volunteers and pinoxaden

American sloughgrass is a troublesome annual grass weed in winter wheat field rotated with rice in China. The overreliance on acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides has resulted in resistance evolution in this weed. In this study, the cross-resistance patterns to fenoxaprop-p-ethyl, clodinafop-propargyl, fluazifop-p-butyl, haloxyfop-p-methyl, sethoxydim, clethodim and pinoxaden were established using purified plants individually homozygous for specific mutant ACCase alleles. Results indicated that 1781Leu allele endows high-level resistance to APPs, CHDs and pinoxaden while confers moderate resistance to haloxyfop-p-methyl. The 2027Cys and 2041Asn alleles endow high-level resistance to APPs and pinoxaden and lower level resistance to CHDs. The 2078Gly allele confers high-level resistance to all herbicides tested in this study, however, moderate resistance to sethoxydim. The 2096Ala very likely endows high-level resistance to fluazifop-p-butyl, haloxyfop-p-methyl and moderate resistance to sethoxydim. In addition, one undefined resistance mechanism was involved in population SD-04.

Topics: Acetyl-CoA Carboxylase; Cyclohexanones; Dose-Response Relationship, Drug; Herbicide Resistance; Herbicides; Heterocyclic Compounds, 2-Ring; Oxazoles; Plant Proteins; Poaceae; Propionates; Pyridines

Shortawn foxtail (Alopecurus aequalis) is a troublesome grass weed infesting winter wheat and oilseed rape productions in China. Fenoxaprop-p-ethyl and mesosulfuron-methyl failed to control shortawn foxtail of AHSX-1 population collected from a wheat field in Shou County, Anhui province. Molecular analyses revealed that Asp2078Gly mutation of ACCase and Trp574Leu mutation of AHAS were present in plants of the AHSX-1 population. The homozygous plants were isolated and cultured until seed maturity. Whole-plant herbicide bioassays were conducted in the greenhouse using the purified seeds of F1 generation. Dose-response experiments showed that the AHSX-1 population has evolved a very high level resistance to fenoxaprop-p-ethyl (RI = 275) and mesosulfuron-methyl (RI = 788). To determine the sensitivity to other herbicides, assays were conducted at the single recommended rate of each herbicide. Based on the results, the AHSX-1 population was considered to be highly resistant to clodinafop-propargyl, pyroxsulam and flucarbazone-sodium, moderately or highly resistant to quizalofop-p-ethyl, clethodim, sethoxydim and pinoxaden, and susceptible to isoproturon and chlorotoluron. This is the first report of Asp2078Gly mutation in shortawn foxtail and the two robust dCAPS markers designed could quickly detect Asp2078 and Trp574 mutations in ACCase and AHAS gene of shortawn foxtail, respectively.

Topics: Acetolactate Synthase; Acetyl-CoA Carboxylase; China; Cyclohexanones; Herbicide Resistance; Herbicides; Heterocyclic Compounds, 2-Ring; Mutation; Oxazoles; Propionates; Pyridines; Quinoxalines; Sulfonylurea Compounds

American sloughgrass (Beckmannia syzigachne) is a troublesome weed in winter wheat field rotated with rice in China. Fenoxaprop-p-ethyl and pinoxaden were observed failing to control American sloughgrass in the same filed in Lujiang county in 2011 and 2012, respectively. Whole-plant bioassay was conducted to determine the resistance to fenoxaprop-p-ethyl, pinoxaden and other herbicides in American sloughgrass. Dose-response experiment indicated that Lujiang population was highly resistant to fenoxaprop-p-ethyl (199.8-fold), pinoxaden (76.2-fold), clodinafop-propargyl (334.1-fold) and sethoxydim (15.9-fold); moderately resistant to clethodim (6.3-fold), susceptible to mesosulfuron-methyl, flucarbazone-sodium, pyroxsulam and isoproturon. Partial gene of CT domain was cloned and sequenced to confirm the molecular mechanism of resistance to ACCase-inhibiting herbicides. A Trp2027Cys mutation was found in Lujiang population according to the sequencing result. This mutation is the molecular mechanism of resistance to fenoxaprop-p-ethyl in Lujiang population. Furthermore the Trp2027Cys mutation very likely results in cross resistance to clodinafop-propargyl and pinoxaden in Lujiang population. 103 mutant homozygotes were detected from the 108 plants tested using a rapid dCAPS method developed in this paper. This is the first report of pinoxaden resistance and a mutation at position of 2027 for American sloughgrass.

Topics: Acetyl-CoA Carboxylase; Amino Acid Sequence; China; Cyclohexanones; Herbicide Resistance; Herbicides; Heterocyclic Compounds, 2-Ring; Lolium; Molecular Sequence Data; Mutation; Oxazoles; Propionates; Pyridines

The design of sustainable weed management strategies requires a good understanding of the mechanisms by which weeds evolve resistance to herbicides. Here we have conducted a study on the mechanism of resistance to ACCase inhibiting herbicides in a Lolium multiflorum population (RG3) from the UK.. Analysis of plant phenotypes and genotypes showed that all the RG3 plants (72%) that contained the cysteine to arginine mutation at ACCase codon position 2088 were resistant to ACCase inhibiting herbicides. Whole plant dose response tests on predetermined wild and mutant 2088 genotypes from RG3 and a standard sensitive population indicated that the C2088R mutation is the only factor conferring resistance to all ten ACCase herbicides tested. The associated resistance indices ranged from 13 for clethodim to over 358 for diclofop-methyl. Clethodim, the most potent herbicide was significantly affected even when applied on small mutant plants at the peri-emergence and one leaf stages.. This study establishes the clear and unambiguous importance of the C2088R target site mutation in conferring broad resistance to ten commonly used ACCase inhibiting herbicides. It also demonstrates that low levels "creeping", multigenic, non target site resistance, is not always selected before single gene target site resistance appears in grass weed populations subjected to herbicide selection pressure.

Topics: Acetyl-CoA Carboxylase; Arginine; Cyclohexanones; Cysteine; Genes, Plant; Genetics, Population; Genotyping Techniques; Herbicide Resistance; Herbicides; Heterocyclic Compounds, 2-Ring; Lolium; Mutation; Plant Leaves; Propionates; Pyridines; Reproducibility of Results; Seeds; Selection, Genetic