Glyphosate affects micro-organisms in rhizospheres of glyphosate-resistant soybeans

Abstract

Aims: Glyphosate‐resistant (GR) soybean production increases each year because of the efficacy of glyphosate for weed management. A new or ‘second’ generation of GR soybean (GR2) is now commercially available for farmers that is being promoted as higher yielding relative to the previous, ‘first generation’ (GR1) cultivars. Recent reports show that glyphosate affects the biology and ecology of rhizosphere micro‐organisms in GR soybean that affect yield. The objective of this research was to evaluate the microbiological interactions in the rhizospheres of GR2 and GR1 soybean and the performance of the cultivars with different rates of glyphosate applied at different growth stages. Methods and Results: A greenhouse study was conducted using GR1 and GR2 soybean cultivars grown in a silt loam soil. Glyphosate was applied at V2, V4 and V6 growth stages at three rates. Plants harvested at R1 growth stage had high root colonization by Fusarium spp.; reduced rhizosphere fluorescent pseudomonads, Mn‐reducing bacteria, and indoleacetic acid–producing rhizobacteria; and reduced shoot and root biomass. Conclusions: Glyphosate applied to GR soybean, regardless of cultivar, negatively impacts the complex interactions of microbial groups, biochemical activity and root growth that can have subsequent detrimental effects on plant growth and productivity. Significance and Impact of the Study: The information presented here will be crucial in developing strategies to overcome the potential detrimental effects of glyphosate in GR cropping systems.

Glyphosate-Induced Specific and Widespread Perturbations in the Metabolome of Soil Pseudomonas Species

“…In fact, decreased abundance in Pseudomonas spp. was found to be positively correlated with reduced populations of IAA-producing bacteria in a glyphosate-treated soil (Zobiole et al, 2011). Due to the important connection of shikimate pathway to the biosynthesis of both primary and secondary metabolites in Pseudomonas spp., elucidating the effects of glyphosate on both the initiation of this metabolic pathway as well as its associated synthesis of aromatic AAs is warranted.…”

“…Due to their production of a range of antibiotic compounds, iron-scavenging molecules (or siderophores), and plant growth promoters, several Pseudomonas species have been employed as effective biocontrol agents to protect plants against pathogens and promote plant health (Timmis, 2002). A decreased abundance in Pseudomonas species was reported in greenhouse soils wherein glyphosate was applied to soybeans in a manner similar to agricultural applications (Zobiole et al, 2011). Furthermore, a previous study revealed greater inhibition of the EPSP synthase activity in P. fluorescens AFT36 than in P. putida W1616 at the same glyphosate concentration (Schulz et al, 1985).…”

“…There have been numerous reports of adverse effects of glyphosate treatments on various microbial species and communities (Lévesque et al, 1987;Larson et al, 2006;Kremer and Means, 2009;Zobiole et al, 2011;Lane et al, 2012;Druille et al, 2013Druille et al, , 2015. Here we seek to gain insights into the intracellular targets underlying the response of soil Pseudomonas species, such as P. putida, P. fluorescens, and P. protegens, to glyphosate exposure.…”

“…and a decrease in Pseudomonas spp. (Zobiole et al, 2011). Interestingly, certain soil Pseudomonas species are known to produce pyrrolnitrin, an important potent antifungal metabolite, that requires the aromatic AA tryptophan as a metabolite precursor (Kirner et al, 1998).…”

Use of genetically modified crops and pesticides in Brazil: growing hazards

“…Several factors associated with the cultivation of herbicide-resistant GM crops may contribute to the increased use of pesticides and losses in productivity, including biological vulnerability, weed resistance, and decreased soil fertility 14,[21][22][23][24][25][26][27][28][29][30] .…”