Mechanism of Resistance to Penoxsulam in Late Watergrass [Echinochloa phyllopogon (Stapf) Koss.]

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) GR(50) (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 [(14)C]-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.

Cytochrome P450 CYP81A12 and CYP81A21 Are Associated with Resistance to Two Acetolactate Synthase Inhibitors in Echinochloa phyllopogon

“…The BSM and PX resistances were shown to be reduced by cytochrome P450 inhibitors in R plants (Osuna et al, 2002;Yasuor et al, 2009). Also, the P450 inhibitors reduced PX metabolism in R plants to the level of that in S plants (Yasuor et al, 2009). These observations suggested that nontarget site resistance mediated by enhanced activities of P450s is involved in the mechanism of BSM and PX resistance.…”

“…Sensitivity of the ALS enzyme to BSM and PX did not significantly differ between R and susceptible (S) plants (Osuna et al, 2002;Yasuor et al, 2009), and the nucleotide sequences encoding ALS were identical in the R and S lines, lacking amino acid substitutions known to confer resistance (Iwakami et al, 2012). The BSM and PX resistances were shown to be reduced by cytochrome P450 inhibitors in R plants (Osuna et al, 2002;Yasuor et al, 2009). Also, the P450 inhibitors reduced PX metabolism in R plants to the level of that in S plants (Yasuor et al, 2009).…”

“…In the late 1990s, R populations were found in the Sacramento Valley of California (Fischer et al, 2000a). R plants exhibited resistance to at least nine herbicides from seven different chemical groups: sulfonylurea, triazolopyrimidine, pyrimidinyl carboxy herbicides, aryloxyphenoxypropionate, thiocarbamate, quinclorac, and clomazone (Fischer et al, 2000b;Osuna et al, 2002;Ruiz-Santaella et al, 2006;Bakkali et al, 2007;Yasuor et al, 2009Yasuor et al, , 2010Yasuor et al, , 2012. Today, there seems to be only one herbicide left to control this weed in California (Yasuor et al, 2012).…”

“…The multiple herbicide-resistant E. phyllopogon exhibits resistance to bensulfuron-methyl (BSM), a sulfonylurea herbicide, and penoxsulam (PX), a triazolopyrimidine herbicide (Osuna et al, 2002;Yasuor et al, 2009), both of which are absorbed via roots (PX can also be absorbed via shoots) and inhibit acetolactate synthase (ALS), a key enzyme for the biosynthesis of the branched-chain amino acids Val, Leu, and Ile (Duggleby, 2005). Sensitivity of the ALS enzyme to BSM and PX did not significantly differ between R and susceptible (S) plants (Osuna et al, 2002;Yasuor et al, 2009), and the nucleotide sequences encoding ALS were identical in the R and S lines, lacking amino acid substitutions known to confer resistance (Iwakami et al, 2012).…”

Study on the molecular mechanism of non-target-site resistance in several paddy weeds

“…米国カリフォルニア州で発見された除草剤抵抗性タイヌビ エ（Echinochloa phyllopogon = E. oryzicola）は，異なる作用 機構の除草剤に抵抗性を示す多剤抵抗性型であることが知ら れていた（Fischer et al 2000;Osuna et al 2002;Ruiz-Santaella et al 2006;Bakkali et al 2007;Yasuor et al 2008Yasuor et al , 2009 …”