A mechanism of chlorotoluron resistance in Lolium rigidum |
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Authors: | M W M Burnet B R Loveys J A M Holtum S B Powles |
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Institution: | (1) Department of Crop Protection, Waite Agricultural Research Institute, University of Adelaide, P.O. Bag 1, 5064 Glen Osmond, SA, Australia;(2) Division of Horticulture, Commonwealth Scientific and Industrial Research Organisation, GPO Box 350, 5001 Adelaide, SA, Australia |
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Abstract: | Many biotypes of Lolium rigidum Gaud, (annual ryegrass) have developed resistance to herbicides; however, few have developed resistance to phenylurea herbicides. Two biotypes with different histories of herbicide selection pressure were six to eight times less sensitive to the phenylurea herbicide, chlorotoluron, than a susceptible biotype. Resistance was not due to differences in the herbicide target site as oxygen evolution by thylakoids isolated from resistant and susceptible biotypes was similarly inhibited by diuron and chlorotoluron. There was no difference in the uptake and distribution of chlorotoluron into resistant and susceptible plants. There was a twofold greater rate of chlorotoluron detoxification in resistant plants with N-demethylation being a major detoxification reaction. Resistant plants treated with a 3-h pulse of 120 M chlorotoluron recovered net carbon fixation after 42 h, half the time taken by susceptible plants. The mixed-function oxidase inhibitor 1-aminobenzotriazole (70 M) intensified the effects of chlorotoluron in resistant plants when applied in combination with the herbicide for 7 d. 1-Aminobenzotriazole also inhibited the metabolism of chlorotoluron in both resistant and susceptible plants. The cytochrome P-450 inhibitor, piperonyl butoxide piperonyl butoxide, interacted with chlorotoluron when applied to plants growing in soil. Chlorotoluron applied with reduced plant dry weight to a greater extent than chlorotoluron alone. It appears, therefore, that enhanced detoxification is the major mechanism of resistance to chlorotoluron in the resistant biotypes studied.Abbreviations ABT
1-aminobenzotriazole
- VLR1
Victorian L. rigidum biotype 1 — herbicide susceptible
- VLR69
Victorian L. rigidum biotype 69 — herbicide resistant
- WLR2
Western Australian L. rigidum biotype 2 — herbicide resistant
M.W.M.B, was supported by an Australian Postgraduate Research Award and a supplementary scholarship from the Grains Research and Development Corporation. We are very grateful to Dr. E. Ebert, Ciba Geigy, Basal, Switzerland for providing 14C]chlorotoluron and standards of chlorotoluron metabolites. We express our gratitude to Dr. John Huppatz of the CSIRO Division of Plant Industry for providing ABT. We also thank Ciba Geigy Australia for providing technical-grade chlorotoluron and formulated phenylurea herbicides. |
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Keywords: | 1-Aminobenzotriazole Chlorotoluron Herbicide metabolism Lolium (herbicide resistance) |
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