Abstract
Glyphosate-resistant (GR) soybean is widely used in agriculture, however, plants exposed to herbicide show physiological changes. This study investigated the effect of treatments with glyphosate on the metabolism of N compounds, crop yield and physiological quality of seeds in GR soybean. The plants were grown in field experiment, located in the city of Selvíria, MS, Brazil. Glyphosate was applied postemergence at V4 crop stage in a dose-response, including four rates (0; 360; 720 and 1440 g e. a. ha-1) with four replicates. Crop yield, physiological and biochemical features were determined. The results revealed previously unreported stimulant effects of glyphosate on GR soybean plants. Glyphosate changed the ureide shape in leaves, but did not change the concentration of total ureides, indicating maintenance of biological nitrogen fixation in plants exposed to herbicide. Amino acids concentration increased in plants submitted to higher doses. GR soybean showed higher crop yield and seed vigor with increased glyphosate doses. The results of this study indicate that glyphosate does not cause stress to the plant; however, it modulates a distinct response in plant development due to the protective gene inserted. This study can serve as a matrix for additional studies in order to seek clarification of responses of resistant/tolerant plants to glyphosate.
Highlights
Soybean (Glycine max (L.) Merrill) stand out as one of the world’s main commodities, with the United States being the largest producer nations, followed by Brazil and Argentina (Krenchinsk et al, 2017)
The gene inserted is from the soil bacterium Agrobacterium tumefaciens strain CP4, which encodes a variant enzyme of EPSPs, CP4-EPSPs, conferring GR soybean resistance to glyphosate (Franz et al, 1997)
Glyphosate did not alter the concentration of total protein, total ureides, allantoin and soluble ammonia in the leaves in any of the treatments used in GR soybeans (p > 0.05) (Table 1)
Summary
Soybean (Glycine max (L.) Merrill) stand out as one of the world’s main commodities, with the United States being the largest producer nations, followed by Brazil and Argentina (Krenchinsk et al, 2017). Soybean cultivars with the Roundup Ready® gene was developed through genetic engineering, aiming at improvements in integrated management of weeds. After spraying crop with the herbicide, only the weeds are affected, while the lethal effect is absent in GR soybean. The gene inserted is from the soil bacterium Agrobacterium tumefaciens strain CP4, which encodes a variant enzyme of EPSPs, CP4-EPSPs, conferring GR soybean resistance to glyphosate (Franz et al, 1997). GR soybean displays distinct resistance to glyphosate, little is known about its effect on physiological processes and plant development, since that there are other modes of action of glyphosate, specific inhibition of EPSPs (Franz et al, 1997; Reddy et al, 2004). In some non-transgenic plants subjected to low glyphosate doses, the stimulant effect is frequently observed (Cedergreen, 2008; Dalley & Richard, 2010)
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