To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Glyphosate resistance is spreading in Spain and Portugal due to excessive herbicide use, in both annual and perennial crops. Compact brome (Bromus madritensis L.) is increasing in frequency in these different cropping systems when under conservation agriculture, particularly when glyphosate fails to control it. Fourteen populations from different areas in the Iberian Peninsula were confirmed as being B. madritensis using simple sequence repeat markers and clearly separated from the closely related species red brome (Bromus rubens L.) and ripgut brome (Bromus diandrus Roth). Six B. madritensis populations were classified as resistant, according to both their shikimic acid accumulation levels and their resistance factors based on LD50 or GR50 (values between 4 and 8). Populations with higher resistance factors also showed lower shikimic acid concentrations. Moreover, these resistant populations were able to survive the minimum registered dose for glyphosate in Spain in perennial crops (1,080 g ae ha−1, five populations) or in arable crops before seeding for annual weeds (540 g ae ha−1, one population), under both greenhouse and field conditions. The trials carried out in a glyphosate-resistant field during 2 consecutive years showed that acceptable control (≥90%) was only consistently achieved 90 d after application for preemergence treatment with flazasulfuron in a tank mix with glyphosate, while control with postemergence treatments, such as propaquizafop plus glyphosate, was below 80%. This research describes the first herbicide-resistance report for the weed species B. madritensis, confirming the presence of glyphosate-resistant populations mainly in perennial cropping systems but also in winter cereals from Spain. Due to the limited chemical tools to manage these populations, there is an urgent need for farmers to implement integrated weed management strategies.
The experiments reported in this Research Communication aimed to determine if a domestic strip test to detect ethanol residues in breast milk (Milkscreen®) is comparable to a previously established official method for detecting ethanol residues in milk. The two methods are examined in terms of overall sensitivity, robustness against storage and acidity and selectivity against formaldehyde residues. Here, Milkscreen® provided advantages, with faster results (2 min), good sensitivity (≥0.017%), no false results due formaldehyde residues and equal robustness against storage, but with lower sensitivity in acid milk samples. In summary, strip tests for the rapid detection of ethanol residues in breast milk can be used for screening purposes by dairy manufacturers, combining it with the official method to make a final diagnosis.
Wild mustard (Sinapis arvensis L.) is a weed that frequently infests winter wheat (Triticum aestivum L.) fields in Golestan province, Iran. Tribenuron-methyl (TM) has been used recurrently to control this species, thus selecting for resistant S. arvensis populations. The objectives were: (1) to determine the resistance level to TM of 14 putatively resistant (PR) S. arvensis populations, collected from winter wheat fields in Golestan province, Iran, in comparison to one susceptible (S) population; and (2) to characterize the resistance mechanisms and the potential evolution of cross-resistance to other classes of acetolactate synthase (ALS)-inhibiting herbicides in three populations (AL-3, G-5, and Ag-Sr) confirmed as being resistant (R) to TM. The TM doses required to reduce the dry weight of the PR populations by 50% were between 2.2 and 16.8 times higher than those needed for S plants. The ALS enzyme activity assays revealed that the AL-3, G-5, and Ag-Sr populations evolved cross-resistance to the candidate ALS-inhibiting herbicides from the sulfonylureas (SU), triazolopyrimidines (TP), pyrimidinyl-thiobenzoates (PTB), sulfonyl-aminocarbonyl-triazolinone (SCT), and imidazolinones (IMI) classes. No differences in absorption, translocation, or metabolism of [14C]TM between R and S plants were observed, suggesting that these non-target mechanisms were not responsible for the resistance. The ALS gene of the R populations contained the Trp-574-Leu mutation, conferring cross-resistance to the SU, SCT, PTB, TP, and IMI classes. The Trp-574-Leu mutation in the ALS gene conferred cross-resistance to ALS-inhibiting herbicides in S. arvensis from winter wheat fields in Golestan province. This is the first TM resistance case confirmed in this species in Iran.
Five rigid ryegrass populations suspected of being resistant to both glyphosate and oxyfluorfen were collected in southern Spain and tested under laboratory-controlled conditions. Four populations (Depuradora, Condado, AlamoRasilla, and Portichuelo) were treated with glyphosate for at least 15 consecutive years, and treatments during the last 5 yr were mixed with oxyfluorfen. The fifth population (4alamos) followed the same glyphosate treatment, although oxyfluorfen was never used to control it. Dose–response assays confirmed glyphosate resistance in all populations, with resistance indexes ranging from 11.7 to 37.5 (GR90). Shikimate accumulation assays consistently supported these data, as the most glyphosate-resistant populations (Depuradora and Condado) displayed the lowest shikimate levels. Surprisingly, four populations (Depuradora, Condado, AlamoRasilla, and Portichuelo) displayed 7.93- to 70.18-fold more resistance (GR90) to oxyfluorfen, despite limited selection pressure, showing a similar resistance pattern as that for glyphosate. The 4alamos population displayed oxyfluorfen GR90 values that were similar to those observed in susceptible plants; however, this population was significantly more resistant in terms of plant survival (LD90). Protoporphyrin IX accumulation assays supported the results of dose–response assays, in that the most oxyfluorfen-resistant populations accumulated less protoporphyrin IX. Although more studies are needed, it seems that these five glyphosate-resistant weed populations display a natural tendency to easily develop resistance to oxyfluorfen, with the populations that have higher resistance to glyphosate also having higher resistance to oxyfluorfen.
Some species of the genus Echinochloa are troublesome weeds in rice fields. The taxonomy of this genus leads to confusion in many cases due to its great morphological diversity. Because of the differential sensitivity to the herbicide quinclorac shown by Echinochloa spp., it was necessary to assess the botanical and molecular characterization of this weed. Echinochloa colonum, E. oryzoides, and E. oryzicola were very susceptible to quinclorac treatment; by contrast, E. crus-galli and E. hispidula showed some degree of natural tolerance. Physiological and molecular results agreed with the botanical classification of the genus Echinochloa in Flora Europea. The importance of these results is due to yield losses produced by the infestation of Echinochloa and the need for a strategy for Echinochloa management depending on the distribution of the Echinochloa species.
The effect of chlorotoluron on different slender foxtail populations that survived normal agricultural rates of this herbicide (2.5 to 3.5 kg ai ha–1) was investigated under controlled laboratory conditions. Among five populations tested, two had tolerance for the herbicide. The ED50 values for these biotypes ranged from 0.33 to 2.43 kg ha–1. Assays with radiolabeled 14C-chlorotoluron indicated similar absorption and translocation of the herbicide between susceptible and resistant biotypes. Chlorophyll fluorescence and Hill reaction analysis seem to support the view that the mechanism of resistance of one biotype to the herbicide is due to degradation/detoxification rather than to modification of the target site, although compartmentation processes cannot be ruled out. This resistant biotype had high tolerance to other photosynthetic inhibiting phenylureas, including linuron, chlorbromuron, diuron, monolinuron, and neburon.
Triazine-resistant (R) biotypes of common lambsquarters, yellow foxtail, and hairy fleabane were found in the Province of Córdoba (Andalusia, Southern Spain). The former two R biotypes came from atrazine-treated cornfields, whereas the latter came from simazine-treated nontilled olive orchards. The R biotypes of common lambsquarters and yellow foxtail and the R biotype of hairy fleabane survived at doses up to 5 kg ai/ha of soil-applied atrazine or simazine, respectively. Photosynthetic electron transport in R biotypes was unaffected by atrazine and simazine but was inhibited by diuron, as shown by fluorescence induction measurements in whole leaves. In Hill reaction assays, the R biotypes showed high resistance to atrazine and simazine (resistance factors in the range of 350 to 550), medium to high resistance to ametryn, terbumeton, metribuzin, and monolinuron (resistance factors in the range of 80 to 250), slight resistance to diuron and methabenzthiazuron (resistance factors in the range of 1.1 to 15.7), and reverse resistance to swep, ioxynil, and DNOC (resistance factors less than 1). It is concluded that the R biotypes have a chloroplast mode of resistance similar to that previously described for other triazine-resistant weed biotypes.
Biotypes of smallflower umbrella sedge and ricefield bulrush resistant to acetolactate synthase (ALS)-inhibiting herbicides have been reported in several rice areas of the world. Here, we present results of a study conducted on whole plants of seven smallflower umbrella sedge and four ricefield bulrush biotypes collected in Italian, Spanish, and Californian rice fields to evaluate cross-resistance to ALS herbicides in these important weeds of temperate rice. The following herbicides were tested: bensulfuron-methyl, halosulfuron, cinosulfuron, imazamox, and bispyribac-sodium. The smallflower umbrella sedge and ricefield bulrush biotypes studied exhibited different cross-resistance patterns, some of which have not been previously reported. The Italian smallflower umbrella sedge biotype was cross-resistant to bensulfuron-methyl, cinosulfuron, imazamox, and bispyribac-sodium, but was susceptible to halosulfuron. One smallflower umbrella sedge biotype from California was also resistant to bensulfuron-methyl, imazamox, and bispyribac-sodium, but had a lower level of resistance to halosulfuron. In contrast, the second smallflower umbrella sedge biotype from California was strongly resistant to halosulfuron and was also resistant to bensulfuron-methyl and bispyribac-sodium, but moderately resistant to imazamox. The Spanish smallflower biotype was resistant to the sulfonylurea herbicides bensulfuron-methyl and halosulfuron. Different responses were observed in ricefield bulrush. The Italian biotype was resistant to the sulfonylureas only, whereas the biotype from California exhibited broad cross-resistance to all the ALS herbicides tested. Knowledge on cross-resistance is needed to formulate herbicide use and weed management strategies for delaying the evolution of resistance to ALS herbicides in rice systems.
Glyphosate behavior was examined in Italian ryegrass plants from Chile that were sensitive (S) and resistant (R) to this herbicide. In order to explain the resistance to glyphosate, contact angles, spray retention, foliar uptake, herbicide translocation, and target enzyme activity were studied. Contact angles of glyphosate solutions at a field concentration were 40° to 45° on the abaxial surface of R leaves as compared to 70° on S. Glyphosate spray retention by R plants was 35% lower than by S plants. Glyphosate uptake by the abaxial leaf surface of R plants was about 40% lower than that of S plants. In addition, in the R plants more glyphosate migrated to the tip of the treated leaves. The target enzyme in R and S plants was sensitive to the herbicide. Based on these and previous results, it is concluded that resistance in this Italian ryegrass biotype results from lower spray retention, lower foliar uptake from the abaxial leaf surface, and altered translocation pattern. The decreases in spray retention and foliar uptake constitute new mechanisms of glyphosate resistance.
In Europe, 18 weedy grass species had been confirmed to have biotypes with resistance to herbicides. The most frequent is that of atrazine resistance, with nine resistant biotypes found. These biotypes are mainly resistant because of changes in the D1 protein of photosystem II. All atrazine-resistant biotypes, except that of bristly foxtail, show cross-resistance to s-triazine and as-triazines. From an agriculture point of view, the most important cases of resistance are those found in blackgrass, wild oat, Italian ryegrass, rigid ryegrass, and barnyardgrass. In these species, cross- and multiple resistances were observed due to metabolism or changes in the target protein by genetic mutations or both. These biotypes are extremely difficult to control with alternative herbicides.
Littleseed canarygrass is a troublesome grass weed in wheat fields in Iran.
Predicting weed emergence dynamics can help farmers more effectively control
weeds. In this work, four nonlinear regression models (beta, three-piece
segmented, two-piece segmented, and modified Malo's exponential sine) were
compared to describe the cardinal temperatures for the germination of
littleseed canarygrass. Two replicated experiments were performed with the
same temperatures. An iterative optimization method was used to calibrate
the models and different statistical indices (mean absolute error [MAE],
coefficient of determination [R2], intercept and slope of the regression equation of predicted
vs. observed hours to germination) were applied to compare their
performance. The three-piece segmented model was the best model to predict
the germination rate (R2 = 0.99, MAE = 0.20 d, and coefficient of variation 1.01 to
4.06%). Based on the model outputs, the base, the lower optimum, the upper
optimum, and the maximum temperatures for the germination of littleseed
canarygrass were estimated to be 4.69, 22.60, 29.62, and 38.13 C,
respectively. The thermal time required to reach 10, 50, and 90% germination
was 31.98, 39.26 and 45.55 degree-days, respectively. The cardinal
temperatures depended on the model used for their estimation. Overall, the
three-piece segmented model was better suited than the other models to
estimate the cardinal temperatures for the germination of littleseed
A Lolium multiflorum Lam. biotype resistant to diclofop-methyl was found in a Triticum aestivum field in France (Normandy) that had been treated for several years with diclofop-methyl. Based on plant survival evaluated 21 d after herbicide application, the biotype exhibited a high level of resistance to diclofop-methyl and moderate resistance to CGA-184927-propargil and PP-604. The resistant biotype exhibited a small increase in tolerance to haloxyfop-methyl, quizalofop-ethyl, sethoxydim, and BAS-517-H, but was controlled by recommended field rates for these herbicides. The mechanism of resistance was investigated for diclofop-methyl. There was little or no difference in diclofop-methyl absorption by leaves of resistant and susceptible biotypes measured 48 h after treatment. For both biotypes, less than 1% of absorbed radiolabel was translocated during 48 h following foliar application of 14C-diclofop-methyl. Metabolism of diclofop-methyl was not significantly altered in the resistant biotype. In both biotypes, diclofop-methyl was rapidly metabolized to diclofop acid followed by a slow rate of formation of a polar conjugate. Two multifunctional acetyl coenzyme A carboxylase isoforms (ACCase I and ACCase II) were isolated from leaf tissue of resistant and susceptible biotypes. Both isoforms exhibited a subunit molecular mass of 203 kDa. For both resistant and susceptible biotypes, ACCase I constituted approximately 80% of total ACCase activity. Graminicide concentrations required to inhibit ACCase activity by 50% (I50 values) were determined for both ACCase isoforms from resistant and susceptible biotypes. The ACCase II isoform was highly resistant to graminicides in both biotypes. In contrast, the I50 value for diclofop inhibition of ACCase I was 19-fold greater for the enzyme isolated from the resistant biotype compared with the susceptible biotype. It is concluded that diclofop resistance in the L. multiflorum biotype from Normandy is caused by the presence of a resistant form of the ACCase I isoform.
A set of universal and degenerate primers has been designed to clone (by polymerase chain reaction [PCR]) the conserved domains of the acetolactate synthase (ALS) gene where mutations confer resistance to ALS herbicides in plants. These primers were successful in cloning conserved domains of ALS in all monocotyledonous and dicotyledonous plants tested to date, as well as that of bacteria. Total genomic DNA was used as the source of target DNA because no introns were found in the sequences to be amplified. The design of the universal primers was performed after subtle modifications of the consensus degenerate hybrid oligonucleotide primers approach, which implies the synthesis of hybrid oligonucleotide primers containing fixed clamp 5′ and degenerate core 3′ sequences. Optimizations of PCR reactions were done according to a Taguchy approach described for the first time with degenerate oligonucleotides. This method optimizes a PCR reaction using four variables (deoxynucleoside triphosphate, DNA, primers, and Mg2+) under three different concentrations per variable using just nine reactions. The ALS herbicide-binding domains from many susceptible and resistant plants can be cloned and sequenced in a few hours by using only 100 mg of starting plant material, like one leaf or several small seedlings or seeds.
Tribenuron-methyl has been used widely for the last 15 yr to control white mustard in cereal crops from southern Spain. Since 2007, several cases of tribenuron-methyl resistance have been reported in wheat fields. Greenhouse and laboratory studies were conducted to characterize the mechanism of suspected tribenuron-methyl resistance in a white mustard biotype (hereafter AR16) from Malaga (southern Spain). Under greenhouse conditions, the dose (g ai ha−1) inhibiting fresh weight by 50% (ED50) was 5.20 and 0.57 for the AR16 and AR3 (known susceptible) biotypes, respectively. With the use of 14C-tribenuron-methyl, absorption and translocation from treated leaves were similar between biotypes. Thin-layer chromatography indicated foliar metabolism of tribenuron-methyl was low in both R and S biotypes. Assays on the binding affinity of tribenuron-methyl on acetolactate synthase (ALS) revealed enzyme activity was reduced by 50% (I50 value) at 638.7 and 0.23 nM for the AR16 and AR3 biotypes, respectively. This resulted in 2,777-fold greater resistance to tribenuron-methyl for the AR16 compared to AR3 biotype. Sequencing the gene encoding ALS, a proline/serine amino-acid substitution, was detected in position 197 of the A domain. Based on these results, it is concluded that tribenuron-methyl resistance in the AR16 biotype is due to a target-site mutation in the ALS enzyme, resulting in a lack of affinity to tribenuron-methyl.
A biotype of green foxtail found in Spain exhibited cross-resistance among acetyl-CoA carboxylase (ACCase)–inhibiting herbicides. Field doses that totally inhibited shoot fresh weight in the susceptible (S) biotype were determined for six aryloxyphenoxypropionates (clodinafop, diclofop, fenoxaprop-P, fluazifop-P, haloxyfop-P, and propaquizafop) and six cyclohexanediones (clefoxydim, clethodim, cycloxydim, sethoxydim, tepraloxydim, and tralkoxydim). The resistant (R) biotype showed cross-resistance to all herbicides except fenoxaprop-P, propaquizafop, clefoxydim, and tepraloxydim. There were no differences in the absorption, translocation, and metabolism of [14C]diclofop between the S and R biotypes. On the basis of herbicide dose that inhibited ACCase activity by 50% (I50 values), ACCase of the R biotype was 5.8-, 13.9-, 20.0-, 102.4-, 416.7-, and 625.0-fold less sensitive to clethodim, haloxyfop, diclofop, fluazifop, cycloxydim, and sethoxydim, respectively, than that of the S biotype. Two multifunctional ACCase isoforms (ACCase I and ACCase II) were purified partially and separated. ACCase II was highly resistant to diclofop acid in both biotypes, with I50 values ranging between 92 and 95 μM. However, the I50 values observed for ACCase I revealed that the R biotype was 30.8-fold less sensitive to diclofop than the S biotype. These results suggest the mechanism of resistance in green foxtail to diclofop relates to an altered ACCase I isoform.
Continuous use of herbicides has triggered a phenomenon called herbicide resistance. Nowadays, herbicide resistance is a worldwide problem that threatens sustainable agriculture. A study of over a decade on herbicides in Iran has revealed that herbicide resistance has been occurring since 2004 in some weed species. Almost all the results of these studies have been published in national scientific journals and in conference proceedings on the subject. In the current review, studies on herbicide resistance in Iran were included to provide a perspective of developing weed resistance to herbicides for international scientists. More than 70% of arable land in Iran is given over to cultivation of wheat, barley, and rice; wheat alone covers nearly 52%. Within the past 40 years, 108 herbicides from different groups of modes of action have been registered in Iran, of which 28 are for the selective control of weeds in wheat and barley. Major resistance to ACCase-inhibiting herbicides has been shown in some weed species, such as winter wild oat, wild oat, littleseed canarygrass, hood canarygrass, and rigid ryegrass. With respect to the broad area of wheat crop production and continuous use of herbicides with the sole mechanism of action of ACCase inhibition, the provinces of West Azerbaijan, Tehran, Khorasan, Isfahan, Markazi, and Semnan are at risk of resistance development. In addition, because of continuous long-term use of tribenuron-methyl, resistance in broadleaf species is also being developed. Evidence has recently shown resistance of turnipweed and wild mustard populations to this herbicide. Stable monitoring of fields in doubtful areas and providing good education and training for technicians and farmers to practice integrated methods would help to prevent or delay the development of resistance to herbicides.
The susceptibility to glyphosate and genetic diversity based on intersimple sequence repeat markers were characterized for 17 tropical sprangletop populations collected from two separate regions mainly in Persian lime groves in Veracruz, Mexico. The whole-plant dose response together with shikimic acid assays indicated different levels of glyphosate resistance in those populations. Genetic diversity values (h) estimated using POPGENE ranged from 0.119 to 0.198 and 0.117 to 0.214 within susceptible and resistant populations, respectively. The average genetic diversity (HS) within the susceptible populations was 0.157, and the total genetic diversity (HT) was 0.218. The HS of the resistant populations was 0.144, and the HT was 0.186. The analysis of molecular variance based on the response to glyphosate indicated that most of the genetic variation was found within groups of susceptible and resistant populations (90% of the genetic variation), whereas 10% or less was among groups. The high level of genetic diversity between glyphosate-resistant tropical sprangletop populations from distant and adjacent locations is likely due to both short- and long-distance seed dispersal and independent evolutionary events in tropical sprangletop populations among Persian lime groves in Veracruz.
Sourgrass is a perennial weed infesting annual and perennial crops in Brazil. Three biotypes (R1, R2, and R3) of sourgrass suspected to be glyphosate-resistant (R) and another one (S) from a natural area without glyphosate application, in Brazil, were tested for resistance to glyphosate based on screening, dose-response, and shikimic acid assays. Both screening and dose-response assays confirmed glyphosate resistance in the three sourgrass biotypes. Dose-response assay indicated a resistance factor of 2.3 for biotype R1 and 3.9 for biotypes R2 and R3. The hypothesis of a glyphosate resistance was corroborated on the basis of shikimic acid accumulation, where the S biotype accumulated 3.3, 5.0, and 5.7 times more shikimic acid than biotypes R1, R2, and R3, respectively, 168 h after treatment with 157.50 g ae ha−1 of glyphosate. There were no differences in contact angle of spray droplets on leaves and spray retention, indicating that differential capture of herbicide by leaves was not responsible for resistance in these biotypes. The results confirmed resistance of sourgrass to glyphosate in Brazil.
A downy brome population in a winter wheat field at Córdoba, Spain, survived use rates of chlortoluron (2.5 to 3.5 kg ai ha−1) over 2 consecutive yr, where wheat monoculture and multiple annual chlortoluron applications had been carried out. The resistant (CR) biotype showed a higher ED50 value (7.4 kg ai ha−1; the concentration required for 50% reduction of fresh weight) than the susceptible (S) control (2.2 kg ai ha−1), with a 3.4-fold increase in chlortoluron tolerance. Chlortoluron resistance in the CR downy brome biotype was not caused by altered absorption, translocation, or modification of the herbicide target site but by enhanced detoxification. The inhibition of both the recovery of photosynthetic electron transport and chlortoluron metabolism in the CR biotype due to the presence of the Cyt P450 inhibitor 1-aminobenzotriazole (ABT) indicates that herbicide metabolism catalyzed by Cyt P450 monooxygenases is related to chlortoluron resistance in CR plants. Although both biotypes degraded chlortoluron by N-dealkylation and ring-methyl hydroxylation and seem to share the same ability to form polar conjugates, degradation in the resistant biotype is more efficacious as this biotype metabolizes the parent herbicide faster and to a greater extent than its susceptible counterpart. The ability of the susceptible biotype to ring-hydroxylate chlortoluron, albeit at much slower rate, probably explains its moderate tolerance to chlortoluron observed in the growth assays and its minor photosynthetic electron transport recovery observed in fluorescence measurements.
Field, greenhouse, and laboratory experiments were conducted to investigate resistance to glyphosate in tropical sprangletop biotypes (Lv8 and Lv9) collected in Persian lime from Veracruz, Mexico. Assays to determine the dose required to reduce seedling fresh weight by 50% indicated a resistance factor (RF) of 4.9 and 3.2 for biotypes Lv8 and Lv9, respectively; whereas the LD50 showed a RF of 4.4 and 3.3 for biotypes Lv8 and Lv9, respectively. On the other hand, the RFs using whole plant dose–response assays were lower (RF of 3 for Lv8 and 2.3 for Lv9). The susceptible biotype (LvS) accumulated 5.5 and 11.8 times more shikimate than biotypes Lv8 and Lv9, respectively, at 96 h after treatment (HAT). In field experiments, alternatives to glyphosate-resistant tropical sprangletop management were identified. Indaziflam + glufosinate and paraquat + diuron provided over 80% control of in-field populations of tropical sprangletop at 60 d after treatment (DAT). These results confirmed the first reported case of glyphosate-resistant tropical sprangletop.