Synthetic auxin herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D), are widely used for selective control of broadleaf weeds in cereals and transgenic crops. Although the troublesome weed wild radish (Raphanus raphanistrum) has developed resistance to 2,4-D, no populations have yet displayed an enhanced capacity for metabolic detoxification of the herbicide, with both susceptible and resistant wild radish plants readily metabolizing 2,4-D. Using mass spectrometry and nuclear magnetic resonance, the major 2,4-D metabolite was identified as the glucose ester, and its structure was confirmed by synthesis. As expected, both the endogenous and synthetic compounds retained auxin activity in a bioassay. The lack of detectable 2,4-D hydroxylation in wild radish and the lability of the glucose ester suggest that metabolic 2,4-D resistance is unlikely to develop in this species.
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Authors: Danica E. Goggin, Gareth L. Nealon, Gregory R. Cawthray, Adrian Scaffidi, Mark J. Howard, Stephen B. Powles, Gavin R. Flematti