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Glyphosate effects on diseases of plant
Abstract
Glyphosate, N-(phosphonomethyl)glycine, is the most extensively used herbicide in the history of agriculture. Weed management programs in glyphosate resistant (GR) field crops have provided highly effective weed control, simplified management decisions, and given cleaner harvested products. However, this relatively simple, broad-spectrum, systemic herbicide can have extensive unintended effects on nutrient efficiency and disease severity, thereby threatening its agricultural sustainability. A significant increase in disease severity associated with the wide spread application of the glyphosate herbicide can be the result of direct glyphosate-induced weakening of plant defenses and increased pathogen population and virulence. Indirect effects of glyphosate on disease predisposition result from immobilization of specific micronutrients involved in disease resistance, reduced growth and vigor of the plant from accumulation of glyphosate in meristematic root, shoot, and reproductive tissues, altered physiological efficiency, or modification of the soil microflora affecting the availability of nutrients involved in physiological disease resistance. Strategies to ameliorate the predisposing effects of glyphosate on disease include judicious selection of herbicide application rates, micronutrient amendment, glyphosate detoxification in meristematic tissues and soil, changes in cultural practices to enhance micronutrient availability for plant uptake, and biological amendment with glyphosate-resistant microbes for nitrogen fixation and nutrient availability. Given that recommended doses of glyphosate are often many times higher than needed to control weeds, we believe the most prudent method to reduce the detrimental effects of glyphosate on GR crops will be to use this herbicide in as small a dose as practically needed. Such a frugal approach will not only curtail disease predisposition of GR crops, but will also benefit the grower and the environment.
... This regulatory divergence adds complexity to global trade and raises questions about the adequacy of harmonized international standards. The debate surrounding the use of Glyphosate, a widely used herbicide, see Duke [29], Carlisle, and Trevors [22], Sammons, and Gaines [70], Duke, and Powles [28], Johal, and Huber [41], is complex and multifaceted. Glyphosate is a key component in many herbicides and has been used extensively in agriculture to control weeds. ...
... Many more arguments speak against banning glyphosate, see Brookes, Taheripour, and Tyner [18], Cuhra, Bøhn, and Cuhra [24], Wynn, and Webb [83], Wiese, and Steinmann [80], Kanissery, Gairhe, Kadyampakeni, Batuman, and Alferez [45], Duke [29], Carlisle, and Trevors [22], Sammons, and Gaines [70], Duke, and Powles [28], and Johal, and Huber [41]. Glyphosate is credited with contributing to increased agricultural productivity by allowing for efficient weed control, which can lead to higher crop yields and lower costs for farmers. ...
The integrity of environmental toxicology is undermined by selective risk assessments that focus intently on certain chemicals while overlooking others. Glyphosate, one of the most widely used herbicides, serves as a case study of how regulatory decisions can be shaped by incomplete or biased evidence. This paper argues for a holistic approach to toxicology, calling for balanced assessments that consider both health risks and societal benefits. It critically examines current regulatory practices concerning glyphosate, investigating its association with non-Hodgkin’s lymphoma and its positive effects on agricultural productivity and food security. While definitive evidence linking glyphosate to cancer remains inconclusive, its role in enhancing crop yields, by as much as 20 % in some regions, has had measurable benefits for food security and public health. The paper advocates for regulatory frameworks that transparently weigh these societal benefits against potential health risks, particularly in settings of occupational exposure, where the need for balanced assessment is especially pressing. Through a narrative review of major studies, this paper underscores the need for transparency, accountability, and evidence-based approaches in environmental regulation. Such practices are essential for crafting policies that not only mitigate risk but also promote global food security and well-being. By integrating both risks and benefits into the regulatory process, the study proposes an inclusive and data-driven approach to chemical policy that aligns with the broader goals of sustainability and public health.
... Due to the RR technology conferring soybean tolerance to Gly, many studies have been conducted, such as those relating Gly application to the occurrence of plant diseases (Altman and Campbell 1977;Johal and Huber 2009;Mengistu et al. 2013;Hammerschmidt 2018;Martinez et al. 2018;Sardrood and Goltapeh 2018;Einhardt et al. 2020), whether when applied directly to RR cultivars or not, for pre-planting weed control. Gly applications in RR crops are reported to be responsible for both increasing and reducing plant diseases (Sardrood and Goltapeh 2018). ...
... When used in foliar applications in RR soybean, an increase in some diseases, such as those caused by Corynespora cassiicola (Huber et al. 2005) and Fusarium solani f. sp. glycines (Johal and Huber 2009), has been described. Conversely, it is related to the reduction of diseases such as those caused by Phakopsora pachyrhizi (Feng et al. 2005;Feng et al. 2008) and Erysiphe diffusa (Silva 2016). ...
Genetic engineering has facilitated the development of more productive crops with enhanced capabilities for pest and weed management. The transgenic soybean variety DAS44406-6, known as Enlist E3™ (E3), combines genes for insect resistance (Bt) and tolerance to herbicides such as glyphosate, 2,4-D, and glufosinate-ammonium. While this technology has proven effective for weed and insect control, its impact on disease behavior, particularly powdery mildew, remains unclear. This study aims to assess the potential of herbicide applications to reduce severity of powdery mildew in E3 soybeans. We tested preventive and curative treatments against powdery mildew in post-emergence E3 soybeans. Three assays were carried out with six treatments (NC - not controlled; 2,4-D; Glu — glufosinate-ammonium; Gly — glyphosate; Gly + 2,4-D; and PC – positive control with fungicide) and four repetitions in a completely randomized design. The area under the disease progress curve (AUDPC) was assessed. The disease inhibition occurred in both preventive and curative treatments, showcasing a systemic and residual effect. On average, glyphosate + 2,4-D, glyphosate, and glufosinate-ammonium reduced powdery mildew severity by 88.28%, 74.06%, and 64.41%, respectively. The isolated application of 2,4-D did not alter the disease severity during applications at the V4 stage. This pioneering study demonstrates that the E3 technology may confer advantages for powdery mildew management in addition to its well-established benefits for weed and insect control.
... Moreover, knowing the behavior of Glyph at a molecular level is important to be able to design new removal techniques and new detection methods taking into account the serious consequences of water pollution 12 and the deleterious Glyph-induced oxidative stress in plants. [13][14][15] In this context, considerable knowledge on the molecular structure and complex chemistry of Glyph was gained through the determination and harnessing of X-ray crystallography data of Glyph 16,17 and some of its complexes derivatives [18][19][20][21][22][23][24][25] over the four last decades. This compound was determined to exist in the zwitterionic form with a phosphonate proton delocalized on the amino nitrogen. ...
... c E nonel. is the nonelectrostatic contribution. d DZC 10 , DZC 11 , DZC 12 , DZC 13 , NZP 2 and all DZP and AC (except DZP 9 and AC 9 ) ionized structures are not stable in the gas phase. Thus, the gas-phase computation was done using the geometry optimized in solution. ...
A computational study on the structure and stability of different series of glyphosate (Glyph) dimers comprising nonionized (N) and zwitterionic structures (Z) for neutral monomers, followed by an analysis of energetics of Glyph dimerization process have been performed by means of quantum chemical calculations in different media. Optimized geometries for energy minima, as well as relative potential and free energies of the possible various conformers of each series of Glyph dimer were computed as a function of the medium at B3LYP-D3/6-311++G(2d,2p) level. The solvation model based on density (SMD) is employed for all solution phase computations. Non-ionized dimers (DN), anion–cation (AC) and either zwitterion–zwitterion (DZP and DZC) or non-ionized-phosphonate zwitterion (NZP) ionized neutral forms of Glyph dimer are predicted to exist in the gas phase and in solution in large contrast to Glyph monomers. The DZC dimer form exhibiting a centrosymmetric arrangement of two carboxylate zwitterion units was found to be the most stable dimer structure in all media. In aqueous solution, the DZP and AC dimer type structures are significantly stabilized by hydration. The tautomerisms between DZC, DZP and AC dimer type structures have been investigated in the gas phase and in solution. The DZC type structures are more prone to experience proton transfer in water than in the gas phase and in cyclohexane. The mechanism for the tautomerization process in neutral ionized Glyph dimers proceeds via two direct proton transfer paths: DZP ⇋ AC ⇋ DZC. Results show that solvents play a key role in modulating the energetics of the dimerization process of Glyph. Solvation in cyclohexane, favors the dimerization process however, hydration opposed it. In aqueous solution, the mechanism of the dimerization of Glyph from its phosphonate zwitterionic monomer form (ZP) could be described by a set of equilibria including direct proton transfer paths as follows: 2ZP ⇋ DZP ⇋ AC ⇋ DZC. According to our results, in aqueous solution, DZC Glyph dimers and their corresponding DZP and AC tautomers should be present in higher concentration than phosphonate zwitterionic Glyph monomers for high Glyph concentration, a fact that seems controversial in the literature.
... The hypothesis was raised that this symptom was the result of the induced deficiency of micronutrients, especially manganese (Mn), caused by the application of this herbicide (GORDON;HUBER, 2007). Glyphosate appears to increase the population of oxidizing microorganisms and decrease that of reducing Mn in the soil, making it unavailable to plants (KREMER et al., 2005;JOHAL;HUBER, 2009;NEWMAN et al., 2016). It has been also suggested that low herbicide doses can reduce the absorption and translocation of Mn and other essential micronutrients in other plant species (EKER et al., 2006;OZTURK et al., 2008;CAKMAK et al., 2009), but not observed for soybean (ROSOLEM et al., 2010;ZOBIOLE et al., 2010a, LOECKER et al., 2010, CARRARO et al., 2018. ...
... The hypothesis was raised that this symptom was the result of the induced deficiency of micronutrients, especially manganese (Mn), caused by the application of this herbicide (GORDON;HUBER, 2007). Glyphosate appears to increase the population of oxidizing microorganisms and decrease that of reducing Mn in the soil, making it unavailable to plants (KREMER et al., 2005;JOHAL;HUBER, 2009;NEWMAN et al., 2016). It has been also suggested that low herbicide doses can reduce the absorption and translocation of Mn and other essential micronutrients in other plant species (EKER et al., 2006;OZTURK et al., 2008;CAKMAK et al., 2009), but not observed for soybean (ROSOLEM et al., 2010;ZOBIOLE et al., 2010a, LOECKER et al., 2010, CARRARO et al., 2018. ...
The glyphosate herbicide when applied in post-emergence in transgenic soybean can influence manganese (Mn) nutrition, with differentiated response when parceled out. The objective of this study was to evaluate the soybean response to Mn sources applied via leaf, in different phenological stages. Two experiments were carried out in areas with different Mn contents in the soil, using four Mn sources, sulphate and nitrate (experiment A), phosphite and Mn-EDTA (experiment B). Leaf application of Mn was done at V8 and V12 (150+150 g ha-1), V8 (single application at 300 g ha-1) and V12 (single application at 300 g ha-1). In experiment A, the plants treated with nitrate, in split application, had greater leaf area and height of insertion of the first pod. The nitric source resulted in higher soybean yield when applied at V12. On the other hand, sulphate provided plants with higher height at harvest and higher yield with split application. In experiment B, it was found a larger leaf area with application of Mn-EDTA in V12. The application of phosphite provided higher at harvest height when applied in V8 and higher leaf Mn content when applied in V12. The insertion of the first pod was lower in plants treated in V12 with phosphite or with Mn-EDTA and V8. The Mn-EDTA source resulted in higher yield of transgenic soybeans at a dose of 300 g ha-1, applied at V8 or V12, in no-till area with low Mn content in the soil.
... However, regardless of benefits, pesticides contain xenobiotics which have a negative impact on bio-magnification, beneficial soil microbes, [5,6] and ecosystem [7]. They have a direct and indirect impact to yield components and yield because they interfere with soil-beneficial organisms and plant nutrition [8,9]. ...
... However, regardless of benefits, pesticide contain xenobiotics which have a negative impact on bio-magnification, beneficial soil microbes, [5,6] and ecosystem [7]. They have direct and indirect impact to yield components and yield because they interfere with soil beneficial organism and plant nutrition [8,9]. ...
Pesticide xenobiotics have a great impact on bio argumentation, bio-magnification, and environment degradation regardless of being adopted by green revolution technologies. Bioremediation is widely accepted because it’s cheap, practical at the same time environmentally friendly. Bioremediation advocates indigenous microbes use to degrade pesticides, therefore a study has been performed to show prospects of degrading microorganisms. The study isolated microbes from different agro ecological zones to assess their capacity to utilize some pesticide as sole carbon source complimented by the presence of laccase gene. Biochemical test and genetic characterization using 16S rDNA genes were used in identification. Diversified species and strains of genus Enterobacter, Klebsiella, Pseudomonas, Pantoea and Leclercia, were found to degrade cypermethrin and acetochlor but no microbe was found to degrade dimethoate. The study adds new strain of microbes involved in degradation of cypermethrin and acetochlor and also strains that that can degrade both. The study puts proposition that pest infestation in fields is a result of abundance of xenobiotic degrading microbes due to natural selection pressure not pesticide resistance of the pest.
... This shows that the use of all dosages of IPA Glyphosate herbicide effectively controls the Setaria palmifolia. This indicates that glyphosate has been transplanted to all parts of the weed, especially the roots which can cause more effective weed death (Johal and Huber, 2009) [6] . ...
... This shows that the use of all dosages of IPA Glyphosate herbicide effectively controls the Setaria palmifolia. This indicates that glyphosate has been transplanted to all parts of the weed, especially the roots which can cause more effective weed death (Johal and Huber, 2009) [6] . ...
... From 15 to 45 DAA, the highest Fe levels were observed under glyphosate treatment. Our results differ from most studies, which report that residues or spray drift of glyphosate can reduce the absorption and translocation of micronutrients, such as Mn and Fe (Gordon 2007;Johal and Huber 2009), due to the formation of glyphosate-metal complexes that are poorly soluble in plant tissues, which prevent uptake by roots and translocation (Eker et al. 2006;Cakmak et al. 2009;Magri et al. 2023). Silva et al. (2018) studied the nutrient content in sugarcane biomass and reported 98.7 mg kg À1 of Fe in the first ratoon regrowth cycle, which is lower than that observed in our study after the application of ripeners. ...
... Besides the poorly soluble glyphosate forms, such as glyphosate-metal complexes, in plant tissues, which prevent Zn and Mn absorption by roots and their translocation in plants (Eker et al. 2006;Magri et al. 2023), studies are reporting that glyphosate increases oxidant microorganism population and decreases Mn-reducing microorganisms in the soil, thereby reducing the availability of Mn for the plants (Johal and Huber 2009;Kumar et al. 2017). Ferrari et al. (2020) studied the effects of trinexapac-ethyl on the nutritional status of upland rice and also found increased Mn concentration in the leaves after spraying this product. ...
... Where there is the potential for the plant material to host pathogens such as viruses, plasmids, bacteria that are not visually detectable, there is no evidence that devitalisation with glyphosate will prevent transmission. Glyphosate will not directly kill pathogens and it has been suggested that the herbicidal effect is in parts a result of this (Johal and Rahe 1984;Levesque and Rahe 1992;Johal and Huber 2009). There is evidence from field studies that application of glyphosate as a herbicide can increase pathogen prevalence and disease severity in the field (Johal and Huber 2009). ...
... Glyphosate will not directly kill pathogens and it has been suggested that the herbicidal effect is in parts a result of this (Johal and Rahe 1984;Levesque and Rahe 1992;Johal and Huber 2009). There is evidence from field studies that application of glyphosate as a herbicide can increase pathogen prevalence and disease severity in the field (Johal and Huber 2009). Thus, it is likely that pathogens will still be present in the plant material post-devitalisation and are liable to further transmission. ...
Devitalisation of biological materials is used as a phytosanitary measure to reduce the risk of establishment of unwanted plants in the environment and eliminate the spread of pests and diseases from imported material. For cut flowers and foliage, the treatment aims to prevent germination, propagation or any form of further growth without physical damage. Glyphosate is the primary chemical used. However, there is little data showing that the herbicide-based treatments are suitable to achieve the goals of the protocols. Limited research exists on their effectiveness or the impact different herbicide formulations and treatment conditions might have on different plant species. No scientific information was found on aspects of health and safety of handlers and end-users. Furthermore, the literature reviewed revealed that the devitalising effect of glyphosate can be reversed. We conclude that the limited scientific basis for current devitalisation protocols using glyphosate, or other herbicides, means the devitalisation process is questionable in its ability to meet the stated aims. To justify the continued requirement for devitalisation an extensive research programme would be required to develop protocols, confirm the efficacy of procedures and provide evidence-based guidelines for the pre-import treatment of fresh cut flowers and foliage.
... 5,6 Additionally, this herbicide can cause structural disturbances in soil microbial communities, potentially promoting the growth of phytopathogenic fungi. 3,7 This intensive glyphosate use has also raised regulatory concerns about residue levels in food and soil. The National Health Surveillance Agency (ANVISA) in Brazil establishes the maximum residue limits (MRL) for registered agrochemicals, setting the MRL for glyphosate in food at 1.0 mg kg −1 . ...
This study aimed to isolate glyphosate-tolerant bacteria and characterize their plant-beneficial traits. Using a bioprospecting and glyphosate enrichment methodology, we isolated 35 bacterial strains that were tested for tolerance to glyphosate on solid and liquid media (0, 11, 22, 44, and 88 g L −1 of glyphosate). Sixteen isolates with high tolerance to glyphosate (≥22 g L −1) were identified and characterized by their ability to fix atmospheric nitrogen, solubilize inorganic phosphate, and produce indole-3-acetic acid (IAA). After similarity analysis and compatibility testing, a consortium composed of three bacteria (Priestia sp.; Achromobacter sp.; Pseudomonas sp.) were selected to be applied in a model plant (tomato) and Arabica coffee beans. The bacterial consortium promoted the germination (96.6%) and development of tomato seedlings, while also degrading residual glyphosate (31.25%) in coffee beans, as evidenced by the reduced levels of the herbicide. These results demonstrate the bacterial consortium's potential to reduce glyphosate residues and sustainably increase plant productivity.
... These findings raise concerns about the potential risks that GBHs could cause to microbial diversity and global health. In addition to its antimicrobial properties, the chelation capacity of glyphosate, even at low concentrations, enables it to bind to macro-and micronutrients, inhibitors or activators of numerous critical physiological processes in plants, mammals, and microorganisms 69 . Further investigation is crucial to understand the effects of other glyphosate formulations on microbial antibiotics sensitivity. ...
The emission of glyphosate and antibiotic residues from human activities threatens the diversity and functioning of the microbial community. This study examines the impact of a glyphosate-based herbicide (GBH) and common antibiotics on Gram-negative bacteria within the ESKAPEE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp. and Escherichia coli). Ten strains, including type and multidrug-resistant strains for each species were analysed and eight antibiotics (cefotaxime, meropenem, aztreonam, ciprofloxacin, gentamicin, tigecycline, sulfamethoxazole-trimethoprim, and colistin) were combined with the GBH. While most combinations yielded additive or indifferent effects in 70 associations, antagonistic effects were observed with ciprofloxacin and gentamicin in five strains. GBH notably decreased the minimum inhibitory concentration of colistin in eight strains and displayed synergistic activity with meropenem against metallo-β-lactamase (MBL)-producing strains. Investigation into the effect of GBH properties on outer membrane permeability involved exposing strains to a combination of this GBH and vancomycin. Results indicated that GBH rendered strains sensitive to vancomycin, which is typically ineffective against Gram-negative bacteria. Furthermore, we examined the impact of GBH in combination with three carbapenem agents on 14 strains exhibiting varying carbapenem-resistance mechanisms to assess its effect on carbapenemase activity. The GBH efficiently inhibited MBL activity, demonstrating similar effects to EDTA (ethylenediaminetetraacetic acid). Chelating effect of GBH may have multifaceted impacts on bacterial cells, potentially by increasing outer membrane permeability and inactivating metalloenzyme activity.
... It boasts high herbicidal efficiency, low toxicity, broad herbicidal range, and easy degradability, making it an environmentally friendly herbicide. [1][2][3] As glyphosate is gradually phased out of the market and issues related to glufosinate become increasingly apparent, [4][5] the application of glufosinate-ammonium, which has low toxicity, high herbicidal activity, and good environmental compatibility, is expected to have a broader prospect. However, the glufosinate-ammonium herbicides currently sold in the market are typically composed of a racemic mixture of two isomers. ...
The biocatalytic oxidative deamination‐ reductive amination process for the production of l‐phosphinothricin (l‐PPT) from D,L‐phosphinothricin (d,l‐PPT) is a green and environmentally friendly approach with significant development potential. In this study, the adopted technological route involves the oxidative deamination of the d‐PPT component in d,l‐PPT to 2‐oxo‐4‐(hydroxymethylphosphinyl)butanoic acid (PPO) by utilizing D‐amino acid oxidase (DAAO), followed by the catalytic reductive amination of PPO to l‐PPT using phosphinothricin dehydrogenase (PpDH). In order to enhance the catalytic rate and reduce the inhibitory effect of the intermediate product PPO on the catalytic process, optimization of both oxidative deamination and reductive amination phases was conducted through separate strategies of constant‐pressure oxygen supply and substrate feeding, respectively. A “two‐step one‐pot” method was employed to link the optimized reactions, significantly shortening the production time. Furthermore, the “two‐step one‐pot” catalytic strategy was optimized, ultimately achieving a high 97.7% yield of l‐PPT with ee of l‐PPT>99.9% after 5.5 h of reaction under 800 mM d,l‐PPT catalytic conditions, D‐PPT and PPO could not bedetected in the reaction system, further enchanced the catalytic efficiency, production efficiency and product quality. The aforementioned results demonstrate that this proposed approach has great potential for industrial‐scale production of l‐PPT as well as significant competitive advantages in terms of economic feasibility.
... Pest control by natural predators, insect pollination, and the functional structure of the soil are threatened by the elimination of wild plants from agricultural fields and nearby lands. Additionally, there are direct toxic effects on many species within soil microbial communities, worms, pollinators, and the plant's defense mechanism, rendering them more susceptible to pathogens and diseases [26]. ...
Glyphosate is a broad-spectrum pesticide that has become the most widely used herbicide globally. However, concerns have risen regarding its potential health impacts due to food contamination. Studies have detected glyphosate in human blood and urine samples, indicating human exposure and its persistence in the organism. A growing body of literature has reported the health risks concerning glyphosate exposure, suggesting that the daily intake of contaminated food and water poses a public health concern. Furthermore, countries with high glyphosate usage and lenient regulations regarding food and water contamination may face more severe consequences. In this context, in this review, we examined the literature regarding food contamination by glyphosate, discussed its detection methods, and highlighted its risks to human health.
... 19 Glyphosate and surfactant use was also suggested to be a cause of increased plant disease. 20,21 However, follow-up research studies and reviews have indicated that there are no associations between herbicide tolerance traits, glyphosate use, and surfactant use with an increase in plant disease and Goss's wilt. [22][23][24][25] This suggests genes other than glyphosate-resistance are responsible for susceptibility to Goss's wilt. ...
BACKGROUND
Goss's bacterial wilt and leaf blight (Goss's wilt), caused by the bacterium Clavibacter nebraskensis, is a corn disease that has been a top ten yield‐reducing disease in North America in the past 15 years. Isoxadifen‐ethyl is an herbicide safener that effectively increases cytochrome P450 activity in corn which enhances a plant's metabolism of herbicide molecules. Recent research found a potential link between isoxadifen‐ethyl and increased Goss's wilt severity.
RESULTS
The application of isoxadifen‐ethyl increased (P = 0.014–0.046) area under disease progress curve (AUDPC) by 19%, 7%, and 9% at three environments, independent of accompanying herbicide or herbicide application timing. However, no significant differences in incidence of systemic wilt or corn grain yield occurred among treatments at any environment.
CONCLUSION
These data provide evidence for an association between isoxadifen‐ethyl safener and Goss's wilt in corn. The reason for this association is unknown, but the safener may affect plant or pathogen physiological mechanisms. While the increased disease severity did not result in decreased grain yield in these experiments, an increase in pathogen inoculum due to higher disease severity could influence Goss' wilt epidemics in future years. © 2024 Society of Chemical Industry.
... It is noteworthy that the fungal family Plectosphaerellaceae commonly found in the roots of potato and soils from potato fields (Giraldo and Crous 2019) was highly abundant in the treatments with GBH compared to the controls. Plectosphaerellaceae includes numerous plant pathogenic genera such as Plectosphaerella cucumerina, one of the main genus causing wilt particularly in potato(Alam et al. 2021) and several other crops in the tropic and temperate regions(Carrieri et al. 2014;Gilardi et al. 2012;Mirtalebi et al. 2022).Shifts in bacterial community composition due to GBH may imbalance the plant beneficial bacteria that otherwise control pathogens, possibly risking plant health(Johal and Huber 2009;Van Bruggen et al. 2021). ...
Glyphosate, the active ingredient of glyphosate-based herbicide (GBH) controls the growth of weeds by inhibiting shikimate pathway, thereby interrupting amino acid biosynthesis in plants. However, several microbes have shikimate pathway and the action of glyphosate on these non-target organisms are ignored. Along with other agrochemicals such as phosphate fertilizers, the action of GBH is further complicated, often varying their mode of action depending on soil type or plant species. To address the impact of GBH and phosphate fertilizer, we simulated agricultural application of GBH and phosphate fertilizer in a field study, investigating the composition of endophytic microbial communities and correlation of phytohormone concentrations with the microbial diversity of potato (Solanum tuberosum). In leaves, glyphosate residues in soil from GBH treatment alone and in combination with phosphate significantly shifted bacterial community whereas phosphate alone and in combination with glyphosate significantly altered the composition of fungal community. There were no significant changes in microbial communities in roots and tubers. Plants treated with GBH showed higher ratios of potentially glyphosate-resistant bacteria, with Xanthomonadaceae and Moraxallaceae being more abundant. Additionally, phytohormone concentrations showed various correlations with bacterial and fungal diversity in different treatments. The study highlights the impact of GBH residues in soil, particularly in combination with phosphate fertilizers on the composition of plant-associated microbial communities. Together with changes in phytohormone concentrations, plant health may be affected. Moreover, future studies could provide insights to whether these agrochemicals influence plant microbiome, leading to changes in phytohormones or vice-versa.
... Several hypotheses surrounding the increased incidence of fungal disease in plants following glyphosate application have been proposed and include; (a) pathogen exposure to glyphosate predisposes the infectious agent to exogenous synthetic chemicals heightening virulence and fungicide resistance, (b) glyphosate may provide an alternate carbon source for pathogens, and (c) glyphosate-induced death of problematic weeds that act as reservoirs for certain phytopathogens cause sudden increases to field colony density during decay [132]. In addition to these, we propose that glyphosate may harm components of the phyllosphere, including the Methylobacterium, which prevent infection irrespective of the GR status of the host. ...
Symbiotic Methylobacterium comprise a significant portion of the phyllospheric microbiome, and are known to benefit host plant growth, development, and confer tolerance to stress factors. The near ubiquitous use of the broad-spectrum herbicide, glyphosate, in farming operations globally has necessitated a more expansive evaluation of the impacts of the agent itself and formulations containing glyphosate on important components of the plant phyllosphere, including Methylobacterium.
This study provides an investigation of the sensitivity of 18 strains of Methylobacterium to glyphosate and two commercially available glyphosate-based herbicides (GBH). Nearly all strains of Methylobacterium showed signs of sensitivity to the popular GBH formulations WeatherMax® and Transorb® in a modified Kirby Bauer experiment. However, exposure to pure forms of glyphosate did not show a significant effect on growth for any strain in both the Kirby Bauer test and in liquid broth, until polysorbate-20 (Tween20) was added as a surfactant. Artificially increasing membrane permeability through the introduction of polysorbate-20 caused a 78–84% reduction in bacterial cell biomass relative to controls containing glyphosate or high levels of surfactant only (0–9% and 6–37% reduction respectively). Concentrations of glyphosate as low as 0.05% w/v (500 µg/L) from both commercial formulations tested, inhibited the culturability of Methylobacterium on fresh nutrient-rich medium.
To better understand the compatibility of important phyllospheric bacteria with commercial glyphosate-based herbicides, this study endeavours to characterize sensitivity in multiple strains of Methylobacterium, and explore possible mechanisms by which toxicity may be induced.
... ynthase (EPSPS) by binding to it to form a complex EPSPS in the Shikimate pathway.Gao et al., (2014) andDuke & Powles (2010) explained that this process causes the accumulation of shikimic acid and other precursors of the chorismate pathway that are necessary for the synthesis of three aromatic amino acids (phenylalanine, tryptophan, and tyrosine).Johal & Huber (2009) stated that reductions in the amino acids cause several metabolic disturbances: such as inhibition of protein and secondary product synthesis, and may also make the plant susceptible to various plant pathogens. This may cause the plant to wither and die.(Nandula et al., 2005).Busse et al(2001) indicated that the shikimic acid pathway is ...
Investigation of the tendency of glyphosate herbicide sprayed on maize farms to be transported and become bioavailable in mature maize fruits
... In many crops, the constant application of glyphosate is related to an increase in disease severity [31]. In addition, it may also cause immobilization of specific micronutrients involved in disease resistance, and a reduction in plant growth and vigor [32]. Even herbicide-resistant crops may be susceptible to diseases. ...
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.
... Glyphosate residues were detected both in crops and weeds throughout the season following herbicide application (Helander et al., 2018). Glyphosate was found to interfere with plant resistance by enhancing susceptibility to below-and aboveground pathogens (Johal and Huber, 2009) and to negatively impact the attraction of beneficial insects (Fuchs et al., 2021), both representing essential elements for the management of healthy agricultural systems. Finally, increased glyphosate levels resulted in decreased nutrient accumulation, nodulation, roots and shoots biomass (Velini et al., 2008;Zobiole et al., 2011;Zobiole et al., 2010). ...
Herbicides are widely used for weed control in agriculture, though their fate and impact on non-target organisms like soil microbes and their function remain relatively unknown. A further complication is that herbicide effects vary depending on how they are applied and due to varying soil moisture conditions. In this study we tested the hypothesis that spraying glyphosate or terbuthylazine directly onto bare soil and when soil moisture is high would impact the soil microbial communities and their function most strongly. We measured similar amounts of glyphosate and terbuthylazine in soil whether the herbicides were directly applied to soil or first sprayed on the weed Chenopodium album and we found evidence for more rapid metabolization at high soil moisture. We found that the soil bacterial rather than the fungal community was mainly affected by a single application of the two tested herbicides. The identified shifts in community composition were independent of the modes of herbicide application but strongly dependent on soil moisture. We further found that herbicide applications only had a small impact on soil microbial function, which was approximated with analyses of the activities of N-β-acetyl-glucosaminidase, acid phosphatase and β-glucosidase enzymes in soil. Finally, we also assessed the post-application performance of the subsequent crop and found that the herbicides did not affect maize height, chlorophyll content and biomass. Overall, our study revealed that a single application of herbicides in recommended doses had minor effects on the soil microbiome with a temporal and soil moisture dependency. The latter finding points out that to avoid repercussions on non-target organisms and soil function, key research needs to solve the context-dependency of rapid herbicide degradation in soil.
... Another adverse effect that has been claimed is increases in plant diseases (sometimes linked to claims of effects on mineral nutrition) [21,22]. Such effects would be expected to affect yield and grain quality. ...
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.
... Some authors suggest glyphosate as an environmentally friendly herbicide [8][9][10], which has no effect on other organisms, when used at recommended rates [11]. Others indicate that glyphosate leaching from the soil through the rhizosphere may adversely affect non-target plants by affecting the availability of nutrients, associated with physiological disease resistance [12][13][14]. ...
Glyphosate is one of the most widely used herbicides, but is still in the spotlight due to its controversial impact on the environment and human health. The main purpose of this study was to explore the effects of different glyphosate usages on harvested grain/seed contamination. Two field experiments of different glyphosate usage were carried out in Central Lithuania during 2015–2021. The first experiment was a pre-harvest application, with two timings, the first according to the label (14–10 days), and the other applied 4–2 days before harvest (off-label), performed in winter wheat and spring barley in 2015 and 2016. The second experiment consisted of glyphosate applications at label rate (1.44 kg ha⁻¹) and double dose rate (2.88 kg ha⁻¹) at two application timings (pre-emergence of crop and at pre-harvest), conducted in spring wheat and spring oilseed rape in 2019–2021. The results suggest that pre-emergence application at both dose rates did not affect the harvested spring wheat grain or spring oilseed rape seeds—no residues were found. The use of glyphosate at pre-harvest, despite the dosage and application timing, led to glyphosate’s, as well as its metabolite, aminomethosphonic acid’s, occurrence in grain/seeds, but the amounts did not reach the maximum residue levels according to Regulation (EC) No. 293/2013. The grain storage test showed that glyphosate residues remain in grain/seeds at steady concentrations for longer than one year. A one year study of glyphosate distribution within main and secondary products showed that glyphosate residues were mainly concentrated in wheat bran and oilseed rape meal, while no residues found in cold-pressed oil and wheat white flour, when glyphosate used at pre-harvest at the label rate.
... Glyphosate residues were detected both in crops and weeds throughout the season following herbicide application (Helander et al., 2018). Glyphosate was found to interfere with plant resistance by enhancing susceptibility to below-and aboveground pathogens (Johal and Huber, 2009) and to negatively impact the attraction of beneficial insects (Fuchs et al., 2021), both representing essential elements for the management of healthy agricultural systems. Finally, increased glyphosate levels resulted in decreased nutrient accumulation, nodulation, roots and shoots biomass (Velini et al., 2008;Zobiole et al., 2011;Zobiole et al., 2010). ...
Herbicides are widely used for weed control in agriculture, though their fate and impact on non-target organisms like soil microbes and their functioning remain relatively unknown. A further complication is that herbicide effects vary depending on how they are applied and due to environmental conditions like soil moisture. In this study we tested the hypothesis that spraying glyphosate and terbuthylazine directly onto soil and when soil moisture is high would impact the soil microbial communities and their functioning to a stronger degree. In our experiments we measured a high context dependency of glyphosate and terbuthylazine bioavailability in soil and found evidence for rapid metabolization at high soil moisture. We found that the soil bacterial rather than the fungal community was mainly affected by a single application of the two tested herbicides of contrasting chemistry and activity. The identified shifts in community composition were independent of the modes of herbicide application (directly applied to soil vs sprayed on Chenopodium album) but strongly dependent on soil moisture. We further found that herbicide applications only had a small impact on soil microbial functioning, which was approximated with analyses of the activities of N-β-acetylglucosaminidase, acid phosphatase and β-glucosidase in soil. Finally, we also assessed the post-application performance of the subsequent crop and found that the herbicides did not affect maize height, chlorophyll content and biomass. Overall, our study revealed that a single application of herbicides in recommended doses had minor effects on the soil microbiome with a high temporal and soil moisture dependency. The latter finding points out that to avoid repercussions on non-target organisms and soil functioning, key research needs to solve the context-dependency of rapid herbicide degradation in soil.
... Herbicides, including glyphosate, can also increase plant diseases by altering plants' ability to absorb nutrients and reduce soil health by killing microbes. These chemical-dependent strategies, peddled by major chemical and biotech companies, will keep farmers dependent on increasingly toxic pesticides in a race that nature always wins [25]. ...
The production of genetically modified crops for commercial release and agriculture resulting in a number of changes in the life style of an individual and farmers particularly. Scientists who analyze the impact of agricultural biotechnology from the socio-legal perspective; looked the tall claim of genetic engineering with suspicion. They claim alterations can change the organism's metabolism, growth rate, and/or may have down side effect on external environmental factors. This research paper tries to explore and examine the concerns raised from the socio-legal perspective as society should have minimum scientific knowledge in reference to use of GMOs and its derivatives. It is concluded with the finding that a reasonable policy with regard to their use by the farmers and others stake holders need to be prepared.
... Glyphosate effects on the soil microbiome have been studied extensively. Although the herbicide has been associated with crop mineral imbalances [164] and increased disease incidences [165], presumably resulting from glyphosate effects on the rhizosphere microbiome [166], most studies find that it has no or only transient effects on the soil microbiome when applied at recommended rates [167][168][169]. However, the long-term effects of repeated applications of herbicides and other agrochemical pesticides are not yet clear and they require long-term trials. ...
Agroecosystems are comprised of environmental compartments where associated microbial communities interact with one another. These microbial communities, called microbiomes, inhabit livestock, insects, and plants. Microbiomes are also present in the soil and watersheds. Clarifying the nature and extent of microbial interactions between compartments both at intra-farm and global scales can promote sustainable production systems, healthier animals, increased crop yields, and safer meat products. Early research on microbiomes was hindered by a lack of expertise and the high cost of molecular sequencing. However, these limitations have been largely resolved with advances in and reduced costs of sequencing technologies. In this paper, we summarize sequencing and bioinformatics approaches, and review the crucial roles of diverse microbiomes in livestock, plants and soil, as well as pollinators and pest insects. These crucial roles include nutrient cycling, nutrient acquisition, metabolism of toxins and enhanced host immune function. Additionally, we examine potentially undesirable effects of microbiomes associated with climate change and agri-food production such as their role in the release of greenhouse gases from cattle and their impact on meat safety and spoilage. By increasing the awareness of microbiomes and the growing ease with which they can be studied, we hope to foster a greater adoption of microbiome research. Further understanding of the diverse effects and interactions of microbiomes will advance our efforts to increase agricultural production while reducing its negative environmental footprint, thus making the agroecosystems more sustainable.
... Infections by endophytic bacteria such as Xylella spp. cause little damage, except in plants that are deficient in Mn and Zn (Johal and Huber, 2009). Deficiency of Mn and Zn may be induced by high soil pH or extensive use of the herbicide glyphosate (Kirkby and Römheld, 2004;Martinez et al., 2018). ...
... Field concentrations of glyphosate (0.5-7.02 kg ha − 1 ) have been shown to have no effect on microbial community structure (Barriuso et al., 2011;Hart et al., 2009;Kepler et al., 2019;Weaver et al., 2007;Zabaloy et al., 2012), but high concentrations simulating a spill (e. g., 100 times field rate) can stimulate some bacteria (Ratcliff et al., 2006;Weaver et al., 2007). Some of the detrimental effects of glyphosate reported on soil microbes include a decrease in arbuscular mycorrhizae spore viability and root colonization (Druille et al., 2013a(Druille et al., , 2013b(Druille et al., , 2016, a decrease in dark septate endophyte colonization and growth (Druille et al., 2016;Spagnoletti and Chiocchio, 2019), a decrease in nitrogen fixers and growth-promoting taxa (Druille et al., 2016;Zobiole et al., 2010Zobiole et al., , 2011, and an increase in plant pathogens such as Fusarium (Johal and Huber, 2009;Zobiole et al., 2011). These previous studies are limited by the broad taxonomic descriptions (e.g., bacteria, fungi, actinomycetes), focus on one taxonomic group, or focus on agricultural settings, while glyphosate-based herbicides are also commonly used in native plant community restoration projects to control non-native and invasive plant species (Bell, 1997;Bohn et al., 2011;Irvine et al., 2013;Kulmatiski and Beard, 2006;Leahy et al., 2018;Mozdzer et al., 2008;Robertson et al., 2013;Simmons et al., 2007;Stover et al., 2017). ...
Glyphosate is a widely used herbicide in agricultural, domestic, and restoration settings to manage weeds and invasive plants and is the active ingredient in the herbicide formulation Roundup. Concurrently with its drastic increase in usage, concern over indirect ecosystem effects and effects on non-target species has grown. In restoration, glyphosate is often used to remove invasive plants so native plants may be re-introduced. However, successful reintroductions require soils and microbial communities that support native plant growth, and it is critical that glyphosate applications do not harm soil microbes such as mycorrhizal fungi. Despite previous studies investigating the effects of glyphosate on soils and microbial communities, comprehensive field experiments combining soil chemistry and next generation sequencing technologies to describe both bacterial and eukaryotic responses to glyphosate are limited, especially in the contexts of ecosystem restoration and soil health. We studied the effects of the glyphosate-based herbicide Roundup Promax at frequencies of 0, 2, 4, and 5 applications over the course of 12 months on soil biotic and abiotic soil health indicators in a Colorado prairie dominated by the invasive cool-season grass Bromus inermis. Here we report cascading effects on soil chemistry, with increases in nitrate and acidity and consequent decreases in calcium content and cation exchange capacity. Bacterial and archaeal communities were more affected by Roundup Promax than eukaryotic communities, with decreases in phylogenetic diversity and changes in community structure following Roundup Promax applications, particularly after five applications. More critically, the colonization of plant roots by arbuscular mycorrhizal fungi decreased significantly in plots receiving even just two applications of Roundup Promax, and dark septate endophytes decreased after four applications. Our work shows that Roundup Promax had multiple negative effects on soil biota in this field study due to either direct effects or indirect effects mediated through plant removal. Our results suggest that repeated herbicide applications are especially damaging to soil health and microbe-plant associations. These effects in turn could severely hamper the ability of native plants to establish during ecosystem restoration projects.
... Due to its non-selective and high-activity characteristics (Lee et al. 2002), glyphosate has gradually taken over the herbicide market since its commercialization in 1974, and now it has become one of the most used herbicides in the world (Duke et al. 2008;Benbrook et al. 2016), whereas glyphosate can accumulate in the ecosystem and cause environmental pollution. Studies have linked glyphosate to more than 30 types of plant diseases (Johal and Huber 2009;Huang et al. 2015). Additionally, glyphosate and its derivatives can cause widespread pollution of groundwater, surface water, marine sediments, seawater, and rainwater (Allinson et al. 2016;Bradley et al. 2017;Okada et al. 2018). ...
In present study, bovine serum albumin (BAS)-stabilized gold nanoclusters (AuNCs) combined with Cu2+ were used for rapid fluorimetric detection of glyphosate in water samples. The morphology and optical properties of synthesized BSA-AuNCs were characterized by TEM, UV–Vis spectroscopy and fluorescence techniques. Theoretically, Cu2+ would react with the tryptophan of BSA-AuNCs, thereby disrupting the surface structure of BSA-AuNCs and allowing aggregation of dispersed BSA-AuNCs, which showed the function to quenching the red fluorescence of BSA-AuNCs at 680 nm. However, in the presence of glyphosate in the system, there are strong chelation interactions between Cu2+ and glyphosate, so the fluorescence of BSA-AuNCs was restored and the recovered intensity is related to the glyphosate concentration. As a result, a linear graph between the fluorescence intensity with glyphosate concentration in the range of 0.06–12 μg/mL was plotted and used for quantification of glyphosate with a detection limit of 8 ng/mL. Satisfactory recoveries were obtained in the determination of spiked water samples, demonstrating that the prepared BSA-AuNCs can be used as a promising tool in the field of environment monitoring of glyphosate residue.
... Glyphosate has been well known for being environmentally friendly and toxicologically safe (Duke & Powles, 2008). However, the potential effects of glyphosate on plant mineral nutrition, diseases and soil microorganisms have attracted increasing attention (Duke & Powles, 2008;Johal & Huber, 2009;Sihtmäe et al., 2013). Through the analysis of more than 8000 citations, Duke et al. (2012) believed that whether the glyphosate application has a significant impact on mineral nutrition on crops is still controversial. ...
Plant roots significantly influence soil microbial diversity, and soil microorganisms play significant roles in both natural and agricultural ecosystems. Although the genetically modified (GM) crops with enhanced insect and herbicide resistance are thought to have unmatched yield and stress resistance advantages, thorough and in‐depth case studies still need to be carried out in a real‐world setting due to the potential effects of GM plants on soil microbial communities. In this study, three treatments were used: a recipient soybean variety Jack, a triple transgenic soybean line JD321, and the glyphosate‐treated JD321 (JD321G). Three sampling stages (flowering, seed filling and maturing), as well as three host niches of soybean rhizosphere [intact roots (RT), rhizospheric soil (RS) and surrounding soil (SS)] were established. In comparison to Jack, the rhizospheric soil of JD321G had higher urease activity and lower nitrite reductase at the flowering stage. Different treatments and different sampling stages existed no significant effects on the compositions of microbial communities at different taxonomic levels. However, at the genus level, the relative abundance of three plant growth‐promoting fungal genera (i.e. Mortierella, Chaetomium and Pseudombrophila) increased while endophytic bacteria Chryseobacterium and pathogenic bacteria Streptomyces decreased from the inside to the outside of the roots (i.e. RT → RS → SS). Moreover, two bacterial genera, Bradyrhizobium and Ensifer were more abundant in RT than in RS and SS, as well as three species, Agrobacterium radiobacter, Ensifer fredii and Ensifer meliloti, which are closely related to nitrogen‐fixation. Furthermore, five clusters of orthologous groups (COGs) associated to nitrogen‐fixation genes were higher in RT than in RS, whereas only one COG annotated as dinitrogenase iron‐molybdenum cofactor biosynthesis protein was lower. Overall, the results imply that the rhizosphere host niches throughout the soil–plant continuum largely control the composition and function of the root‐associated microbiome of triple transgenic soybean.
... The most widespread method is a termination herbicide, usually glyphosate. However, this practice has been criticized because of undesirable side effects on the agroecosystem and the environment (Johal and Huber 2009;Yamada et al. 2009;Mamy et al. 2016). Glyphosate may also reduce main crop yields when applied too close to the main crop seeding date (Nascente et al. 2013) or it may interact with P-fertilizer application (Rose et al. 2018). ...
Phosphorus (P) is one of the most limiting plant nutrients for agricultural production. The soil microbial community plays a key role in nutrient cycling, affecting access of roots to P, as well as mobilization and mineralization of organic P (Porg). This thesis aimed to better understand the potential of cover crops to enhance plant-soil-microbe interactions to improve the availability of P. This dissertation consists of a meta-analysis of and two field experiments. The used methods showed that microbial P, the activity of P-cycling enzymes and PLFAs increased under cover crops, indicating an enhanced potential for organic P cycling. Gram- positive and Gram-negative bacteria, and to a lesser extent also arbuscular mycorrhizal fungi, increased their abundance with cover crops. However, saprotrophic fungi could benefit most from the substrate input derived from cover crop roots or litter. Enzyme-stable Porg shifted towards pools of a greater lability in the active soil compartments (rhizosheath and detritusphere). The effects of agricultural management, such as cover crop species choice and tillage, were detectable, but weaker compared to the effect of the presence of cover crops. With the obtained results, the research aims of this thesis could be successfully addressed. We were able to confirm that cover crops have the potential to improve main crops access to P. Furthermore, we presented and discussed three pathways of P benefit. In the plant biomass pathway, P is cycled through cover crop biomass and becomes available for the main crop upon litter decomposition. The microbial enhancement pathway describes how the cover crops interaction with soil microbes increases their abundance and activity, thereby increasing the availability of Porg. Some cover crop species seem to be capable of utilizing a biochemical modification pathway, where changes in the sorption capacity of the soil result in a greater quantity of plant-available phosphate. However, the latter pathway was apparently not important in the crop rotations used in our field experiments. The data also allowed us to characterize ways in which plant-soil-microbe interactions under cover crops affected the relationship of soil microbial functions to the enzymatic availability of Porg pools. Cover crops increased the abundance and activity of microbes, especially fungi, as well as microbial P. This enhancement in P-cycling potential shifted Porg toward pools of greater availability to added enzymes. However, the relation between enzymes and Porg pools is complex and is possibly affected by soil P composition and other site characteristics, indicating the need for further research in this area. Finally, we elucidated how the choice of cover crop species and agricultural management can shift the relative importance of the pathways for the P benefit of the main crop, while site-specific management allows farmers to adapt to local conditions and to optimize the functions of their agroecosystems. In conclusion, our results indicate that the pathways of cover crop derived P benefit take place simultaneously. We confirmed the potential of cover crop biomass for the cycling of P, and we suggest that our observed increases in the availability of soil Porg are related to microbial abundance and activity. The interactions of cover cropping and tillage indicate also that P benefit can be optimized by management decisions. Finally, these new insights into soil phosphorus cycling in agroecosystems have the potential to support further development of more sustainable agricultural systems.
... Glyphosate can chelate vital nutrients making them not physiologically available (Kr€ uger et al. 2013). Deficiencies of elements like Mn, Cu, Zn, Se, Co, B, and Fe in diets, alone or in combination, are known to interfere with vital enzyme systems and cause disorders and diseases (Cakmak et al. 2009;Johal and Huber 2009). The other tested feeds do not report any GM product on the warning label. ...
Forty-two samples of feed, saliva, urines, and faeces collected from a cattle farm were investigated with the aim to evaluate the occurrence of glyphosate in faeces, urine and saliva. Glyphosate in the feed was also quantified to understand how it was assimilated by mammals. All cows excreted glyphosate in their faeces at concentrations between 57 and 983 ng g-1. In contrast, only 55% of urine and one sample of saliva tested positive. Most of the feeds demonstrated a non-negligible presence of glyphosate. In particular, a silage containing soybeans from genetically modified cultivation showed a concentration one order of magnitude higher than the other feeds. This study aims to provide the first complete determination of glyphosate in a cattle farm, considering the possible re-entry into the environment through the spreading of liquid and solid sewage and its possible impact on groundwater.
... Glyphosate (NA-(phosphono-methyl) glycine) was introduced commercially in 1974 [1] and is considered to be the most widely used herbicide in the history of agriculture [2,3], a postemergent, systemic, non-selective chemical [4,5] that poses a high risk to human health and the environment [4]. In 2014, farmers in the United States sprayed enough glyphosate to reach about 1 kg per hectare of cultivated land, amounting to nearly 0.53 kg/ha for all crops in the world [6]. ...
Glyphosate is still the subject of much debate, as several studies report its effects on the environment. Sunflower (GK Milia CL) was set up as an experimental plant and treated with glyphosate concentrations of 500 ppm and 1000 ppm in two treatments. Glyphosate was found to be absorbed from the soil into the plant organism through the roots, which was also detectable in the leaf and root. Glyphosate was also significantly detected in the plant 5 weeks after treatment and in plants that did not receive glyphosate treatment directly, so it could be taken up through the soil. Based on the morphological results, treatment with higher concentrations (1000 ppm) of glyphosate increased the dried mass and resulted in shorter, thicker roots. Histological results also showed that basal and transporter tissue distortions were observed in the glyphosate-treated plants compared to the control group. Cells were distorted with increasing concentration, vacuoles formed, and the cell wall was weakened in both the leaf-treated and inter-row-treated groups. In the future, it will be worth exploring alternative agricultural technologies that can reduce the risk of glyphosate while increasing economic outcomes. This may make the use of glyphosate more environmentally conscious.
Canola ( Brassica napus ) production in Australia widely uses glyphosate‐tolerant (Roundup Ready [RR]) cultivars. White leaf spot (WLS; Neopseudocercosporella capsellae ) significantly threatens canola globally, but particularly in Australia. Studies were undertaken on Hyola RR 500, with moderate resistance, and Hyola RR 504, which is highly susceptible to WLS, to determine how glyphosate application at various timings before and after N . capsellae infection affects WLS development. There were significant ( p < 0.05) effects for leaf disease incidence (LDI), leaf area diseased (LAD), and leaf area collapsed (LAC) for both canola cultivars, for disease development period (days post‐inoculation), and for glyphosate application time (before or after inoculation). Although applying glyphosate before or after inoculation on both cultivars significantly ( p < 0.05) increased LDI, LAD and LAC area under disease progress curve (AUDPC) values, glyphosate application before inoculation exerted a significantly greater effect on these values than glyphosate application after inoculation. On both cultivars across 21 days, glyphosate application 7 days before inoculation resulted in the greatest increases for LDI, LAD and LAC AUDPC values, while glyphosate application 7 days after had the least effect. This study highlighted potential significant benefit for farmers by withholding glyphosate applications until N . capsellae infections are well established in order to minimize predisposition to WLS by glyphosate applied prior to the main N . capsellae infection period.
Studies were undertaken on two atrazine-tolerant canola (Brassica napus) cultivars (moderately resistant Crusher TT and highly susceptible Thunder TT) to white leaf spot (WLS) (Neopseudocercosporella capsellae), to determine how atrazine application affects WLS development. There were significant main treatment effects in relation to percent leaf disease incidence (%LDI), percent leaf area diseased (%LAD) and percent leaf area collapsed (%LAC) for canola cultivar, disease development period (days-post-inoculation), atrazine spray (before or after inoculation), and %LDI for atrazine spray timing (0, 1, 3, 7 days), along with significant two- and three-way interactions between treatments. For %LDI across a 21-day period, Crusher TT showed greatest disease suppression from atrazine application 0 or 7 days before inoculation, and Thunder TT from application 0 days before and 7 days after inoculation. In terms of %LAD, Crusher TT showed greatest suppression from application at 0 and 7 days before inoculation, and Thunder TT from application 0 days before or 1 day after inoculation. In relation to %LAC, Crusher TT showed greatest suppression from application 7 days before inoculation and Thunder from application 0 days before or 1 day after inoculation. That the extent of suppression of WLS by atrazine application was substantial and that it varied with cultivar susceptibility, application timing, and that there was a strong interaction of cultivar x application timing, highlights potential opportunities for farmers to exploit better cultivar choices in conjunction with manipulating the timing of atrazine application to maximize WLS suppression and consequent canola yield.
Hundreds of new woody ornamental plant cultivars are introduced into the nursery industry each year which have many desirable aesthetic traits. However, in recent years growers have reported a higher level of herbicide sensitivity with certain cultivars compared with older cultivars that have been in the trade for multiple years. The objective of this research was to determine the tolerance of 12 different cultivars of five ornamental species including four cultivars of Loropetalum chinense [‘Ruby’, ‘Shang-hi’ PP18331 (Purple Diamond®), ‘Irodori’ USPP 27713 (Jazz Hands®), and ‘PIILC-I’ (Crimson Fire™), and two cultivars of Gardenia jasminoides (‘Frostproof’ and ‘Buttons’), Lagerstroemia indica [‘JM7’ PP34092 (Thunderstruck™ Ruby) and ‘Tuscarora’], Rhododendron [‘Conlet’ PP12111 (Autumn Carnival Encore®) and ‘Fashion’], and Ligustrum sinense Sunshine (‘Sunshine’ PP20379 and ‘Variegatum’) to spray-applied applications of dimethenamid-P or isoxaben + prodiamine and granular applications of dimethenamid-P + pendimethalin and indaziflam. While little to no injury was observed in gardenia or crape myrtles, significant injury and differences among cultivars of the same species were observed in azalea, loropetalum, and ligustrum. Results indicate that all new cultivars should be evaluated for herbicide tolerance by growers prior to wide scale application as significant differences in both growth and injury ratings were observed between different cultivars of the same species.
Species used in this study: Ruby Loropetalum (Loropetalum chinense (R.Br.) Oliv. ‘Ruby’); Purple Diamond® loropetalum (Loropetalum chinense ‘Shang-hi’ PP18331); Jazz Hands loropetalum (Loropetalum chinense ‘Irodori’ USPP 27713); Crimson Fire™ loropetalum (Loropetalum chinense var. rubrum ‘PIILC-I’); Frostproof gardenia (Gardenia jasminoides J.Ellis ‘Frostproof’); Buttons gardenia (Gardenia jasminoides ‘Buttons’); Thunderstruck™ Ruby crape myrtle (Lagerstroemia × ‘JM7’ PP34092); Tuscarora crape myrtle (Lagerstroemia indica L. ‘Tuscarora’); Autumn Carnival Encore® azalea (Rhododendron ‘Conlet’ PP12111); Fashion azalea (Rhododendron × ‘Fashion’); Sunshine ligustrum (Ligustrum sinense Lour. ‘Sunshine’ PP20379); Variegated ligustrum (Ligustrum sinense ‘Variegatum’).
Chemicals used in this study: dimethenamid-P (Tower®), (S)-2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)-acetamide; dimethenamid-P+ pendimethalin (FreeHand®) (S)-2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)-acetamide + N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenam; indaziflam (Marengo®G) N-[(1R,2S)-2,3-dihydro-2,6-dimethyl-1H-inden-1-yl]-6-[(1RS)-1 fluoroethyl]-1,3,5-triazine-2,4-diamine; prodiamine + isoxaben (Gemini® SC) 2,6-Dinitro-N1,N1-dipropyl-4-(trifluoromethyl)benzene-1,3-diamine + 2,6-Dimethoxy-N-[3-(3-methylpentan-3-yl)-1,2-oxazol-5-yl]benzamide.
Manganese (Mn) deficiency is a widespread occurrence across different landscapes, including agricultural systems and managed forests, and causes interruptions in the normal metabolic functioning of plants. The microelement is well-characterized for its role in the oxygen-evolving complex in photosystem II and maintenance of photosynthetic structures. Mn is also required for a variety of enzymatic reactions in secondary metabolism, which play a crucial role in defense strategies for trees. Despite the strong relationship between Mn availability and the biosynthesis of defense-related compounds, there are few studies addressing how Mn deficiency can impact tree defense mechanisms and the ensuing ecological patterns and processes. Understanding this relationship and highlighting the potentially deleterious effects of Mn deficiency in trees can also inform silvicultural and management decisions to build more robust forests. In this review, we address this relationship, focusing on forest trees. We describe Mn availability in forest soils, characterize the known impacts of Mn deficiency in plant susceptibility, and discuss the relationship between Mn and defense-related compounds by secondary metabolite class. In our review, we find several lines of evidence that low Mn availability is linked with lowered or altered secondary metabolite activity. Additionally, we compile documented instances where Mn limitation has altered the defense capabilities of the host plant and propose potential ecological repercussions when studies are not available. Ultimately, this review aims to highlight the importance of untangling the effects of Mn limitation on the ecophysiology of plants, with a focus on forest trees in both managed and natural stands.
Glyphosate (Gly) and its formulations are broad-spectrum herbicides globally used for pre- and post-emergent weed control. Glyphosate has been applied to terrestrial and aquatic ecosystems. Critics have claimed that Gly-treated plants have altered mineral nutrition and increased susceptibility to plant pathogens because of Gly ability to chelate divalent metal cations. Still, the complete resistance of Gly indicates that chelation of metal cations does not play a role in herbicidal efficacy or have a substantial impact on mineral nutrition. Due to its extensive and inadequate use, this herbicide has been frequently detected in soil (2 mg kg−1, European Union) and in stream water (328 µg L−1, USA), mostly in surface (7.6 µg L−1, USA) and groundwater (2.5 µg L−1, Denmark). International Agency for Research on Cancer (IARC) already classified Gly as a category 2 A carcinogen in 2016. Therefore, it is necessary to find the best degradation techniques to remediate soil and aquatic environments polluted with Gly. This review elucidates the effects of Gly on humans, soil microbiota, plants, algae, and water. This review develops deeper insight toward the advances in Gly biodegradation using microbial communities. This review provides a thorough understanding of Gly interaction with mineral elements and its limitations by interfering with the plants biochemical and morphological attributes.
Symbiotic Methylobacterium comprise a significant portion of the phyllosphere, and are known to benefit host plant growth, development, and confer tolerance to stress factors. The near ubiquitous use of the broad-spectrum herbicide, glyphosate, in farming operations globally has necessitated a more expansive evaluation of the impacts of the agent itself and formulations containing glyphosate on important components of the plant phyllosphere, including Methylobacterium.
This study provides an investigation of the sensitivity of 18 strains of Methylobacterium to glyphosate and two commercially available glyphosate-based herbicides (GBH). Nearly all strains of Methylobacterium showed signs of sensitivity to the popular GBH formulations WeatherMax® and Transorb® in a modified Kirby Bauer experiment. However, exposure to pure forms of glyphosate did not show a significant effect on growth for any strain in both the Kirby Bauer test and in liquid broth, until polysorbate-20 (Tween20) was added as a surfactant. Artificially increasing membrane permeability through the introduction of polysorbate-20 caused a 78–84% reduction in dry cell biomass relative to controls containing glyphosate or high levels of surfactant only (0–9% and 6–37% reduction respectively). The observable high sensitivity of Methylobacterium to the tested GBH formulations, including complete bactericidal activity in liquid broth at concentrations as low as 0.05% w/v (500 µg/L), was shown by the inability to recover culture viability when transferred to fresh media.
To better understand the compatibility of important phyllospheric bacteria with commercial herbicides, this study endeavours to uncover the feasibility of synthetic products with biofertilizers and explores possible mechanisms by which toxicity may be induced in Methylobacteria.
Approximately 20 years ago, commercial pest control used genetic
engineering techniques. In 1995, modified insecticidal plants harbouring BT
genes were introduced in the United States. Plants that were resistant to the
herbicide glyphosate followed these in 1996. Traditional farming practices
have been altered by glyphosate-resistant crops. Without cultivating the soil
first, seeds are poked into it. Fields are treated with glyphosate aerially when
weeds start to grow. GE crops have had unforeseen effects on ecology and the
environment. Glyphosate has wiped out the milkweed habitat of the monarch
butterfly, Danaus plexippus, in the Midwest. The monarch depends on
milkweed, and numbers in the Midwest have decreased by 81%. Significant
Rise in Glyphosate Glyphosate use has increased significantly as a result of a
significant increase in GE crops generally. In 1994, glyphosate was used in
around 3 million pounds (1.36 million kg), while in 2013, it was used in 280
million pounds (127.3 million kg) (Benbrook 2009; USGS 2015). Frequent
applications likely diminished amphibian numbers and polluted the land and
water. Several studies have demonstrated that glyphosate accumulation in the
soil increases soil pathogens like Fusarium (Johal and Huber 2009; Kremer).
As a result of glyphosate saturation, several important weed species have
developed resistance (Duke and Powles 2009; Fernandez -Cornejo et al.
2014). BT Crops BT crops have also caused problems. BT proteins target
specific insects such as European corn borer, Ostrinia nubilalis; pink
bollworm, Pectinophora gossypiella and others. Since insecticidal effects are
so specific, BT crops tend to encourage development of secondary pests that
are not affected by the pesticide (Tabashnik et al. 2013). Because pests are
constantly exposed, several insect species are now resistant. Insect resistance
and invasion of secondary pests have led to treatment of crops with
neonicotinoid insecticides that can have toxic effects on bees, birds, and
beneficial insects (Goulson 2013; Tabashnik et al. 2013; Quarles 2014b;
Hopwood et al. 2012).
Penyakit blas yang disebabkan Pyricularia oryzae merupakan penyakit yang paling merusak di semua negara penghasil padi. Namun epidemi penyakit blas pada padi di Indonesia tergolong baru, yang sebelumnya dikenal sebagai penyakit utama padi gogo. Penelitian ini bertujuan menganalisis faktor agronomi dan tanah yang berhubungan dengan perkembangan penyakit blas padi. Penyakit blas dinilai pada 50 petak sawah menggunakan sistem skor IRRI. Petani yang menanam padi di petak pengamatan diwawancarai menggunakan kuesioner terstruktur tentang teknik budi daya yang meliputi varietas, pupuk organik dan pupuk sintetik NPK, penggunaan insektisida, fungisida, dan herbisida. Analisis kimia tanah dilakukan terhadap pH, C organik, N, P, K, Ca, Mg, Si, Zn, Mn, Cu pada tanah yang diperoleh dari ledakan penyakit blas berat dan ringan, dengan lima sampel untuk masing-masing kategori. Data faktor teknik budi daya (varietas, pemupukan, penggunaan pestisida, penggunaan bahan organik) ditabulasi silang dalam tabel kontingensi terhadap dua tingkat keparahan penyakit, dan selanjutnya dianalisis tingkat nyata keterkaitan. Sifat kimia tanah plot yang keparahan penyakitnya berbeda dianalisis. Faktor agronomi yang berhubungan dengan tingginya keparahan penyakit blas padi sawah ialah penggunaan varietas Ciherang, penggunaan pestisida frekuensi tinggi, dan penggunaan herbisida. Sifat tanah yang berhubungan dengan tingkat epidemi ledakan penyakit ialah kadar N, P, K, S, Si, dan unsur mikro tanah.
In modern agriculture, the problem of the use of various pesticides, including non-selective herbicides and copper-containing fungicides, is acute. Rhizospheric bacteria can serve as one of the factors of increasing the resistance of plants to adverse chemical influences. The subject of this research was study the effect of bacteria Ochrobactrum cytisi IPA 7.2 on the white mustard (Sinapis alba L.) resistance to copper ions (Cu(II)), glyphosate and copper complexes with glyphosate [Cu(II)-GL]; as well as on the accumulation and translocation of pollutants in plants. It was shown that the combination of glyphosate or its complexes [Cu(II)-GL] and IPA 7.2 inoculation inhibited the growth of mustard more intensively than in the variants with pollutants alone. In the case of copper, on the contrary, an increase in the accumulation of wet and dry root mass by 1.8 times was found in inoculated plants. Colonization of mustard with strain IPA 7.2 reduced the accumulation of Cu(II) in the plant’s shoot system by two times and simultaneously stabilized the metal in the root zone. However, IPA 7.2 did not effect on the accumulation and translocation of chelated copper in the complexes. The current result is important for understanding about processes of interaction in the plant-rhizosphere bacteria-pollution system and can be used in the technology of growing environmentally friendly products.
Telah dilakukan analisis vegetasi secara berkala di kebun kelapa sawit IPB Jonggol pada tanaman menghasilkan umur 1 tahun (2016), tanaman menghasilkan umur 3 tahun (2018), dan tanaman menghasilkan umur 5 tahun (2020). Penelitian terdiri atas dua percobaan. Percobaan I untuk mengetahui pergeseran gulma dominan dan percobaan II untuk mengetahui kemungkinan terjadinya resistensi gulma terhadap herbisida glifosat. Percobaan I adalah analisis vegetasi menggunakan metode kuadran 1 m x 1 m pada 5 blok, dan 20 sampel diambil secara acak dari setiap blok sehingga terdapat 100 sampel pengamatan. Percobaan II adalah penanaman biji gulma dari jenis gulma terpilih pada percobaan I, dan sebagai kontrol menggunakan biji gulma dari percobaan I yaitu dari gulma berasal dari lokasi yang tidak pernah mendapatkan herbisida. Asam amino yang diamati berhubungan dengan cara kerja glifosat yaitu fenilalanin, tirosin, L-triptofan. Hasil analisis vegetasi menunjukkan telah terjadi pergeseran gulma dominan. Tahun 2016 didominasi Rolandra fruicosa dan Melastoma malabathricum, tahun 2018 di domimasi Ottochloa nodosa, tahun 2020 O. nodosa dan Cyrtoccum patens. Asystasia gangetica terus meningkat populasinya. Nisbah resistensi, gulma uji O. nodosa dan C. patens termasuk resistensi rendah. Kandungan fenilalanin, tirosin dan L-triptofan gulma uji O. nodosa lebih tinggi dari gulma susceptible O. nodosa.
Kata kunci: analisis vegetasi, asam amino, gulma dominan, nisbah resistensi
Bakkour, F., A. El-Meamar and Z. El-Naser. 2021. Effect of Spraying Glyphosate Herbicide on Solanum elaeagnifolium in Uncultivated Fields and on Physicochemical and Biological Soil Characteristics. Arab Journal of Plant Protection, 39(4): 296-308. https://doi.org/10.22268/AJPP-39.4.296308 Glyphosate herbicide is used in uncultivated fields infested with Solanum elaeagnifolium plants several times a year in all Syrian governorates by the Ministry of Agriculture. This research aimed to study the effect of repeated spraying of glyphosate in uncultivated fields in five different locations in the Syrian governorates, Deir Ezzor (Tebni), Aleppo (Dakwani), Hama (Bostan AL-Omahat), Homs (ALZahoria) and Rural Damascus (Bohter) during the period 2017-2020, on the physiochemical and biological characteristics of the treated soils. Herbicide residues were measured in the leaves of the treated Solanum elaeagnifolium plants and in the soils surrounding the roots of the Solanum elaeagnifolium plants. It was found that the repetition of the pesticide spray 3 and 6 times during the study period did not alter the physical composition, salinity, pH and calcium carbonate content in all study locations. Whereas, spraying glyphosate 3 and 6 times increased the percentage of organic matter and phosphorus available, with a significant difference with the control. The values of available phosphorous after 6 pesticide spray applications reached 176, 203, 196, 227 and 205 mg/kg of soil in Deir Ezzor, Aleppo, Hama, Homs and Rural Damascus, respectively. In addition, repeated spraying with glyphosate of the treated soils led to increase the average general bacteria and fungi populations. These indicators were increased with the increase in the number of pesticide sprays applied. Furthermore, the pesticide residues increased in the soil and Solanum elaeagnifolium leaves with the increase in number of pesticide sprays. Pesticide residue values after 6 sprays were 1.72, 3.53, 4.89, 4.43 and 2.29 mg/kg of soil in Deir Ezzor, Aleppo, Hama, Homs and Rural Damascus locations, respectively. Keywords: Glyphosate, S. elaeagnifolium, residues, microorganisms, soil.
Kabupaten Bangli, Bali merupakan salah satu sentra produksi jeruk di Indonesia. Kendala pada produksi jeruk di antaranya ialah penyakit busuk pangkal batang yang disebabkan oleh Lasiodiplodia theobromae. Tujuan penelitian ini menentukan faktor budi daya, letak geografis, dan curah hujan yang berkaitan dengan penyakit ini. Pengamatan kondisi penyakit dan wawancara mengenai teknik budi daya ditanyakan kepada 50 petani pemilik. Keterkaitan antara teknik budi daya dan keparahan penyakit dianalisa dari data korespondensi yang dipetakan dengan grafik biplot dan analisis kontingensi dengan uji khi kuadrat. Berdasarkan pada analisis korespondensi dan kontingensi terdapat 4 faktor cara budi daya dan 1 faktor tanaman yang berkaitan nyata terhadap keparahan busuk batang jeruk. Faktor tersebut ialah frekuensi penyiangan secara mekanis, umur tanaman, populasi tanaman per hektar, aplikasi herbisida, dan dosis pupuk nitrogen.
Dalam usaha peningkatan produksi tanaman kopi salah satu faktor yang perlu diperhatikan adalah pemeliharaan tanaman khususnya pengendalian gulma. Pengendalian gulma pada perkebunan kopi yang dinilai cukup efektif dan efisien yaitu dengan pengendalian secara kimiawi menggunakan herbisida berbahan aktif glifosat. Herbisida berbahan aktif glifosat merupakan herbisida yang bersifat non selektif dan memiliki spektrum pengendalian yang luas. Tujuan penelitian adalah (1) mengetahui kinerja herbisida glifosat dalam mengendalikan gulma pada pertanaman kopi menghasilkan dan (2) mengetahui tingkat toksisitas herbisida glifosat terhadap tanaman kopi menghasilkan. Penelitian terdiri dari enam perlakuan yang disusun dalam rancangan acak kelompok dengan empat ulangan. Perlakuan yang diuji yaitu glifosat 1,08 kg ha-1, glifosat 1,44 kg ha-1, glifosat 1,80 kg ha-1, dan glifosat 2,16 kg ha-1, penyiangan manual, dan kontrol. Data dianalisis ragam dan uji lanjut dengan Uji Beda Nyata Terkecil (BNT). Hasil penelitian menunjukkan bahwa (1) aplikasi herbisida glifosat pada dosis 1,08 – 2,16 kg ha-1 mampu menekan penutupan dan bobot kering gulma total, bobot kering gulma golongan daun lebar dan golongan rumput hingga 12 MSA dan (2) perlakuan herbisida glifosat yang digunakan untuk mengendalikan gulma tidak meracuni tanaman kopi hingga 6 MSA.
Penelitian ini bertujuan untuk mengetahui efektifitas herbisida Isoprofil Amina (IPA) Glifosat, untuk mempelajari perubahan komposisi jenis gulma setelah aplikasi IPA glifosat, dan untuk mengetahui pengaruh keracunan herbisida IPA glifosat pada tanaman karet menghasilkan. Penelitian ini dilaksanakan di lahan perkebunan PTPN VII Unit Usaha Way Galih dan Laboratorium Ilmu Gulma Fakultas Pertanian Universitas Lampung. Penelitian ini disusun dengan 6 perlakuan dengan 4 ulangan. Susunan perlakuan sebagai berikut yaitu isopropil amina glifosat 720 g ha -1, isopropil amina glifosat 960 g/ha, isopropil amina glifosat 1200 g ha -1 , isopropil amina glifosat 1440 g ha -1 , pengendalian mekanis dan kontrol. Homogenitas ragam diuji dengan uji Bartlet, aditivitas diuji dengan uji Tukey, dan perbedaan nilai tengah diuji dengan Uji Beda Nyata Terkecil (BNT) pada taraf 5 %. Hasil penelitian menunjukkan bahwa herbisida glifosat pada dosis 720 g ha -1 - 1440 g ha -1 mampu menekan pertumbuhan gulma total, gulma golongan rumput dan gulma dominan (Centocheca lappacea, Cyrtococcum acrescens,Ottochloa nodosa) pada tanaman karet dari 4 MSA sampai dengan 12 MSA, sedangkan gulma golongan daun lebar dan gulma dominan Sellaginella willdenowii hanya pada 4 MSA pada perkebunan karet menghasilkan, dan terdapat perubahan komposisi gulma yang tumbuh setelah aplikasi herbisida glifosat, gulma golongan daun lebar menjadi dominan.
Penelitian ini bertujuan untuk mengetahui efektifitas herbisida Isoprofil Amina (IPA) Glifosat, untuk mempelajari perubahan komposisi jenis gulma setelah aplikasi IPA glifosat, dan untuk mengetahui pengaruh keracunan herbisida IPA glifosat pada tanaman karet menghasilkan. Penelitian ini dilaksanakan di lahan perkebunan PTPN VII Unit Usaha Way Galih dan Laboratorium Ilmu Gulma Fakultas Pertanian Universitas Lampung. Penelitian ini disusun dengan 6 perlakuan dengan 4 ulangan. Susunan perlakuan sebagai berikut yaitu isopropil amina glifosat 720 g ha -1, isopropil amina glifosat 960 g/ha, isopropil amina glifosat 1200 g ha -1 , isopropil amina glifosat 1440 g ha -1 , pengendalian mekanis dan kontrol. Homogenitas ragam diuji dengan uji Bartlet, aditivitas diuji dengan uji Tukey, dan perbedaan nilai tengah diuji dengan Uji Beda Nyata Terkecil (BNT) pada taraf 5 %. Hasil penelitian menunjukkan bahwa herbisida glifosat pada dosis 720 g ha -1 - 1440 g ha -1 mampu menekan pertumbuhan gulma total, gulma golongan rumput dan gulma dominan (Centocheca lappacea, Cyrtococcum acrescens,Ottochloa nodosa)pada tanaman karet dari 4 MSA sampai dengan 12 MSA, sedangkan gulma golongan daun lebar dan gulma dominan Sellaginella willdenowii hanya pada 4 MSA pada perkebunan karet menghasilkan, dan terdapat perubahan komposisi gulma yang tumbuh setelah aplikasi herbisida glifosat, gulma golongan daun lebar menjadi dominan.
Time intervals between applying glyphosate to kill volunteer cereals and weeds and planting spring barley by direct drilling (no-till) into Rhizoctonia-infested soil were evaluated in field plots at Pendleton, Oregon, and Lacrosse and Lind, Washington. As the interval was shortened from autumn to spring application or from 3 wk to 3 days before planting in the spring, severity of Rhizoctonia root rot increased and grain yield decreased. When glyphosate applications were delayed until 2 or 3 days before planting (commonly used in production of spring barley in the Pacific Northwest), spring barley yields were reduced as much as 50% compared to when glyphosate was applied in the autumn or early spring. Disease was not as prevalent when glyphosate was applied 1 or 2 days after direct drilling compared with applications made 3 days before planting. Rhizoctonia root rot was least on spring barley when tillage or application of glyphosate was performed in the autumn or in spring 3 wk before planting. Tilling soil 2 days before planting at one site nullified the yield-depressing effect of a preplant glyphosate application. These results suggest that the inoculum potential for R. solani AG-8 as a pathogen of spring barley is strongly influenced by the timing of volunteer cereal and weed elimination and that adjustments in such practices can minimize crop damage and maximize yield.
Three-year field experiments were conducted to assess the development of sudden death syndrome (caused by Fusarium solani f. sp. glycines) in three soybean cultivars, tolerant (P9344 and A3071) and nontolerant (BSR101), to glyphosate following foliar application of four herbicides (acifluorfen, glyphosate, imazethapyr, and lactofen) commonly applied to soybeans in the north-central region of the United States. Cultivar A3071 is resistant to sudden death syndrome, whereas cultivars P9344 and BSR101 are susceptible to this disease. There was no statistically significant cultivar-herbicide interaction with respect to the severity of foliar symptoms of the disease and the frequency of isolation of F. solani f. sp. glycines from roots of soybean plants. Across all herbicide treatments, the level of sudden death syndrome was lower in the disease-resistant cultivar than in the susceptible ones. There was an increase in the disease levels under application of acifluorfen, glyphosate, and imazethapyr compared with nontreated or lactofen-treated plants. The results obtained indicate that the response of glyphosate-tolerant soybeans to sudden death syndrome is not different from the response of conventional soybeans to this disease following application of the selected herbicides, and the resistance of soybean to sudden death syndrome was not changed with application of glyphosate.
Transgenic bromoxynil-, glufosinate-, and glyphosate-resistant crops have been commercialized and grown extensively in the Western Hemisphere and, to a lesser extent, elsewhere. Bromoxynil-resistant crops have been removed from the market. Few new herbicide-resistant crops (HRCs) are likely to be introduced in the near future. Glyphosate-resistant cotton and soybean have become dominant in those countries where they can be grown. Previous and potential effects of glufosinate and glyphosate on contamination of soil, water, and air are minimal, compared to that caused by the herbicides that they replace when HRCs are adopted. No risks have been found with food or feed safety or nutritional value in products from currently available HRCs. Both glufosinate- and glyphosate-resistant crops promote the adoption of reduced- or no-tillage agriculture. In the U.S.A. and Argentina, the advent of glyphosate-resistant soybeans resulted in a significant shift to reduced- and no-tillage practices, strongly reducing environmental degradation by agriculture. Weed species in HRC fields have shifted to those that can more successfully withstand glyphosate or to those that avoid the time of its application. One species has evolved resistance in glyphosate-resistant crops due to selection pressure from glyphosate. HRCs have a greater potential to become problematical as volunteer crops than do conventional crops. In canola, herbicide resistance transgenes have been found in fields of canola that are supposed to be non-transgenic. Under some circumstances, transgene flow (introgression) to plants that might become problematical in natural ecosystems may be the largest risk of HRCs. The HRC transgene itself is highly unlikely to be a risk in wild populations, but when linked to transgenes that may impart fitness benefits outside of agriculture, natural ecosystems could be affected. The development and use of failsafe introgression barriers in crops with such linked genes is highly encouraged.
Although glyphosate-resistant (GR) technology is used in most countries producing soybeans (Glycine max L.), there are no particular fertilize recommendations for use of this technology, and not much has been reported on the
influence of glyphosate on GR soybean nutrient status. An evaluation of different cultivar maturity groups on different soil
types, revealed a significant decrease in macro and micronutrients in leaf tissues, and in photosynthetic parameters (chlorophyll,
photosynthetic rate, transpiration and stomatal conductance) with glyphosate use (single or sequential application). Irrespective
of glyphosate applications, concentrations of shoot macro- and micronutrients were found lower in the near-isogenic GR-cultivars
compared to their respective non-GR parental lines Shoot and root dry biomass were reduced by glyphosate with all GR cultivars
evaluated in both soils. The lower biomass in GR soybeans compared to their isogenic normal lines probably represents additive
effects from the decreased photosynthetic parameters as well as lower availability of nutrients in tissues of the glyphosate
treated plants.
KeywordsGlyphosate resistant soybean (Glycine max L.)-Glyphosate-Nutrient status-Photosynthesis
ABSTRACT Sudden death syndrome of soybean, caused by Fusarium solani f. sp. glycines, is a disease of increasing economic importance in the United States. Although the ecology of sudden death syndrome has been extensively studied in relation to crop management practices such as tillage, irrigation, and cultivar selection, there is no information on the effects of herbicides on this disease. Three herbicides (lactofen, glyphosate, and imazethapyr) commonly used in soybean were evaluated for their effects on the phenology of F. solani f. sp. glycines and the development of sudden death syndrome in four soybean cultivars varying in resistance to the disease and in tolerance to glyphosate. Conidial germination, mycelial growth, and sporulation in vitro were reduced by glyphosate and lactofen. In growth-chamber and greenhouse experiments, there was a significant increase in disease severity and frequency of isolation of F. solani f. sp. glycines from roots of all cultivars after application of imazethapyr or glyphosate compared with the control treatment (no herbicide applied). Conversely, disease severity and isolation frequency of F. solani f. sp. glycines decreased after application of lactofen. Across all herbicide treatments, severity of sudden death syndrome and isolation frequency were lower in disease-resistant than in susceptible cultivars. Results suggest that glyphosate-tolerant and -nontolerant cultivars respond similarly to infection by F. solani f. sp. glycines after herbicide application.
Mineral nutrition affects a plant's susceptibility to plant diseases, especially when the element is deficient or the plant is under environmental stress. Both macro- and micronutrients as well as beneficial elements affect plant health via numerous mechanisms, such as activating enzymes that produce defense metabolites, for example, lignin and phytoalexins, and indirectly by altering the root exudates, rhizosphere pH, and microbial activity. The role that each nutrient plays in plant disease suppression must be viewed holistically due to the numerous interactions with other elements, the host plant, rooting medium, and with beneficial and pathogenic microorganisms.
Colonization of root tissues in tomato seedlings genetically resistant to Fusarium oxysporum f.sp. radicis-lycopersici Jarvis & Shoemaker occurred following exposure to a sublethal concentration of the herbicide glyphosate (1.0 mM for 24 h prior to inoculation). The glyphosate-induced colonization was associated with an inefficiency in incorporation of phenolic materials into the papillae and into the modified cortical cell walls normally formed in response to this pathogen. Glyphosate-induced susceptibility decreased when the glyphosate was applied at 24 or 48 h after inoculation. Plants supplied with exogenous L-phenylalanine failed to exhibit reduced susceptibility after glyphosate exposure. In radial growth bioassays, growth of the fungus was unaffected by 4.0 mM glyphosate. α-Aminooxyacetic acid, an inhibitor of phenylalanine ammonia lyase, also increased the severity of the disease in resistant plants. Glyphosate also induced susceptibility to an isolate of F. solani f.sp. pisi, which was normally n...
The take-all disease, caused by Gaeumannomyces graminis var. tritici, is one of the world's most damaging root diseases of wheat. It has been hypothesized that the fungus reduces the host's defense mechanism prior to invasion by catalyzing the oxidation of soluble Mn 2+ to insoluble Mn 4+ on the rhizoplane and in the soil surrounding the root. For the first time, a direct test of this hypothesis has been accomplished using micro-X-ray absorption near edge structure (XANES) spectroscopy to obtain information about the spatial distribution of Mn oxidation states in and around live wheat roots growing in agar infected with G. graminis var. tritici. Mn in clear agar occurred only as Mn 2+ , whereas Mn around dark roots infected with G. graminis var. tritici was predominately present as Mn 4+ . The distribution of Mn oxidation states clearly showed the presence of Mn 4+ -containing precipitates in the interior of a root infected with G. graminis var. tritici. This was consistent with a map of Mn concentration that showed a relative accumulation of total Mn in the interior of the root as a result of G. graminis var. tritici-catalyzed biomineralization. Given the penetrating nature of X rays, the micro-XANES technique should be applicable to roots growing in soil, thus providing a technique to measure Mn oxidation states during pathogenesis under conditions that closely simulate the natural soil environment.
Several possible mechanisms for the glyphosate-induced predisposition of bean roots (Phaseolus vulgarisL.) to colonization byPythiumspp. were investigated. Glyphosate at 0.1 and 1.0 μg ml-1from the surfactant-containing formulation Roundup® and the non surfactant-containing formulation Accord® did not affect mycelial growth ofPythium ultimumandPythium sylvaticumon water agar and cornmeal agar. One microgram per millilitre of glyphosate from both formulations significantly stimulated germination of sporangia ofP. ultimum. Germination and growth of germ tubes ofP. ultimumwere significantly greater in root exudates from bean plants whose primary leaves had been treated with glyphosate than in exudates from non-treated plants. The lignin content of roots was increased significantly whenP. ultimumorP. sylvaticumwas added to the hydroponic system in which the roots were growing. When glyphosate was applied 2 days prior toPythium, deposition of lignin in response toPythiumin the bean roots was significantly reduced. These results suggest that predisposition by glyphosate of bean roots to colonization byPythiumspp. may involve changes in root exudates that enhance germination and growth of pathogen propagules, and suppression of a pathogen-induced lignification response by plant roots.
Recent reports indicate that manganese (Mn), applied as a foliar fertilizer in tank mixtures with glyphosate, has the potential to antagonize glyphosate efficacy and reduce weed control. It was hypothesized that Mn2+ complexed with glyphosate in a similar manner to Ca2+, forming salts that were not readily absorbed and, thereby, reducing glyphosate efficacy. This study was conducted to confirm the interaction of Mn2+ and glyphosate and to measure the effect of Mn on glyphosate absorption and translocation in velvetleaf. In aqueous solutions, Mn2+ binds with solvent molecules and with chelating agents to form hexacoordinate complexes. The distribution of paramagnetic species, both the free manganous ion ([Mn{H2O}6]2+) and the Mn2+–glyphosate complex, in Mn–glyphosate solutions at various pH values were analyzed using electron paramagnetic resonance (EPR) spectroscopy. Glyphosate interaction with Mn appeared to increase as the pH was increased from spray solution levels (2.8 to 4.5) to levels common in the plant symplast (7.5). Growth chamber bioassays were conducted to measure absorption and translocation of 14C-labeled glyphosate in solution with four Mn fertilizers: Mn-ethylaminoacetate (Mn-EAA), Mn-ethylenediaminetetraacetate (Mn-EDTA), Mn-lignin sulfonate (Mn-LS), and Mn-sulfate (MnSO4). Mn-EDTA did not interfere with glyphosate efficacy, absorption, or translocation. However, both MnSO4 and Mn-LS reduced glyphosate efficacy, absorption, and translocation. Mn-EAA severely antagonized glyphosate efficacy, and although glyphosate in tank mixtures with Mn-EAA was absorbed rapidly, little was translocated from the treated leaf. The Mn-EAA fertilizer contained approximately 0.5% iron (Fe) not reported on the fertilizer label. Iron is presumed to be partially responsible for the very limited translocation of glyphosate from the treated leaf in Mn-EAA tank mixtures. Adding ammonium sulfate increased the efficacy, absorption, and translocation of glyphosate for each Mn fertilizer tank mixture. Nomenclature: Glyphosate; velvetleaf, Abutilon theophrasti Medicus. ABUTH.
Fusarium head blight (FHB) has been increasing in western regions of the Canadian Prairies. The objective of this 4-yr study was to identify crop production factors (CPF), associated with FHB development in spring wheat (Triticum aestivum L.). From 1999 to 2002, 659 crops were sampled in eastern Saskatchewan for FHB levels, and information gathered on agronomic practices used on these fields. In 2000 and 2001, percent Fusarium-damaged kernels (FDK) was also determined. Differences in the FHB index among years indicated that environment was the most important factor affecting disease development. The effects of CPFs on FHB were lower in years with high (2001) and low (1999 and 2002) disease pressure, compared with a year with moderate (2000) disease pressure. Previous application of glyphosate [N-(phosphonomethyl)glycine] formulations (GF) within tillage system, tillage system, previously grown crop, and cultivar susceptibility were the only CPFs that affected FHB. GF application in the previous 18 mo within tillage system was significantly associated with higher FHB levels every year; it was the only CPF in 1999, and one of two CPFs in 2002, that affected FHB, suggesting that its effect was not influenced as much by environmental conditions as that of other CPFs. Percentage FDK was also higher in fields previously treated with GF in 2000 and 2001. Because of the nature of this study, we could not determine if the association between previous GF use and FHB development was a cause-effect relationship. Thus, further research is needed to elucidate the nature of this association and the underlying mechanisms.
Glyphosate is a broad spectrum herbicide that can lead to root rot like damage on crops. This study was undertaken to investigate the effect of glyphosate on the root-colonizing Fusarium spp. The research was conducted at two sites. Site one was densely covered with perennial weeds, and site two with annuals. At site one, spraying the weed cover with glyphosate increased (p < 0.05) the level of colonization by Fusarium spp. in Ranunculus repens and Holcus lanatus, but not in Stellaria media and Plantago lanceolata. At site two, glyphosate enhanced colonization in Spergula arvensis, Stellaria media, Echinochloa crusgalli, and Chenopodium album, but not in Capsella bursa-pastoris and Polygonum persicaria. At both sites, the number of colony-forming units of Fusarium spp. per gram of dried soil was increased by the application of glyphosate. Nevertheless, crops subsequently sown in the field containing the annual weeds were not detrimentally affected by glyphosate treatment of these weeds.
At isolated sites of compatible interactions of bean hypocotyls with Colletotrichum lindemuthianum, lesions typically become delimited and phytoalexins accumulate. In plants treated with glyphosate at doses of 2.5 /jg or higher, accumulation of phytoalexins was reduced compared to untreated controls, and colorless, spreading lesions developed, coalesced, and rotted the entire hypocotyl. Glyphosate applied after phytoalexins had started to accumulate did not prevent development of delimited lesions. Among plants treated with a range of doses of glyphosate, the size and phytoalexin content of lesions were negatively correlated. In glyphosate treated plants, normal levels of phytoalexins accumulated at infection sites that received phenylalanine, and lesions at these sites did not spread. Phytoalexin accumulation during incompatible interactions was not affected by glyphosate during the initial stages of infection, but a subsequent decline in the rate of accumulation resulted in overall lower levels of phytoalexins in glyphosate treated than in control plants. Conditions that may have competed for, or depleted, phenylalanine reserves (exposure to light, removal of cotyledons enhanced the capacity of glyphosate to suppress phytoalexin accumulation. However, the accumulation of phytoalexins was suppressed only when infection sites were numerous and close together. The data support the interpretation that the ability of glyphosate to suppress accumulation of phytoalexins depends on the availability and demand for precursors, such as phenylalanine, and further provide evidence for the role of phytoalexins in restricting colonization of bean tissue by incompatible races of the bean anthracnose pathogen.
N-Phosphonomethylglycine, a unique postemergence herbicide, appears to inhibit the aromatic amino acid biosynthetic pathway. The growth inhibition of Lemna gibba in the presence of this herbicide can be alleviated by the addition of L-phenylalanine to the nutrient medium. The growth inhibition of Rhizo-bium japonicum caused by N-phosphonpmethylglycine can only be alleviated by the addition of both L-phenylalanine and L-tyrosine. The data suggest that N-phosphonomethylglycine may inhibit or repress chorismate mutase and/or prephenate dehydratase.
The mobility in phloem of several substituted phosphonic acids and a sulfonic acid was studied in the castor bean plant, Ricinus communis L. For a series of14C-labelled phosphonate mono-esters applied to the petioles of mature leaves, phloem transport was modest, becoming poor over longer distances in the plant. Substituted phenylphosphonic acids were more efficiently moved in phloem; uptake from the petiole and subsequent redistribution were slow, but these dibasic compounds were very stable in plants and substantial amounts reached the roots after 72 to 120 h. Glyphosate was very efficiently transported to phloem sinks even within 24 h, with high concentrations in phloem sap. Toluene-4-sulfonic acid moved predominantly in the xylem to the mature leaves and its phloem transport was poor. Transport patterns are considered in relation to the physico-chemical properties of the compounds. Ion trapping appears to play little part in the phloem transport of these strong acids, though the good accumulation and transport in phloem of the complex molecule glyphosate cannot at present be explained.
In controlled environment experiments, the bioherbicidal fungus Myrothecium verrucaria (Alb. & Schwein.) Ditmar:Fr. was tested alone, in combination with, prior to, and following treatment with glyphosate [N -(phosphonomethyl)glycine] for control of kudzu [Pueraria lobata (Willd.) Ohwi], redvine [Brunnichia ovata (Walt.) Shinners], and trumpetcreeper [Campsis radicans (L.) Seem. ex Bureau] at temperatures of 20, 30, and 408C. At all temperatures, kudzu was most adversely affected by the fungus, followed by trumpetcreeper and redvine, as indicated by greater mortality and dry weight reductions. Trumpetcreeper and redvine mortalities and dry weight reductions significantly increased when the fungus was applied 2 days after the glyphosate treatment. Application of the fungus combined with or prior to glyphosate treatment resulted in reduced weed control. Although pathogenesis and mortality also occurred at 208C, disease development was favored by higher temperatures (30 and 408C). Infected weeds of each species exhibited similar disease symptomatology within 12 h following treatment at incubation temperatures of 30 and 408C. Disease symptomatology was characterized by necrotic flecking on leaves that coalesced into large lesions. Symptoms progressed, initially infecting cotyledons and leaves, and later (within 48 h) producing stem lesions. The fungus sporulated profusely on infected tissue and was easily reisolated. These results suggest that timing of glyphosate application in relation to combined treatment with the bioherbicide M. verrucaria can improve the control of kudzu, redvine, and trumpetcreeper.
Fusarium head blight (FHB) in barley (Hordeum vulgare L.) is well established in the eastern Canadian Prairies and appears to be moving westward. A survey of 192 barley crops in eastern Saskatchewan was conducted to determine the impact of agronomic practices on FHB (1999-2002) and Fusarium-damaged kernels (FDK) (2000-2001). The most common species isolated from spikes and kernels were F. sporotrichioides, F. avenaceum, and F. graminearum, followed by F. poae and F culmorum. Disease tended to be higher under minimum-till compared with conventional- or zero-till. Fusarium sporotrichioides was favored by a previous cereal crop, whereas F avenaceum was higher after a pulse crop, and F graminearum decreased after a pulse but not an oilseed crop. The latter two pathogens were also more prevalent after diversified cropping sequences than after two cereal crops. Summer fallow, or summer fallow alternated with cereals, decreased FDK. Previous glyphosate (Group 9 herbicides) use was associated with increased infection by all Fusarium spp., whereas Group 1 herbicides were associated with increased infection by F poae and F sporotrichioides. Effects of both herbicide groups depended on tillage system. Number of previous glyphosate applications was also correlated with FHB caused by F. avenaceum and F. graminearum. We concluded that in eastern Saskatchewan, barley grown under minimum-till where glyphosate had been sprayed and following diversified cropping sequences would sustain the greatest damage due to FHB and FDK caused by F avenaceum and F. graminearum.
The application of diquat + paraquat, glyphosate and trifluralin to unsterilized field soil increased take-all caused by the fungus, Gaeumannomyces graminis var. tritici Walker by 13.0% 16.6% and 10.8% respectively, while no effect on disease was recorded in sterilized soil treated with the same herbicides. The herbicides tested had no effect on the saprophytic growth of the pathogen with the exception of glyphosate, which increased its growth in unsterilized soil. The application of diquat + paraquat and glyphosate to unsterile soil had no effect on the numbers of actinomycetes. The diquat + paraquat treatment, however, increased populations of fungi while the glyphosate decreased the numbers of bacteria. The proportion of soil fungi antagonistic to the pathogen was reduced in glyphosate-treated soil. The frequency of occurrence of Eupenicillium euglaucum (v. Beyma) Stolk & Samson (strain B), and Penicillium verruculosum Peyr. (strain B), which were strong and low level antagonists of Ggt on agar, were reduced in their occurrence in soil by 7.7% and 2.5% respectively, following glyphosate treatment. Moreover, the numbers of Aspergillus viridinutans Ducker & Thrower, which showed moderate antagonism to the pathogen, was decreased by 1.9% and 4.1% in diquat + paraquat and glyphosate treatments respectively. The proportion of antagonists rather than total numbers of fungi appears to be related to the treatment effect observed on the soil growth and pathogenicity of G. graminis var. tritici in our investigation. The increase in disease of wheat in certain herbicide-treated soils may be due to the shift in soil microbial populations away from those which are antagonistic to the pathogen.
The relationship between micronutrient efficiency of four wheat (Triticum aestivum L.) genotypes, tolerance to take-all disease (caused by Gaeumannomyces graminis (Sacc.) Arx and Olivier var. tritici Walker), and bacterial populations in the rhizosphere was tested in soil fertilized differentially with Zn and Mn. Plant growth was reduced by Mn or Zn deficiency and also by take-all. There was an inverse relationship between micronutrient efficiency of wheat genotypes when grown in deficient soils and the length of take-all lesions on roots (efficient genotypes had shorter lesions than inefficient ones). In comparison to the rhizosphere of control plants of genotypes Aroona and C8MM receiving sufficient Mn and Zn, the total numbers of bacterial cfu (colony forming units) were greater in the rhizosphere of Zn-efficient genotype Aroona under Zn deficiency and in Mn-efficient genotype C8MM under Mn deficiency. These effects were not observed in other genotypes. Take-all decreased the number of bacterial cfu in the rhizosphere of fully-fertilized plants but not of those subjected to either Mn or Zn deficiency. In contrast, the Zn deficiency treatment acted synergistically with take-all to increase the number of fluorescent pseudomonads in the rhizosphere. Although numbers of Mn-oxidising and Mn-reducing bacteria were generally low, take-all disease increased the number of Mn reducers in the rhizosphere of Mn-efficient genotypes Aroona and C8MM. Under Mn-deficiency conditions, the number of Mn reducers in the rhizosphere increased in Aroona but not in C8MM wheat. The results suggest that bacterial microflora may play a role in the expression of Mn and Zn efficiency and tolerance to take-all in some wheat genotypes.
The herbicide glyphosate, an inhibitor of the shikimic acid pathway and aromatic amino acid biosynthesis in plants, reduced the potential of Phaseolus vulgaris to defend itself effectively against races of Colletotrichum lindemuthianum without changing the nature of the interaction phenotype. Glyphosate did not block or diminish the occurrence of the hypersensitive reaction (HR) per se which is characteristic of the incompatible P. vulgaris-C. lindemuthianum host-pathogen interaction. The accumulation of phytoalexins which accompanies the HR was partially suppressed. Glyphosate at its sites of application sometimes enabled infection hyphase to grow from hypersensitive cells. Consequently, a spreading lesion formed which resulted in the collapse of the plant. The occurrence of glyphosate-induced spreading lesions was increased by treatments (e.g. light exposure, removal of cotyledons) that presumably competed for or depleted phenylalanine reserves in the plant. Spreading lesions developed at high frequency at wound sites on inoculated, glyphosate-treated plants. The increased frequency of spreading lesions caused by wounding cannot be accounted for solely by the presumed effect of glyphosate on accumulation of phytoalexins. The data indicate that infection hyphase of C. lindemuthianum remain viable at HR sites on P. vulgaris, and additionally, that the HR itself is not responsible for containment of the pathogen. The results support the conclusion that phytoalexin accumulation is a major feature of HR and a determinant of resistance in this host-parasite system.
Kievitone, phaseollinisoflavan and phaseollin were detected in roots of bean seedlings (Phaseolus vulgaris L.) grown in natural soil. Comparison of phytoalexin production by roots grown in different media indicated that these phytoalexins were probably induced by microorganisms in soil. The influence of common root rot pathogens of bean, Pythium spp., on phytoalexin production was determined. Pythium ultimum elicited kievitone, phaseollinisoflavan and phaseollin in roots grown in sterilized silica sand. P. sylvaticum induced only kievitone and phaseollin in the same growth medium. Glyphosate did not significantly affect the accumulation of phytoalexins within 3 days. However, by day 5, significantly more phaseollin was detected in the roots of Pythium inoculated plants treated with glyphosate than in Pythium inoculated plants not treated with glyphosate. In a hydroponic system, both Pythium spp. elicited accumulation of kievitone and phaseollin in root tissue, and both phytoalexins were exuded into the bathing solution. Glyphosate application did not significantly affect accumulation or exudation of phytoalexins by bean roots in the hydroponic system. The results from this study illustrate the nature and extent of phytoalexin production by bean roots in the absence and presence of microbes.
A new technique for assessing the number and location of fungal colonizers of entire root systems was developed, and the effect of the herbicide glyphosate on fungal colonization of roots evaluated. Fungal colonization of roots of wheat and green bush bean seedlings grown at a 25:18 °C day:night regime took place less than 48 h after treatment of the plants with glyphosate. For both plant species grown under each of four environmental conditions (a combination of two temperatures, 17° and 25°, and two soil matric potentials, −6 and −100 kPa), Pythium spp. were the most frequent colonizers of glyphosate-treated seedlings and Fusarium spp. were the second-most frequent colonizers. Colonization of control seedlings by Pythium spp. was only observed in beans grown at 17°. In glyphosate-treated wheat seedlings, less colonization by Pythium spp. occurred at 17° than at 25°, but soil water content had no significant effect. Under low soil water content, colonization by Fusarium spp. was always higher in glyphosate-treated bean or wheat seedlings than in control seedlings, whereas this differential effect was observed only for wheat grown at 25° under higher soil moisture.
Identifies a number of herbicide-disease interactions. The characteristics and interactions of glyphosate with soil fungi are emphasised, and some new or potential uses of herbicides in phytopathology are discussed. Major sections are on: characteristics of glyphosate, a broad-spectrum, water-soluble herbicide; the nature of herbicide effects on root diseases; and soil microflora and glyphosate. Combinations of weakly pathogenic fungi and low doses of herbicides may have potential for weed control. -P.J.Jarvis
Summary The functions of phenylpropanoid compounds in plant defence range from preformed or inducible physical and chemical barriers against infection to signal molecules involved in local and systemic signalling for defence gene induction. Defensive functions are not restricted to a particular class of phenylpropanoid compound, but are found in the simple hydroxycinnamic acids and monolignols through to the more complex flavonoids, isoflavonoids, and stilbenes. The enzymatic steps involved in the biosynthesis of the major classes of phenylpropanoid compounds are now well established, and many of the corresponding genes have been cloned. Less is understood about the regulatory genes that orchestrate rapid, coordinated induction of phenylpropanoid defences in response to microbial attack. Many of the biosynthetic pathway enzymes are encoded by gene families, but the specific functions of individual family members remain to be determined. The availability of the complete genome sequence of Arabidopsis thaliana, and the extensive expressed sequence tag (EST) resources in other species, such as rice, soybean, barrel medic, and tomato, allow, for the first time, a full appreciation of the comparative genetic complexity of the phenylpropanoid pathway across species. In addition, gene expression array analysis and metabolic profiling approaches make possible comparative parallel analyses of global changes at the genome and metabolome levels, facilitating an understanding of the relationships between changes in specific transcripts and subsequent alterations in metabolism in response to infection.
In greenhouse and field trials, transgenically modified wheat (Triticum aestivum) genotypes with tolerance to glyphosate had extremely low infection types to leaf rust caused by Puccinia triticina when treated with a labeled rate of the herbicide glyphosate prior to inoculation with leaf rust. A surfactant solution and a nonglyphosate herbicide had no effect on leaf rust development on the glyphosate tolerant wheat. Glyphosate had a systemic effect in reducing leaf rust development. The leaf rust control by glyphosate decreased with reduced application rates and longer periods of time between glyphosate application and leaf rust infections. The field and greenhouse tests indicated that control of leaf rust in wheat conditioned by glyphosate is transitory and is effective for at least 21, but not more than 35, days after application. Application of glyphosate also reduced infection types on wheat caused by the stem rust fungus, Puccinia graminis f. sp. tritici. Given these results and evidence from the literature that glyphosate can have adverse effects on other pathogens, including other rust fungi, additional investigation of the fungicidal properties of glyphosate are warranted, with particular attention to the timing of glyphosate application relative to fungal infection. The effects of glyphosate on the soybean rust fungus, Phakopsora pachyrhizi, an emerging pathogen in North America, merit immediate investigation.
Manganese chemistry plays a crucial role in the etiology of take-all root, crown, and stem rot of wheat caused by Gaeumannomyces graminis var. tritici (Ggt). The purpose of this field and growth chamber research was to establish the impact of rhizosphere organisms and cultural practices on Mn availability, and verify the role of Mn in take-all. This research confirmed the positive correlation of Mn oxidation as a virulence factor of Ggt, and identified temperature as a significant interactive factor with both Mn oxidation and virulence. Among the rhizophere microbes interacting with take-all, Bacillus cereus was found to inhibit Mn oxidation by Ggt, reduce take-all, and increase wheat yield. In contrast, Agrobacterium radiobacter, a strong Mn oxidizer, reduced Mn uptake by wheat and increased take-all. These important findings explain differences reported by researchers from different wheat production areas. However, oxidation-reduction reactions with other organisms was not consistently correlated with an effect on take-all. Light and electron microscopy evaluation, combined with energy dispersive X-ray microanalysis, confirmed the presence of Mn oxides on and near fungal mycelium and infection structures. The extra-cellular Mn-oxidative factor produced by Ggt oxidized Mn in advance of the mycelium. Barrier type plant defense reactions were not observed following oxidation of Mn in the infection court. In contrast, membrane-bound Mn oxidation limited to the lobed hyphopodia and adjacent infection structures of the closely related G. graminis var. graminis (Ggg), facilitated epiphytic growth, but limited penetration of Ggg to epidermal cortical tissues. This may explain Ggg's failure to induce extensive necrosis or vascular occlusion characteristic of take-all. Micro-X-ray Absorption Near Edge Structure spectroscopy (XANES), a new high energy X-ray fluorescence technique, was used to establish that direct oxidation of Mn occurred during Ggt pathogenesis on wheat roots. Manganese accumulated inside the root as a result of Ggt-catalyzed mineralization. These findings provide new and exciting direct evidence that Ggt oxidizes Mn in the rhizosphere of wheat seedlings, and provides the ground work for future in-situ research using this powerful technique to study microbial interactions in the rhizosphere involved in micronutrient availability, disease suppression, and biological control.
Glyphosate has broad spectrum herbicidal activity against a wide range of annual and perennial weeds. The environmental properties of this herbicide such as its soil immobility, rapid soil inactivation and soil biodegradation are outstanding. This herbicide is practically non-toxic to non-plant life forms such as aquatic and avian species, animals and man. Metabolism studies with pure bacterial cultures indicate that glyphosate is metabolized to either aminomethylphosphonate and glyoxylate or sarcosine and phosphate in most bacteria. The enzyme C-P lyase, which catalyzes the cleavage of the carbon-phosphorus bond of phosphonates including glyphosate, appears to be complex, containing multiple subunits. Mode of action studies have demonstrated that glyphosate kills plants by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase, involved in the biosynthesis of aromatic compounds. The status of our understanding of these aspects of glyphosate is reviewed.
Several economically important diseases of unknown or recently determined cause are reviewed. Citrus blight (CB), first described over 100 years ago, was shown in 1984 to be transmitted by root-graft inoculations; the cause remains unknown and is controversial. Based on graft transmission, it is considered to be an infectious agent by some; others suggest that the cause of CB is abiotic. Citrus variegated chlorosis, although probably long present in Argentina, where it was considered to be a variant of CB, was identified as a specific disease and shown to be caused by a strain of Xylella fastidiosa after if reached epidemic levels in Brazil in 1987. Citrus psorosis, described in 1933 as the first virus disease of citrus, is perhaps one of the last to be characterized. In 1988, it was shown to be caused by a very unusual virus. The cause of lettuce big vein appears to be a viruslike agent that is transmitted by a soilborne fungus. Double-stranded RNAs were associated with the disease, suggesting it may be caused by an unidentified RNA virus. Rio Grande gummosis, dry rot root, peach tree short life, and some replant diseases may be diseases of complex etiology. Various microorganisms have been isolated from trees with these diseases, but the diseases may be attributable in part to environmental factors. Determination of the cause of these diseases of complex etiology has proven difficult, in part, because they affect only mature trees.
The commercial launch of glyphosate-resistant soybeans in 1996 signaled the beginning of a new era in weed management in row crops. Today, over 80% of the soybeans grown in the USA are glyphosate resistant. Since that time, many crops have been transformed that have allowed crop applications of many classes of herbicide chemistries. Crops currently under production include maize, soybean, cotton and canola. Transformation technology and selection methods have improved and the rate of development as well as the breadth of crops being considered as commercial targets has increased. On the basis of recent adoption rates by growers around the world, it appears that glyphosate-resistant crops will continue to grow in number and in hectares planted. However, global public acceptance of biotechnology-derived products will continue to impact the rate of adoption of this and other new innovations derived from transformation technology.
Manganese chemistry in soils is a function of complex, competing biotic and abiotic reactions. The role of soil-borne fungi in mediating these reactions is poorly understood. The objective of this article is to document direct observation of fungal Mn oxidation in soil under near in situ conditions, and to isolate, describe and confirm the role of fungi in the observed Mn oxidation, and present a model to explain our observations. We incubated soil under different moisture contents in sample cells designed to allow us to use synchrotron microspectroscopic techniques to analyse areas as small as 38x40 microm2. Mn was redistributed and accumulated in distinct small circular shapes or in dendritic patterns near the air-soil interface when water-saturated soil was incubated for >or=7 days. Mn oxidation did not occur at 3 or 52 degrees C indicating that oxidation was caused by microbial activity. Mn-oxidizing fungi were isolated from the sample cells and cultured on agar. Reinoculation of sterile soil with the Mn-oxidizing isolates resulted in the formation of Mn oxides around fungal hyphae. A model to describe the distinct zonal distribution of Mn oxides in the sample cells is presented. We believe that our data are the first direct observation of Mn oxidation by soil-inhabiting fungi under in situ conditions. Mn-oxidizing fungi may play an underappreciated role in the cycling of Mn in soils.