Impacts of glyphosate-based herbicides on disease resistance and health of crops: a review

Abstract

Based on experimental data from laboratory and field, numerous authors have raised concern that exposure to glyphosate-based herbicides (GBHs) may pre-dispose crops to damage by microbial pathogens. In this review, we distinguish and evaluate two principal pathways by which GBHs may affect the susceptibility of crops to disease: pathway 1—via disruptions to rhizosphere microbial ecology, and pathway 2—via restriction of nutrients to crops. We conclude that GBHs have the potential to undermine crop health in a number of ways, including: (i) impairment of the innate physiological defences of glyphosate-sensitive (GS) cultivars by interruption of the shikimic acid pathway; (ii) impairment of physiological disease defences has also been shown to occur in some glyphosate-resistant (GR) cultivars, despite their engineered resistance to glyphosate’s primary mode of action; (iii) interference with rhizosphere microbial ecology (in particular, GBHs have the potential to enhance the population and/or virulence of some phytopathogenic microbial species in the crop rhizosphere); and finally, (iv) the as yet incompletely elucidated reduction in the uptake and utilisation of nutrient metals by crops. Future progress will best be achieved when growers, regulators and industry collaborate to develop products, practices and policies that minimise the use of herbicides as far as possible and maximise their effectiveness when used, while facilitating optimised food production and security.

Lack of effects of glyphosate and glufosinate on growth, mineral content, and yield of glyphosate- and glufosinate-resistant maize

“…Recent research has provided strong evidence that glyphosate does not cause mineral deficits, increased plant disease, or yield losses in GR soybeans (Bøhn et al 2014;Kandel et al 2015;Duke et al 2018). Despite this, concerns are still brought up regarding the effects of glyphosate on GR crops (e.g., Martinez et al 2018;Mertens et al 2018).…”

Re-registration Challenges of Glyphosate in the European Union

“…Moreover, ecotoxicological and resistance-related consequences of the extended use of glyphosate (Schütte et al, 2017) or of the use of GT GM crops (Pandolfo et al, 2018) have been emphasized, along with effects non-target terrestrial plants as well (Cederlund, 2017). As for emerging plant resistance against glyphosate, glyphosate itself and glyphosate-based herbicides have been shown to affect the disease resistance and health of plants by undermining their innate physiological defenses in mechanisms related to the mode of action of glyphosate, even in crops engineered for glyphosate-tolerance, and by interferences with the local microbial ecology in the rhizosphere (Martinez et al, 2018). The evolution of resistance was shown to occur due to gene amplification (Chen et al, 2017;Dolatabadian et al, 2017;Fernandez-Escalada et al, 2017;Han et al, 2017;Jugulam and Gill, 2018).…”

Soil microbial communities in diverse agroecosystems exposed to glyphosate

“…A review of all GR crops by Hammerschmidt [13] determined there is no conclusive evidence that glyphosate increases the susceptibility of GR crops to disease. Another review [14] challenges this conclusion. For example, several studies have observed that GR beets and soybean have increased susceptibility to pathogens when glyphosate is applied at recommended rates [14–16].…”

“…Another review [14] challenges this conclusion. For example, several studies have observed that GR beets and soybean have increased susceptibility to pathogens when glyphosate is applied at recommended rates [14–16]. One study found no effect of glyphosate on disease induction in GR beets until rates exceeded normal field application rates by one order of magnitude [17].…”