Accumulation of aminomethylphosphonic acid (AMPA), the main glyphosate metabolite, has been found in glyphosate-treated, glyphosate-resistant (GR) soybean, apparently due to plant glyphosate oxidoreductase (GOX). AMPA is mildly phytotoxic, and under some conditions the AMPA accumulating in GR soybean correlates with glyphosate-caused phytotoxicity. A bacterial GOX is used in GR canola, and an altered bacterial glyphosate N-acetyltransferase is planned for use in a new generation of GR crops. In some weed species, glyphosate degradation could contribute to resistance. However, a plant GOX enzyme has not yet been reported in plants. Gene amplification of plant GOX or transfer of microbial genes for glyphosate-degrading enzymes could produce GR weeds. Yet, there is no evidence that metabolic degradation plays a significant role in weed resistance to glyphosate. The lack of evidence of metabolic degradation of glyphosate as a resistance mechanism in GR weeds us puzzling, considering the tremendous selection pressure of glyphosate on weeds.

Glyphosate metabolism in glyphosate-resistant crops and weeds vs. susceptible crops and weeds

239th National Meeting (2010)

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