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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.
... Figures were created using the software biorender (app.biorender.com). See [2,3,7,[12][13][14][15][16][17]20,[25][26][27][28][29]33,46,53,64,65,72]. Abbreviations: ET, ethylene; IAA, indole-3-acetic acid; SA, salicylic acid; VOCs, volatile organic compounds. ...
... This makes it difficult to predict the outcome of plant-pathogen interactions when glyphosate residues interact with a plant's biochemistry. In a literature review by Johal and Huber [16], it was clearly demonstrated that there is an enhanced susceptibility of plants to pathogenic infections following treatment with sublethal glyphosate doses, both above and belowground. Some plant defense strategies involving the PP pathway, such as lignification, are repressed by glyphosate, while the phytoalexin-mediated defense is temporarily maintained [16]. ...
... In a literature review by Johal and Huber [16], it was clearly demonstrated that there is an enhanced susceptibility of plants to pathogenic infections following treatment with sublethal glyphosate doses, both above and belowground. Some plant defense strategies involving the PP pathway, such as lignification, are repressed by glyphosate, while the phytoalexin-mediated defense is temporarily maintained [16]. Whereas lignification is a so called 'quantitative plant defense trait' that requires many lignan components, many phytoalexins are 'qualitative plant defense compounds' effective in small amounts [70]. ...
Glyphosate has become the best-selling herbicide used in agriculture, horticulture, silviculture, and urban environments. It disrupts the shikimate metabolic pathway and thereby blocks the production of aromatic amino acids, which are the basis for several plant metabolites. Glyphosate residues are reported in soils from diverse environments, but the effects on plant physiology and consequences for species interactions are largely unknown. Here, we emphasize the complexity of these physiological processes, and argue that glyphosate residues modulate biosynthetic pathways, individually or interactively, which may affect interactions between plants and heterotrophic organisms. In this way, glyphosate residues can substantially interfere with plant resistance and the attraction of beneficial insects, both of which are essential elements in integrated pest management and healthy ecosystems.
... 4 2,4-dichlorphenoxyacetic acid. nodular nitrogen fixation upon glyphosate application [19] and/or (iii) a weaker defence response [20]. Application of glyphosate seemed to affect nodule number and mass which have been correlated with nitrogen fixation [21] and cause the symptom of "yellow flashing" which leads to a decrease in grain yield (see discussion in [9]). ...
... Glyphosate impacts plant uptake and transport of micronutrients (e.g. Mn, Fe, Cu, and Zn) whose undersupply can reduce disease resistance and plant growth [20,23]. In Argentine soils, residue levels of up to 1500 µg/kg (1.5 ppm) glyphosate and 2250 µg/kg (2.25 ppm) AMPA have been found [29]. ...
Farmland biodiversity is an important characteristic when assessing sustainability of agricultural practices and is of major international concern. Scientific data indicate that agricultural intensification and pesticide use are among the main drivers of biodiversity loss. The analysed data and experiences do not support statements that herbicide-resistant crops provide consistently better yields than conventional crops or reduce herbicide amounts. They rather show that the adoption of herbicide-resistant crops impacts agronomy, agricultural practice, and weed management and contributes to biodiversity loss in several ways: (i) many studies show that glyphosate-based herbicides, which were commonly regarded as less harmful, are toxic to a range of aquatic organisms and adversely affect the soil and intestinal microflora and plant disease resistance; the increased use of 2,4-D or dicamba, linked to new herbicide-resistant crops, causes special concerns. (ii) The adoption of herbicide-resistant crops has reduced crop rotation and favoured weed management that is solely based on the use of herbicides. (iii) Continuous herbicide resistance cropping and the intensive use of glyphosate over the last 20 years have led to the appearance of at least 34 glyphosate-resistant weed species worldwide. Although recommended for many years, farmers did not counter resistance development in weeds by integrated weed management, but continued to rely on herbicides as sole measure. Despite occurrence of widespread resistance in weeds to other herbicides, industry rather develops transgenic crops with additional herbicide resistance genes. (iv) Agricultural management based on broad-spectrum herbicides as in herbicide-resistant crops further decreases diversity and abundance of wild plants and impacts arthropod fauna and other farmland animals. Taken together, adverse impacts of herbicide-resistant crops on biodiversity, when widely adopted, should be expected and are indeed very hard to avoid. For that reason, and in order to comply with international agreements to protect and enhance biodiversity, agriculture needs to focus on practices that are more environmentally friendly, including an overall reduction in pesticide use. (Pesticides are used for agricultural as well non-agricultural purposes. Most commonly they are used as plant protection products and regarded as a synonym for it and so also in this text.)
... Las lesiones en el tejido radical ocasionadas por el herbicida favorecen el ingreso de fitopatógenos, lo que va acompañado de cambios en los exudados, que a su vez alteran la microbiota rizosférica y las propiedades fisicoquímicas del suelo 40,44 . Por tal motivo, se recurre al uso de coberturas plásticas, para evitar una alta percolación del glifosato a través del suelo y como barrera entre las raíces del frijol y el químico 20,44 . Además, dados los reportes de residualidad de pesticidas en alimentos, es necesario reevaluar los beneficios agrícolas de la aplicación de químicos sobre el rendimiento de los cultivos en relación con su calidad e inocuidad. ...
... En contraste, sí se observó una relación con la inmovilización del manganeso, probablemente debida a la formación de complejos de glifosato-metal poco solubles en tejidos vegetales, o a interacciones en la rizósfera 12,20 . Por otro lado, Sirinathsinghji 37 precisa que esto sucede porque a través de la quelación del manganeso se inhibe la enzima vegetal 5-enolpiruvilshikimato-3-fosfato sintetasa (EPSPS), que participa en la producción de aminoácidos aromáticos en la vía shikimato EPSPS de plantas y microorganismos como Pseudomonas, Bradyrhizhobium y Agrobacterium 11 . ...
Las estrategias en seguridad alimentaria con cultivos de alto contenido nutricional deben enmarcarse en prácticas agrícolas sostenibles, orientadas a la conservación del suelo, el alto rendimiento y la inocuidad. Esta última característica implica la producción de alimentos sin trazas detectables de agroquímicos, los que podrían amenazar la salud del consumidor. Se des-arrolló un estudio con el objetivo de evaluar el efecto del herbicida glifosato sobre la fertilidad química y microbiológica del suelo, así como su residualidad en la semilla de frijol biofortificado cultivado en el departamento de Cesar, Colombia. La metodología comprendió un análisis corre-lacional de indicadores de calidad de suelo, rendimiento del cultivo y residualidad en los granos.Los tratamientos evaluados incluyeron la aplicación o no de glifosato, el uso de coberturas sintéticas (mulch) o naturales, frente al control manual de las malezas. Se hallaron diferencias de rendimiento y de la respuesta de los indicadores químicos y microbiológicos en función deltratamiento y las condiciones iniciales de la rizósfera de frijol. La aplicación del herbicida glifosato en suelo sin mulch generó una disminución del 29% en el rendimiento, asociada a la mayorprevalencia de plagas y enfermedades fúngicas. En ninguno de los tratamientos con aplicación de glifosato se observó residualidad de este herbicida en semillas, pero sí de otras moléculas derivadas de insecticidas usados en el sistema local de producción. De este estudio se concluyó que en lotes de frijol biofortificado con alta presión de la maleza Cyperus rotundus (coquito), se recomienda el uso del herbicida glifosato acompa˜nado de mulch como alternativa para man-tener la productividad en el tiempo. Esto constituye un sistema de protección frente al efecto negativo del herbicida sobre ambos, el sistema radical de la planta y la microbiota del suelo.
... ARAÚJO et al. (2003) detected an increase of 10-15% found an increase of 10-15% in the CO2 evolved and a 9-19% increase in fluorescein diacetate (FDA) hydrolyses in the presence of glyphosate compared to the same type of soil which had never received glyphosate. Consecutive use of glyphosate in crops can cause significantly increase the severity of various diseases, reduced growth, impaired defenses and alter the physiology of plants affecting the susceptibility or tolerance to diseases (FERNANDEZ ET AL., 2009;JOHAL & HUBER, 2009;YAMADA et al., 2009), which leads to the use of other types of pesticides that may further harm the environment and the health of the final consumers of this crop. When plants are attacked by pathogens, they trigger a complex defense mechanism that may be related to structural barriers, molecules stored in cells that have different types of biological activity, synthesis of protease inhibitors in tissues or even inducing enzymes such as peroxidases (ALMAGRO et al., 2009). ...
... Thus, it should be expected that as HRP is a metal-enzyme, whose active site possess Fe +3 , and when at the fundamental state The production of free radicals is continuously regulated by the antioxidant defense system in health organisms. Nevertheless, herbicides like glyphosate induce oxidative stress and/or an impairment of the antioxidant defensive mechanisms (DE AGUIAR et al., 2016;JOHAL & HUBER, 2009). Therefore, characterization of the activity of xenobiotic metabolizing enzymes is useful to monitor the effects of pesticide exposure. ...
Among several pesticides used in agriculture, glyphosate herbicide is one of the most employed in crop fields in spite of its recognized toxic effects on human health and on the environment. Consecutive use of glyphosate in crops can cause significantly increase the severity of various diseases, reduced growth, impaired defenses and alter the physiology of plants affecting the susceptibility or tolerance to diseases. Peroxidase enzymes play an important role in some physiological and pathological processes, involving active oxygen species occurring at the level of plasma membrane and cell wall. The aim of this work was to evaluate the effect of glyphosate on the enzymatic activity of horseradish peroxidase. For this purpose, tests were conducted to determine the optimal pH range and then reaction kinetic where was added, the substrate (catechol), mediator (H 2 O 2), glyphosate and enzyme (horseradish peroxidase), varying the substrate concentration glyphosate to assess the activity of this reaction and the influence of herbicide on the enzyme activity. Results demonstrate that glyphosate increases the activity of horseradish peroxidase in low concentration and can decrease the resistance of the plant to the entry of pathogens.
... Las lesiones en el tejido radical ocasionadas por el herbicida favorecen el ingreso de fitopatógenos, lo que va acompañado de cambios en los exudados, que a su vez alteran la microbiota rizosférica y las propiedades fisicoquímicas del suelo 40,44 . Por tal motivo, se recurre al uso de coberturas plásticas, para evitar una alta percolación del glifosato a través del suelo y como barrera entre las raíces del frijol y el químico 20,44 . Además, dados los reportes de residualidad de pesticidas en alimentos, es necesario reevaluar los beneficios agrícolas de la aplicación de químicos sobre el rendimiento de los cultivos en relación con su calidad e inocuidad. ...
... En contraste, sí se observó una relación con la inmovilización del manganeso, probablemente debida a la formación de complejos de glifosato-metal poco solubles en tejidos vegetales, o a interacciones en la rizósfera 12,20 . Por otro lado, Sirinathsinghji 37 precisa que esto sucede porque a través de la quelación del manganeso se inhibe la enzima vegetal 5-enolpiruvilshikimato-3-fosfato sintetasa (EPSPS), que participa en la producción de aminoácidos aromáticos en la vía shikimato EPSPS de plantas y microorganismos como Pseudomonas, Bradyrhizhobium y Agrobacterium 11 . ...
Cómo citar este artículo: Tofiño Rivera AP, et al. Efecto del glifosato sobre la microbiota, calidad del suelo y cultivo de frijol biofortificado en el departamento del Cesar, Colombia. Rev Argent Microbiol. 2019.
... Glyphosate used in conjunction with glyphosate-tolerant GE crops alters the rhizosphere fungal community with increases in growth and virulence of potential root pathogenic Fusarium spp. and of the pathogens Phytophthora, Pythium, and Gaeumannomyces (Johal and Huber 2009;Kremer and Means 2009). Interestingly, most of these fungi are also increased in the rhizospheres of many weeds that develop resistance to glyphosate and other herbicides by mechanisms similar to transgenic crop (Kremer 2014). ...
... Apart from toxicity to plants themselves, the possibility of toxicity to other life forms also exist (Tsatsakis et al. 2017). Several studies have demonstrated how glyphosate weakened plant defense and increased root pathogen virulence in both glyphosate-resistant and -susceptible plants (Johal and Huber 2009;Kremer and Means 2009). Glyphosate inhibits the plant's defense and structural barriers and immobilizes micronutrients such as manganese (Mn), which play vital roles in disease resistance, and modifies plant nitrogen metabolism. ...
Information on the impacts of genetically engineered (GE) crops on the soil microbial community, biological processes, soil health, and ecosystem services is limited. Assessments to acquire this information are challenged further because the necessary comparisons of GE crops with non-GE crops are practically nonexistent. The objectives of this chapter are to provide a background on the impacts of genetically engineered (GE) crops on soil health, with a focus on the soil microbiome and biological processes and on ecosystem services. Genetic materials and pesticide chemicals are released from GE crops into soil and impose variable effects on the soil microbiome and other soil organisms that can cause changes in plant nutrient availability, soil properties, and ecosystem services such as water quality. However, some studies show little effect of GE crops on soil biological and ecosystem processes suggesting the need for balanced research approaches to assure the fair monitoring of impacts of GE crops on the environment. Soil health and ecosystem processes may be maintained or improved under GE cropping only when sustainable management is integrated into these systems. Several vital action approaches are suggested for conducting critical examination and assessment of the potential risks of GE crops.
... El mecanismo de acción del herbicida glifosato consiste en la inhibición de la enzima 5enolpiruvilsikimato-3-fosfato sintasa (EPSPS), la cual participa metabólicamente en la producción de aminoácidos aromáticos y otros componentes aromáticos esenciales para la sobrevivencia de las plantas (Petter et al., 2016). La inhibición de la EPSPS evita que la planta produzca los compuestos esenciales para el crecimiento de la planta, incluyendo aquellos involucrados en la defensa de la planta (Caetano, Ramalho, Botrel, da Cunha, & de Mello, 2012), perturbando el crecimiento microbiano esencial para la nutrición vegetal (Johal & Huber, 2009). ...
... Del mismo modo, la población microbiana del suelo, que ayuda a descomponer los residuos de las plantas y a mineralizar la materia orgánica, se ve afectada debido al incremento de patógenos y el consumo de nutrientes (Zaller, Heigl, Ruess, & Grabmaier, 2014;Zobiole et al., 2010). También existe un estudio sobre afectaciones en los mecanismos de defensa de las plantas debido a la presencia de glifosato en el medio (Johal & Huber, 2009). ...
... The latter features could be related to the reduced manganese, copper, and zinc content found in Salento soils and olive leaves [45], as well as in Brazil in leaves of orange trees infected by X. f. subsp. pauca that were grown in glyphosate-treated soil [65]. A perturbation of metabolic pathways in the beneficial pseudomonads has been also observed in soils repeatedly treated with glyphosate [66], leading to a reduced capacity to face disease [67]. ...
... A perturbation of metabolic pathways in the beneficial pseudomonads has been also observed in soils repeatedly treated with glyphosate [66], leading to a reduced capacity to face disease [67]. Impairment of the shikimic acid pathway due to the utilization of glyphosate has been observed to be strictly linked to crop vulnerability to disease [65,67]. It should be added that soil fertilization has been rarely performed on a regular basis in the Salento area. ...
... Glyphosate, a post-emergence nonselective broadspectrum herbicide and glyphosate containing herbicides are the most extensively used herbicides in agriculture for the control of many annual and perennial weeds [1,2]. The widespread use of glyphosate may result in weed resistance or alter the biological functions of soil. ...
... Glyphosate can have extensive unintended effects on nutrient availability and disease severity [3] resulting from direct glyphosate-induced weakening of plant diseases and increased pathogen population and virulence [1]. ...
This study was carried out to investigate the potentials of Commelina erecta and triton X-100 in
remediating glyphosate polluted soil. Humus soil sample was collected from a vegetable garden in Alakahia
community in Rivers State, Nigeria and was subsequently divided into different treatment groups I-VI each containing
2 kilograms of the soil sample mixed with 50ml of glyphosate in a polypropylene bag. The different treatment groups
were incubated at 28-30 oC for 60 days and thereafter analysed for pH, conductivity, heavy metals, mineral elements,
organic ions, total organic carbon (TOC) and nitrogen (TON) contents of the soil. The least pH value (7.01) was
recorded in group III while the highest conductivity value (4173.33µs/cm) was observed in group IV. Copper, nickel
and cadmium levels in all the amended groups were reduced when compared with the control. Generally, the mineral
levels were increased in the amended groups when compared with the control. The TOC and TON contents of the
amended soil did not exhibit significant difference when compared with the control except for group IV
... Glyphosate used in conjunction with glyphosate-tolerant GE crops alters the rhizosphere fungal community with increases in growth and virulence of potential root pathogenic Fusarium spp. and of the pathogens Phytophthora, Pythium, and Gaeumannomyces (Johal and Huber 2009;Kremer and Means 2009). Interestingly, most of these fungi are also increased in the rhizospheres of many weeds that develop resistance to glyphosate and other herbicides by mechanisms similar to transgenic crop (Kremer 2014). ...
... Apart from toxicity to plants themselves, the possibility of toxicity to other life forms also exist (Tsatsakis et al. 2017). Several studies have demonstrated how glyphosate weakened plant defense and increased root pathogen virulence in both glyphosate-resistant and -susceptible plants (Johal and Huber 2009;Kremer and Means 2009). Glyphosate inhibits the plant's defense and structural barriers and immobilizes micronutrients such as manganese (Mn), which play vital roles in disease resistance, and modifies plant nitrogen metabolism. ...
Information on the impacts of genetically engineered (GE) crops on the soil microbial community, biological processes, soil health, and ecosystem services is limited. Assessments to acquire this information are challenged further because the necessary comparisons of GE crops with non-GE crops are practically nonexis-tent. The objectives of this chapter are to provide a background on the impacts of genetically engineered (GE) crops on soil health, with a focus on the soil microbi-ome and biological processes and on ecosystem services. Genetic materials and pesticide chemicals are released from GE crops into soil and impose variable effects on the soil microbiome and other soil organisms that can cause changes in plant nutrient availability, soil properties, and ecosystem services such as water quality. However, some studies show little effect of GE crops on soil biological and ecosystem processes suggesting the need for balanced research approaches to assure the fair monitoring of impacts of GE crops on the environment. Soil health and ecosystem processes may be maintained or improved under GE cropping only when sustainable management is integrated into these systems. Several vital action approaches are suggested for conducting critical examination and assessment of the potential risks of GE crops.
... In that particular study, one of the tested selective pressure was the spray of GBH-, which has been shown to adversely affect plant uptake and transport of micronutrients (e.g. Mn, Fe, Cu, and Zn) and consequently, reduce disease resistance and plant growth [6,7]. ...
... Differently, Zobiole et al. [42] found negative correlation between levels of lignin in single-transgene GM soy and increasing rates of GBH applications. Previous studies also reported higher susceptibility levels to diseases after application of GBH in transgenic varieties which were associated with changes in lignin contend and, consequently, with morphological and functional quality of the plant defense organs [6,43,44]. ...
Background
World agricultural production of genetically modified (GM) products, in particular, the combination of different traits/genes in the same plant has been a trend over the last decade. There have been concerns raised over stacking multiple herbicide and insect-resistant transgenes that could result in fitness costs depending on the type and strength of selection pressures exerted by the environment. Here, we report the results of transcriptomic analysis comparing the effect of glyphosate-based herbicide (GBH) in the single-transgene versus stacked, herbicide-resistant soybean varieties on various biological processes, metabolic pathways, and key shikimic enzymes.
Results
Gene expression data showed that defense metabolism and redox homeostasis were equally modulated in single-transgene and stacked-variety samples. Carbon accumulation and energy metabolisms were distinct between the varieties and photosynthesis metabolism was found negatively affected in the single-transgene variety only. In the stacked variety, the shikimate pathway was modulated by the accumulation of transcripts from phenylalanine gene and other cascade genes. As expected, the expression of native EPSPS was upregulated in both varieties when herbicide was applied. On the other hand, transgenic EPSPS expression was down-regulated in both GM varieties upon herbicide application which cannot be explained.
Conclusion
Glyphosate-based herbicides toxicity suggests its effects on carbon central metabolism and flux, redox metabolism, photosynthesis, and to hormone and defense response in plants. The observed unintended effects in GM herbicide-tolerant varieties unravel the deleterious effects previously observed on GM-tolerant varieties growth and production. The impact of GBH on shikimate and cascade pathways was observed in terms of both native and transgenic insensitive EPSPS modulation, alteration of jasmonic acid and lignin metabolism in both single-transgene and stacked variety. The energy metabolism and carbon flux were differently affected in these varieties. Oxidative stress, more specifically glutathione metabolism, induced by GBH, was also observed in this study. The stacked variety showed a more pronounced stress response (activation of specific stress defense proteins, Rboh, WRKY) and secondary compounds (β-glucosidase, isoflavone 7-O-methyltransferase). Omics profiling techniques, such as transcriptomics, can be considered tools to support risk assessment in detecting unintended effects due to the GBH application.
... The latter features could be related to the reduced manganese, copper, and zinc content found in Salento soils and olive leaves [45], as well as in Brazil in leaves of orange trees infected by X. f. subsp. pauca that were grown in glyphosate-treated soil [65]. A perturbation of metabolic pathways in the beneficial pseudomonads has been also observed in soils repeatedly treated with glyphosate [66], leading to a reduced capacity to face disease [67]. ...
... A perturbation of metabolic pathways in the beneficial pseudomonads has been also observed in soils repeatedly treated with glyphosate [66], leading to a reduced capacity to face disease [67]. Impairment of the shikimic acid pathway due to the utilization of glyphosate has been observed to be strictly linked to crop vulnerability to disease [65,67]. It should be added that soil fertilization has been rarely performed on a regular basis in the Salento area. ...
Recently, a new severe disease has been reported in the Salento area (Apulia region, southern Italy) in the multimillennial olive agro-ecosystem, given the common name "olive quick decline syndrome" (OQDS). Together with Xylella fastidiosa subsp. pauca, some pathogenic fungi such as Phaeoacremonium spp. have been found associated with the disease. The main predisposing factors to the disease seem to be local cultivar susceptibility, depletion of some micronutrients in the soil that could be related to some agronomical practices favoring the depletion of soil fertility, an incorrect pruning cycle, climatic changes that result in increased soil waterlogging, and frost and drought events. The possible synergistic action of microorganisms other than X. f. subsp. pauca cannot be excluded. The features characterizing the areas where OQDS first appeared and subsequently spread, described and discussed here, would point to a rather fragile environment where one or more adverse climatic and/or edaphic factors could have acted together. The intrinsic peculiarities and management of the Salento olive agro-ecosystem could also have played a fundamental role in enhancing the virulence of X. f. subsp. pauca once introduced from abroad.
... So, although the plant may be resistant at the foliar level, the concentrations that accumulate in meristems, flower buds, and other metabolic sinks may overwhelm the resistance mechanism. Johal and Huber (2009), said that, 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. Vereecken, (2005) Tillering capacity of alfalfa plants represented by number of stems per unit area as affected by the interaction between population and selection cycle (Table 4) showed that alfalfa population significantly varied in response to selection for glyphosate tolerance, since, the first cycle of selection to tolerance gave reduction in tillering capacity of C.U.F101, Siriver and Siwa populations (-0.598, -10.612 and -1.715%, respectively). ...
... found negative correlation between levels of lignin in singletransgene GM soy and increasing rates of GBH applications. Previous studies also reported higher susceptibility levels to diseases after application of GBH in transgenic varieties which were associated with changes in lignin contend and, consequently, with morphological and functional quality of the plant defense organs [6][43] [44]. ...
Background: World agricultural production of genetically modified (GM) products, in particular, the combination of different traits/genes in the same plant has been a trend over the last decade. There has been concerns raised over stacking multiple herbicide and insect-resistant transgenes that could result in fitness costs depending on the type and strength of selection pressures exerted by the environment. Here, we report the results of transcriptomic analysis comparing the effect of glyphosate-based herbicide (GBH) in the single-transgene versus stacked, herbicide resistant soybeans varieties on various biological processes, metabolic pathways, and main shikimic enzymes.
Results: Gene expression data were grouped according to the 'herbicide treatment factor'. Defense metabolism and redox homeostasis were equally modulated in single-transgene and stacked variety samples. Carbon accumulation and energy metabolisms were distinct between the varieties and photosynthesis metabolism was found negatively affected in the single-transgene variety only. In the stacked variety, the shikimate pathway was modulated by the accumulation of transcripts from phenylalanine gene and other cascade genes. As expected, the RT-PCR results confirmed that the expression of native EPSPS was upregulated in both varieties when herbicide was applied. On the other hand, transgenic EPSPS expression was down regulated in both GM varieties upon herbicide application which cannot be explained.
Conclusion: Glyphosate-based herbicides toxicity suggests its effects on carbon central metabolism and flux, redox metabolism, photosynthesis, and to the plant’s hormone and defense response. The observed unintended effects in GM herbicide-tolerant varieties unravels the deleterious effects previously observed on GM tolerant varieties growth and production. The impact of GBH on shikimate and cascade pathways was observed in terms of both native and transgenic insensitive EPSPS modulation, alteration of jasmonic acid and lignin metabolism in both single-transgene and stacked variety. Whereas the energy metabolism and carbon flux were differently affected in these varieties. Oxidative stress, more specifically glutathione metabolism, induced by GBH, was observed in this study. The stacked variety showed a more pronounced stress response (activation of specific stress defense proteins, Rboh, WRKY) and secondary compounds (β-glucosidase, isoflavone 7-O-methyltransferase). Omics profiling techniques, such as transcriptomic, can be considered tools to support risk assessment based on detecting unintended effects due to the GBH application.
... So, although the plant may be resistant at the foliar level, the concentrations that accumulate in meristems, flower buds, and other metabolic sinks may overwhelm the resistance mechanism. Johal and Huber (2009), said that, 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. Vereecken, (2005) Tillering capacity of alfalfa plants represented by number of stems per unit area as affected by the interaction between population and selection cycle (Table 4) showed that alfalfa population significantly varied in response to selection for glyphosate tolerance, since, the first cycle of selection to tolerance gave reduction in tillering capacity of C.U.F101, Siriver and Siwa populations (-0.598, -10.612 and -1.715%, respectively). ...
... In addition, glyphosate, which has chelating properties, may affect the plant bioavailability of several elements, both reducing their uptake or mobilizing it [11][12][13], but these aspects are still debated [5,6]. Also, glyphosate can reduce the resistance of plants to pathogens [6,14]. Besides glyphosate mainly being used in agriculture with about 1.2 million km 2 of crop land treated annually alone in the United States (U.S.) [15], it is also applied in non-agricultural sectors such as forestry, urban, and resident weed control practices, in the control of aquatic weeds and along railroads [15][16][17][18]. ...
Glyphosate is the active ingredient of numerous commercial formulations of herbicides applied in different sectors, from agriculture to aquaculture. Due to its widespread use around the world, relatively high concentrations of glyphosate have been detected in soil and aquatic environments. The presence of glyphosate in aquatic ecosystems has aroused the attention of researchers because of its potential negative effects on living organisms, both animals and plants. In this context, this review intends to summarize results of studies aimed at evaluating the effects of glyphosate (both as active ingredient and component of commercial formulations) on marine invertebrates. Generally, data obtained in acute toxicity tests indicate that glyphosate and its commercial formulations are lethal at high concentrations (not environmentally realistic), whereas results of long-lasting experiments indicate that glyphosate can markedly affect biological responses of marine invertebrates. Consequently, more efforts should be addressed at evaluating chronic or sub-chronic effects of such substances to marine invertebrate species.
... The use of glyphosate herbicides on a large scale can have direct impacts, such as inducing attenuation in plant defenses and increasing population and pathogen virulence (Altman & Campbell, 1977). Moreover, indirect effects such as inhibiting plant growth and vigor due to accumulation of glyphosate in the root system, shoots and reproductive tissue, affect the availability of nutrients needed in the physiological process related to plant resilience (Johal & Huber, 2009) and the reduced phytoalexin which results in weaker plant resistance (Duke et al., 2007). Herbicide residues interfere with the growth of horticultural crops and food and some types of weeds (Carpenter & Boutin, 2010). ...
Analysis of Causative Factors for Canker Disease Epidemic on Rubber Plants in South Sumatra. Lasiodiplodia theobromae is the cause of stem canker in the rubber plant (Hevea brasiliensis), this is a new disease and has never been reported in Indonesia. Currently, data on environmental factors and cultivation techniques related to the development of stem canker are not available so research needs to be done on this subject. The objective of the study was to analyze environmental factors and cultivation techniques related to stem canker on rubber trees in southern Sumatra. The study was conducted by collecting data on environmental factors and cultivation techniques and then analyzed the association with stem canker. Field observation was carried out at 21 locations in PT. Perkebunan Nusantara VII Business Unit Padang Plawi Bengkulu, Tulung Buyut Lampung, Musilandas Palembang and Experimental Garden of Sembawa Research Center, Indonesian Rubber Research Institute at Palembang to measure the severity and incidence of this disease. Besides that, the data of cultivation technique and the condition of the garden were taken from the officer at those locations. Soil sample from each location was taken in a composite way, then its physical and chemical components were analyzed. The analysis was conducted to find out the correlation between cultivation and disease severity using chi-square test. The relationship between chemical and physical factors of the soil with the disease severity was analyzed using a multivariate test of principal component analysis/PCA. Regression analysis was conducted to show the possible relation to the incidence and severity of this disease. The location, clones, weed control and the number of plants per hectare showed a correlation with the disease severity. There was a positive correlation between incidence and severity of the disease. The highest disease severity occurred at the Sembawa location on clone BPM 24, with the number of plant population per ha was ≥ 555 trees and weed control using herbicide. Content of soil nitrogen, dust, clay and water as well as cation exchange capacity (CEC)were suggested to significantly contribute to the severity of stem canker.
... Glyphosate acts on plants by inhibiting the activity of enolpyruvyl shikimate-3-phosphate synthase, an enzyme for aromatic amino acid biosynthesis in the shikimate pathway [6]. The massive use of this molecule has been reported to weaken plant defense systems [7], disturb the metabolism [8] and cause DNA or liver damage [9] both for terrestrial and aquatic animals [10,11]. In 2015, the International Agency for Research on Cancer of World Health Organization (WHO) classified glyphosate as "probably carcinogenic to humans" based on epidemiological, animal and in vitro studies. ...
The acclimation process of activated sludge from a wastewater treatment plant for degradation of glyphosate and its biodegradation kinetics were studied in a batch reactor. The parameters monitored included the concentrations of glyphosate, as well as aminomethylphosphonic acid (AMPA), its main metabolite, total organic carbon (TOC), pH, dissolved oxygen (DO) and biomass concentration. At the end of the acclimation process, glyphosate removal efficiency of the acclimated sludge was compared to the fresh sludge one. The results showed that the acclimation process highly increaseddegradation efficiency. Complete glyphosate removal has been achieved during kinetics experiments. Glyphosate removal kinetic of the acclimated sludge was modeled by Monod model that accurately fitted the experimental results with a maximum growth rate (μmax) of 0.34 h⁻¹ and half-saturation constant (Ks) of 1600 mg L⁻¹. Finally, a biodegradation pathway of glyphosate used as carbon source was proposed.
... Application of glyphosate to bean plants temporarily arrested their growth in sterile soils; in non-sterile soils, however, the plants died quickly due to root infection by Pythium and Fusarium species (Johal 1984). Because glyphosate inhibits the biosynthesis of phenylalanine and chorismite-which are precursors of several important components of the defense response including lignin, salicylic acid and phytoalexins-the study authors suggested that glyphosate predisposes the treated plants to infection by opportunistic pathogens to which they would otherwise be resistant (Johal and Huber 2009). If weak pathogens drive MDH, then this implies that superior disease resistance in hybrids is a key mechanism of heterosis. ...
Hybrids account for nearly all commercially planted varieties of maize and many other crop plants, because crosses between inbred lines of these species produce F1 offspring that greatly outperform their parents. The mechanisms underlying this phenomenon, called heterosis or hybrid vigor, are not well understood despite over a century of intensive research (Birchler et al. 2003). The leading hypotheses-which focus on quantitative genetic mechanisms (dominance, overdominance, and epistasis) and molecular mechanisms (gene dosage and transcriptional regulation)-have been able to explain some but not all of the observed patterns of heterosis (Stuber et al. 1992; Birchler 2015). However, possible ecological drivers of heterosis have largely been ignored. Here we show that heterosis of root biomass and germination in maize is strongly dependent on the belowground microbial environment. We found that, in some cases, inbred lines perform as well by these criteria as their F1 offspring under sterile conditions, but that heterosis can be restored by inoculation with a simple community of seven bacterial strains. We observed the same pattern for seedlings inoculated with autoclaved vs. live soil slurries in a growth chamber, and for plants grown in fumigated vs. untreated soil in the field. Together, our results demonstrate a novel, ecological mechanism for heterosis whereby soil microbes generally impair the germination and early growth of inbred but not hybrid maize.
... Zinc deficiency in the soil increases the citrus decline/blight and abnormal zinc metabolism develop before the real dysfunction of water translocation becomes apparent (Ouyang et al. 1984;Raina 1988;Srivastava and Singh 2005). Increasing the Manganese and Zinc concentration respectively from 12.3 to 49 and 13.3 to 57.3 mg.kg À1 dry weight, significantly improves citrus variegated chlorosis (Johal and Huber 2009). Deficiency of zinc is particularly critical because of their low mobility in plant and their essential roles in vegetative and reproductive growth (Marschner 2012). ...
Citrus decline is developing in the southern part of Iran. NH4–N form and factors that limit the uptake of calcium, magnesium and micronutrients by root cause increased citrus decline severity. In this study, the effect of nutritional management on the control of the complication of citrus loss in Valencia orange trees (Citrus scinensis L. Osbeck) was investigated. The experiment was conducted in a randomized complete block design with seven treatments in four replications and four trees per each plot, during 2016 and 2018. - Control (nutrition based on soil test and with ammonium sulfate nitrogen source) - Supplementary soil fertigation with micronutrients iron + zinc + copper + manganese EDDHA chelates at three times during the growth of shoots in the spring; calcium nitrate; magnesium nitrate - Foliar nutrition with micronutrients zinc sulfate + manganese sulfate + boric acid + copper sulfate; potassium nitrate and magnesium nitrate. The results showed that, leaf potassium concentration had a positive correlation with root decay and shoot dieback. Supplemental soil fertigation with micronutrients, calcium and magnesium nitrate caused a significant increase in fibrous root density and reduction of root decay percentage. Supplemental soil fertigation with calcium nitrate and foliar nutrition with magnesium nitrate resulted in significant improvement of citrus decline indices in Valencia oranges, including leaf fall, shoot diebacks, leaf special weight, leaf water content, and quantitative and qualitative of fruits. Due to the negative effect of excessive potassium concentration on aggravation of citrus decline, balanced consumption of potassium in citrus orchards is recommended.
... Glyphosate is commonly considered environmentally safe, but certain follow-up studies have reported glyphosate's and its metabolites' negative environmental effects, such as toxicity (Li et al. 2016). The excessive use of glyphosate in large areas can lead to weakened defenses and increased risk incidence in plants (Johal and Huber 2009). In addition, glyphosate affects the synthesis of DNA in sea urchins (Marc et al. 2004) and estrogen activity in humans (Thongprakaisang et al. 2013). ...
Cyanobacterial blooms and their associated toxins are growing issues for many aquatic ecosystems. Microcystin-LR (MC-LR) is a toxic and common cyanobacterial toxin, whereas glyphosate is a commonly used herbicide that is massively applied in agriculture. In this study, the effects of glyphosate on the growth of Microcystis aeruginosa and MC-LR synthesis and release from M. aeruginosa at different temperatures are investigated. In addition, the MC-LR pollution in the Huangpu River in Shanghai urban area is studied. Results indicated that the MC-LR concentration in the Huangpu River is related to water temperature. The laboratory experiments revealed that the growth of M. aeruginosa was slightly promoted at 15 °C and glyphosate concentrations of 1 and 5 mg/L and inhibited in the presence of glyphosate and high temperatures (20 °C, 25 °C, 30 °C, and 35 °C). The intracellular MC-LR contents were remarkably increased by glyphosate at 15 °C, 20 °C, 25 °C, and 30 °C and remarkably decreased at 35 °C. Meanwhile, the extracellular MC-LR contents were remarkably increased at all temperatures and all concentrations except when treated with 1 mg/L glyphosate at 35 °C. The highest extracellular MC-LR content, which was 143.9% higher compared with that of the control, was observed at 30 °C and treatment with 10 mg/L glyphosate. These results were consistent with those of MC-LR investigation in Huangpu River. Furthermore, in accordance with the intracellular MC-LR contents, the ability of a single cell to synthesize MC-LR was enhanced at 15 °C, 20 °C, 25 °C, and 30 °C and decreased at 35 °C. These results provide an understanding on the toxic effects of glyphosate on cyanobacteria and the effects of temperature on MC release. Moreover, these results will be helpful in protecting aquatic ecosystems and human health.
... Biologist Don Huber 4 from the United States (represented during the Tribunal by biologist Art Dunham) provided evidence on the ecological damage glyphosate caused through its antibiotic activity, which drastically disrupted the natural biological balance of soil, human, and animal microbiomes (see Johal & Huber, 2009). Huber advocated to regulate the use of glyphosate, if not a total ban. ...
The global food system has severe implications for human health, soil quality, biodiversity, and quality of life. This paper provides an analysis on how transnational alliances challenge the global food system. We illustrate this by focusing on the activities and hearings of the International Monsanto Tribunal (IMT), held in the Hague in 2016. The IMT provided a platform for civil society and enabled transnational alliances to demand attention for local struggles and legal disputes in relation to Monsanto’s products. With the involvement of independent and renowned experts, the knowledge exchange between local victims and civil society was enhanced, and the IMT reinforced social movement’s goals towards demanding justice for the negative effects associated with the global food system. The advisory opinion determined that Monsanto’s practices are in violation with human rights standards. The IMT exemplified that there is an immediate need for structural change in the current global food system.
... It was also reported that glyphosate could increase plant pathogenic like Fusarium spp. [9] and Phytium, and also affected micronutrient availability [10] . Many studies also reported that glyphosate increased prevalence of rare liver and kidney tumors in chronic animal feeding studies, epidemiological studies reporting positive associations with non-Hodgkin lymphoma, and strong mechanistic evidence of genotoxicity and ability to trigger oxidative stress [6] . ...
Glyphosate is one of the most widely used herbicide for weed eradication.
Excessive usage of glyphosate may lead to contamination of soil, water, and crops. Soil
bioremediation using microorganisms to degrade glyphosate is an effective and cheap method when the level of glyphosate is higher than maximum permitted level. The resistance of the microorganism to glyphosate can be determined by observing IC50 parameter. The microorganisms which are resistant to high concentration of glyphosate can be selected as candidate for glyphosate biodegradation process. The objective of this study was to determine IC50 for consortium bacterial culture isolated from glyphosate-contaminated soil and uncontaminated soil. Generally IC50 value is determined by measuring optical density, but in this study IC50 value was determined using total number of cell to observe the real effect of glyphosate toward bacteria cell in the soil. Higher tolerance was observed for bacterial consortium culture isolated from uncontaminated soil (IC50 is 263.38mg/L) compared with the culture from glyphosate-contaminated soil (IC50 is 2.04 mg/L). Glyphosate at low concentration below 10 mg/L could increase bacterial growth. This study suggested that the bacteria could use low concentration glyphosate as nutrition source.
... In addition to the possibility of killing crops, herbicides can reduce plant yield and increase susceptibility to diseases. For example, glyphosate significantly increases the severity of various plant diseases, and lead to weakening plant capacity to resist against pathogens, and immobilizes soil and plant nutrients (Johal and Huber, 2009). Due to these effects and increased weed tolerance and resistance, farmers have to use fungicides and supplemental herbicides in cereals, causing excessive ecological effects. ...
Herbicides are used in agricultural areas to reduce harmful of weeds. Herbicides could decimate some weeds and slow down growth in others. Using herbicide has increased significantly since the mid-20th century. In case that herbicides are not used, significant quantitative and qualitative losses will have occurred in agricultural production. However, the side effects caused by the wide and irrational use of herbicides threaten the environment and human health. Although herbicides are the least harmful among pesticides, many studies have shown the serious negative effects of herbicides on the environment and human health. Every year a list of herbicides that cause cancer or leave large residues in the soil and water are published. However, many herbicides have been banned, but only after they have been used in tons and causing environmental pollution. The chemical structure of herbicides degrades quite slowly in nature, which causes its accumulation in the soil and the environment. The effects of these herbicides have reached rivers, lakes, seas and oceans. Also, the effect of chemically degradation herbicides on living organisms under different environmental conditions is still unknown. Due to the widespread use of herbicides, it also negatively affects the use of traditional control methods, which can be also effective in some cases. In this article, some alternative control methods that can reduce the use of herbicides and reduce some of the herbicide's harm to the living organisms of the ecosystem will be included.
... In addition to the possibility of killing crops, herbicides can reduce plant yield and increase susceptibility to diseases. For example, glyphosate significantly increases the severity of various plant diseases, and lead to weakening plant capacity to resist against pathogens, and immobilizes soil and plant nutrients (Johal and Huber, 2009). Due to these effects and increased weed tolerance and resistance, farmers have to use fungicides and supplemental herbicides in cereals, causing excessive ecological effects. ...
Herbicides are used in agricultural areas to reduce harmful of weeds. Herbicides could decimate some weeds and slow down growth in others. Using herbicide has increased significantly since the mid-20th century. In case that herbicides are not used, significant quantitative and qualitative losses will have occurred in agricultural production. However, the side effects caused by the wide and irrational use of herbicides threaten the environment and human health. Although herbicides are the least harmful among pesticides, many studies have shown the serious negative effects of herbicides on the environment and human health. Every year a list of herbicides that cause cancer or leave large residues in the soil and water are published. However, many herbicides have been banned, but only after they have been used in tons and causing environmental pollution. The chemical structure of herbicides degrades quite slowly in nature, which causes its accumulation in the soil and the environment. The effects of these herbicides have reached rivers, lakes, seas and oceans. Also, the effect of chemically degradation herbicides on living organisms under different environmental conditions is still unknown. Due to the widespread use of herbicides, it also negatively affects the use of traditional control methods, which can be also effective in some cases. In this article, some alternative control methods that can reduce the use of herbicides and reduce some of the herbicide's harm to the living organisms of the ecosystem will be included.
... It was shown that the quantification of Gly could be done well with this method. Although qualification of the traces of Gly in cane fiber, cane roots, as well as cane shoot was not involved in this study, studies on the persistence of Gly in crops revealed that the accumulation of Gly in these parts of a crop was below the limit of detection [40][41][42]. More interestingly, application of GLy on sugar beet only found trace amounts of glyphosate residue in its shoots and roots during two weeks' treatment [43]. ...
The use of plant growth regulators is one effective solution to improve sugarcane yields and sugar content in several countries. In this study, we examined the role of gibberellin acid (GA3) and glyphosate (Gly) plant growth regulators to determine the appropriate concentration of GA3 and Gly to increase the yield of sugarcane and sugar accumulation, respectively. The statistical results showed that GA3 was sprayed at 150 ppm to increment the actual yield by 19.94%; sucrose accumulation increased by 2.21%. With Gly treatment, although the yield decreased by 3.17%, sucrose accumulation increased by 11.27% compared to control trials. In this study, the combined concentration of 150 ppm of both GA3 and Gly gave the best results, for which sucrose accumulation increased from 2.21% to 10.74% and from 19.94% to 20.97% for actual yield. The results led to increased net income compared to the control. To address concerns about residues of plant growth regulators, residues of GA3 and Gly were evaluated after the sugarcane harvest using the HPLC and UV-vis methods, respectively. The analyzed results showed that their residues were lower than what is permitted in several countries. This showed the applicability of the study, on a large scale, to increase sucrose accumulation, productivity of sugarcane, and profit for farmers.
... Glyphosate possesses mineral-chelating properties (Madsen et al., 1978), and in plants and soil, this property has been shown to affect micronutrient availability for plants (Johal and Huber, 2009). Potential effects of glyphosate on mineral availability and status have not been investigated in animals, and, to our knowledge, the only work that link glyphosate to livestock mineral status is that of Krüger et al. (2013). ...
Glyphosate is the active ingredient in a wide range of herbicides used for weed control, including weed control in genetically modified, glyphosate-insensitive crops. In addition, glyphosate herbicides are used for pre-harvest desiccation of glyphosate-sensitive crops. Together, the use of glyphosate leads to residues in livestock feed. In addition to its herbicidal property, glyphosate has documented antimicrobial and mineral-chelating properties. The aim of the present paper is to address, based on the published literature and own observations, whether dietary glyphosate residues may affect livestock gut microbiota and/or mineral status potentially with derived unfavourable effects on animal health and productivity. However, and as reported, literature on the potential effects of glyphosate on livestock is very scarce and mainly reporting in vitro studies; hence, a solid basis of in vivo studies with livestock in physiological and productive phases, particularly sensitive to disorders in mineral status and in the gut microbiota, is needed for drawing final conclusions.
... Some species of fungi have already been used in bioremediation [9]. Glyphosate [N-(phosphonomethyl) glycine, glyphosate], a postemergence nonselec¬tive broad-spectrum herbicide, and glyphosate-containing herbicides are the most extensively used herbicides in agriculture for the control of many annual and perennial weeds [10][11]. In some cases, glyphosate usage may threaten agricultural production. ...
This study determined the abilities of indigenous microorganisms to utilise atrazine, xtravest, gramoxone and glyphosate as a carbon source and for their growth. Isolation of microorganisms was done using the spread plate method on the solid mineral salts medium with each herbicide added to separate plates. The plates were incubated at 30°C for 5 days for bacteria and at 30 o C for 7days for fungi. B. subtilis, P. aeruginosa, P. florescences, P. putida, Aspergillus niger, A. tamarii, Fusarium oxysporum, and P. chrysogenum were isolated in all the herbicide treated soils. Bacillus subtilis recorded the highest optical density value of 1.401 (logCFU/ml) on the 25 th day and viable count value of 9.08 (log CFU/ml) (1.21×10 9 cfu/ml) on the 20 th day during growth on glyphosate. F. oxysporum recorded the lowest pH of 4 in gramoxone on the 25 th day of incubation and the highest count of 6.10×10 4 cfu/g on the 20 th day during atrazine utilisation. B. subtilis, A. niger and F. oxysporum showed the best abilities to utilise the herbicides for growth and as carbon source. Indigenous microorganisms used in this study successfully utilised the herbicides as carbon source and for growth hence they could be used in bioremediation.
... In our study, the diversity in soil microbial carbon source usage was lower in monospecific Chinese hickory stands that were ten or more years old than in the Chinese hickory-broad-leaved mixed forest stands. The reasons for this difference may be the above-ground plant community composition that affects soil microbiome through, for example, litter deposition and root exudates [55][56][57][58], and the overall lower organic carbon content. Another possible explanation is the different structure of soil organic C in the stands managed intensively for the longest period of time; lower proportions of easily degradable compounds may have resulted in lower abundances of microbe functional groups that decompose these compounds. ...
To assess the effects of long-term intensive management on soil carbon cycle and microbial functional diversity, we sampled soil in Chinese hickory (Carya cathayensis Sarg.) stands managed intensively for 5, 10, 15, and 20 years, and in reference Chinese hickory–broad-leaved mixed forest (NMF) stands. We analyzed soil total organic carbon (TOC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC) contents, applied 13C-nuclear magnetic resonance analysis for structural analysis, and determined microbial carbon source usage. TOC, MBC, and WSOC contents and the MBC to TOC ratios were lower in the intensively managed stands than in the NMF stands. The organic carbon pool in the stands managed intensively for twenty years was more stable, indicating that the easily degraded compounds had been decomposed. Diversity and evenness in carbon source usage by the microbial communities were lower in the stands managed intensively for 15 and 20 years. Based on carbon source usage, the longer the management time, the less similar the samples from the monospecific Chinese hickory stands were with the NMF samples, indicating that the microbial community compositions became more different with increased management time. The results call for changes in the management of the hickory stands to increase the soil carbon content and restore microbial diversity.
... Since this EPSPS-driven pathway exists only in plants, fungi, and some bacteria, most regulators assumed that glyphosate would pose minimal risk to higher organisms, but this has been found to be incorrect (Myers et al. 2016). For instance, glyphosate is a chelating agent with the potential to sequester essential micronutrient metals such as zinc, cobalt, and manganese, thereby altering the availability of these micronutrients (Johal and Huber 2009). Micronutrient metals are enzymatic cofactors; so, their loss has the potential to contribute to a number of deleterious effects, especially on kidney and liver function in mammals (Krüger et al. 2013). ...
Glyphosate is the active ingredient in Roundup formulations. Glyphosate-based herbicides are used globally in agriculture, forestry, horticulture, and in urban settings. Glyphosate can persist for years in our soil, potentially impacting the soil-dwelling arthropods that are primary drivers of a suite of ecosystem services. Furthermore, although glyphosate is not generally classified as neurotoxic to insects, evidence suggests that it may cause nerve damage in other organisms. In a series of experiments, we used food to deliver environmentally realistic amounts of Roundup ready-to-use III, a common 2% glyphosate-based herbicide formulation that lists isopropylamine salt as its active ingredient, to Madagascar hissing cockroaches. We then assessed the impact of contamination on body mass, nerve health, and behavior. Contaminated food contained both 30.6 mg glyphosate and so-called inert ingredients. Food was refreshed weekly for 26–60 days, depending on the experiment. We found that consumption of contaminated food did not impact adult and juvenile survivorship or body weight. However, consumption of contaminated food decreased ventral nerve cord action-potential velocity by 32%, caused a 29% increase in respiration rate, and caused a 74.4% decrease in time spent on a motorized exercise wheel. Such changes in behavior may make cockroaches less capable of fulfilling their ecological service, such as pollinating or decomposing litter. Furthermore, their lack of coordination may make them more susceptible to predation, putting their population at risk. Given the decline of terrestrial insect abundance, understanding common risks to terrestrial insect populations has never been more critical. Results from our experiments add to the growing body of literature suggesting that this popular herbicide can act as a neurotoxin.
... Apart from these control approaches, herbicides commonly used to manage weeds in oil palm plantation could be explored for their effects towards G. boninense. The side effects of herbicides on plant pathogens and hosts either promoting or supressing the disease development have been discussed extensively by researchers (Hess, 2018;Johal and Huber, 2009;Manju et al., 2015;Sanogo et al., 2000). The interaction of herbidices with G. boninense and oil palm roots, however, have not yet fully investigated and tested. ...
The use of herbicides for weed management is a common practice in oil palm plantation. However, previous studies have shown that herbicide can reduce plant susceptibility and could also cause physiological injury to plant parts such as roots which will ultimately provide entry points for pathogens. This study aimed to investigate the effect of commonly used herbicides in the oil palm plantation as a predisposing factor to Ganoderma disease development. In vitro study on 11 commercial herbicides with four different dosages have shown that the highest percentage inhibition of radial growth (PIRG) of Ganoderma boninense was recorded by paraquat dichloride treatment (100%) followed by diuron (87%) and monosodium methyl arsenate (MSMA) (79%) at concentration of 100 µg ml–1. Based on nursery trial, oil palm seedlings inoculated with G. boninense and treated with diuron showed the highest Ganoderma disease progression at 92.73% followed by seedlings treated with metsulfuron-methyl and glyphosate monoammonium (83.27%) and by glyphosate glyphosate isopropylammonium with (73.81%). These findings will help the oil palm industry in Malaysia to choose the best herbicides in order to mitigate the development of Ganoderma disease incidence.
... Furthermore, pesticides, their residues, heavy metals, and other xenobiotics (Lutts and Lefèvre 2015) remaining and accumulating in agricultural soils may have detrimental effects on the introduced beneficial microorganisms. The potential hazards of the globally used herbicide glyphosate for many beneficial soil microorganisms, including Acidobacteria (Newman et al. 2016), Mn-reducing microorganisms, fluorescent pseudomonads, and IAA-producing rhizobacteria (Johal and Huber 2009;Zobiole et al. 2011), as well as rhizobia, arbuscular mycorrhizal fungi, dark septate endophytes, and free-living diazotrophs (Druille et al. 2015(Druille et al. , 2016 have been reported. Heavy metals are also well-known to have significant impact on soil microbiota (Olaniran et al. 2013;Jaiswal et al. 2018). ...
The application of plant growth-promoting bacteria in agricultural systems is an efficient and environment-friendly strategy to improve crop yields and maintain soil quality. However, as different soils have diverse and specific ecological characteristics and may represent adverse abiotic conditions, in vivo application requires the careful selection of the desired beneficial microorganisms. In this study we report Ensifer adhaerens SZMC 25856 and Pseudomonas resinovorans SZMC 25875 isolates recovered from glyphosate-treated soil to possess yet undiscovered plant growth-enhancing potential. The strains were found to promote the growth of tomato seedlings significantly, to have the ability of synthesizing indole-3-acetic acid and siderophores, to tolerate pH in the range of 6.59–7.96, salinity up to 12.5 g L−1 NaCl and drought up to 125 g L−1 polyethylene glycol 6000, as well as to survive in the presence of various pesticides including glyphosate, diuron, chlorotoluron, carbendazim and thiabendazole, and heavy metals such as Al, Fe, Mn, Zn, Pb and Cu. The plant growth-promoting traits of the examined E. adhaerens and P. resinovorans isolates and their tolerance to numerous abiotic stress factors make them promising candidates for application in different agricultural environments, including soils polluted with glyphosate.
... El biólogo Don Huber 4 de los Estados Unidos (representado durante el Tribunal por el biólogo Art Dunham) proporcionó evidencia sobre el daño ecológico que el glifosato causó a través de su actividad antibiótica, alterando drásticamente el equilibrio biológico natural de los microbios del suelo, humanos y animales (véase Johal & Huber, 2009). Huber no sólo abogó por regular el uso del glifosato, si no que además propone una prohibición total. ...
Genetic transformation in plants agreements a great potential to modify crops for improved agronomic traits including resistance to diseases, pests and good nutritional quality along with enhanced productivity. The transgene could be derived from unrelated plant species and even from non-plant sources leading to a revolution in molecular agriculture. In this chapter, the main approach lies on concept of genetic engineering techniques to improve the plant architect. The concept of GM crops and environmental implications besides their safety assessment is documented in detail and also in the end future perspective for adopting the next generation quantitative genetics is also elaborated.
Glyphosate is widely used in the control of agricultural crops due to its high efficiency in weed removal. Pertaining to Class IV pesticides, which classify the herbicides of low toxicity, current studies prove that glyphosate can cause acute and chronic damage to human health. The search for simpler methods for its detection and quantification is still a challenge. Current detection technologies require expensive resources, as well as making it impossible to detect them in the field in real time. This work presents the studies aimed at the application of a multi-analytical and portable analysis platform for the detection of glyphosate, seeking the possibility of its day-to-day detection in a simple, effective and real-time way. The platform used in this work is a Smartphone-based SPR (Surface Plasmon Resonance) Biosensor Device that transforms a commercial portable computing device into an effective tool for analyzing substances, aiding traditional methods and allowing them to be applied in difficult access locations in real time.
Background
Glyphosate (GP) is one of the main pesticides used for maize production. Fusarium sp. is a fungal genus with several phytopathogenic species and toxigenic features. In the present study, the culturable soil mycota was evaluated by the surface sprayed method. Besides, the effect of GP on the growth parameters (growth rate and lag phase) of Fusarium spp. was tested on solid media conditioned at different water activity. Finally, it was studied the GP effect on the disease severity on maize seedlings caused by Fusarium sp.
Results
The results showed that Fusarium species are frequently isolated from GP‐exposed soils. GP concentrations tested had a significant effect on F. graminearum, F. verticillioides and F. oxysporum growth parameters on solid media. The pathogenicity tests showed that the disease severity of the maize seedlings significantly increased with increasing GP concentrations.
Conclusions
This study showed that Fusarium species are frequently isolated from pesticides‐exposed soils and the GP concentrations tested had a significant effect on both growth parameters and disease severity on maize. This study provides an approach about GP effect on Fusarium sp. growth and pathogenicity reinforcing the importance of evaluating all the factors that could affect feed and food production.
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The extensification of tillage in farming the steppe regions of the earth with the goal of reducing erosion and maintaining soil fertility has been leading to a more intensive use of chemical plant protection products for a while now. Field hygiene and stable yields have been achieved as a result of this method to date. However, the excessive application of herbicides leads to an increase in resistance among weeds and higher expenses. The application of glyphosate as an effective and inexpensive general herbicide is very common in the agricultural steppes of America, Eurasia and Australia. However, its use is limited to short periods before seeding and after harvesting due to climate conditions in these areas. An application to the entire soil surface is effective but also very cost intensive against the background of the vast farm lands in these regions. A selective use and targeted application to weeds without coating free soil surface areas saves product and time while reducing the dangers of resistances in the agricultural ecosystem. A technical method of optical selection between weeds which need to be sprayed and areas which do not need to be treated was developed over several years as a part of Kulunda research project. The strong decrease in the overall amount of the applied herbicide results in greater productivity due to a reduction of filling downtimes and higher driving speeds in the field. The money saved is reinvested in better agents and higher concentrations. This promises more treatment success and lower resistance development. Chemical fallow periods therefore represent an effective tool instead of mechanical black fallow in the summer, even without extensive application of chemical agents to the soil, making them an adequate means to fight soil erosion and water loss.
Hybrids account for nearly all commercially planted varieties of maize and many other crop plants because crosses between inbred lines of these species produce first-generation [F1] offspring that greatly outperform their parents. The mechanisms underlying this phenomenon, called heterosis or hybrid vigor, are not well understood despite over a century of intensive research. The leading hypotheses-which focus on quantitative genetic mechanisms (dominance, overdominance, and epistasis) and molecular mechanisms (gene dosage and transcriptional regulation)-have been able to explain some but not all of the observed patterns of heterosis. Abiotic stressors are known to impact the expression of heterosis; however, the potential role of microbes in heterosis has largely been ignored. Here, we show that heterosis of root biomass and other traits in maize is strongly dependent on the belowground microbial environment. We found that, in some cases, inbred lines perform as well by these criteria as their F1 offspring under sterile conditions but that heterosis can be restored by inoculation with a simple community of seven bacterial strains. We observed the same pattern for seedlings inoculated with autoclaved versus live soil slurries in a growth chamber and for plants grown in steamed or fumigated versus untreated soil in the field. In a different field site, however, soil steaming increased rather than decreased heterosis, indicating that the direction of the effect depends on community composition, environment, or both. Together, our results demonstrate an ecological phenomenon whereby soil microbes differentially impact the early growth of inbred and hybrid maize.
Increased concerns associated with interactions between herbicides, inorganic fertilizers, soil nutrient availability, and plant phytotoxicity in perennial tree crop production systems have renewed interest in the use of cover crops in the inter-row middles or between trees as an alternative sustainable management strategy for these systems. Although interactions between the soil microbiome and cover crops have been examined for annual cropping systems, there are critical differences in management and growth in perennial cropping systems that can influence the soil microbiome and, therefore, the response to cover crops. Here, we discuss the importance of cover crops in tree cropping systems using multispecies cover crop mixtures and minimum tillage and no-tillage to not only enhance the soil microbiome but also carbon, nitrogen, and phosphorus cycling compared to monocropping, conventional tillage, and inorganic fertilization. We also identify potentially important taxa and research gaps that need to be addressed to facilitate assessments of the relationships between cover crops, soil microbes, and the health of tree crops. Additional evaluations of the interactions between the soil microbiome, cover crops, nutrient cycling, and tree performance will allow for more effective and sustainable management of perennial cropping systems.
Melanin is a black-brown pigment found throughout all kingdoms of life playing diverse roles including: UV protection, thermoregulation, oxidant scavenging, arthropod immunity, and microbial virulence. Given melanin's broad functions in the biosphere, particularly in insect immune defenses, it is important to understand how environmental conditions affect melanization. Glyphosate, the most widely used herbicide, inhibits melanin production. Here we elucidate the mechanism underlying glyphosate's inhibition of melanization demonstrate the herbicide's multifactorial effects on insects. Glyphosate acts as an antioxidant and disrupts the oxidation-reduction balance of melanization. The drug reduced wax moth larvae survival after infection, increased parasite burden in malaria-transmitting mosquitoes, and altered midgut microbiome composition in adult mosquitoes. These findings suggest that glyphosate's environmental accumulation could contribute to the so called insect apocalypse, characterized by species declines, by rendering them more susceptible to microbial pathogens due to melanization inhibition, immune impairment, and perturbations in microbiota composition.
Tarımsal alanlarda Herbisitler yabancı otların zararını azaltmak amacı ile kullanılmaktadır. Herbisitler, bazı yabancı otları öldürebildiği gibi bazı türlerinde gelişimini yavaşlatmaktadır. Herbisit kullanımı, yirminci yüzyılın ortasından itibaren önemli ölçüde artmıştır. Herbisitlerin kullanılmaması halinde tarımsal üretimde önemli verim ve kalite kayıpları meydana gelmektedir. Bununla birlikte, herbisitlerin geniş yelpazede ve irrasyonel kullanımının oluşturduğu yan etkiler çevreyi ve insan sağlığını tehdit etmektedir. Herbisitler pestisitler arasında en az zararlısı olsa da, yapılan birçok çalışmada herbisirtlerin çevre ve insan sağlığı üzerindeki ciddi olumsuz etkilerini göstermiştir. Her yıl kanserojene neden olan veya toprak ve suda önemli oranda kalıntılara neden olan herbisitlerin lisetesi yayınlanmaktadır. Ancak bir çok herbisitlerin kullanımından ve çevreye tonlarca miktarda yayılmasından sonra kullanımı yasaklanmaktadır. Herbisitlerin kimyasal yapısı doğada oldukça yavaş bozulmakata, bu durum toprakta ve çevrede birikimine yol açmaktadır. Bu herbisitlerin etkileri nehirlere, göllere, denizlere ve okyanuslara kadar ulaşmıştır. Ayrıca kimyasal yapısı bozulmuş herbisitlerin farklı çevresel koşullar altında canlı organizmalar üzerindeki etkisi hala bilinmemektedir. Herbisitlerin yaygın kullanılması nedeni ile bazı durumlarda etkili olabilecek geleneksel kontrol yöntemlerinin kullanılmasını da olumsuz etkilemektedir. Bu araştırmada, ekosistemin canlı unsurları üzerinde bazı herbisit zararları ve herbisitlerin kullanımını değiştirebilecek veya azaltabilecek çeşitli alternatif yöntemlere yer verilmiştir.
Elements essentially required for the proper functioning of plants are termed as
“essential nutrients” that are classified into macro (H, O, C, P, K, N, Ca, Mg, S)
and micro (B, Fe, Cu, Mn, Zn, Ni, Mo, Cl) nutrients. Micronutrients though
required in minute quantity are an integral part of plant nutrition, and their
absence from the system significantly affects plant growth and biochemical
functioning. Metallic micronutrient availability in soil being dependent upon soil pH and redox potential has become an issue for alkaline soils. In general, all
micronutrients are bioavailable in acidic to neutral soil pH except Mo. Thus,
making the nonsignificant supply of these nutrients in alkaline soil a constraint for
sustainable agriculture. Besides soil chemical properties, soil biota and rhizosphere
root chemistry and plant symbiotic associations also affect micronutrient
solubilization and uptake by plants. Modification of rhizosphere chemistry, the
introduction of mycorrhizal association and biofertilizers can be an option for
increasing bioavailability of these nutrients in alkaline soils. Using biofertilizers
and screening, enrichment and incorporation of Fe, Zn, Cu, and Mn solubilizing,
and S reducing bacteria are only useful if we can sustain proper microbial count
per gram of soil. Application of different inorganic and organic amendments,
fertigation of synthetic nutrient formulation, and foliar application of micronutrient
products are acceptable and economical options for tackling this issue in
alkaline soils. This chapter is an effort to summarize all issues associated with the
availability of micronutrients in alkaline soils and possible options for enhancement
of bioavailable fraction, uptake and assimilation of these nutrients by
various crop plants.
Due to widespread adoption of no-till management and use of glyphosate-resistant transgenic crops, glyphosate is the most widely used herbicide worldwide. However, its effect on soil microbial communities is inconsistent. We studied the effects of glyphosate, tillage, and crop rotation on the diversity and composition of soil bacterial communities in wheat (Triticum turgidum var. durum Desf.) rhizosphere after 6 and 7 yr of glyphosate applications. In a 2 × 2 × 2 factorial design, there were two crop rotation treatments: continuous wheat (W–W) and wheat in rotation with field pea (Pisum sativum L.) (P–W); two tillage treatments: minimum tillage (MT) and no-till (NT); and two glyphosate treatments: no application or pre-seeding application at the recommended rate. None of the treatments affected wheat rhizobacterial α-diversity or the relative abundances of most bacterial groups. The most abundant phyla were Proteobacteria (25.1% relative abundance), Actinobacteria (21.7%), Acidobacteria (8.7%), Bacteroidetes (5.9%), Firmicutes (1.4%), Armatimonadetes (1.3%), and Verrucomicrobia (1.2%). Glyphosate reduced the relative abundance of Alphaproteobacteria in W–W rotation but increased it in P–W rotation, and it reduced the relative abundance of Opitutus spp. The W–W rotation had greater relative abundances of the classes Bacilli (Firmicutes) and Gammaproteobacteria, and genera Bacillus and Opitutus (Verrucomicrobia), than the P–W rotation. Compared with MT, NT increased the relative abundance of the phylum candidate division WPS-1, but it reduced that of Phenylobacterium spp. in W–W rotation. These treatment effects probably had implications for soil functioning, including nutrient cycling and biological disease/pest control.
Plant nutrition practice in organic agricultural systems is sometimes reduced to a renunciation of applying readily soluble mineral fertilisers. In organic farming, however, soil nutrient stocks are regarded as an additional source of plant-available nutrients that can be mobilised by crop plants through rhizosphere effects. Therefore, unlike in conventional farming, the focus is not on replacement of the nutrients removed by the harvested products through readily soluble fertilisers enhancing nutrient concentrations in the soil solution. Instead, it is on minimising nutrient losses and supplying plant nutrients through soil-plant-microorganism interactions in which improved soil structure and enhanced soil biological activity facilitate plant-induced nutrient mobilisation and nutrient uptake under conditions of limited nutrient availability in the soil. This paper reviews these soil processes that improve the availability of macro- and micronutrients to plant roots under conditions of limited nutrient availability. It focuses on providing a conceptual framework for the different processes contributing to nutrient mobilisation and within which the various strategies for improving nutrient efficiency can be integrated in organically managed soils. Essential farm management options based on scientific views of nutrient dynamics to maintain soil fertility are addressed. With diverse, legume-based crop rotations with an adequate proportion of time dedicated to fertility building crops, careful management of manure and organic residues, and by using permitted inputs for phosphorus (P) and potassium (K), organic farms can be managed sustainably. However, efforts for recycling nutrients, mainly phosphorus, need to be enhanced.
Agri-biotechnological approaches have introduced an expansion of genetically modified crops (GM) which has immense potential for betterment of agricultural practices. There are several possible benefits of GM crops includes high yield thereby solving food and nutritional security, producing herbicide tolerance, insecticide resistance varieties, reducing dependency on agrochemical thus reducing formers exposure to chemicals. However, potential risk and biosafety concerns are associated directly and indirectly with it. Flow of genetic information, generation of super-weed, adverse effects on beneficial species, development of resistance verities, and adverse effects on existing biodiversity reveal its unintentional adverse impacts on environment. Several health implications such as allergenicity, genetic hazards, and toxicity to different organs are associated with it. Moreover, studies revealed its negative impacts not only in existing biodiversity but in evolutionary patterns also. However, controversial data and ill-conducted investigations are few solid limitations. A matter of high significance is to deliver existing information available along with various concerns, that is, socioeconomic, political, and ethical concerns in GM crop adaptation.
Glyphosate is the most used herbicide globally. It is a unique non-selective herbicide with a mode of action that is ideal for vegetation management in both agricultural and non-agricultural settings. Its use was more than doubled by the introduction of transgenic, glyphosate-resistant (GR) crops. All of its phytotoxic effects are the result of inhibition of only 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), but inhibition of this single enzyme of the shikimate pathway results in multiple phytotoxicity effects, both upstream and downstream from EPSPS, including loss of plant defenses against pathogens. Degradation of glyphosate in plants and microbes is predominantly by a glyphosate oxidoreductase to produce aminomethylphosphonic acid and glyoxylate and to a lesser extent by a C-P lyase to produce sarcosine and phosphate. Its effects on non-target plant species are generally less than that of many other herbicides, as it is not volatile and is generally sprayed in larger droplet sizes with a relatively low propensity to drift and is inactivated by tight binding to most soils. Some microbes, including fungal plant pathogens, have glyphosate-sensitive EPSPS. Thus, glyphosate can benefit GR crops by its activity on some plant pathogens. On the other hand, glyphosate can adversely affect some microbes that are beneficial to agriculture, such as Bradyrhizobium species, although GR crop yield data indicate that such an effect has been minor. Effects of glyphosate on microbes of agricultural soils are generally minor and transient, with other agricultural practices having much stronger effects.
Background World agricultural production of genetically modified (GM) products, in particular, the combination of different traits/genes in the same plant has been a trend over the last decade. There has been concerns raised over stacking multiple herbicide and insect-resistant transgenes that could result in fitness costs depending on the type and strength of selection pressures exerted by the environment. Here, we report the results of transcriptomic analysis comparing the effect of glyphosate-based herbicide (GBH) in the single-transgene versus stacked, herbicide resistant soybean varieties on various biological processes, metabolic pathways, and key shikimic enzymes.
Results Gene expression data showed that defense metabolism and redox homeostasis were equally modulated in single-transgene and stacked variety samples. Carbon accumulation and energy metabolisms were distinct between the varieties and photosynthesis metabolism was found negatively affected in the single-transgene variety only. In the stacked variety, the shikimate pathway was modulated by the accumulation of transcripts from phenylalanine gene and other cascade genes. As expected, the expression of native EPSPS was upregulated in both varieties when herbicide was applied. On the other hand, transgenic EPSPS expression was down regulated in both GM varieties upon herbicide application which cannot be explained.
Conclusion Glyphosate-based herbicides toxicity suggests its effects on carbon central metabolism and flux, redox metabolism, photosynthesis, and to hormone and defense response in plants. The observed unintended effects in GM herbicide-tolerant varieties unravels the deleterious effects previously observed on GM tolerant varieties growth and production. The impact of GBH on shikimate and cascade pathways was observed in terms of both native and transgenic insensitive EPSPS modulation, alteration of jasmonic acid and lignin metabolism in both single-transgene and stacked variety. The energy metabolism and carbon flux were differently affected in these varieties. Oxidative stress, more specifically glutathione metabolism, induced by GBH, was also observed in this study. The stacked variety showed a more pronounced stress response (activation of specific stress defense proteins, Rboh, WRKY) and secondary compounds (β-glucosidase, isoflavone 7-O-methyltransferase). Omics profiling techniques, such as transcriptomics, can be considered tools to support risk assessment in detecting unintended effects due to the GBH application.
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.
Glyphosate is a broad-spectrum herbicide used for the control of weeds in glyphosate-resistant crops. Glyphosate inhibits 5-enolpyruvyl shikimate 3-phosphate synthase, a key enzyme in the synthesis of aromatic amino acids in plants, fungi, and bacteria. Studies with glyphosate-resistant wheat have shown that glyphosate provided both preventive and curative activities against Puccinia striiformis f. sp. tritici and Puccinia triticina, which cause stripe and leaf rusts, respectively, in wheat. Growth-chamber studies demonstrated wheat rust control at multiple plant growth stages with a glyphosate spray dose typically recommended for weed control. Rust control was absent in formulation controls without glyphosate, dependent on systemic glyphosate concentrations in leaf tissues, and not mediated through induction of four common systemic acquired resistance genes. A field test with endemic stripe rust inoculum confirmed the activities of glyphosate pre- and postinfestation. Preliminary greenhouse studies also demonstrated that application of glyphosate in glyphosate-resistant soybeans suppressed Asian soybean rust, caused by Phakopsora pachyrhizi.
• Phakopsora pachyrhizi
• Puccinia striiformis f. sp. tritici
• Puccinia triticina
• disease control
Glyphosate [N-(phosphonomethyl) glycine]-resistant crops (GRCs), canola (Brassica napus L.), cotton (Gossypium hirsutum L.), maize (Zea mays L.), and soybean [Glycine max (L.) Merr.] have been commercialized and grown extensively in the Western Hemisphere and, to a lesser extent, elsewhere. Glyphosate-resistant cotton and soybean have become dominant in those countries where their planting is permitted. Effects of glyphosate on contamination of soil, water, and air are minimal, compared to some of the herbicides that they replace. No risks have been found with food or feed safety or nutritional value in products from currently available GRCs. Glyphosate-resistant crops have promoted the adoption of reduced- or no-tillage agriculture in the USA and Argentina, providing a substantial environmental benefit. Weed species in GRC fields have shifted to those that can more successfully withstand glyphosate and to those that avoid the time of its application. Three weed species have evolved resistance to glyphosate in GRCs. Glyphosate-resistant crops have greater potential to become problems as volunteer crops than do conventional crops. Glyphosate resistance transgenes have been found in fields of canola that are supposed to be non-transgenic. Under some circumstances, the largest risk of GRCs may be transgene flow (introgression) from GRCs to related species that might become problems in natural ecosystems. Glyphosate resistance transgenes themselves are highly unlikely to be a risk in wild plant populations, but when linked to transgenes that may impart fitness benefits outside of agriculture (e.g., insect resistance), natural ecosystems could be affected. The development and use of failsafe introgression barriers in crops with such linked genes is needed.
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.
This study tests the effect of glyphosate application on disease severity in glyphosate-resistant sugar beet, and examines whether the increase in disease is fungal or plant mediated. In greenhouse studies of glyphosate-resistant sugar beet, increased disease severity was observed following glyphosate application and inoculation with certain isolates of Rhizoctonia solani Kuhn and Fusarium oxysporum Schlecht. f. sp. betae Snyd. & Hans. Significant increases in disease severity were noted for R. solani AG-2-2 isolate R-9 and moderately virulent F. oxysporum isolate FOB13 on both cultivars tested, regardless of the duration between glyphosate application and pathogen challenge, but not with highly virulent F. oxysporum isolate F-19 or an isolate of R. solani AG-4. The increase in disease does not appear to be fungal mediated, since in vitro studies showed no positive impact of glyphosate on fungal growth or overwintering structure production or germination for either pathogen. Studies of glyphosate impact on sugar beet physiology showed that shikimic acid accumulation is tissue specific and the rate of accumulation is greatly reduced in resistant cultivars when compared with a susceptible cultivar. The results indicate that precautions need to be taken when certain soil-borne diseases are present if weed management for sugar beet is to include post-emergence glyphosate treatments.