Co-Authors:
Yasuor, H., Weed Science Program, Department of Plant Sciences, University of California, Davis, CA 95616, United States
Osuna, M.D., Departamento de Hortofruticultura, Centro de Investigación Finca La Orden, 06781 Guadajira, Badajoz, Spain
Ortiz, A., Universidad Central de Venezuela, Estado de Aragua, Maracay, Venezuela
Saldain, N.E., Instituto Nacional de Investigacíon Agropecuaria, Treinta y Tres, Uruguay
Eckert, J.W., Weed Science Program, Department of Plant Sciences, University of California, Davis, CA 95616, United States
Fischer, A.J., Weed Science Program, Department of Plant Sciences, University of California, Davis, CA 95616, United States
Abstract:
Late watergrass [Echinochloa phyllopogon (Stapf.) Koss.] is a major weed of California rice that has evolved P450-mediated metabolic resistance to multiple herbicides. Resistant (R) populations are also poorly controlled by the recently introduced herbicide penoxsulam. Ratios (R/S) of the R to susceptible (S) GR50 (herbicide rate for 50% growth reduction) ranged from 5 to 9. Although specific acetolactate synthase (ALS) activity was 1.7 higher in R than in S plants, the enzyme in R plants was about 6 times more susceptible to the herbicide. R plants exhibited faster (2.8 times) oxidative [ 14C]- penoxsulam metabolism than S plants 24 h after treatment. Addition of malathion (P450 inhibitor) enhanced herbicide phytotoxicity and reduced penoxsulam metabolism in R plants. Tank mixtures with thiobencarb (can induce P450) antagonized penoxsulam toxicity in R plants, suggesting penoxsulam may be broken down by a thiobencarb-inducible enzyme. These results suggest E. phyllopogon resistance to penoxsulam is mostly due to enhanced herbicide metabolism, possibly via P450 monooxidation. © 2009 American Chemical Society.
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