may be greater. Additional research
is needed for assessing the total uses of glyphosate throughout the crop rotations in EU countries.
In perennial systems, within the scope for which data was available in the EU 28+4, 39% of the fruit orchard acreage, 32% of the vineyard acreage and 45% of the olive grove acreage were treated with
glyphosate. Across countries, the use of glyphosate ranged from 13% to 95% of the national vineyard acreage, from 20% to 92% of the fruit orchard acreage and from 13% to 80% of the olive grove acreage.
Finally, 19% of the temporary grassland acreage was treated with glyphosate annually.
A diversity of non-chemical alternatives to glyphosate treatments can be identified. Their effectiveness, cost and adoption implications for crops and the environment can vary widely, or may not be quantified.
They include both preventive measures and curative control measures, such as mechanical and biological control. In annual cropping systems, these practices include: use of cover crops and of a
roller-crimper for their destruction, mulching, crop rotation diversification, delaying crop sowing dates, higher seed rates, increasing crop competitiveness, inter-row cultivation, tillage for controlling weeds at the post-harvest and pre-sowing stages, use of early-ripening varieties and weed seed removal during harvest. In perennial crops, the following alternatives were identified: greening, grazing, mowing, mulching, cover crops, tillage, mechanical weeding and the use of bioherbicides for weed control.
Different approaches to using glyphosate were identified through the survey. Occasional uses are related to exceptional contexts, such as meteorological conditions or specific farm constraints.
Recurrent uses are widespread practices that are already embedded in farming systems. Other agronomic solutions may exist but are not mobilised; instead farmers plan to, and recurrently do, use
glyphosate. Two types of recurrent uses can be distinguished: uses related to structural conditions and systematic uses that are not related to structural conditions. First, uses related to structural conditions appear when equipment or infrastructure are not compatible with alternative practices. Examples of such structural conditions include irrigation systems that are located above ground in fruit orchards and narrow rows in orchards or vineyards which prevent weed management using mechanical methods. For replacing glyphosate with non-chemical alternatives, a change in these structural aspects is required, which may involve significant investments. Second, systematic uses not related to structural conditions result from the evolution of farming systems generally characterised by reduced tillage systems, largescale farms and the availability of highly efficient, low-priced herbicides such as glyphosate. Examples of systematic uses include the use of glyphosate for crop desiccation, for the destruction of cover crops
and temporary grasslands, and for weed management in annual and perennial crop systems. In the case of systematic uses, multiple inter-related factors may hinder the shift to non-chemical alternatives.
These include: limited, and in some cases no, availability of and access to alternative inputs and adapted machinery; constraints and opportunities due to regulations and subsidies; lack of advice, knowledge and references regarding alternative practices; uncertainties, risks and variability in agronomic performance and profitability of alternative practices; constraints in farm resources; commercial context; challenges in terms of labour organisation; and cultural and cognitive aspects.
Further research is needed to assess the conditions, including the economic and technical aspects as well as systemic contexts, that are required for enhancing the adoption of non-chemical alternatives to
glyphosate.
Since the introduction of glyphosate-resistant crops, glyphosate has become the most common and widely used herbicide around the world. Due to its intensive use and ability to bind to soil particles, it can be found at low concentrations in the environment. The effect of these remnants of glyphosate in plants has not been broadly studied; however, glyphosate 1,000 to 100,000 times less concentrated than the recommended field dose promoted growth in several species in laboratory and greenhouse experiments. However, this effect is rarely observed in agricultural fields, where complex communities of microbes have a central role in the way plants respond to external cues. Our study reveals how root-associated bacteria modulate the responses of Arabidopsis to low doses of glyphosate, shifting between growth promotion and growth inhibition.
The widespread use of pesticides has resulted in detectable residues throughout the environment, sometimes at concentrations well above regulatory limits. Therefore, the development of safe, effective, field-practical, and economically feasible strategies to mitigate the effects of pesticides is warranted. Glyphosate is an organophosphorus herbicide that is degraded to aminomethylphosphonic acid (AMPA), a toxic and persistent metabolite that can accumulate in soil and sediment and translocate to plants. In this study, we investigated the binding efficacy of activated carbon (AC) and calcium montmorillonite (CM) clay to decrease AMPA bioavailability from soil and AMPA translocation to plants. Adsorption isotherms and thermodynamic studies on AC and CM were conducted and showed tight binding (enthalpy values >-20 kJ/mol) for AMPA with high capacities (0.25 mol/kg and 0.38 mol/kg, respectively), based on derivations from the Langmuir model. A hydra assay was utilized to indicate toxicity of AMPA and the inclusion of 1% AC and CM both resulted in 90% protection of the hydra (**p ≤ 0.01). Further studies in glyphosate-contaminated soil showed that AC and CM significantly reduced AMPA bioavailability by 53% and 44%, respectively. Results in genetically modified (GM) corn showed a conversion of glyphosate to AMPA in roots and sprouts over a 10-day exposure duration. Inclusion of AC and CM reduced AMPA residues in roots and sprouts by 47%–61%. These studies collectively indicate that AC and CM are effective sorbents for AMPA and could be used to reduce AMPA bioavailability from soil and AMPA residues in GM corn plants.
Monitoring pesticide use is essential for assessing farming practices and the risks associated with the use of pesticides. Currently, there are neither consolidated, public data available on glyphosate use in Europe, nor a standardized categorization of its major uses. In this study, data on glyphosate sales and use in Europe were collected from multiple sources and compiled into a dataset of the agricultural use of glyphosate from 2013 to 2017. The survey shows that glyphosate represented 33% of the herbicide volume sold in Europe in 2017. One third of the acreage of annual cropping systems and half of the acreage of perennial tree crops received glyphosate annually. Glyphosate is widely used for at least eight agronomic purposes, including weed control, crop desiccation, terminating cover crops, terminating temporary grassland and renewing permanent grassland. Glyphosate use can be classified into occasional uses-i.e., exceptional applications, triggered by meteorological conditions or specific farm constraints-and recurrent uses, which are widespread practices that are embedded in farming systems and for which other agronomic solutions may exist but are not frequently used. This article proposes a framework for the precise monitoring of glyphosate use, based on the identification of the cropping systems in which glyphosate is used, the agronomic purposes for which it is employed, the dose used and the rationale behind the different uses.
Honey bees are important agricultural pollinators that rely on a specific gut microbiota for the regulation of their immune system and defense against pathogens. Environmental stressors that affect the bee gut microbial community, such as antibiotics and glyphosate, can indirectly compromise bee health. Most of the experiments demonstrating these effects have been done under laboratory conditions with pure chemicals. Here, we investigated the oral and topical effects of various concentrations of glyphosate in a herbicide formulation on the honey bee gut microbiota and health under laboratory and field conditions. Under all of these conditions, the formulation, dissolved in sucrose syrup or water, affected the abundance of beneficial bacteria in the bee gut in a dose-dependent way. Mark-recapture experiments also demonstrated that bees exposed to the formulation were more likely to disappear from the colony, once reintroduced after exposure. Although no visible effects were observed for hives exposed to the formulation in field experiments, challenge trials with the pathogen Serratia marcescens, performed under laboratory conditions, revealed that bees from hives exposed to the formulation exhibited increased mortality compared with bees from control hives. In the field experiments, glyphosate was detected in honey collected from exposed hives, showing that worker bees transfer xenobiotics to the hive, thereby extending exposure and increasing the chances of exposure to recently emerged bees. These findings show that different routes of exposure to glyphosate-based herbicide can affect honey bees and their gut microbiota.
Glufosinate is a key herbicide to manage glyphosate‐resistant weeds mainly because it is a broad‐spectrum herbicide, and transgenic glufosinate‐resistant crops are available. Although glufosinate use has increased exponentially over the past decade, the treated area with this herbicide is far less than that with glyphosate. This is because glufosinate often provides inconsistent performance in the field, which is attributed to several factors including environmental conditions, application technology, and weed species. Glufosinate is also highly hydrophilic and does not translocate well in plants, generally providing poor control of grasses and perennial species. In the soil, glufosinate is rapidly degraded by microorganisms, leaving no residual activity. While there have been concerns regarding glufosinate toxicology, its proper use can be considered safe. Glufosinate is a fast‐acting herbicide that was first discovered as a natural product, and is the only herbicide presently targeting glutamine synthetase. The mode of action of glufosinate has been controversial, and the causes for the rapid phytotoxicity have often been attributed to ammonia accumulation. Recent studies indicate that the contact activity of glufosinate results from the accumulation of reactive oxygen species and subsequent lipid peroxidation. Glufosinate disrupts both photorespiration and the light reactions of photosynthesis, leading to photoreduction of molecular oxygen, which generates reactive oxygen species. The new understanding of the mode of action provided new ideas to improve the herbicidal activity of glufosinate. Finally, a very few weed species have evolved glufosinate resistance in the field, and the resistance mechanisms are generally not well understood requiring further investigation. © 2020 Society of Chemical Industry
Glyphosate is the active ingredient of numerous commercial formulations of herbicides applied in different sectors, from agriculture to aquaculture. Due to its widespread use around the world, relatively high concentrations of glyphosate have been detected in soil and aquatic environments. The presence of glyphosate in aquatic ecosystems has aroused the attention of researchers because of its potential negative effects on living organisms, both animals and plants. In this context, this review intends to summarize results of studies aimed at evaluating the effects of glyphosate (both as active ingredient and component of commercial formulations) on marine invertebrates. Generally, data obtained in acute toxicity tests indicate that glyphosate and its commercial formulations are lethal at high concentrations (not environmentally realistic), whereas results of long-lasting experiments indicate that glyphosate can markedly affect biological responses of marine invertebrates. Consequently, more efforts should be addressed at evaluating chronic or sub-chronic effects of such substances to marine invertebrate species.
To evaluate the hormetic effect of glyphosate on Echinochloa colona, two pot studies were done in the screenhouse at the Gatton Campus, the University of Queensland, Australia. Glyphosate was sprayed at the 3–4 leaf stage using different doses [(0, 5, 10, 20, 40, 80 and 800 g a.e. ha⁻¹) and (0, 2.5, 5, 10, 20 and 800 g a.e. ha⁻¹)] in the first and second study, respectively. In the second study, two soil moistures (adequately-watered and water-stressed), and two E. colona biotypes, glyphosate-resistant and glyphosate-susceptible, were included. In both studies, plants that were treated with glyphosate at 2.5–40 g ha⁻¹ grew taller and produced more leaves, tillers, inflorescences and seeds than the control treatment. In the first study, 5 g ha⁻¹ glyphosate resulted in the maximum aboveground biomass (increase of 34% to 118%) compared with the control treatment. In the second study, the adequately-watered and glyphosate low dose treatments caused an increase in all the measured growth parameters for both biotypes. For example, total dry biomass was increased by 64% and 54% at 5 g ha⁻¹ in the adequately-watered treatments for the resistant and susceptible biotypes, respectively, compared with the control treatment. All measured traits tended to decrease with increasing water stress and the stimulative growth of low doses of glyphosate could not compensate for the water stress effect. The results of both studies showed a hormetic effect of low doses of glyphosate on E. colona biotypes and such growth stimulation was significant in the range of 5 to 10 g ha⁻¹ glyphosate. Water availability was found to be effective in modulating the stimulatory outcomes of glyphosate-induced hormesis. No significant difference was observed between the resistant and susceptible biotypes for hormesis phenomenon. The study showed the importance of precise herbicide application for suppressing weed growth and herbicide resistance evolution.
The widely successful use of synthetic herbicides over the past 70 years has imposed strong and widespread selection pressure, leading to the evolution of herbicide resistance in hundreds of weed species. Both target-site resistance (TSR) and non-target-site resistance (NTSR) mechanisms have evolved to most herbicide classes. TSR often involves mutations in genes encoding the protein targets of herbicides, affecting the binding of the herbicide either at or near catalytic domains or in regions affecting access to them. Most of these mutations are non-synonymous single-nucleotide polymorphisms, but polymorphisms in more than one codon or entire codon deletions have also evolved. Some herbicides bind multiple proteins, making TSR mechanisms more difficult to evolve. Increased amounts of protein target, by increased gene expression or by gene duplication, is an important, albeit less common, TSR mechanism. NTSR mechanisms include reduced absorption or translocation and increased sequestration or metabolic degradation. The mechanisms that can contribute to NTSR are complex and often involve genes that are members of large gene families. For example, enzymes involved in herbicide metabolism–based resistances include cytochromes P450, glutathione-S-transferases, glucosyl and other transferases, aryl acylamidase, and others. Both TSR and NTSR mechanisms can combine at the individual level to produce higher resistance levels. The vast array of herbicide-resistance mechanisms for generalist (NTSR) and specialist (TSR and some NTSR) adaptations that have evolved over a few decades illustrate the evolutionary resilience of weed populations to extreme selection pressures. These evolutionary processes drive herbicide and herbicide-resistant crop development and resistance management strategies.
In this work, earthworm effect on the efficiency of biobeds for glyphosate degradation was studied. Three biomixtures with and without the addition of earthworms (Eisenia fetida species) were evaluated. The initial concentration of glyphosate was 1000 mg/kg biomixture. Glyphosate and biological parameters were measured as a function of time. Earthworm survival, biomass, and reproduction were evaluated as well. All biomixtures that contain earthworms reached 90% of glyphosate degradation at 90 days in comparison with the biomixtures without earthworms that reached 80% approximately at the same time. Also, within the biomixtures that contained earthworms, glyphosate degradation rate was significantly higher in the one made up with soil and wheat stubble (Ws-E) showing excellent capacity for aminomethylphosphonic acid (AMPA) degradation, the main metabolite of glyphosate degradation. In addition, a study performed after the vermiremediation process showed that E. fetida can tolerate high glyphosate concentration without modifications in its life traits. It can be concluded that the use of E. fetida within the biobeds is an excellent combination to improve glyphosate and AMPA removal.
The herbicide glyphosate inhibits the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in the aromatic amino acid (AAA) biosynthetic pathway, also known as the shikimate pathway. Amaranthus palmeri is a fast-growing weed, and several populations have evolved resistance to glyphosate through increased EPSPS gene copy number. The main objective of this study was to elucidate the regulation of the shikimate pathway and determine whether the regulatory mechanisms of glyphosate-sensitive and glyphosate-resistant plants were different. Leaf disks of sensitive and resistant (due to EPSPS gene amplification) A. palmeri plants were incubated for 24 h with glyphosate, AAA, glyphosate + AAA, or several intermediates of the pathway: shikimate, quinate, chorismate and anthranilate. In the sensitive population, glyphosate induced shikimate accumulation and induced the gene expression of the shikimate pathway. While AAA alone did not elicit any change, AAA applied with glyphosate abolished the effects of the herbicide on gene expression. It was not possible to fully mimic the effect of glyphosate by incubation with any of the intermediates, but shikimate was the intermediate that induced the highest increase (three-fold) in the expression level of the genes of the shikimate pathway of the sensitive population. These results suggest that, in this population, the lack of end products (AAA) of the shikimate pathway and shikimate accumulation would be the signals inducing gene expression in the AAA pathway after glyphosate application. In general, the effects on gene expression detected after the application of the intermediates were more severe in the sensitive population than in the resistant population. These results suggest that when EPSPS is overexpressed, as in the resistant population, the regulatory mechanisms of the AAA pathway are disrupted or buffered. The mechanisms underlying this behavior remain to be elucidated.
Glyphosate is the world's most widely used herbicide. The commercial success of this molecule is due to its nonselectivity and its action, which would supposedly target specific biosynthetic pathways found mainly in plants. Multiple studies have however provided evidence for high sensitivity of many nontarget species to glyphosate and/or to formulations (glyphosate mixed with surfactants). This herbicide, found at significant levels in aquatic systems through surface runoffs, impacts life history traits and immune parameters of several aquatic invertebrates' species, including disease‐vector mosquitoes. Mosquitoes, from hatching to emergence, are exposed to aquatic chemical contaminants. In this study, we first compared the toxicity of pure glyphosate to the toxicity of glyphosate‐based formulations for the main vector of avian malaria in Europe, Culex pipiens mosquito. Then we evaluated, for the first time, how field‐realistic dose of glyphosate interacts with larval nutritional stress to alter mosquito life history traits and susceptibility to avian malaria parasite infection. Our results show that exposure of larvae to field‐realistic doses of glyphosate, pure or in formulation, did not affect larval survival rate, adult size, and female fecundity. One of our two experimental blocks showed, however, that exposure to glyphosate decreased development time and reduced mosquito infection probability by malaria parasite. Interestingly, the effect on malaria infection was lost when the larvae were also subjected to a nutritional stress, probably due to a lower ingestion of glyphosate.
Gene copy number variation is a predominant mechanism used by organisms to respond to selective pressures from the environment. This often results in unbalanced structural variations that perpetuate as adaptations to sustain life. However, the underlying mechanisms that give rise to gene proliferation are poorly understood. Here, we show a unique result of genomic plasticity in Amaranthus palmeri: a massive, ~ 400 kbp extrachromosomal circular DNA (eccDNA), that harbors the 5-ENOYLPYRUVYLSHIKIMATE-3-PHOSPHATE SYNTHASE (EPSPS) gene and 58 other genes whose encoded functions traverse detoxification, replication, recombination, transposition, tethering, and transport. Gene expression analysis under glyphosate stress showed transcription of 41 of these 59 genes, with high expression of EPSPS, as well as genes coding for aminotransferases, zinc-finger proteins and several uncharacterized proteins. The genomic architecture of the eccDNA replicon is comprised of a complex arrangement of repeat sequences and mobile genetic elements interspersed among arrays of clustered palindromes that may be crucial for stability, DNA duplication and tethering, and/or a means of nuclear integration of the adjacent and intervening sequences. Comparative analysis of orthologous genes in grain amaranth (Amaranthus hypochondriacus) and water-hemp (Amaranthus tuberculatus) suggest that higher-order chromatin interactions contribute to the genomic origins of the Amaranthus palmeri eccDNA replicon structure.
Background
Since the classification of glyphosate as a Group 2A substance “probably carcinogenic to humans” by the IARC in 2015, human health concerns have been raised regarding the exposure of operators, bystanders, and consumers. Urine measurement studies have been conducted, but since toxicokinetic data on glyphosate in humans is lacking, a meaningful interpretation of this data regarding exposure is not possible.
Objective
This study aims to determine the fraction of glyphosate and AMPA excretion in urine after consuming ordinary food with glyphosate residue, to estimate dietary glyphosate intake.
Methods
Twelve participants consumed a test meal with a known amount of glyphosate residue and a small amount of AMPA. Urinary excretion was examined for the next 48 h.
Results
Only 1% of the glyphosate dose was excreted in urine. The urinary data indicated the elimination half-life was 9 h. For AMPA, 23% of the dose was excreted in urine, assuming that no metabolism of glyphosate to AMPA occurred. If all of the excreted AMPA was a glyphosate metabolite, this corresponds to 0.3% of the glyphosate dose on a molar basis.
Conclusion
This study provides a basis for estimating oral glyphosate intake using urinary biomonitoring data.
The evolution of resistance to herbicides in weeds has become a great challenge for global agricultural production. Weeds have evolved resistance to herbicides through many different physiological mechanisms. Some weed species are known to secrete herbicide molecules from roots into the rhizosphere upon being treated. However, root exudation of herbicides as a mechanism of resistance has only recently been identified in two weed species. Root exudation pathways have been investigated in Arabidopsis, and this work suggested that ATP‐binding cassette (ABC) and multidrug and toxic compound extrusion (MATE) transporters play a role in the secretion of primary and secondary plant products from roots. We hypothesize that the mechanisms involved in root exudation of herbicides that result in resistance are mediated by overactive or overexpressed transporters, probably similar to those found for the exudation of primary and secondary compounds from roots. Elucidating the molecular and physiological basis of root exudation in herbicide‐resistant weeds would improve our understanding of the pathways involved in herbicide root secretion mediated by transporters in plants. © 2020 Society of Chemical Industry
This commentary does not concern itself with the need for, or the value of glyphosate as an agrochemical: rather it examines the scientific basis for the various conclusions reached at different times by a number of regulatory authorities and by the International Agency on Research on Cancer (IARC). Why do they differ? An appropriate regulatory stance depends critically on the application of good science and consistency in the application of established criteria. Constant reappraisal of the methodology used is essential. © 2020 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
No herbicide with a new molecular site of action (SOA) has been introduced since the 1980s. Since then, the widespread evolution of resistance of weeds to most commercial herbicides has greatly increased the need for herbicides with new SOAs. Two untried strategies for the discovery on new herbicide SOAs are discussed. Some primary metabolism intermediates are phytotoxic (e.g., protoporphyrin IX and sphingoid bases), and, because of this, the in vivo concentrations of these compounds are maintained at very low levels by plants. The determination of all primary metabolite phytotoxicities and pool sizes will identify targets of interest. Targeting SOAs that result in accumulation of phytotoxic compounds is the first novel approach to herbicide discovery. The second approach is to identify potential SOAs with very low in vivo enzyme levels. We know that higher numbers of enzyme molecules for a SOA requires more herbicide to kill a plant. Modern proteomic methods can identify low enzyme level SOAs for biorational herbicide discovery. These approaches might be useful in discovery of herbicides more closely related to natural compounds and that can be used in lower doses.
Six Johnsongrass populations suspected of being glyphosate resistant were collected from railways and freeways near Cordoba (SW Spain), where glyphosate is the main weed control tool. The 50% reduction in shoot fresh weight (GR50) values obtained for these six populations ranged from 550.4 to 1169 g ae ha−1, which were 4.2 to 9 times greater than the value obtained for the susceptible population. Glyphosate was equally metabolized to the same extent in both resistant and susceptible populations, with no significant differences in either 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibition or basal activity. No amino acid substitutions were observed in any of the resistant populations. Slight but significant differences in glyphosate penetration were observed among some but not all of the resistant populations and for the times of incubation assayed, although these differences were not considered further. The proposed primary mechanism of resistance in these six glyphosate-resistant Johnsongrass populations is reduced herbicide translocation, because the amount of glyphosate that translocated from treated leaves to shoots and roots in the susceptible population was double that observed in the resistant populations. As glyphosate multiple resistance due to more than one mechanism is not uncommon, this is the first time that glyphosate-resistant Johnsongrass populations have been fully described for all known mechanisms.
The herbicide glyphosate is widely used to control weeds in grain crops. The overuse of glyphosate has induced issues such as contamination of surface water, decreased soils fertility, adverse effects on soil microbiota and possible incorporation in food chains. Here we review biochemical, agricultural, microbiological and analytical aspects of glyphosate. We discuss uptake, translocation, toxicity, degradation, complexation behaviour, analytical monitoring techniques and resistance emergence in crops. We provide data of glyphosate toxicity on different ecosystems. Experiments reveal that excessive glyphosate use induces stress on crops and on non-target plants, and is toxic for mammalians, microorganisms and invertebrates. The long half-life period of glyphosate and its metabolites under different environmental conditions is a major concern. Development of analytical methods for the detection of glyphosate is important because glyphosate has no chromophoric or fluorophoric groups.
Background:
Glyphosate-based herbicides are one of the most commonly used compounds to control perennial weeds around the world. This compound is very persistent in the environment and tends to filter into aquatic ecosystems, affecting non-target species such as mosquito larvae. Aedes aegypti mosquitoes are vectors of multiple arboviruses such as dengue and Zika. Glyphosate can be degraded into non-harmful environmental compounds by Lysinibacillus sphaericus, a spore forming bacterium which can also kill Ae. aegypti larvae. In this study, we assessed the effect of glyphosate concentrations, typically used in Colombia, on the entomopathogenic activity of L. sphaericus against Ae. aegypti larvae.
Methods:
Bioassays and toxicity curves were performed to compare the larval mortality between different treatments with and without bacteria and glyphosate (Roundup 747®). Larvae were exposed to both bacteria and glyphosate by adding the compound on chloride-free water. Comparisons were made using both probit regression and ANOVA analysis.
Results:
ANOVA showed a significant difference in larval mortality when adding glyphosate and L. sphaericus at the same time. Thus, a positive synergic effect on larval mortality was found when L. sphaericus and glyphosate were mixed. According to probit analysis, median lethal dose (LD50) for bacterial mixture was of 106.23 UFC/ml and for glyphosate was 2.34 g/l.
Conclusions:
A positive synergic effect on the mortality of larval Ae. aegypti when exposed to L. sphaericus mixture and glyphosate was found. Molecular studies focusing on the toxin production of L. sphaericus are required to understand more about this synergistic effect.
Since the introduction of glyphosate-tolerant genetically-modified plants, the global use of glyphosate has increased dramatically making it the most widely used pesticide on the planet. There is considerable controversy concerning the carcinogenicity of glyphosate with scientists and regulatory authorities involved in the review of glyphosate having markedly different opinions. One key aspect of these opinions is the degree to which glyphosate causes cancer in laboratory animals after lifetime exposure. In this review, twenty-one chronic exposure animal carcinogenicity studies of glyphosate are identified from regulatory documents and reviews; 13 studies are of sufficient quality and detail to be reanalyzed in this review using trend tests, historical control tests and pooled analyses. The analyses identify 37 significant tumor findings in these studies and demonstrate consistency across studies in the same sex/species/strain for many of these tumors. Considering analyses of the individual studies, the consistency of the data across studies, the pooled analyses, the historical control data, non-neoplastic lesions, mechanistic evidence and the associated scientific literature, the tumor increases seen in this review are categorized as to the strength of the evidence that glyphosate causes these cancers. The strongest evidence shows that glyphosate causes hemangiosarcomas, kidney tumors and malignant lymphomas in male CD-1 mice, hemangiomas and malignant lymphomas in female CD-1 mice, hemangiomas in female Swiss albino mice, kidney adenomas, liver adenomas, skin keratoacanthomas and skin basal cell tumors in male Sprague-Dawley rats, adrenal cortical carcinomas in female Sprague-Dawley rats and hepatocellular adenomas and skin keratocanthomas in male Wistar rats.
The honey bee Apis mellifera is the most abundant managed pollinator in diverse crops worldwide. Consequently, it is exposed to a plethora of environmental stressors, among which are the agrochemicals. In agroecosystems, the herbicide glyphosate (GLY) is one of the most applied. In laboratory assessments, GLY affects the honey bee larval development by delaying its moulting, among other negative effects. However, it is still unknown how GLY affects larval physiology when there are no observable signs of toxicity. We carried out a longitudinal experimental design using the in vitro rearing procedure. Larvae were fed with food containing or not a sub-lethal dose of GLY in chronic exposure (120 h). Individuals without observable signs of toxicity were sampled and their gene expression profile was analyzed with a transcriptomic approach to compare between treatments. Even though 29% of larvae were asymptomatic in the exposed group, they showed transcriptional changes in several genes after the GLY chronic intake. A total of 19 transcripts were found to be differentially expressed in the RNA-Seq experiment, mainly linked with defensive response and intermediary metabolism processes. Furthermore, the enriched functional categories in the transcriptome of the exposed asymptomatic larvae were linked with enzymes with catalytic and redox activity. Our results suggest an enhanced catabolism and oxidative metabolism in honey bee larvae as a consequence of the sub-lethal exposure to GLY, even in the absence of observable symptoms.
BACKGROUND
Stimulation of plant growth by low doses of a toxic compound is defined as a hormetic effect. Exposure of plants to low doses of glyphosate can cause stimulatory effects on growth or other variables. Sugarcane is the major biofuel and sugar‐production crop cultivated in Brazil, but its expansion to new areas is limited; therefore, there is a demand for new technologies to improve sugarcane production per unit area. The use of pesticides to stimulate growth through the hormetic effect might be a suitable strategy to increase sugarcane yields. The purpose of this research was to investigate the effect of a low dose of glyphosate on metabolic compound accumulation, leaf phosphorus (P) concentration, and morphological variables across a one‐year sugarcane cycle, as well as to determine whether the glyphosate effect was sustained and effective in improving the yield and technological quality of the sugarcane at harvest.
RESULTS
The application of a low dose of glyphosate led to higher concentrations of shikimic acid and quinic acid, higher leaf P concentrations, and improved plant growth, yield, and technological quality of the sugarcane, by increasing the Brix% juice, pol% cane, total recoverable sugar, tons of culms per hectare, and tons of pol per hectare, relative to the results for an untreated control.
CONCLUSIONS
The increased growth stimuli, observed through several variables, promoted an improvement in sugarcane yield. Therefore, the application of a low dose of glyphosate to sugarcane is a promising practice for crop management. © 2020 Society of Chemical Industry
The repeated evolution of herbicide resistance has been cited as an example of genetic parallelism, wherein separate species or genetic lineages utilize the same genetic solution in response to selection. However, most studies that investigate the genetic basis of herbicide resistance examine the potential for changes in the protein targeted by the herbicide rather than considering genome-wide changes. We used a population genomics screen and targeted exome re-sequencing to uncover the potential genetic basis of glyphosate resistance in the common morning glory, Ipomoea purpurea, and to determine if genetic parallelism underlies the repeated evolution of resistance across replicate resistant populations. We found no evidence for changes in 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSPS), glyphosate’s target protein, that were associated with resistance, and instead identified five genomic regions that showed evidence of selection. Within these regions, genes involved in herbicide detoxification—cytochrome P450s, ABC transporters, and glycosyltransferases—are enriched and exhibit signs of selective sweeps. One region under selection shows parallel changes across all assayed resistant populations whereas other regions exhibit signs of divergence. Thus, while it appears that the physiological mechanism of resistance in this species is likely the same among resistant populations, we find patterns of both similar and divergent selection across separate resistant populations at particular loci.
Six experiments were conducted in 2018 on field sites located in Arkansas, Indiana, Michigan, Nebraska, Ontario, and Wisconsin to evaluate the off-target movement (OTM) of dicamba under field-scale conditions. The highest estimated dicamba injury in non-dicamba-resistant (DR) soybean was 50, 44, 39, 67, 15, and 44% injury for non-covered areas and 59, 5, 13, 42, 0, and 41% injury for covered areas during dicamba application in Arkansas, Indiana, Michigan, Nebraska, Ontario, and Wisconsin, respectively. The level of injury generally decreased exponentially as the downwind distance increased under covered and non-covered areas at all sites. There was an estimated 10% injury in non-DR soybean at 113, 8, 11, 8, and 8 m; and estimated 1% injury at 293, 28, 71, 15, and 19 m from the edge of treated field downwind when plants were not covered during dicamba application in Arkansas, Indiana, Michigan, Ontario and Wisconsin, respectively. Filter paper collectors placed from 4 up to 137 m downwind from the edge of the sprayed area suggested that the dicamba deposition reduced exponentially with distance. The greatest injury to non-DR soybean from dicamba OTM occurred at Nebraska and Arkansas (as far as 250 m). Non-DR soybean injury was greatest adjacent to the dicamba sprayed area but, injury decreased with no injury beyond 20 m downwind or any other direction from the dicamba sprayed area in Indiana, Michigan, Ontario, and Wisconsin. The presence of soybean injury under covered and non-covered areas during the spray period for primary drift suggests that secondary movement of dicamba was evident at five sites. Further research is needed to determine the exact forms of secondary movement of dicamba under different environmental conditions.
BACKGROUND
The noxious annual herb, Parthenium hysterophorus L. (Asteraceae), is an invasive weed of global significance, threatening food security, biodiversity and human health. In South Africa, chemical control is frequently used to manage P. hysterophorus, however, concern surrounds increasing atmospheric CO2 levels, which may reduce the efficacy of glyphosate against the weed. Therefore, this study aimed to determine the susceptibility of P. hysterophorus to glyphosate (1L/ha: recommended) after being grown for five generations in Convirons under ambient (400 ppm) and elevated (600 and 800 ppm) CO2.
RESULTS
Glyphosate efficacy decreased with increasing CO2, with mortalities of 100, 83 and 75% recorded at 400, 600 and 800 ppm, respectively. Parthenium hysterophorus experienced enhanced growth and reproduction under elevated CO2, however, glyphosate application was highly damaging, reducing the growth and flowering of plants across all CO2 treatments. Physiologically, glyphosate‐treated plants, in all CO2 treatments, suffered severe declines of >90% in chlorophyll content, maximum quantum efficiency (F v/Fm), photon absorption (ABS/RC), electron transport (ET 0/RC) and performance index (PI ABS), albeit at slower rates for plants grown under elevated CO2. Low levels of recovery from glyphosate were documented only for plants grown under elevated CO2 and was attributed to their increased biomass.
CONCLUSION
These results suggest that increasing CO2 levels may hinder chemical control efforts used against P. hysterophorus in the future, advocating for further investigation using multigenerational CO2 studies and the maintenance of effective spraying programs at present. © 2020 Society of Chemical Industry
This book is part of the "CABI Invasive Series", which addresses all topics relating to invasive species, including biosecurity surveillance, mapping and modelling, economics of invasive species and species interactions in plant invasions. Aimed at researchers, upper-level students and policy makers, titles in the series provide international coverage of topics related to invasive species, including both a synthesis of facts and discussions of future research perspectives and possible solutions. This book specifically aims to examine the nexus of climate change and biological invasions, and the resulting impacts, and to identify means to reduce the vulnerability and increase the resiliency of managed and unmanaged ecosystems. It is divided into four parts: (i) the dimensions of the problem: background and science; (ii) case studies; (iii) management: detection and prevention; and (iv) management: control and adaptation.
Glyphosate-resistant (GR) crops, commercially referred to as glyphosate-tolerant (GT), started the revolution in crop biotechnology in 1996. Growers rapidly accepted GR crops whenever they became available and made them the most rapidly adopted technology in agriculture history. Adoption usually meant sole reliance on glyphosate [N-(phosphonomethyl)glycine, CAS No. 1071-83-6] for weed control. Not surprisingly, weeds eventually evolved resistance and are forcing growers to change their weed management practices. Today, the widespread dissemination of GR weeds that are also resistant to other herbicide modes-of-action (MoA) has greatly reduced the value of the GR crop weed management systems. However, growers continue to use the technology widely in six major crops throughout North and South America. Integrated chemistry and seed providers seek to sustain glyphosate efficacy by promoting glyphosate combinations with other herbicides and stacking the traits necessary to enable the use of partner herbicides. These include glufosinate {4-[hydroxy(methyl)phosphinoyl]-DL-homoalanine, CAS No. 51276-47-2}, dicamba (3,6-dichloro-2-methoxybenzoic acid, CAS No. 1918-00-9), 2,4-D [2-(2,4-dichlorophenoxy)acetic acid, CAS No. 94-75-7], 4-hydroxyphenyl pyruvate dioxygenase inhibitors, acetyl coenzyme A carboxylase (ACCase) inhibitors, and other herbicides. Unfortunately, herbicide companies have not commercialized a new MoA for over 30 years and have nearly exhausted the useful herbicide trait possibilities. Today, glyphosate-based crop systems are still mainstays of weed management, but they cannot keep up with the capacity of weeds to evolve resistance. Growers desperately need new technologies, but no technology with the impact of glyphosate and GR crops is on the horizon. Although the expansion of GR crop traits is possible into new geographic areas and crops such as wheat and sugarcane and could have high value, the Roundup Ready® revolution is over. Its future is at a nexus and dependent on a variety of issues.
The chemical and biological properties of glyphosate are key to understanding its fate in the environment and potential risks to non-target organisms. Glyphosate is polar and water soluble and therefore does not bioaccumulate, biomagnify, or accumulate to high levels in the environment. It sorbs strongly to particles in soil and sediments and this reduces bioavailability so that exposures to non-target organisms in the environment are acute and decrease with half-lives in the order of hours to a few days. The target site for glyphosate is not known to be expressed in animals, which reduces the probability of toxicity and small risks. Technical glyphosate (acid or salts) is of low to moderate toxicity; however, when mixed with some formulants such as polyoxyethylene amines (POEAs), toxicity to aquatic animals increases about 15-fold on average. However, glyphosate and the formulants have different fates in the environment and they do not necessarily co-occur. Therefore, toxicity tests on formulated products in scenarios where they would not be used are unrealistic and of limited use for assessment of risk. Concentrations of glyphosate in surface water are generally low with minimal risk to aquatic organisms, including plants. Toxicity and risks to non-target terrestrial organisms other than plants treated directly are low and risks to terrestrial invertebrates and microbial processes in soil are very small. Formulations containing POEAs are not labeled for use over water but, because POEA rapidly partitions into sediment, risks to aquatic organisms from accidental over-sprays are reduced in shallow water bodies. We conclude that use of formulations of glyphosate under good agricultural practices presents a de minimis risk of direct and indirect adverse effects in non-target organisms.
Widespread adoption of glyphosate-resistant crops and concomitant reliance on glyphosate for weed control set an unprecedented stage for the evolution of herbicide-resistant weeds. There are now 48 weed species that have evolved glyphosate resistance. Diverse glyphosate-resistance mechanisms have evolved, including single, double, and triple amino acid substitutions in the target-site gene, duplication of the gene encoding the target site, and others that are rare or nonexistent for evolved resistance to other herbicides. This review summarizes these resistance mechanisms, discusses what is known about their evolution, and concludes with some of the impacts glyphosate-resistant weeds have had on weed management.
The adverse effects of glyphosate herbicide on plants are well recognised, however, potential hormetic effects have not been well studied. This study aimed to use tomato as a model organism to explore the potential hermetic effects of glyphosate in water (0–30 mg L⁻¹) and in compost soil (0–30 mg kg⁻¹). The growth-promoting effects of glyphosate at concentrations of 0.03–1 mg L⁻¹ in water or 0.03–1 mg kg⁻¹ in compost were demonstrated in tomato for the first time. These hormetic effects were manifest as increased hypocotyl and radicle growth of seedlings germinated on paper towel soaked in glyphosate solution and also in crops which had been sprayed with glyphosate. Increased rates of photosynthesis (up to 2-fold) were observed in 4-week old crops when seeds were sown in compost amended with glyphosate and also when leaves were sprayed with glyphosate. The examination of chloroplast morphology using transmission electron microscopy revealed that the hormetic effects were associated with elongation of chloroplasts, possibly due to lateral expansion of thylakoid grana.
The intensive use of glyphosate in industrial agriculture may lead to freshwater contamination, encouraging studies of its toxic effect on non-target aquatic organisms. Glyphosate-based commercial formulations contain adjuvants, making them even more toxic than the active ingredient (a.i.) itself. The golden mussel Limnoperna fortunei is a freshwater invasive species which has been found to increase glyphosate dissipation in water and to accelerate eutrophication. The aim of this study is to evaluate the capability of L. fortunei to reduce the concentration of glyphosate in two commercial formulations, Roundup Max® and Glifosato Atanor®. Results were compared with the decay of the a.i. alone and in presence of mussels. Evasive response and toxicity tests were performed in a first set of trials to analyze the response of L. fortunei exposed to Roundup Max® and Glifosato Atanor®. Subsequently, we conducted a 21-day degradation experiment in 2.6-L microcosms applying the following treatments: 6 mg L⁻¹ of technical-grade glyphosate (G), Glifosato Atanor® (A), Roundup Max® (R), 20 mussels in dechlorinated tap water (M), and the combination of mussels and herbicide either in the technical-grade (MG) or formulated form (MA and MR) (all by triplicate). Samples were collected at days 0, 1, 7, 14 and 21. No significant differences in glyphosate decay were found between treatments with mussels (MG: 2.03 ± 0.40 mg L⁻¹; MA: 1.60 ± 0.32 mg L⁻¹; MR: 1.81 ± 0.21 mg L⁻¹), between glyphosate as a.i. and the commercial formulations, and between the commercial formulations, suggesting that the adjuvants did not affect the degrading potential of L. fortunei. In addition to the acceleration of glyphosate dissipation in water, there was an increase in the concentration of dissolved nutrients in water (N–NH4⁺ and P-PO4³⁻) even higher than that caused by the filtering activity of the mussels, probably resulting from stress or from the degradation of glyphosate and adjuvants. We believe that a larger bioavailability of these nutrients due to glyphosate metabolization mediated by mussels would accelerate eutrophication processes in natural water bodies. The approach used here, where L. fortunei was exposed to two commercial formulations actually used in agricultural practices, sheds light on the potential impact of glyphosate decay on water bodies invaded by this species.
The literature of biological activity of herbicides is vast. Thus, this short review contains only what we consider to the most important aspects of the topic. We divide the herbicides into three main groups: 1) herbicides that target biochemical pathways
and physiological processes involved with photosynthesis, 2) herbicides that inhibit the formation of biological building blocks (i.e., sugars, amino acids and fatty acids) or their assembly into biopolymers, and 3) herbicides with other modes of action.
The widespread use and increasing reliance on herbicides for weed control has resulted in a global epidemic of evolved herbicide resistance in weed populations. In response, there has been a great deal of research effort to document resistance cases, understand the genetic and physiological mechanisms of resistance and use models and model organisms to explore resistance management strategies. Here, we argue that the field of epidemiology, which systematically studies the extent, distribution and determinants of a harmful organism or condition, can greatly contribute to our efforts to understand the emergence, selection and spread of herbicide resistance. By systematically collecting data on weed abundance and distribution, the frequency and mechanisms of resistance, and agronomic and environmental metadata, it is possible to develop statistical models that identify the underlying relationships between these elements. In doing so, these approaches can provide novel insight into the relative importance, origin and spread of different resistance mechanisms, and the agronomic, ecological and evolutionary drivers that dictate the dynamics of resistance evolution at local to global scales. Emerging technologies in weed surveillance, genomics and resistance diagnostics, statistics and data science will greatly facilitate the collection and analysis of large‐scale data sets, providing unprecedented potential for epidemiological analyses of the evolution of herbicide resistance at landscape scales.
The glyphosate controversy before the renewal of the authorization of glyphosate in the European Union (EU) once again turned the spotlight on pesticide regulation in the EU. In the EU, pesticides are attracting more public attention than in other parts of the world, and many nongovernmental organizations specifically target pesticide regulation, trying to influence politicians and other decision makers. Following an overview of the EU pesticide legislation and the impact hitherto on EU agriculture, this paper outlines the glyphosate controversy and presents the outcome of desk studies conducted in Germany, the United Kingdom, France, and Sweden on the potential effects of a glyphosate ban on agricultural productivity and farm income. All studies concluded that the loss of income depends very much on farm type and cropping practice, but they all reached the conclusion that particularly no-tillage farming/conservation agriculture will be facing severe problems without glyphosate to control weeds and terminate cover crops. No-tillage/conservation agriculture is viewed as an effective strategy to prevent soil erosion and loss of nutrients, which could become larger problems without glyphosate. Other issues highlighted in the studies were the impact on resistance management, as glyphosate is largely seen as a “herbicide-resistance breaker.” Without glyphosate, fundamental changes in farming practices in the EU are required, and it is hard to imagine that they will come without a cost, at least in the short term.
Glyphosate is easily translocated from shoots to roots and released into the rhizosphere. The objective of this study was to clarify the influence of glyphosate residues in the root tissue of glyphosate-treated weeds on wheat ( Triticum aestivum L.) growth and shikimate accumulation. Foliar application to 5-leaf downy brome ( Bromus tectorum L.) planted in sandy loam soil reduced wheat (cv. Tubbs 06) shoot fresh weight by 37-46% compared to the control when seeds were planted 0 and 1 d after applications. With Italian ryegrass [ Lolium perenne L. ssp. multiflorum (Lam.) Husnot], wheat shoot fresh weight was inhibited by 20-34% compared to the control at 0, 1, 3, and 5 days after applications to 1.5 and 5-leaf stage plants. Using a different wheat cultivar (cv. Stephens), shoot fresh weight was inhibited by 19-43% when seeds were planted 0 days after glyphosate applications to 1.5, 2 and 5-leaf stage B. tectorum and L. perenne planted in sandy loam soil compared with control. In contrast, some studies using treated L. perenne and B. tectorum planted in clay loam soil resulted in increases in wheat shoot fresh weight. L. perenne planted in water-saturated sandy loam soil showed no differences in either shoot or root fresh weight or shikimate accumulation in shoots or roots. Compared to the control plants, shikimate accumulation in roots increased 51- to 59-fold in wheat planted in sandy loam soil that previously contained B. tectorum and 13- to 49-fold in soil that previously contained L. perenne . In both studies, glyphosate was applied at the 1.5-leaf stage and wheat seeds were sown 0, 1 and 3 days after glyphosate applications. Thus, plant damage caused by glyphosate was associated with increased shikimate accumulation in the root tissue. Overall, crop damage caused by glyphosate residue to target plants was strongly influenced by soil type, soil water conditions, glyphosate sensitivity, target weed species identity, and weed densities.
Underlying the risk management of pesticides to protect human health and to facilitate trade among nations is sound scientific data on the levels of compliance with standards set by governments and international from monitoring of the levels of pesticides in foods. Although glyphosate is among the universally used pesticides in the world, monitoring has been hampered by the analytical difficulties in dealing with this highly polar compound. By using a liquid chromatography/tandem mass spectrometry (LC-MS/MS) method that permits accurate and reproducible determination of glyphosate, the prevalence, concentrations and compliance rates were determined. In this work, the glyphosate residues analyses in 7955 samples of fresh fruits and vegetables, milled grain products, pulse products, and finished foods available in Canada from April 2015 to March 2017 are reported. A total of 3366 samples (42.3%) contained detectable glyphosate residues. The compliance rate with Canadian regulations was 99.4 %. There were 46 non-compliant samples. Health Canada determined that there was no long-term health risk to Canadian consumers from exposure to the levels of glyphosate found in the samples of a variety of foods surveyed. Trends regarding glyphosate content with respect to food origin and food type are analyzed and discussed. The high level of compliance (99.4% of samples with the Canadian regulatory limits) and the lack of a health risk for non-compliant samples indicate that, with respect to glyphosates, the food available for sale in Canada is safe.
Robotic weed control for vegetables is necessary to increase crop productivity, avoid intensive hand weeding as labour shortages in developed countries such as United States has led to a surge in food production costs. However, development of a reliable, intelligent robotic system for weed control in real-time for vegetables still remains a challenging task. The main issue arises while distinguishing crops from weeds in real-time. In this paper, a novel technique to crop signalling to distinguish crops from in-row weeds in complex natural scenarios, such as high weed densities commonly found on organic farms, in real-time using machine vision is presented. Crop signalling is a simple and low-cost technique in which a signalling compound is produced by or applied to the crop and where the signalling compound is machine readable and helps to create visual features that uniquely distinguish the crops from weeds. The crop and weed mapping algorithm presented here were specially designed and developed for a vision-based weeding robot equipped with a micro-jet herbicide-spraying system for weed control in a lettuce field. The proposed technique involves weed/crop mapping and decision making. Experimental results show that the crop detection accuracy was 99.75%, and 98.11% of sprayable weeds were detected. The proposed technique is highly accurate, reliable and more robust than other sensor-based techniques presented in the literature.
Here we examined whether glyphosate affects the microbiota of herbivores feeding on non-target plants. Colorado potato beetles (Leptinotarsa decemlineata) were reared on potato plants grown in pots containing soil treated with glyphosate-based herbicide (GBH) or untreated. Per the manufacturer's safety recommendations, the GBH soil treatments were done two weeks prior to planting the potatoes. Later, two-day-old larvae were introduced to the potato plants and then collected in two phases, 4th instar larvae and adults. The larvae's internal microbiota and the adults' intestinal microbiota were examined by 16S rRNA gene sequencing. The beetles' microbial composition was affected by the GBH treatment and the differences in microbial composition between the control and insects exposed to GBH were more pronounced in the adults. The GBH treatment increased the relative abundance of Agrobacterium in the larvae and the adults. This effect may be related to the tolerance of some Agrobacterium species to glyphosate or to glyphosate-mediated changes in potato plants. On the other hand, the relative abundance of Enterobacteriaceae, Rhodobacter, Rhizobium and Acidovorax in the adult beetles and Ochrobactrum in the larvae were reduced in GBH treatment. These results demonstrate that glyphosate can impact microbial communities associated with herbivores feeding on non-target crop plants.
Glyphosate is a widely used herbicide worldwide. In 2015, the International Agency for Research on Cancer (IARC) reviewed glyphosate cancer bioassays and human studies and declared that the evidence for carcinogenicity of glyphosate is sufficient in experimental animals. We analyzed ten glyphosate rodent bioassays, including those in which IARC found evidence of carcinogenicity, using a multi-response permutation procedure that adjusts for the large number of tumors eligible for statistical testing and provides valid false-positive probabilities. The test statistics for these permutation tests are functions of p-values from a standard test for dose-response trend applied to each specific type of tumor. We evaluated three permutation tests, using as test statistics the smallest p-value from a standard statistical test for dose-response trend and the number of such tests for which the p-value is less than or equal to 0.05 or 0.01. The false-positive probabilities obtained from two implementations of these three permutation tests are: smallest p-value: 0.26, 0.17, p-values ≤ 0.05: 0.08, 0.12, p-values ≤ 0.01: 0.06, 0.08. In addition, we found more evidence for negative dose-response trends than positive. Thus, we found no strong evidence that glyphosate is an animal carcinogen. The main cause for the discrepancy between IARC's finding and ours appears to be that IARC did not account for the large number of tumor responses analyzed and the increased likelihood that several of these would show statistical significance simply by chance. This work provides a more comprehensive analysis of the animal carcinogenicity data for this important herbicide than previously available.
Since the capacity of river biofilms to degrade glyphosate has been proven to increase when the availability of dissolved phosphorus (P) in water decreases, the present study investigates the diversity responses of bacterial and eukaryotic microbial communities from biofilms in a search for glyphosate-degrader candidates. Glyphosate and P interactions were observed for eukaryotic communities, the highest community richness and diversity being preserved at low concentrations of glyphosate and P. This trend marked by glyphosate was also observed in the structure of eukaryotic communities. Therefore, phosphorus and glyphosate had a synergistic effect in decreasing the richness and diversity of eukaryotes species in biofilms. However, species richness and diversity in bacterial communities were not affected by glyphosate, though shifts in the structure of these communities were concomitant with the degradation of the herbicide. Bacterial communities capable of using glyphosate as P source were characterized by increases in the relative abundance of certain Bacteroidetes, Chloroflexi, Cyanobacteria, Planctomycetes and alpha-Proteobacteria members. Glyphosate-degrader candidates found in natural river biofilms can be further isolated for better understanding of glyphosate degradation pathways, and used as bioremediation strategies in heavily contaminated sites.
The direct effects of large-scale disturbances are readily studied because their effects are often apparent and result in large changes to ecosystems. Direct effects can cascade through the ecosystem, leading to indirect effects that are often subtle and difficult to detect. Managing anthropogenic disturbances, such as chemical contamination, requires an understanding of both direct and indirect effects to predict, measure, and characterize the impact. Using a replicated whole-ecosystem experiment and path analyses (assesses the effects of a set of variables on a specified outcome, similar to multiple regression), we examined the direct and indirect effects of a glyphosate-based herbicide and nutrient enrichment on wetland communities. The latter did not impact any measured endpoints. The strongest drivers of macrophyte, benthic invertebrate, and amphibian assemblages were the ephemerality and the size of wetlands, factors which were not altered by herbicide applications. The herbicide had a direct negative effect on macrophyte cover, amphibian larval abundance, and the proportion of predatory benthic invertebrates. However, both amphibians and invertebrates were positively affected by the reduction in the macrophyte cover caused by the herbicide applications. The opposing directions of the direct and indirect effects lead to no net change in either group. The compensatory dynamics observed herein highlight the need for a better understanding of indirect effects pathways to determine whether common anthropogenic disturbances alter the ecological communities in small wetland ecosystems.
Glyphosate is the most popular herbicide used worldwide. This study aimed to investigate the adverse effects of glyphosate on the small intestine and gut microbiota in rats. The rats were gavaged with 0, 5, 50, and 500 mg/kg of body weight glyphosate for 35 continuous days. The different segments of the small intestine were sampled to measure indicators of oxidative stress, ion concentrations and inflammatory responses, and fresh feces were collected for microbiota analysis. The results showed that glyphosate exposure decreased the ratio of villus height to crypt depth in the duodenum and jejunum. Decreased activity of antioxidant enzymes (T-SOD, GSH, GSH-Px) and elevated MDA content were observed in different segments of the small intestine. Furthermore, the concentrations of Fe, Cu, Zn and Mg were significantly decreased or increased. In addition, the mRNA expression levels of IL-1β, IL-6, TNF-α, MAPK3, NF-κB, and Caspase-3 were increased after glyphosate exposure. The 16 S rRNA gene sequencing results indicated that glyphosate exposure significantly increased α-diversity and altered bacterial composition. Glyphosate exposure significantly decreased the relative abundance of the phylum Firmicutes and the genus Lactobacillus, but several potentially pathogenic bacteria were enriched. In conclusion, this study provides important insight to reveal the negative influence of glyphosate exposure on the small intestine, and the altered microbial composition may play a vital role in the process.
Glyphosate, one of the most popular herbicides, has become a prominent aquatic contaminant because of its huge usage. The eco-safety of glyphosate is still in controversy, and it is inconclusive how glyphosate influences aquatic microbial communities. In the present study, the effects of glyphosate on the structure and function of microbial communities in a freshwater microcosm were investigated. 16S/18S rRNA gene sequencing results showed that glyphosate treatment (2.5 mg L-1, 15 days) did not significantly alter the physical and chemical condition of the microcosm or the composition of the main species in the community, but metatranscriptomic analyses indicated that the transcriptions of some cyanobacteria were significantly influenced by glyphosate. The microbial community enhanced the gene expression in pathways related to translation, secondary metabolites biosynthesis, transport and catabolism to potentially withstand glyphosate contamination. In the low phosphorus (P) environment, a common cyanobacterium, Synechococcus, plays a special role by utilizing glyphosate as P source and thus reducing its toxicity to other microbes, such as Pseudanabaena. In general, addition of glyphosate in our artificial microcosms did not strongly affect the aquatic microbial community composition but did alter the community's transcription levels, which might be potentially explained by that some microbes could alleviate glyphosate's toxicity by utilizing glyphosate as a P source.