, Volume 201, Issue 2, pp 202–208 | Cite as

Light-dependent enhanced metabolism of chlorotoluron in a substituted urea herbicide-resistant biotype ofLolium rigidum Gaud.



A population ofLolium rigidum Gaud. displays resistance to the herbicide chlorotoluron endowed by enhanced metabolism of this herbicide. The level of resistance in intact plants of this population is light dependent. Resistance is about 4-fold at 110 μ mol photons·m−2·s−1, but increases to 11-fold at 600 μ mol photons·m−2·s−1. For seedlings grown in the dark, the rate of chlorotoluron metabolism is identical between biotypes; however, seedlings of the resistant biotype grown in the light display enhanced chlorotoluron metabolism compared to the susceptible biotype. Specifically, light with blue wavelengths induces chlorotoluron metabolism in the resistant biotype. An analysis of the metabolites produced indicates that two routes of chlorotoluron metabolism occur inL. rigidum. These are characterised by initial reactions leading to ringmethyl hydroxylation orN-demethylation of the herbicide. The ring-methyl hydroxylation pathway is increased greatly in light-grown resistant seedlings compared to susceptible seedlings, whereas theN-demethylation pathway is only slightly increased. The differential induction of these two pathways in resistantL. rigidum by light suggests that enhanced activity of two different enzymes may be involved in chlorotoluron resistance.

Key words

Chlorotoluron Herbicide metabolism Lolium (herbicide resistance) 





dose giving 50% mortality


liquid scintillation spectroscopy


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Copyright information

© Springer-Verlag 1997

Authors and Affiliations

  1. 1.Co-operative Research Centre for Weed Management Systems and Department of Crop Protection, Waite CampusThe University of AdelaideGlen OsmondAustralia

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