Department of Plant Sciences

A detrimental effect of glyphosate on soybean Mn nutrition has been reported, which could happen even when applying the herbicide to weeds infesting soybean crops. Three experiments were conducted to study the effect of glyphosate on Mn absorption kinetics, accumulation, distribution within the soybean plant and soybean response to Mn as affected by this herbicide. In a nutrient solution experiment, using the solution depletion technique, Mn uptake kinetics (Vmax, Km and Cmin) were determined for a conventional and its near-isogenic glyphosate-resistant counterpart cultivar as affected by glyphosate applied to the nutrient solution. In another nutrient solution experiment, differential Mn accumulation and distribution were studied for the same cultivars. In the third experiment, with Mn-deficient soil in pots, the response of glyphosate-resistant soybean cultivars to Mn application was studied in the presence of the herbicide. A few days after herbicide treatment, soybean plants developed yellowish leaves, a symptom that, in the field, could be misinterpreted as Mn deficiency. But there was no evidence of deleterious effects of glyphosate on Mn absorption, accumulation, distribution in the plant and response by soybean cultivars.