How glyphosate affects plant disease development: it is more than enhanced susceptibility

Abstract

Glyphosate has been shown to affect the development of plant disease in several ways. Plants utilize phenolic and other shikimic acid pathway-derived compounds as part of their defense against pathogens, and glyphosate inhibits the biosynthesis of these compounds via its mode of action. Several studies have shown a correlation between enhanced disease and suppression of phenolic compound production after glyphosate. Glyphosate-resistant crop plants have also been studied for changes in resistance as a result of carrying the glyphosate resistance trait. The evidence indicates that neither the resistance trait nor application of glyphosate to glyphosate-resistant plants increases susceptibility to disease. The only exceptions to this are cases where glyphosate has been shown to reduce rust diseases on glyphosate-resistant crops, supporting a fungicidal role for this chemical. Finally, glyphosate treatment of weeds or volunteer crops can cause a temporary increase in soil-borne pathogens that may result in disease development if crops are planted too soon after glyphosate application. © 2017 Society of Chemical Industry.

The history and current status of glyphosate

“…The most publicized claims of problems with GRCs have centered around plant disease, mineral nutrition, yields, and glyphosate toxicology. Two of these topics, mineral nutrition and plant disease as affected by glyphosate, are dealt with in other papers in this special issue of Pest Management Science . Briefly, despite a few highly publicized papers indicating that glyphosate alters plant mineral nutrition in GRCs and that this and other GRC characteristics result in increased fungal pathogen infestation of GRCs, the preponderance of peer‐reviewed literature does not support these theories …”

“…Two of these topics, mineral nutrition and plant disease as affected by glyphosate, are dealt with in other papers in this special issue of Pest Management Science. 34,35 Briefly, despite a few highly publicized papers indicating that glyphosate alters plant mineral nutrition in GRCs and that this and other GRC characteristics result in increased fungal pathogen infestation of GRCs, the preponderance of peer-reviewed literature does not support these theories. [34][35][36] Another issue has been whether there is a yield reduction in GRCs attributable to either the GR transgene(s) used or to glyphosate.…”

“…34,35 Briefly, despite a few highly publicized papers indicating that glyphosate alters plant mineral nutrition in GRCs and that this and other GRC characteristics result in increased fungal pathogen infestation of GRCs, the preponderance of peer-reviewed literature does not support these theories. [34][35][36] Another issue has been whether there is a yield reduction in GRCs attributable to either the GR transgene(s) used or to glyphosate. Some of the early GRC cultivars did not have the more elite germplasms for yield, and in at least GR cotton, the gene for resistance was not expressed highly enough in reproductive tissues to always prevent crop damage from glyphosate in the field.…”

Mechanisms of glyphosate resistance and response to alternative herbicide‐based management in populations of the three Conyza species introduced in southern Spain

“…Glyphosate inhibits the enzyme 5‐enolpyruvlshikimate‐3‐phosphate synthase (EPSPS), which catalyzes the reaction of shikimate‐3‐phosphate (S3P) and phosphoenolpyruvate to form 5‐enolpyruvil‐shikimate‐3‐phosphate (ESP). Inhibition of EPSPS prevents the biosynthesis of aromatic amino acids and thus is highly lethal to sensitive plants …”

“…Inhibition of EPSPS prevents the biosynthesis of aromatic amino acids and thus is highly lethal to sensitive plants. 3 The application of glyphosate, for over four decades as a non-selective herbicide in crop and non-crop situations, has resulted in resistance to this herbicide in populations of three widespread species of the genus Conyza (Asteraceae): Conyza bonariensis, Conyza canadensis and Conyza sumatrensis. 4,5 These three major species of Conyza are native to America, and are considered highly invasive species.…”