ArticlePDF Available

Glyphosate interactions with physiology, nutrition, and diseases of plants: Threat to agricultural sustainability?

Authors:
  • Escola Superior de Agricultura "Luiz de Queiroz", Universidade de São Paulo
Europ. J. Agronomy 31 (2009) 111–113
Contents lists available at ScienceDirect
European Journal of Agronomy
journal homepage: www.elsevier.com/locate/eja
Preface
Glyphosate interactions with physiology, nutrition, and diseases of plants: Threat
to agricultural sustainability?
The transition from biologically based to intensive, chemical-
based agricultural production systems advanced in North America
and Europe soon after World War II as inorganic fertilizers and
organically synthesized pesticides became widely available. This
modern or conventional-type agriculture was adopted by other
major crop production areas throughout the world with a sharp
increase in adoption generated by the input-intensive “Green Rev-
olution” of the 1960s and 1970s. In general, conventional cropping
systems are characterized as large-scale production enterprises
that utilize high-yielding crop varieties often in monoculture or
short-term rotations planted on the most fertile, productive soils
available with high inputs of chemical fertilizers and pesticides. Lit-
tle emphasis is given to managing soil organic matter through use
of traditional legume-based rotations, cover crops, or organic soil
amendments that are central to maintaining the biological activity
and inherent fertility of soils in biologically based cropping systems.
By abandoning the biological management component, many con-
ventionally managed fields have experienced severe disease, insect,
and weed infestations (Drinkwater et al., 1995); serious declines
in soil organic matter, nitrogen, and carbon contents (Khan et al.,
2007); and alterations in the balance of beneficial and detrimental
biological activities due to drastic changes in soil and rhizosphere
microbial communities (Dunfield and Germida, 2004).
One of the most significant inputs necessary for successful
conventional crop production are herbicides for management of
the variety of weed infestations especially encountered in row-
cropping systems. This technology was rapidly adopted because
most weeds could be controlled when matched with selective her-
bicides, which were compatible with the crop, and was considered
more cost-effective than cultural methods of weed management.
Glyphosate, the active ingredient in the herbicide Roundup, became
very popular after introduction in the 1970s for non-selective
weed control in fallowed fields and non-cropped areas of orchards,
vineyards, and timber plantations. The development of no-tillage
systems (“no-till”) for row-cropping systems greatly expanded
the use of glyphosate as it became standard practice to apply
glyphosate to growing vegetation in fields prior to planting. This
“burndown” application eliminated the need for tillage and allowed
farmers to plant crop seeds directly into soil beneath a mulch of
dead plant residues. The no-till practice contributed to reductions
in soil erosion and energy consumption for field preparation and
to expansion of grain production (primarily corn and soybean) in
many areas suitable for row-cropping throughout the world.
Although glyphosate is the most widely used herbicide
worldwide (Woodburn, 2000), several problems associated with
glyphosate interactions with plant nutrient availability, transfer
to and effects on susceptible crops, indirect effects on rhizo-
sphere microorganisms and plant pathogens, and development of
glyphosate-resistant weeds have raised serious concerns regard-
ing the sustainability of cropping systems in which glyphosate is
the primary weed management strategy. Within this context it
was our mandate to assemble a selection of papers for submis-
sion to European Journal of Agronomy. This Special Issue contains
peer-reviewed papers based on contributions presented at the
international symposium on “Mineral Nutrition and Disease Prob-
lems in Modern Agriculture: Threats to Sustainability?” held in
Piracicaba-SP, Brazil, 20–21 September 2007. The symposium,
organized by Dr. T. Yamada of the International Plant Nutrition
Institute-Brasil (IPNI) continued discussions of issues presented
in a previous symposium on herbicide impacts on plant nutrition
and disease convened in 2005 and was held under the auspices
of IPNI, The Agrisus Foundation – Sustainable Agriculture, ESALQ-
University of Sao Paulo, and European Society of Agronomy.
The strategic location of Piracicaba was ideal for convening a
symposium on experiences with nutrition and disease problems in
modern agriculture. Sao Paulo is among Brazil’s leading states in
land use devoted to sugarcane, citrus, and coffee plantations; the
majority of these enterprises are managed following modern and
intensive management, which include use of glyphosate to man-
age vegetation in these perennial crops. To the south, in subtropical
southern Brazil, no-till agriculture was developed to reduce exten-
sive soil erosion resulting from intensive row-cropping; adoption
of no-till accelerated with the introduction of glyphosate to Brazil
in the mid-1970s. To the north in the tropical savannah region
(cerrado) of central Brazil, no-till was introduced in the 1980s as
large farms devoted to soybean, cotton, and maize were established
(Bolliger et al., 2006). After many years of frequent applications
of glyphosate in both plantation and row crops in Brazil, several
problems in plant health and productivity developed, which are
representative of similar situations encountered in conventional
cropping systems all over the world.
A basic understanding of the behavior of glyphosate in plants
and the environment is necessary to set the foundation for the
investigations upon which the Symposium was based. The mode
of action, or the sequence of events leading to plant injury
and/or destruction after herbicide treatment, has been described
in numerous reports as the binding of glyphosate with and inacti-
vation of 5-enolpyruvoylshikimate-3-phosphate synthase (EPSPS),
the critical enzyme in the shikimate pathway required for synthesis
of a variety of aromatic plant metabolites including essential amino
1161-0301/$ – see front matter. Published by Elsevier B.V.
doi:10.1016/j.eja.2009.07.004
112 Preface / Europ. J. Agronomy 31 (2009) 111–113
acids, phenylalanine, tryptophan and tyrosine (Franz et al., 1997).
Tryptophan is necessary for the synthesis of indolylacetic acid (IAA),
the main growth promoter, that can explain the widespread field
observation of reduced in depth root growth of plants. Because a
single, specific enzyme restricted to one plant metabolic pathway
is inactivated by the herbicide resulting in eventual plant death,
glyphosate was proclaimed as environmentally friendly (Franz
et al., 1997). Additional standard assays identified other general
properties of glyphosate including immobilization by soil colloids
and organic matter and rapid degradation by soil microorganisms,
which suggested the herbicide posed no adverse impacts on the
environment or toward desirable plants.
More intensive evaluations revealed that glyphosate was
translocated within plants, accumulated in roots, and was even-
tually released into the rhizosphere (Coupland and Casely, 1979).
Subsequent research on glyphosate interactions with soil microor-
ganisms demonstrated that although glyphosate was metabolized
by a segment of the microbial population, it was also toxic to sev-
eral bacteria and fungi; the net effect of glyphosate appeared to
be a disruption of soil and root microbial community composition
because selected components of the microbial community were
stimulated while others were suppressed (Wardle and Parkinson,
1992; Busse et al., 2001). Interestingly, many studies showed that
glyphosate was not entirely and immediately immobilized by soil
colloids because a portion was available for metabolism by soil and
rhizosphere microorganisms (Haney et al., 2000). In the 1980s, Rahe
and coworkers documented that severe root infection associated
with glyphosate-treated plants was due to disruption of synthesis
of plant defense compounds, or phytoalexins, through the shiki-
mate pathway thereby predisposing plants to attack by soilborne
fungal pathogens (Johal and Rahe, 1988; Lévesque et al., 1987).
Thus, infection by soilborne pathogens caused by the inability of
plants to synthesize phytoalexins contributed to the overall her-
bicidal efficacy of glyphosate and was considered a “secondary
mode of action” of glyphosate. These findings were significant
because the release of glyphosate into the environment was found
to have considerably more and far-reaching effects than the orig-
inal notion that was limited to only the localized disruption of a
specific metabolic pathway within a target plant. As glyphosate use
increased in a number of agricultural systems, substantial evidence
accumulated on multiple adverse effects on crop health and pro-
ductivity and soil–plant–microorganism interactions mediated by
this herbicide.
Based on the concerns of multiple agricultural and environmen-
tal effects associated with widespread use of glyphosate during the
past decades, the Symposium was convened to present and dis-
cuss up-to-date research on problems of plant nutrition and disease
linked to glyphosate use, present and critique sustainable alterna-
tive management strategies, and propose future research efforts.
Key themes of the Symposium included interactions of glyphosate
with nutrient availability to crop plants; interactions of glyphosate
with plant pathogens and disease development in crop plants; and
impacts of glyphosate on plant nutrition and microbial interactions
in transgenic, glyphosate-resistant cropping systems (i.e., Roundup
Ready).
Each presenter addressed one or more of the key themes of the
Symposium. Römheld (Tesfamariam et al., 2009) reviewed the con-
sequences of glyphosate transfer to non-target (crop) plants via the
rhizosphere after herbicide application to target plants (undesir-
able vegetation). Evidence is provided that such transfer occurs
in orchards when weeds in alleys are sprayed with glyphosate,
which is subsequently released through the dying roots to be taken
up through the living roots of trees. This was demonstrated with
glyphosate-killed grass mulch simultaneously grown with citrus
saplings, which contained significantly high contents of shikimate
indicating glyphosate uptake by citrus from the dying grass roots
(Neumann et al., 2006). The cation-chelating ability of glyphosate,
which previously received little attention regarding impacts on
plant nutrition, was highlighted by several presenters as a criti-
cally important factor in nutrient deficiencies of crops observed in
production systems heavily reliant on glyphosate for weed man-
agement. Römheld and Cakmak (Cakmak et al., 2009; Senem Su et
al., 2009; Tesfamariam et al., 2009) discussed impaired micronu-
trient uptake and transport in plants exposed to glyphosate either
through root transfer or by simulated drift of sub-herbicidal rates
was due to the ability of glyphosate to form immobile stable com-
plexes with Fe and Mn (Eker et al., 2006; Neumann et al., 2006). The
possibility of interactive effects of glyphosate with other micronu-
trients was presented by Wood who suggested that the occurrence
of Ni deficiency in pecan (Bai et al., 2006) and other orchard replant
diseases might be exacerbated by release of glyphosate from killed
vegetation in orchards, which then complexes with Ni making it
unavailable for root uptake by trees.
Based on extensive field surveys and large-scale experiments,
Fernandez et al. (2009) demonstrated that previous glyphosate
applications (ranging from 18 to 36 months prior to planting) was
the most important agronomic factor in development of diseases,
primarily Fusarium head blight, in wheat and barley crops. Higher
Fusarium colonization of wheat and barley roots was also asso-
ciated with glyphosate burndown applications prior to planting
(Fernandez et al., 2007). An unknown but interesting aspect of
these observations is the apparent persistent effect of glyphosate
on plant growth two or more years after application. Huber (Johal
and Huber, 2009) reviewed various microbial interactions with
glyphosate including those documented for toxicity toward ben-
eficial microorganisms (i.e., rhizobia, Mn-reducers, mycorrhizae)
and stimulation of detrimental microorganisms (Mn-oxidizers,
pathogenic fungi). Through these interactions, glyphosate changes
nutrient availability and alters pathogen virulence to plants. Some
of the more notable diseases in which glyphosate might be impli-
cated include Corynespora root rot in soybean, Marasmius root
rot of sugarcane, citrus variegated chlorosis (Xylella fastidiosa),
and take-all (Gaeumannomyces graminis) in cereal crops. Many
of the pathogens causing these diseases are stimulated either by
glyphosate exuded from roots, by the altered composition of root
exudates caused by glyphosate treatment, or through a combina-
tion of both exudation processes.
The final key symposium theme addressed the impacts
of glyphosate on plant nutrition and microbial interactions,
and development of herbicide-resistant weeds in transgenic,
glyphosate-resistant (GR) cropping systems (i.e., Roundup Ready).
One of the most significant advancements in intensive agriculture is
the introduction of GR crops in the mid-1990s. By 2008 GR-resistant
soybean occupied 65.8 million ha (53% of the global area planted to
biotech crops), followed by maize (37.3 million ha at 30% of global
area), and cotton (15.5 million ha at 12% of global area) (James,
2008). The GR cropping system provided a more cost-effective
option for farmers, allowing them to spray a broad spectrum of
weeds with glyphosate on “as needed” basis and reducing the need
for pre and post emergence herbicides. However, the repetitive
and dedicated use of glyphosate within a growing season and over
the past decade has resulted in selection for resistance in several
weed species (Johnson et al., 2009) and development of similar crop
nutrition and health problems as those observed in non-GR sys-
tems. Previous findings that glyphosate and high concentrations
of soluble carbohydrates and amino acids were released in root
exudates of glyphosate-treated GR soybean (Kremer et al., 2005)
suggested that impacts on micronutrient uptake and root microbial
interactions might mirror those described for glyphosate interac-
tions in non-transgenic cropping systems. Indeed, presentations
at the Symposium indicated decreased uptake of micronutrients
and subsequent development of deficiency symptoms in some
Preface / Europ. J. Agronomy 31 (2009) 111–113 113
GR soybean cultivars (Tesfamariam et al., 2009; Johal and Huber,
2009); only limited information has been previously reported on
depressed uptake of Mn and Fe in GR soybean (Gordon, 2007; Jolley
et al., 2004), suggesting that genetic modification in the GR soybean
and/or glyphosate released into the rhizosphere affected micronu-
trient uptake. Valuable information on increased colonization by
potential fungal pathogens, increases in Mn-oxidizing microorgan-
isms, and decreases in beneficial bacterial populations (fluorescent
pseudomonads, rhizobia) in the rhizosphere of GR crops is pre-
sented to aid in understanding some of the production problems
often reported for GR-cropping systems (Johal and Huber, 2009;
Kremer and Means, 2009).
In summary, the Symposium provided a forum to bring together
a current understanding of the numerous factors – physiologi-
cal, nutritional, soil chemical, phytopathological, and biological
– that interact with glyphosate management whether situated
in conventional (plantation, orchard, row crops) or in transgenic
agroecosystems. This understanding is essential for developing
alternative approaches within management systems to overcome
the constraints to crop productivity and health. Some of the recom-
mendations that emerged from the Symposium included reducing
the use of glyphosate in perennial culture by using mulching sys-
tems to suppress weeds, which has been successful in many citrus
plantations in Brazil. Development of efficient methods for using
cover crops in annual crops for weed suppression and possible
increased availability of soil micronutrients was discussed. Sev-
eral approaches for improving productivity in GR cropping systems
included selection of cultivars with high Mn-uptake efficiency,
delayed application of micronutrients (Mn, Zn, Fe and Cu) after
glyphosate treatment, and cultural practices, including the use of
gypsum + Mo, and roller knife mulching that minimize glyphosate
impact on crops. The use of biological products such as those con-
taining the plant defense compound salicylic acid and amino acids
by foliar application to improve resistance to root pathogens was
also suggested. We trust that the articles in this Special Issue will
serve as valuable information sources for those interested in a bet-
ter understanding of the interactions of glyphosate with crop plants
and that this information will be used to develop more sustainable
agricultural production systems.
References
Bai, C., Reilly, C.C., Wood, B.W., 2006. Nickel deficiency disrupts metabolism of ure-
ides, amino acids, and organic acids of young pecan foliage. Plant Physiol. 140,
433–443.
Bolliger, A., Magrid, J., Amado, T.J.C., Neto, F.S., Ribeiro, M.F.S., Calegari, A., Ralisch, R.,
Neergaard, A., 2006. Taking stock of the Brazilian “zero-till revolution”: a review
of landmark research and farmers’ practice. Adv. Agron. 91, 47–110.
Busse, M.D., Ratcliffe, A.W., Shestak, C.J., Powers, R.F., 2001. Glyphosate toxicity and
the effects of long-term vegetation control on soil microbial communities. Soil
Biol. Biochem. 33, 1777–1789.
Cakmak, I., Yazici, A., Tutus, Y., Ozturk, L., 2009. Glyphosate reduced seed and leaf
concentrations of calcium, manganese, magnesium, and iron in non-glyphosate
resistant soybean. Eur. J. Agron. 31, 114–119.
Coupland, D., Casely, J.C., 1979. Presence of 14C activity in root exudates and gutation
fluid from Agropyron repens treated with 14C-labelled glyphosate. New Phytol.
83, 17–22.
Drinkwater, L.E., Letourneau, D.K., Workneh, F., van Bruggen, A.H.C., Shennan,
C., 1995. Fundamental differences between conventional and organic tomato
agroecosystems in California. Ecol. Appl. 5, 1098–1112.
Dunfield, K.E., Germida, J.J., 2004. Impact of genetically modified crops on soil- and
plant-associated microbial communities. J. Eviron. Qual. 33, 806–815.
Eker, S., Ozturk, L., Yazici, A., Erenoglu, B., Römheld, V., Cakmak, I., 2006. Foliar-
applied glyphosate substantially reduced uptake and transport of iron and
manganese in sunflower (Helianthus annuus L.) plants. J. Agric. Food Chem. 54,
10019–10025.
Fernandez, M.R., Zentner, R.P., Basnyat, P., Gehl, D., Selles, F., Huber, D., 2009.
Glyphosate associations with cereal diseases caused by Fusarium spp. In the
Canadian Prairies. Eur. J. Agron. 31, 133–143.
Fernandez, M.R., Zentner, R.P., DePauw, R.M., Gehl, D., Stevenson, F.C., 2007.
Impacts of crop production factors on common root rot of barley in Eastern
Saskatchewon. Crop Sci. 47, 1585–1595.
Franz, J.E., Mao, M.K., Sikorski, J.A., 1997. Glyphosate: A Unique Global Herbicide.
ACS Monograph 189. American Chemical Society, Washington, D.C., USA.
Gordon, B., 2007. Manganese nutrition of glyphosate-resistant and conventional
soybeans. Better Crops 91 (4), 12–13.
Haney, R.L., Senseman, S.A., Hons, R.M., Zuberer, D.A., 2000. Effect of glyphosate on
soil microbial activity and biomass. Weed Sci. 48, 89–93.
James, C., 2008. Global status of commercialized biotech/GM crops: 2008. The first
thirteen years, 1996 to 2008. ISAAA Brief No. 39. International Service for the
Acquisition of Agri-biotech Associations, Ithaca, New York, USA.
Johal, G.S., Huber, D.M., 2009. Glyphosate effects on disease and disease resistance
in plants. Eur. J. Agron. 31, 144–152.
Johal, G.S., Rahe, J.E., 1988. Glyphosate, hypersensitivity and phytoalexins accumu-
lation in the incompatible bean anthracnose host-parasite interaction. Physiol.
Mol. Plant Pathol. 32, 267–281.
Johnson, W.G., Davis, V., Kruger, G., Weller, S., 2009. Influence of glyphosate-resistant
cropping systems on weed species shifts and glyphosate-resistant weed popu-
lations. Eur. J. Agron. 31, 162–172.
Jolley, V.D., Hansen, N.C., Shiffler, A.K., 2004. Nutritional and management related
interactions with iron-deficiency stress response mechanisms. Soil Sci. Plant
Nutr. 50, 973–981.
Khan, S.A., Mulvaney, R.L., Ellsworth, T.R., Boast, C.W., 2007. The myth of nitrogen
fertilization for soil carbon sequestration. J. Environ. Qual. 36, 1821–1832.
Kremer, R.J., Means, N.E., 2009. Glyphosate and glyphosate-resistant crop interac-
tions with rhizosphere microorganisms. Eur. J. Agron. 31, 153–161.
Kremer, R.J., Means, N.E., Kim, S.-J., 2005. Glyphosate affects soybean root exudation
and rhizosphere microorganisms. Int. J. Environ. Anal. Chem. 85, 1165–1174.
Lévesque, C.A., Rahe, J.E., Eaves, D.M., 1987. Effects of glyphosate on Fusarium spp.:
its influence on root colonization of weeds, propagule density in the soil, and
crop emergence. Can. J. Microbiol. 33, 354–360.
Neumann, G., Kohls, S., Landsberg, E., Stock-Oliveira Souza, K., Yamada, T., Römheld,
V., 2006. Relevance of glyphosate transfer to non-target plants via the rhizo-
sphere. J. Plant Dis. Protect. Sp. Issue 20, 963–969.
Senem Su, Y., Ozturk, L., Cakmak, I., Budak, H., 2009. Turfgrass species response to
increasing rates of glyphosate application. Eur. J. Agron. 31, 120–125.
Tesfamariam, T., Bott, S., Neumann, G., Cakmak, I., Römheld, V., 2009. Glyphosate in
the rhizosphere—role of waiting time and different glyphosate binding forms in
soils for phytotoxicity to non-target plants. Eur. J. Agron. 31, 126–132.
Wardle, D.A., Parkinson, D.A., 1992. Influence of the herbicides 2,4-D and glyphosate
on soil microbial biomass and activity: a field experiment. Soil Biol. Biochem.
24, 185–186.
Woodburn, A.T., 2000. Glyphosate: production, pricing and use worldwide. Pest
Manage. Sci. 56, 309–312.
Tsuioshi Yamada1(Guest Editor)
AgriNatura Agronomic Consulting, Piracicaba-SP, Brazil
Robert J. Kremer(Managing Guest Editor)
Cropping Systems & Water Quality Unit, USDA-ARS,
302 Natural Resources Bldg., University of Missouri,
Columbia, MO 65211, USA
Paulo Roberto de Camargo e Castro (Guest Editor)
ESALQ, University of Sao Paulo, Piracicaba-SP, Brazil
Bruce W. Wood (Guest Editor)
Southeast Fruit & Tree Nut Laboratory, USDA-ARS,
Byron, GA 31008, USA
Corresponding author.
E-mail address: kremerr@missouri.edu (R.J. Kremer)
1Retired from International Plant Nutrition
Institute, Brazil.
... A deficiency of magnesium in the plant can lead to a reduction in chlorophyll biosynthesis, inhibition of sucrose transport, alteration of nutrient uptake, and secondary metabolism [52,53]. The glyphosate distribution can also cause a reduction in nickel content in the soil [54] due to the well-known chelating activity of this herbicide [55] which also concerns this microelement [56]. Nickel is an activator of metalloenzymes such as urease which hydrolyzes urea in plant tissue, and it is also involved in the degradation of methylglyoxal, a potent cytotoxic compound [57,58]. ...
Article
Full-text available
The initial outbreak of Xylella fastidiosa subsp. pauca (Xfp) on olive groves in Salento (Apulia, Italy) dates back to the years 2008 and 2009 when extensive twig and branch diebacks were observed in the area of Gallipoli area (province of Lecce). Subsequently, the bacterium also spread northwards to other areas of Apulia. In many cases, entire olive groves, also including the centennial ones, died. After the crown collapse, in many cases, it has been observed that the suckers are resprouting at the base of the trunk. After two to three years, such suckers usually died as well. However, during the last four to five years, in the first Xfp outbreak area, a complete restoration of the crown of the Xfp-susceptible cultivars Ogliarola salentina and Cellina di Nardò has been noticed. Such trees or olive groves also started to yield again. To monitor this tree resilience phenomenon, together with local non-profit organizations, a survey in the province of Lecce has been carried out to find olive groves for which any curative or agronomical practices have been applied since the bacterium outbreak. Resilient olive groves are scattered in many municipalities all over the province of Lecce. The phenomenon regards both young and adult olive groves and also includes some centennial trees. In many cases, the trees are yielding fruits, and farmers started to cultivate them again. Olive resilience in Salento is already being studied and can represent a significant opportunity to restore the local and valuable olive germplasm.
... Despite the great success of these crops, some have claimed that glyphosate application to GR crops has significant adverse effects on them. One of the claimed effects is the alteration of plant mineral nutrition, including reductions in levels of both micro and macro nutrients in both soybean and maize [1][2][3][4][5][6][7][8][9]. Because glyphosate is known to chelate divalent metal cations [10], such an effect might be expected. ...
Article
Full-text available
Glyphosate-resistant (GR) maize is dominant in countries where it is grown. Significant, adverse effects of glyphosate application to GR maize have been reported, but few data from robust studies exist to determine if such effects are common. In this study, the effects of recommended application rates (single and sequential applications) were used on GR maize grown at two locations for one season and for two seasons in a third location. No significant effects of glyphosate on mineral content (N, P, K, Ca, Mg, S, Cu, Fe, Mn, and Zn) in leaves or grain, plant height, stem diameter, ear parameters, or yield were found at any location or in any growing season. Likewise, harvested grain quality, as determined by percent starch, protein, and total lipids, was unaffected by glyphosate treatment at any location. Neither glyphosate nor aminomethylphosphonic acid, the primary degradation product of glyphosate, were found in grain from any treatment at any location, except for 20 ng g−1 of glyphosate found in grain from one season at one location. These results support the view that recommended applications of glyphosate have no significant effects on growth, grain composition, mineral content, grain quality, nor yield of GR maize.
... Despite satisfying efficiency against weeds, several authors suggest a connection among excessive use of glyphosate and its effects on non-target organisms in ecosystem (Kaniseri et al. 2019, Yamada et al. 2009) and public health . Moreover, health issues, like birth problems, cancer and hypothyroidism, are known to be associated with glyphosate exposure (Mesnage et al. 2012). ...
Chapter
Full-text available
Glyphosate-based herbicides (GBHs) have been developed under the rationale of specifically targeting plants, since glyphosate mechanism is based on the inhibition of the shikimate pathway, present only in plants. However, this herbicide has been detected in aquatic ecosystems, wildlife and in humans and several studies have demonstrated its toxicity in different organisms. In order to better study the environmental impacts of this herbicide and its commercial formulations, animal models have been applied. Nematodes, aquatic organisms, insects and other organisms have provided important insights on the environmental impacts and important policies have been created for ecological and human health protection. This chapter reviews ecotoxicological and experimental studies on GBHs exposure and strategies that may reduce their environmental impact.
... The reduction of growth of the avocado plants in pots in which weeds were treated with glyphosate suggests that the use of this herbicide in orchards may damage avocado trees through their roots, possibly resulting in reduced water uptake and mineral deficiencies, which in turn increases disease susceptibility (Kremer et al. 2009;Zobiole et al. 2010). It may also be detrimental to beneficial rhizosphere microbes (Zobiole et al. 2011). ...
Article
The ability of organic, microbial or mineral-based soil additives to suppress root rot caused by Phytophthora cinnamomi was compared with disease reduction resulting from the use of the fungicides phosphite or metalaxyl. The effect of glyphosate (commonly used for weed control) on plant health was also examined. Avocado plants were grown in a glasshouse in pots with soils collected under mature commercial avocado trees. To simulate ‘orchard soil’ conditions, chicken manure, wood mulch, and mulch from beneath 20-year-old trees in an avocado orchard were added to the pots. The effect of P. cinnamomi on plant growth and visible root damage was assessed using plants grown under these ‘orchard’ soil conditions, and treatments with further additives (two microbial soil conditioners, one organic and two mineral-based mulches). In two of three experiments, infestation of soil with P. cinnamomi resulted in no significant reduction on fine root dry weight for plants sprayed with phosphite, or treated with a silicate-based mulch. However, when a combination of these two treatments gave no additive effect. In one experiment, a microbial-based conditioner was also beneficial. Phosphite was preferable to metalaxyl as a chemical treatment, as the latter reduced shoot dry weight by 25% and fine root dry weight by 30% of that in non-inoculated plants. Glyphosate treatment of wheat seedlings growing in the pots with the avocados also reduced shoot dry weight (20%) and fine root dry weight (20%) of non-inoculated avocados. These observations need to be confirmed under field conditions.
... In many studies, glyphosate and AMPA have been detected in all treated plant products, but also in non-target plants, the soil, animals that feed on crop products, surface and groundwaters (and the organisms that live there), the atmosphere, and humans (Benbrook, 2016;Perez et al., 2011;Van Bruggen et al., 2018). The use of glyphosate as a herbicide that is non-toxic to non-target organisms (e.g., beneficial insects, aquatic life, humans etc) and as a very efficient way for weed control is controversial, and due to its extensive use (Van Bruggen et al., 2018), there is increasing evidence for its ecotoxicological effects on non-target agroecosystem biodiversity (Cuhra et al., 2016;Kanissery et al., 2019;Yamada et al., 2009). Herbicides can impact not only their application area, but also the non-target plant species growing on the margins of that area (Russo et al., 2020). ...
Article
Full-text available
Pesticide products containing glyphosate as a systemic active ingredient are some of the most extensively used herbicides worldwide. After spraying, residues have been found in nectar and pollen collected by bees foraging on treated plants. This dietary exposure to glyphosate could pose a hazard for flower-visiting animals including bees, and for the delivery of pollination services. Here, we evaluated whether glyphosate contaminates nectar and pollen of targeted crops and non-target wild plants. Oilseed rape was selected as focal crop species, and Rubus fruticosus growing in the hedgerows surrounding the crop was chosen as non-target plant species. Seven fields of oilseed rape, where a glyphosate-based product was applied, were chosen in east and southeast Ireland, and pollen and nectar were extracted from flowers sampled from the field at various intervals following glyphosate application. Pollen loads were taken from honeybees and bumblebees foraging on the crop at the same time. Glyphosate and aminomethylphosphonic acid (AMPA) residues were extracted using acidified methanol and their concentrations in the samples were determined by a validated liquid chromatography tandem mass spectrometry (LC-MS/MS) method. Glyphosate was detected in R. fruticosus nectar and pollen samples that were taken within a timeframe of two to seven days after the application on the crop as a desiccant. No glyphosate was detected when the application took place before or more than two months prior to our sampling in any of the evaluated matrices. The metabolite AMPA was not detected in any samples. To gain further insight into the potential extent of translocation within both plants and soil when a crop is desiccated using glyphosate before harvesting, and the potential impacts on bees, we recommend a longitudinal study of the presence and fate of glyphosate in non-target flowering plants growing nearby crop fields, over a period of several days after glyphosate application.
... Glyphosate strongly inhibits germination, root growth and other processes in plants by reducing/inhibiting the absorption and displacement of macro and micro elements such as Ca, Mg, Mn and Fe 31 . In addition, by blocking the production of tryptophan, glyphosate inhibits the synthesis of indole acetic acid, a growth promoter that plays an important role in root growth of plants 32 . Another reason for reducing root elongation and germination may be that glyphosate inhibits mitotic cell division in stem cells. ...
Article
Full-text available
Abstract In this study, the glyphosate toxicity and the toxicity-reducing role of bitter melon extract (Bmex) (Momordica charantia L.) were investigated in Allium cepa L. test material. The toxicity of glyphosate and protective role of Bmex were investigated with the help of physiological (germination, root elongation and weight gain), cytogenetic (mitotic index-MI, micronucleus-MN and chromosomal abnormalities-CAs), biochemical (malondialdehyde-MDA, superoxide dismutase-SOD and catalase-CAT) and anatomical (root meristem cell damage) parameters. The genotoxicity mechanism of glyphosate was elucidated by spectral analysis. A. cepa bulbs were divided into six groups as one control and five applications. Tap water was applied to the bulbs in the control group for 72 h. Glyphosate (500 mg/L) and two different doses of Bmex (350 and 700 mg/L) were applied to the bulbs in the treatment group for 72 h. At the end of the period, the germinated bulbs were prepared for experimental analyses, measurements and observations by applying routine preparation procedures. As a result, glyphosate administration caused a significant (p
... The most widespread method is a termination herbicide, usually glyphosate. However, this practice has been criticized because of undesirable side effects on the agroecosystem and the environment (Johal and Huber 2009;Yamada et al. 2009;Mamy et al. 2016). Glyphosate may also reduce main crop yields when applied too close to the main crop seeding date (Nascente et al. 2013) or it may interact with P-fertilizer application (Rose et al. 2018). ...
Thesis
Full-text available
Phosphorus (P) is one of the most limiting plant nutrients for agricultural production. The soil microbial community plays a key role in nutrient cycling, affecting access of roots to P, as well as mobilization and mineralization of organic P (Porg). This thesis aimed to better understand the potential of cover crops to enhance plant-soil-microbe interactions to improve the availability of P. This dissertation consists of a meta-analysis of and two field experiments. The used methods showed that microbial P, the activity of P-cycling enzymes and PLFAs increased under cover crops, indicating an enhanced potential for organic P cycling. Gram- positive and Gram-negative bacteria, and to a lesser extent also arbuscular mycorrhizal fungi, increased their abundance with cover crops. However, saprotrophic fungi could benefit most from the substrate input derived from cover crop roots or litter. Enzyme-stable Porg shifted towards pools of a greater lability in the active soil compartments (rhizosheath and detritusphere). The effects of agricultural management, such as cover crop species choice and tillage, were detectable, but weaker compared to the effect of the presence of cover crops. With the obtained results, the research aims of this thesis could be successfully addressed. We were able to confirm that cover crops have the potential to improve main crops’ access to P. Furthermore, we presented and discussed three pathways of P benefit. In the plant biomass pathway, P is cycled through cover crop biomass and becomes available for the main crop upon litter decomposition. The microbial enhancement pathway describes how the cover crop’s interaction with soil microbes increases their abundance and activity, thereby increasing the availability of Porg. Some cover crop species seem to be capable of utilizing a biochemical modification pathway, where changes in the sorption capacity of the soil result in a greater quantity of plant-available phosphate. However, the latter pathway was apparently not important in the crop rotations used in our field experiments. The data also allowed us to characterize ways in which plant-soil-microbe interactions under cover crops affected the relationship of soil microbial functions to the enzymatic availability of Porg pools. Cover crops increased the abundance and activity of microbes, especially fungi, as well as microbial P. This enhancement in P-cycling potential shifted Porg toward pools of greater availability to added enzymes. However, the relation between enzymes and Porg pools is complex and is possibly affected by soil P composition and other site characteristics, indicating the need for further research in this area. Finally, we elucidated how the choice of cover crop species and agricultural management can shift the relative importance of the pathways for the P benefit of the main crop, while site-specific management allows farmers to adapt to local conditions and to optimize the functions of their agroecosystems. In conclusion, our results indicate that the pathways of cover crop derived P benefit take place simultaneously. We confirmed the potential of cover crop biomass for the cycling of P, and we suggest that our observed increases in the availability of soil Porg are related to microbial abundance and activity. The interactions of cover cropping and tillage indicate also that P benefit can be optimized by management decisions. Finally, these new insights into soil phosphorus cycling in agroecosystems have the potential to support further development of more sustainable agricultural systems.
Article
Full-text available
The potential adverse effects of glyphosate on glyphosate‐resistant (GR) crops are still a matter of controversy. The effects of glyphosate at recommended application rates (either a single application of 580 g ae ha⁻¹ of glyphosate at stage V5 or a sequential application of 580 + 980 g ae ha⁻¹ at stage V3 and V7, respectively) on growth, mineral content, and metabolic parameters of GR maize (Zea mays) were determined in greenhouse and field studies, each replicated in different years. No effects on any growth parameter (including grain yield), mineral content (leaf and grain), grain starch, crude protein, or total lipids were found. The only significant negative effect was a slight reduction in tyrosine content of leaf tissue with the sequential treatment, however, there was no increase in shikimic or quinic acids in leaf tissue with any treatment. In a separate greenhouse experiment, there was no sign of oxidative stress, as determined by levels of chlorophylls, carotenoids, and malondialdehyde (MDA) content as well as superoxide dismutase and guaiacol peroxidase activities 4 and 8 days after treatment with 1080 g ha⁻¹ glyphosate. In fact, there was a reduction of MDA in roots of glyphosate‐treated plants 4 DAT, indicating reduced oxidative stress. No aminomethylphosphonic acid, the primary degradation product of glyphosate, was found in either leaves or grain of treated plants, and no glyphosate was found in grain of treated plants from the field studies. All the results are consistent with there being no adverse effects of glyphosate on GR maize at recommended application rates.
Article
Full-text available
New fungicide modes of action are needed for fungicide resistance management strategies. Several commercial herbicide targets found in fungi that are not utilized by commercial fungicides are discussed as possible fungicide molecular targets. These are acetyl CoA carboxylase, acetolactate synthase, 5-enolpyruvylshikimate-3-phosphate synthase, glutamine synthase, phytoene desaturase, protoporphyrinogen oxidase, long-chain fatty acid synthase, dihydropteroate synthase, hydroxyphenyl pyruvate dioxygenase, and Ser/Thr protein phosphatase. Some of the inhibitors of these herbicide targets appear to be either good fungicides or good leads for new fungicides. For example, some acetolactate synthase and dihydropteroate inhibitors are excellent fungicides. There is evidence that some herbicides have indirect benefits to certain crops due to their effects on fungal crop pathogens. Using a pesticide with both herbicide and fungicide activities based on the same molecular target could reduce the total amount of pesticide used. The limitations of such a product are discussed.
Article
Full-text available
In an integrated, multidisciplinary study we compared ecological characteristics and productivity of commercial farms categorized as either organic (ORG) or conventional (CNV) based on their use of synthetic fertilizers and pesticides or reliance on organic soil amendments and biological pest control. We measured belowground parameters: various soil chemical and biological properties and root disease severity; common agronomic indicators: biomass, fruit yield and insect pest damage; and community level indicators, including arthropod diversity and soil microbial activity and diversity. CNV and ORG production systems could not be distinguished based on agronomic criteria such as fruit yield and arthropod pest damage levels. However, differences were demonstrated in many soil, plant, disease, and diversity indicators suggesting that the ecological processes determining yields and pest levels in these two management systems are distinct. In particular, nitrogen mineralization potential and microbial and parasitoid abundance and diversity were higher in ORG farms. Differences between the agroecosystems were sufficiently robust to be distinguished from environmental variation and suggest that biological processes compensated for reductions in the use of synthetic fertilizers and pesticides.
Article
Full-text available
Glyphosate is a non-selective, broad-spectrum herbicide that kills plants by inhibiting the enzyme 5-enolpyruvylshikimic acid-3-phosphate synthase (EPSPS), which is necessary for synthesis of aromatic amino acids. A secondary mode of action involves infection of roots of glyphosate-susceptible plants by soil-borne micro-organisms due to decreased production of plant protection compounds known as phytoalexins. Varieties of several crops, including glyphosate-resistant (GR) or Roundup Ready soybean, are genetically modified to resist the herbicidal effects of glyphosate and provide farmers with an effective weed-management tool. After glyphosate is applied to GR soybean, glyphosate that is not bound to glyphosate-resistant EPSPS is translocated throughout the plant and accumulates primarily in meristematic tissues. We previously reported that fungal colonization of GR soybean roots increased significantly after application of glyphosate but not after conventional postemergence herbicides. Because glyphosate may be released into soil from GR roots, we characterized the response of rhizosphere fungi and bacteria to root exudates from GR and non-GR (Williams 82; W82) cultivars treated with and without glyphosate at field application rates. Using an immunoassay technique, glyphosate at concentrations >1000 ng plant-1 were detected in exudates of hydroponically grown GR soybean at 16 days post-glyphosate application. Glyphosate also increased carbohydrate and amino acid contents in root exudates in both soybean cultivars. However, GR soybean released higher carbohydrate and amino acid contents in root exudates than W82 soybean without glyphosate treatment. In vitro bioassays showed that glyphosate in the exudates stimulated growth of selected rhizosphere fungi, possibly by providing a selective C and N source combined with the high levels of soluble carbohydrates and amino acids associated with glyphosate treatment of the soybean plants. Increased fungal populations that develop under glyphosate treatment of GR soybean may adversely affect plant growth and biological processes in the soil and rhizosphere.
Article
Glyphosate herbicide is the largest-selling single crop-protection chemical product in the market today. This non-selective weedkiller was initially targeted at the non-crop areas in agriculture and for industrial applications but, with the continuing development of minimum- and no-tillage agricultural practices, glyphosate also found usage in a number of crop outlets. Most recently, glyphosate has found direct crop usage on plant varieties that have been genetically modified to be tolerant of glyphosate applications. Such has been the continuing success of the product that its annual volume consumption growth has averaged in excess of 20% in recent years in agricultural use. (C) 2000 Society of Chemical Industry.
Article
S ummary The herbicide, N ‐phosphonomethyl glycine (glyphosate), is readily absorbed by the foliage and translocated in the phloem of Agropyron repent (L.) Beauv. The roots and rhizomes were active sinks and, 8 days following herbicide treatment, ¹⁴ C accumulated at the rhizome nodes, especially at the apical buds. Appreciable amounts of [ ¹⁴ C]glyphosate were exuded from intact roots into surrounding solutions but very low levels occurred in the guttation drops collected from the leaf tips. Some implications of the work are discussed.
Article
Fusarium head blight (FHB) in barley (Hordeum vulgare L.) has been spreading on the Cana- dian Prairies for the last decade. Fusarium spp. causing FHB can also cause crown and root rot of cereal crops. It is therefore of interest to determine the impact of agronomic practices on fungal populations associated with root rot of barley. From 1999 to 2001, 137 barley crops were sampled in eastern Saskatchewan for severity of subcrown internode discoloration and percent- age isolation of fungi. Cochliobolus sativus was the most commonly isolated fungus, whereas the most commonly isolated Fusarium spp. included the FHB pathogens F. avenaceum, F. culmorum, and F. graminearum. Discoloration caused by C. sativus was favored by conven- tional-till, whereas Fusarium spp. increased in reduced tillage systems. Barley grown after a cereal-summer fallow sequence under conven- tional- or minimum-till had increased levels of C. sativus. Fusarium spp. were most affected by the previously grown crop(s); they were more common in barley grown after a nonce- real than a cereal, and after two noncereals, or a noncereal alternated with summer fallow. Previous glyphosate applications were associ- ated with lower C. sativus and higher Fusarium spp. levels in barley grown under minimum-till management. This suggests changes in fun- gal communities; however, the mechanism(s) responsible for these changes in fungal levels are not known. Increased infection of ground and underground tissue by FHB pathogens may contribute to its development in succeed- ing cereal crops. Therefore, measures aimed at reducing root and crown infections by Fusarium spp. may also help reduce FHB development.
Article
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.