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1.
BACKGROUND: Auxinic herbicides are widely used for selective control of many broadleaf weeds, e.g. wild mustard. An auxinic‐herbicide‐resistant wild mustard biotype may offer an excellent model system to elucidate the mechanism of action of these herbicides. Classical genetic analyses demonstrate that the wild mustard auxinic herbicide resistance is determined by a single dominant gene. Availability of near‐isogenic lines (NILs) of wild mustard with auxinic herbicide resistance (R) and herbicide susceptibility (S) will help to study the fitness penalty as well as the precise characterization of this gene. RESULTS: Eight generations of backcrosses were performed, and homozygous auxinic‐herbicide‐resistant and auxinic‐herbicide‐susceptible NILs were identified from BC8F3 families. S plants produced significantly more biomass and seed compared with R plants, suggesting that wild mustard auxinic herbicide resistance may result in fitness reduction. It was also found that the serrated margin of the first true leaf was closely linked to auxinic herbicide resistance. Using the introgressed progeny, molecular markers linked to auxinic herbicide resistance were identified, and a genetic map was constructed. CONCLUSION: The fitness penalty associated with the auxinic herbicide resistance gene may explain the relatively slow occurrence and spread of auxinic‐herbicide‐resistant weeds. The detection of the closely linked markers should hasten the identification and characterization of this gene. Copyright © 2012 Society of Chemical Industry 相似文献
2.
As herbicide‐resistant weeds have spread in the agricultural fields of grain‐exporting countries, their seeds could be introduced into other countries as contaminants in imported grain. The spread of resistance genes through seed and pollen can cause significant economic loss. In order to assess the extent of the problem, we investigated the contamination by herbicide‐resistant annual ryegrass (Lolium rigidum) of wheat imported from Western Australia into Japan. Annual ryegrass seeds were recovered from wheat shipments and seed bioassays were conducted to identify resistance to the herbicides that are commonly used in Australia: diclofop‐methyl, sethoxydim, chlorsulfuron, and glyphosate. Nearly 4500 ryegrass seeds were detected in 20 kg of wheat that was imported in both 2006 and 2007. About 35% and 15% of the seeds were resistant to diclofop‐methyl, 5% and 6% were resistant to sethoxydim, and 56% and 60% were resistant to chlorsulfuron in 2006 and 2007, respectively. None was resistant to glyphosate in either year. As the contamination of crops by herbicide‐resistant weeds is probably a common phenomenon, the monitoring of incoming grain shipments is necessary to stem the further spread of herbicide‐resistant weeds into importing countries. 相似文献
3.
Repeated use of ACCase‐ and ALS‐inhibiting herbicides in northern Greece has resulted in the evolution of a population of Lolium rigidum resistant to diclofop and chlorsulfuron. The biotype from Athos was highly resistant to diclofop and also exhibited differential cross‐resistance to clodinafop, fluazifop, tralkoxydim and sethoxydim. Assay of ACCase activity confirmed that the resistant biotype was tenfold more resistant to diclofop than the susceptible biotype, suggesting that the resistance mechanism could involve an altered target site. The diclofop‐resistant biotype has also exhibited multiple resistance to chlorsulfuron and the mechanism for this is unknown. Seed‐bioassay was found to be a rapid, cheap and reliable method to identify populations of L rigidum resistant to ACCase inhibitors and chlorsulfuron. Moreover, root elongation in the seed bioassay was more sensitive to ACCase inhibitors and chlorsulfuron than shoot elongation. © 2000 Society of Chemical Industry 相似文献
4.
The expansion of atrazine‐resistant Chenopodium album (common lambsquarters) since the 1980s has forced New Zealand's maize‐growers to use an additional postemergence herbicide application. The frequent use of dicamba for this has selected for a common lambsquarters population with reduced sensitivity to dicamba. Initial greenhouse experiments with seeds that had been collected from the plants that survived field applications of dicamba showed that these plants could tolerate ≤1.2 kg ha?1, fourfold the recommended rate. These dicamba‐resistant plants were morphologically distinct from the susceptible population. The leaves of the resistant plants were less dentate and a lighter shade of green. The resistant plants were shorter, had a lower biomass and growth rate and flowered ≤19 days earlier than the susceptible plants. When grown together in various density ratios, the average biomass of both the susceptible and the resistant plants increased as the number of susceptible plants decreased in the mixture. The field experiments demonstrated that the resistant population tolerated dicamba at ≤2.4 kg ha?1, eightfold the recommended rate. Postemergence applications of bromoxynil, pyridate, nicosulfuron and mesotrione effectively controlled both populations. Nicosulfuron and mesotrione provided long‐term residual control, with nicosulfuron being more effective on the grass weeds. High rates of dicamba damaged the maize plants, resulting in an increased weed cover and reduced grain yield. The number of viable common lambsquarters seeds in the soil seed bank at the end of the growing season declined in the treatments in which common lambsquarters was controlled effectively. 相似文献
5.
An Avena sterilis biotype was found to be highly resistant to aryloxyphenoxypropionate (APP) herbicides, especially diclofop-methyl. At the enzyme level, this biotype contained a modified acetyl-coenzyme A carboxylase (ACCase) with six-fold resistance to diclofop acid. Absorption and translocation of [14C]diclofop-methyl applied to the leaf axil of the two-leaf stage plants were similar in both susceptible and resistant biotypes. However, the rate of metabolism of [14C]diclofop was increased 1·5-fold in this resistant biotype compared to the susceptible. Experiments with tetcyclacis, a cytochrome P450 monooxygenase inhibitor, indicated that inhibition of this enhanced diclofop metabolism increased diclofop-methyl phytotoxicity in this biotype. Studies with ten individual families of the resistant biotype indicated that both mechanisms of resistance, an altered target site and enhanced metabolism, are present in each individual of the population. Hence, it is likely that these two mechanisms of resistance both contribute to resistance in this biotype. © 1997 SCI. 相似文献
6.
Reliable in‐season and in‐field tools for rapidly quantifying herbicide efficacy in dicotyledonous weeds are missing. In this study, the maximum quantum efficiency of photosystem II (Fv/Fm) of susceptible and resistant Papaver rhoeas and Stellaria media populations in response to treatments with acetolactate synthase (ALS) inhibitors were examined. Seedlings (4–6 leafs) were transplanted into the field immediately after the application of the ALS inhibitors florasulam, metsulfuron‐methyl and tribenuron‐methyl. The Fv/Fm values were assessed 1–7, 9 and 14 days after treatment (DAT). Based on the Fv/Fm values of all fluorescing pixels in the images of herbicide‐treated plants, discriminant maximum‐likelihood classifiers were created. Based on this classifier, an independent set of images were classified into ‘susceptible’ or ‘resistant’ plants. The classifiers’ accuracy, false‐positive rate and false‐negative rate were calculated. The Fv/Fm values of sensitive P. rhoeas and S. media plants decreased within 3 DAT by 28–43%. The Fv/Fm values of the resistant plants of both species were 20% higher than those of the sensitive plants in all herbicide treatments. The classifier separated sensitive and resistant plants 3 DAT with accuracies of 62–100%. False‐positive and false‐negative classifications decreased with increasing DAT. We conclude that by the assessment of the Fv/Fm value in combination with the classification sensitive and resistant P. rhoeas and S. media populations could be separated 3 DAT. This technique can help to select effective control methods and speed up the monitoring process of susceptible and resistant weeds. 相似文献
7.
Weed populations with resistance to glyphosate have evolved over the last 7 years, since the discovery of the first glyphosate‐resistant populations of Lolium rigidum in Australia. Four populations of L. rigidum from cropping, horticultural and viticultural areas in New South Wales and South Australia were tested for resistance to glyphosate by dose–response experiments. All populations required considerably more glyphosate to achieve 50% control compared with a known susceptible population, indicating they were resistant to glyphosate. Translocation of glyphosate within these resistant populations was examined by following the movement of radiolabelled glyphosate applied to a mature leaf. All resistant plants translocated significantly more herbicide to the tip of the treated leaf than did susceptible plants. Susceptible plants translocated twice as much herbicide to the stem meristematic portion of the plant compared with resistant plants. These different translocation patterns suggest an association between glyphosate resistance in L. rigidum and the ability of glyphosate to accumulate in the shoot meristem. 相似文献
8.
Timely detection of herbicide resistance at an early stage of crop cultivation is essential to help farmers find alternative solutions to manage herbicide resistance in their fields. In this study, maximum quantum yield of PS II [Fv/Fm = (Fm – Fo)/Fm] was measured at the 4–5 leaf stage to discriminate between herbicide‐resistant and susceptible biotypes of Echinochloa species. The differences in Fv/Fm between herbicide‐resistant and susceptible Echinochloa spp. were consistent with the whole‐plant assay based on I50 (herbicide doses causing a 50% inhibition of Fv/Fm) and GR50 (herbicide doses causing a 50% reduction in plant fresh weight) values and R/S ratios (herbicide resistance index), regardless of the mode of action of the tested herbicides. A PS II inhibitor caused the fastest inhibition of Fv/Fm, compared with ACCase and ALS inhibitors, after herbicide treatment. The required time for discrimination between herbicide‐resistant and susceptible Echinochloa spp. was 64 h after PS II inhibitor treatment, much shorter than those of ACCase and ALS inhibitor‐treated plants, which required 168 and 192 h respectively. The leaf chlorophyll fluorescence assay provided reliable diagnostics of herbicide resistance in Echinochloa spp. with significant time savings and convenient measurement in field conditions compared with the conventional whole‐plant assay. 相似文献
9.
Lolium rigidum (annual or rigid ryegrass) is a widespread annual weed in cropping systems of southern Australia, and herbicide resistance in L. rigidum is a common problem in this region. In 2010, a random survey was conducted across the grain belt of Western Australia to determine the frequency of herbicide‐resistant L. rigidum populations and to compare this with the results of previous surveys in 1998 and 2003. During the survey, 466 cropping fields were visited, with a total of 362 L. rigidum populations collected. Screening of these populations with the herbicides commonly used for control of L. rigidum revealed that resistance to the ACCase‐ and ALS‐inhibiting herbicides was common, with 96% of populations having plants resistant to the ACCase herbicide diclofop‐methyl and 98% having plants resistant to the ALS herbicide sulfometuron. Resistance to another ACCase herbicide, clethodim, is increasing, with 65% of populations now containing resistant plants. Resistance to other herbicide modes of action was significantly lower, with 27% of populations containing plants with resistance to the pre‐emergent herbicide trifluralin, and glyphosate, atrazine and paraquat providing good control of most of the populations screened in this survey. Ninety five per cent of L. rigidum populations contained plants with resistance to at least two herbicide modes of action. These results demonstrate that resistance levels have increased dramatically for the ACCase‐ and ALS‐inhibiting herbicides since the last survey in 2003 (>95% vs. 70–90%); therefore, the use of a wide range of integrated weed management options are required to sustain these cropping systems in the future. 相似文献
10.
Michael J. Widderick Kerry L. Bell Luke R. Boucher Steven R. Walker 《Weed Biology and Management》2013,13(3):89-97
Echinochloa colona is the most common grass weed of summer fallows in the grain‐cropping systems of the subtropical region of Australia. Glyphosate is the most commonly used herbicide for summer grass control in fallows in this region. The world's first population of glyphosate‐resistant E. colona was confirmed in Australia in 2007 and, since then, >70 populations have been confirmed to be resistant in the subtropical region. The efficacy of alternative herbicides on glyphosate‐susceptible populations was evaluated in three field experiments and on both glyphosate‐susceptible and glyphosate‐resistant populations in two pot experiments. The treatments were knockdown and pre‐emergence herbicides that were applied as a single application (alone or in a mixture) or as part of a sequential application to weeds at different growth stages. Glyphosate at 720 g ai ha?1 provided good control of small glyphosate‐susceptible plants (pre‐ to early tillering), but was not always effective on larger susceptible plants. Paraquat was effective and the most reliable when applied at 500 g ai ha?1 on small plants, irrespective of the glyphosate resistance status. The sequential application of glyphosate followed by paraquat provided 96–100% control across all experiments, irrespective of the growth stage, and the addition of metolachlor and metolachlor + atrazine to glyphosate or paraquat significantly reduced subsequent emergence. Herbicide treatments have been identified that provide excellent control of small E. colona plants, irrespective of their glyphosate resistance status. These tactics of knockdown herbicides, sequential applications and pre‐emergence herbicides should be incorporated into an integrated weed management strategy in order to greatly improve E. colona control, reduce seed production by the sprayed survivors and to minimize the risk of the further development of glyphosate resistance. 相似文献
11.
JAVID GHEREKHLOO MOHAMMAD H. RASHED MOHASSEL MEHDI NASSIRI MAHALATI ESKANDAR ZAND ALI GHANBARI MARIA D. OSUNA RAFAEL DE PRADO 《Weed Biology and Management》2011,11(1):29-37
Phalaris minor (littleseed canary grass) is a major weed in wheat fields in some parts of Iran. Diclofop‐methyl, fenoxaprop‐P‐ethyl, and clodinafop‐propargyl are three acetyl coenzyme A carboxylase (ACCase)‐inhibiting herbicides that are commonly used to control this grass in wheat fields. Thirty‐four P. minor populations with suspected resistance to ACCase‐inhibiting herbicides were sampled from wheat fields in the provinces of Fars and Golestan in Iran. The dose–response assays that were conducted under controlled greenhouse conditions indicated that 14 populations were resistant to fenoxaprop‐P‐ethyl, seven populations were resistant to both fenoxaprop‐P‐ethyl and diclofop‐methyl, and three populations were resistant to fenoxaprop‐P‐ethyl, diclofop‐methyl, and clodinafop‐propargyl. These populations showed different levels of resistance to the applied herbicides, compared to the susceptible population. These results suggest that different mechanisms of resistance could be involved. The enzyme assay revealed that the existence of modified ACCase in the three most‐resistant populations (AR, MR4, and SR3) is responsible for the resistance of these populations. 相似文献
12.
The mechanisms of herbicide resistance were investigated in two diclofop-methyl-resistant Lolium spp. populations from central Italy, Roma '94 and Tuscania '97. These two populations were compared with two susceptible Italian populations (Vetralla '94, Tarquinia '97) and a resistant and a susceptible population from Australia, SLR31 and VLR1. The activity of acetyl Co-A carboxylase (ACCase) extracted from susceptible (S) or resistant (R) individuals from the Italian populations was inhibited by both aryloxyphenoxypropanoate (diclofop acid and fluazifop acid) and cyclohexanedione (sethoxydim) herbicides. Diclofop-methyl was rapidly de-esterified to diclofop acid at a similar rate in both R and S populations. In all populations, diclofop acid was subsequently degraded to other metabolites. The rate of degradation of diclofop acid was not significantly faster in R than in S populations; however, diclofop acid was degraded more completely in Roma '94 and Tuscania '97 compared with the S populations. Application of the mixed-function oxidase inhibitor 1-aminobenzotriazole (ABT) significantly enhanced diclofop-methyl toxicity towards both R populations, but not in S populations. However, enhanced herbicide metabolism does not completely account for the measured resistance level. A mechanism other than an altered ACCase and enhanced herbicide metabolism appears to be responsible for resistance to diclofop-methyl in Roma '94 and Tuscania '97. 相似文献
13.
Selection pressure effects on the proportion and movement of resistance alleles introgressed from wheat in Aegilops cylindrica 
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下载免费PDF全文 In winter wheat in the USA, Aegilops cylindrica is one of the most troublesome weeds, while the pathogen Oculimacula spp. causes foot rot disease. Imazamox‐resistant (IR) and foot rot‐resistant (FR) wheat cultivars represent effective tools to control the weed and prevent disease infection. However, resistance allele (RA) movement between wheat and A. cylindrica facilitates the introgression process under herbicide and disease selection pressure. Field experiments using IR and FR A. cylindrica plants intermixed with susceptible plants were conducted to measure the proportion of the RAs in the progeny and RA movement with and without herbicide and disease selection. Yield components of A. cylindrica plants were determined across treatments. The herbicide RA proportion in the progeny was greater when plants were treated with the herbicide imazamox in both years. Disease RA proportion was greater with disease occurrence only in one year. Herbicide RA movement from resistant to susceptible plants was greater with herbicide than without it only in one year. Plants carrying the RAs had greater total spikelet weight and 1000‐spikelet weight compared with susceptible plants with or without selection. However, susceptible plants produced more spikelets than the resistant ones in the absence of selection. If plants within an A. cylindrica population acquire the herbicide RA, its proportion will increase each generation under selection. These findings contribute to the understanding of crop allele introgression into related species and the evolution of increased weediness, with weed management implications. 相似文献
14.
Experiments evaluated the effect of glyphosate rate and Anoda cristata density, on crop and weed biomass and weed seed production in wide (70 cm) and narrow rows (35 cm) glyphosate‐resistant soyabean (Glycine max). Soyabean density was higher at 35 cm row spacing as an increase in planting rate in narrow‐row soyabean is recommended for producers in Argentina. Soyabean biomass at growth stage V4 (four nodes on the main stem with fully developed leaves beginning with the unifoliate leaves) was higher when grown on narrow than in wide‐rows but was not affected by the presence of A. cristata. At growth stage R5 (seed initiation – seed 3 mm long in a pod at one of the four uppermost nodes on the main stem, with a fully developed leaf and full canopy development), crop biomass was greater in narrow rows compared with wide rows with 12 plants m?2 of A. cristata. In narrow‐row soyabean, a single application of a reduced rate of glyphosate maintained soyabean biomass at R5 and provided excellent weed control regardless of weed density. In wide‐row soyabean control was reduced at the high weed density. Regardless of row spacing, A. cristata biomass and seed production were severely reduced by half of the recommended dose rate of glyphosate but the relationship between biomass and seed production was not altered. Glyphosate rates as low as 67.5 g a.e. ha?1 in narrow rows or 540 g a.e. ha?1 in wide rows provided excellent control of A. cristata. To minimize glyphosate use, planting narrow‐row soyabean are effective where A. cristata density is low. 相似文献
15.
The effects of a range of herbicide doses on crop:weed competition were investigated by measuring crop yield and weed seed production. Weed competitivity of wheat was greater in cv. Spark than in cv. Avalon, and decreased with increasing herbicide dose, being well described by the standard dose–response curve. A combined model was then developed by incorporating the standard dose–response curve into the rectangular hyperbola competition model to describe the effects of plant density of a model weed, Brassica napus L., and a herbicide, metsulfuron‐methyl, on crop yield and weed seed production. The model developed in this study was used to describe crop yield and weed seed production, and to estimate the herbicide dose required to restrict crop yield loss caused by weeds and weed seed production to an acceptable level. At the acceptable yield loss of 5% and the weed density of 200 B. napus plants m–2, the model recommends 0.9 g a.i. metsulfuron‐methyl ha–1 in Avalon and 2.0 g a.i. in Spark. 相似文献
16.
CHUAH TSE SENG LOW VAN LUN CHA THYE SAN ISMAIL BIN SAHID 《Weed Biology and Management》2010,10(4):229-233
Field and glasshouse studies have confirmed the presence of a glufosinate‐ and paraquat‐resistant goosegrass biotype that has infested a bitter gourd field in Air Kuning, Perak, Malaysia. Glufosinate and paraquat had been applied at least six times per year to the affected fields (originally a rubber plantation) for more than four consecutive years. Paraquat had been used since 1970 for weed control in the rubber plantation. An on‐site field trial revealed that the control of the goosegrass plants, measuring 20–35 cm in height, ranged from 20 to 35% 3 weeks after being treated with each herbicide at twice the recommended rate. Dose–response tests were conducted in the glasshouse, using seedlings at the three‐to‐four‐leaf stage that had been obtained from the plants that had received repeated exposure to these herbicides and a biotype with no history of any herbicide resistance. The comparison of the GR50 (the herbicide rate that is required to reduce the shoot fresh weight by 50%) of the seedlings indicated that the resistant biotype of goosegrass is 3.4‐fold and 3.6‐fold more resistant than the susceptible biotype following treatment with glufosinate and paraquat, respectively. This study has demonstrated the world's first field‐evolved instance of multiple resistance in goosegrass to two non‐selective herbicides, glufosinate and paraquat. 相似文献
17.
BACKGROUND: Haloxyfop‐R‐methyl is a widely used herbicide to control Poaceae weeds. Alopecurus japonicus, a widespread annual grass, can no longer be controlled by haloxyfop‐R‐methyl after continuous use of this herbicide for several years. RESULTS: Dose‐response experiments have established that the Js‐R biotype of A. japonicas has evolved resistance to aryloxyphenoxypropionates (APPs). Target‐site enzyme sensitivity experiments have established that the haloxyfop (free acid) rate causing 50% inhibition of acetyl‐CoA carboxylase (ACCase) activity (I50) for the resistant (Js‐R) biotype is 11 times higher than that for the susceptible (Js‐S) biotype. In many cases, resistance to ACCase‐inhibiting herbicides is due to a resistant ACCase enzyme. Full‐length DNA and mRNA sequences of the plastidic ACCase gene were amplified. Eight single‐nucleotide differences were detected in this region. Four of the nucleotide changes were silent mutations. However, the other four nucleotide mutations caused four amino acid substitutions, replacing Arg‐1734 with Gly, Met‐1738 with Leu, Thr‐1739 with Ser and Ile‐2041 with Asn in the R biotype respectively; the substitution at position 2041 had been reported, while the other three had not. CONCLUSION: The ACCase in the Js‐R biotype was less susceptible to haloxyfop‐R‐methyl than that in the Js‐S biotype. Moreover, the amino acid substitution of Ile‐2041 with Asn might confer resistance to haloxyfop‐R‐methyl in A. japonicas. Copyright © 2012 Society of Chemical Industry 相似文献
18.
In Argentina, Eleusine tristachya has been recently reported as a problematic weed that can occur at high densities in spring and summer in fallows and in maize and soyabean. The reason for the increase in E. tristachya populations is that once the weed is established, it is difficult to eliminate because it produces a high number of seeds and plant regrowth occurs after herbicide treatments. The aim of this study was to determine the effect of post-emergence application of herbicides (glyphosate, haloxyfop-methyl and clethodim) at the seedling, vegetative and reproductive stages on the short-term (biomass 30 days after treatment—30 DAT) and long-term (tiller number and height and seed production—regrowth at 330 DAT) control of E. tristachya selected biotypes in outdoor pot experiments. Data fitted to a log-logistic model. For all the herbicides considered, at the seedling and vegetative stages, short-term control was achieved with low ED50 and ED90 values, whereas at the reproductive stage, ED90 values were three- to sixfold (glyphosate), six- to 52-fold (haloxyfop-methyl) and five- to 13-fold (clethodim) higher. Long-term control at the recommended dose or lower was not possible at the reproductive stage as tiller regrowth and seed production occurred with all herbicides. It is advisable to control Eleusine tristachya when plants are small at the beginning of the growing season using the recommended herbicide dose. A delayed application will produce tiller regeneration the following year, and consequently, control would only be achieved applying an overdose, which can cause risks to health and the environment. We concluded that a management programme based on the combination of glyphosate with post-emergence graminicides applied at early stages will be effective to control future infestations. 相似文献
19.
Resistance to quinclorac and ALS-inhibitor herbicides in Galium spurium is conferred by two distinct genes 总被引：2，自引：0，他引：2
Classical Mendelian experiments were conducted to determine the genetics and inheritance of quinclorac and acetolactate synthase (ALS)‐inhibitor resistance in a biotype of Galium spurium. Plants were screened with the formulated product of either quinclorac or the ALS‐inhibitor, thifensulfuron, at the field dose of 125 or 6 g active ingredient (a.i.) ha?1 respectively. Segregation in the F2 generation indicated that quinclorac resistance was a single, recessive nuclear trait, based on a 1 : 3 segregation ratio [resistant : susceptible (R : S)]. Resistance to ALS inhibitors was due to a single, dominant nuclear trait, segregating in the F2 generation in a 3 : 1 ratio (R : S). The genetic models were confirmed by herbicide screens of F1 and backcrosses between the F1 and the S parent. F2 plants that survived quinclorac treatment set seed and the resulting F3 progeny were screened with either herbicide. Quinclorac‐treated F3 plants segregated in a 1 : 0 ratio (R : S), hence F2 progenitors were homozygous for quinclorac resistance. In contrast, F3 progeny segregated into three ratios: 1 : 0, 3 : 1 and 0 : 1 (R : S) in response to ALS‐inhibitor treatment. This segregation pattern indicates that their F2 parents were either homozygous or heterozygous for ALS‐inhibitor resistance. Therefore, there were clearly two distinct resistance mechanisms encoded by two genes that were not tightly linked as demonstrated by segregation patterns of the F3. 相似文献
20.
Mechanism of resistance to bensulfuron-methyl in Alisma plantago-aquatica biotypes from Portuguese rice paddy fields 总被引：1，自引：0，他引：1
Two Alisma plantago‐aquatica biotypes resistant to bensulfuron‐methyl were detected in rice paddy fields in Portugal’s Mondego (biotype T) and Tagus and Sorraia (biotype Q) River valleys. The fields had been treated with bensulfuron‐methyl‐based herbicide mixtures for 4–6 years. In order to characterize the resistant (R) biotypes, dose–response experiments, absorption and translocation assays, metabolism studies and acetolactate synthase (ALS) activity assays were performed. There were marked differences between R and susceptible (S) biotypes, with a resistance index (ED50R/S) of 500 and 6.25 for biotypes Q and T respectively. Cross‐resistance to azimsulfuron, cinosulfuron and ethoxysulfuron, but not to metsulfuron‐methyl, imazethapyr, bentazone, propanil and MCPA was demonstrated. No differences in the absorption and translocation of 14C‐bensulfuron‐methyl were found between the biotypes studied. Maximum absorption attained 1.12, 2.02 and 2.56 nmol g−1 dry weight after 96 h incubation with herbicide, for S, Q and T biotypes respectively. Most of the radioactivity taken up by the roots was translocated to shoots. Bensulfuron‐methyl metabolism in shoots was similar in all biotypes. The R biotypes displayed a higher level of ALS activity than the S biotype, both in the presence and absence of herbicide and the resistance indices (IC50R/S) were 20 197 and 10 for biotypes Q and T respectively. These data confirm for the first time that resistance to bensulfuron‐methyl in A. plantago‐aquatica is target‐site‐based. In practice, to control target site R biotypes, it would be preferable to use mixtures of ALS inhibitors with herbicides with other modes of action. 相似文献