New research reveals disastrous ecological impacts of the world’s top herbicide and GM crops made tolerant to it. Dr. Mae-Wan Ho and Brett Cherry
Glyphosate tolerant (GT) crops and glyphosate herbicide (commercial formulation, Roundup) poison nitrogen fixing and other beneficial soil bacteria, increase fungal pathogens, undermine plant immunity to diseases, decrease plant micronutrients available in the soil, and more.
Research findings over the past decades paint a damning picture of the cropping system that has taken over 85 percent of the 134 million hectares of global agricultural land now growing genetically modified (GM) crops (see  Scientists Reveal Glyphosate Poisons Crops and Soil, SiS 47). The unprecedented rise in GT crops has been accompanied by a sharp increase in the use of the glyphosate herbicides worldwide, especially in the US  GM Crops Increase Herbicide Use in the United States, SiS 45).
The ecological disaster has been unfolding amid mounting evidence of the herbicide’s adverse impacts on human and animal health [3, 4] (Glyphosate Herbicide Could Cause Birth Defects, Ban Glyphosate Herbicides Now, SiS 43), and the breakdown of the Roundup Ready (RR) cropping system as weeds and superweeds become resistant to the herbicide [5, 6] (GM Crops Facing Meltdown in the USA, Glyphosate Resistance in Weeds - The Transgenic Treadmill, SiS 46) .
How glyphosate works
Glyphosate (N-(phoshonomethyl)glycine) (Figure 1) is a broad-spectrum herbicide initially patented by Monsanto in the 1970s under the trade name Roundup.
Figure 1 Glyphosate (N-(phoshonomethyl)glycine)
Glyphosate kills plants by binding to and inhibiting the enzyme 5- enolpyruvylshikimate-3-phosphate synthase (EPSPS) of the shikimate pathway for the synthesis of the aromatic amino acids, phenylalanine, tyrosine and tryptophan. These amino acids are essential building blocks for all proteins, and also precursors for growth factors and phytoalexins, compounds involved in
the plant’s defence against diseases [8, 9]. Animals do not have the shikimate pathway and depend on getting the essential amino acids from their diet.
GT plants depend on incorporating an EPSPS from the soil bacterium Agrobacterium tumefaciens (which causes crown gall disease) that is insensitive to glyphosate, and hence not killed by the herbicide.
For a long time, glyphosate has been promoted as the safest and most environmentally benign herbicide available. But glyphosate has many of the effects that act synergistically on crop health and productivity that extends well beyond the plant into the soil ecosystem and the wider environment.
The first hints of these effects came from observations that glyphosate application greatly increases the severity and incidence of plant diseases, not just in the GT crops, but also in subsequent crops grown in the same soil.
Glyphosate increases plant disease by several mechanisms that weaken the plant and its defences against disease, and at the same time boosts the virulence of pathogens and their populations in the soil. What makes glyphosate such a strong herbicide is that it is translocated throughout the plant to the growing points of shoots and roots to make the susceptible plants stop growing. In the roots, glyphosate is exuded into the rhizosphere (the soil surrounding the roots) where it exerts powerful effects on the microbial community and soil chemistry.
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