02075naa a2200289 a 450000100080000000500110000800800410001902200140006002400270007410000150010124501250011626000090024150001710025052011040042165000100152565000190153565000280155465000120158265000150159465000150160970000160162470000140164070000170165470000170167170000160168877300810170410502502019-10-11       2009    bl uuuu     u00u1 u    #d  a0021-85617 a10.1021/jf80399992DOI1 aYASOUR, H.  aMechanism of resistance to penoxsulam in late watergrass [Echinochloa phyllopogon (stapf) koss.].h[electronic resource]  c2009  aArticle history: Received for Review December 23, 2008 // Accepted March 11, 2009 // Revised manuscript received March 9, 2009. DOI: https://doi.org/10.1021/jf8039999  aAbstract 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.  aARROZ  aARROZ IRRIGADO  aECHINOCHLOA PHYLLOPOGON  aESCARDA  aHERBICIDAS  aPENOXSULAN1 aOSUNA, M.D.1 aORTIZ, A.1 aECKERT, J.W.1 aFISHER, A.J.1 aSALDAIN, N.  tJournal of Agricultural and Food Chemistry, 2009gv. 57. n. 9, p. 3653-3660.