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1.
Ryegrass (Lolium multiflorum Lam.) is one of the most difficult annual weeds to control in cultivation systems worldwide, especially in temperate regions. The widespread use of herbicides in the past two decades has selected resistant biotypes of ryegrass in crops in Southern Brazil. Ryegrass seeds are dormant when disseminated and germination can be staggered over time (crop‐growing season). Knowledge of the germination behavior of seeds from herbicide‐resistant plants has been little studied, but it would be very useful in integrated weed management. Thus, this study aimed to characterize the dynamics of the soil seed bank of two biotypes of L. multiflorum, one glyphosate‐resistant and the other glyphosate‐susceptible, under a no‐tillage system. The treatments were arranged in a bifactorial scheme, using seeds from biotypes (glyphosate‐resistant and glyphosate‐susceptible) with monthly periods of removal from field (one to 12 months). Seeds of each biotype were placed on the soil surface and covered with soil and straw to simulate no‐till conditions. The percentage of germinated, dormant, and dead seeds was evaluated every 30 days. The ryegrass seed bank of glyphosate‐susceptible and glyphosate‐resistant biotypes was reduced to 11 and 15% of dormant seeds, respectively, at the end of 12 months. However, there was no variation in germination, dormancy, and seed mortality between susceptible and glyphosate‐resistant ryegrass. Seeds of glyphosate‐resistant biotype and susceptible showed germination behavior with similar dynamics in the soil over a period of 12 months.  相似文献   

2.
Glyphosate is one of the most commonly used broad‐spectrum herbicides over the last 40 years. Due to the widespread adoption of glyphosate‐resistant (GR) crop technology, especially corn, cotton and soybean, several weed species have evolved resistance to this herbicide. Research was conducted to confirm and characterize the magnitude and mechanism of glyphosate resistance in two GR common ragweed ( A mbrosia artemisiifolia L.) biotypes from Mississippi, USA. A glyphosate‐susceptible (GS) biotype was included for comparison. The effective glyphosate dose to reduce the growth of the treated plants by 50% for the GR1, GR2 and GS biotypes was 0.58, 0.46 and 0.11 kg ae ha?1, respectively, indicating that the level of resistance was five and fourfold that of the GS biotype for GR1 and GR2, respectively. Studies using 14 C‐glyphosate have not indicated any difference in its absorption between the biotypes, but the GR1 and GR2 biotypes translocated more 14 C‐glyphosate, compared to the GS biotype. This difference in translocation within resistant biotypes is unique. There was no amino acid substitution at codon 106 that was detected by the 5‐enolpyruvylshikimate‐3‐phosphate synthase gene sequence analysis of the resistant and susceptible biotypes. Therefore, the mechanism of resistance to glyphosate in common ragweed biotypes from Mississippi is not related to a target site mutation or reduced absorption and/or translocation of glyphosate.  相似文献   

3.
The rapid range expansion of naturalized Italian ryegrass (Lolium multiflorum Lam.) in farmland is a serious problem in Fukuroi city in Shizuoka Prefecture, Japan. Glyphosate has been used to control Italian ryegrass in the levees of rice paddy fields and wheat fields for ～20 years, but this weed in Fukuroi city is poorly controlled by glyphosate. In order to elucidate the level of resistance to glyphosate in Italian ryegrass populations, seed bioassays and a foliar application experiment, using seeds collected from 16 wild populations in and around Fukuroi city and from three susceptible cultivars, were conducted. For the susceptible cultivars and one population from a site where glyphosate had not been applied for >10 years, the shoot length in the seed bioassays was greatly suppressed at a glyphosate concentration of 10 mg ai L?1 and no seedling survived after the foliar application of glyphosate at a rate of 2.3 kg ai ha?1. Nine wild populations from levees in the southern part of Fukuroi city showed vigorous shoot growth at a glyphosate concentration of 10 mg ai L?1 and had at least a 78% survival rate after the application of glyphosate at 2.3 kg ai ha?1. Four wild populations from levees in the northern part of Fukuroi city showed a slight suppression of the shoot growth as a result of the glyphosate treatment and their survival rates ranged from 20 to 64%. The results suggested that resistance to glyphosate has evolved in the wild populations of Italian ryegrass that are growing on the levees. This is the first report of a glyphosate‐resistant weed in Japan.  相似文献   

4.
Italian ryegrass ( Lolium multiflorum Lam.) is a non‐native annual winter grass that has seriously infested rice paddy levees and wheat fields in Japan. Recently, glyphosate‐resistant Italian ryegrass was found on paddy levees in central Japan, thereby making control of the grass by using glyphosate less effective. In this study, physical control methods were tested that combined the timing and frequency of mowing in order to more effectively control glyphosate‐resistant Italian ryegrass on rice paddy levees. A 3 year field experiment was conducted from 2012 to 2014 in a western region of Shizuoka Prefecture, where glyphosate‐resistant Italian ryegrass has become dominant. Five treatments were tested: (i) mowing once before the flowering of the grass (i.e. conventional mowing measure); (ii) mowing once during flowering; (iii) mowing twice during flowering; (iv) glyphosate application before flowering (i.e. one of the conventional mowing measures); and (v) no treatment. The above‐ground biomass, seed production, soil seed bank and seedling occurrence of Italian ryegrass were measured to determine the effectiveness of these treatments. Mowing during the flowering period resulted in reduced above‐ground biomass, seed production and soil seed bank when compared with the other treatments. Additionally, mowing twice during the flowering period resulted in a lower seedling density than mowing once. The results suggest that, in this region, physical control by mowing during the flowering period would be more effective than conventional measures for controlling glyphosate‐resistant Italian ryegrass.  相似文献   

5.
Recently, glyphosate‐resistant Italian ryegrass (Lolium multiflorum Lam.) was found on rice paddy levees in a western region of Shizuoka Prefecture, Japan. Naturalized populations of Italian ryegrass are frequently infected with fungal Epichloë endophytes. Endophytes often confer benefits to their host grasses. This study investigated the influence of five weed management treatments on glyphosate resistance and endophyte infection in Italian ryegrass that was growing on paddy levees where glyphosate‐resistant individuals were dominant. The weed management treatments were: (i) mowing once before the grass flowered; (ii) mowing once during flowering; (iii) mowing twice during flowering; (iv) glyphosate application before flowering; and (v) no treatment. The seeds were collected from the treatment plots in 2013 and 2014. The seeds were examined for endophyte infection and the seedlings that had been grown from the seeds were tested for the frequency of glyphosate resistance. The seedlings that had been derived from the glyphosate treatment showed higher frequencies of glyphosate resistance than those seedlings that had been derived from all the other treatments. Endophytes were found in all populations of the seeds from the paddy levees, with higher infection rates in the seeds that had been derived from the glyphosate treatment and the twice‐mowed treatment. There was a significant relationship between the endophyte infection frequency in the seeds and glyphosate resistance in the seedlings that had been grown from the same populations. The results indicate that where glyphosate herbicides are frequently used, selection for glyphosate‐resistant Italian ryegrass occurs, and along with this, the frequency of endophyte infection also increases.  相似文献   

6.
Enhanced crop competition could aid in the management of annual sowthistle (Sonchus oleraceus L.), a dominant weed of Australian cropping systems. A two‐year pot study was conducted to evaluate the effect of wheat (Triticum aestivum L.) planting densities (0, 82, and 164 wheat plants/m2) on growth and seed production of glyphosate‐resistant (GR) and glyphosate‐susceptible (GS) biotypes of annual sowthistle. Without competition, both biotypes produced a similar number of leaves and biomass, but the GS biotype produced 80% more seeds (46,050 per plant) than the GR biotype. In competition with 164 wheat plants/m2, the number of leaves in the GR and GS biotypes was reduced by 62 and 61%, respectively, in comparison with the no‐competition treatment, and similarly, weed biomass was reduced by 78 and 77%, respectively. Compared to no‐competition treatment, the seed production of GR and GS biotypes was reduced by 33 and 69%, respectively, when grown with 82 wheat plants/m2, but increasing wheat density from 82 to 164 plants/m2 reduced the number of seeds only in the GS biotype (81%). Both biotypes produced greater than 6,000 seeds per plant when grown in competition with 164 plants/m2, suggesting that increased crop density should be integrated with other weed management strategies for efficient control of annual sowthistle.  相似文献   

7.
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   

8.
Effects of environmental factors on the germination and seedling emergence of glyphosate‐resistant (R) and ‐susceptible (S) biotypes of Eleusine indica (L.) Gaertn. were examined under laboratory and greenhouse conditions. The R biotype exhibited a higher germination percentage compared with the S biotype at constant temperatures of 20 and 35°C under dark conditions, and alternating temperatures of 30/25°C, and 35/25°C during a 12 h photo period. For both biotypes, germination was optimal at alternating temperatures of 30/20°C and 35/20°C. However, there was no significant difference (P > 0.05) in the germination between the R and S biotypes at these temperature regimes. The germination of both biotypes was inhibited by osmotic stress imposed by a water potential of ?0.80 MPa. When the moisture stress was released and the seeds were subsequently transferred to distilled water, the germination was enhanced to approximately 90% and 16% for the R and S biotype seeds, respectively. Higher emergence rates were obtained in shallow seed depths (0 or 2 cm) compared to deep depths. Emergence percentage of the R biotype was higher than that of the S biotype at 0 cm and 2 cm depths. The maximum emergence percentage of the R biotype was higher than that of S biotype when seeds were sown on the surface of either loamy or clay loam soil taken from three different sites.  相似文献   

9.
Saflufenacil is a new herbicide on the market and its effectiveness on horseweed, several populations of which have evolved resistance to glyphosate, is not clear. In this research, the effect of adjuvants on the control of horseweed with saflufenacil in the field, the effect of the interaction between glyphosate and saflufenacil on glyphosate‐resistant and glyphosate‐susceptible horseweed and the patterns of uptake and translocation of glyphosate applied alone and in combination with saflufenacil in horseweed were evaluated. The addition of methylated seed oil to saflufenacil provided the best control of horseweed, with crop oil concentrate being intermediate in effect and non‐ionic surfactant ranking as the least‐effective adjuvant. The interaction between glyphosate and saflufenacil was additive with regards to the control of glyposate‐resistant horseweed. The glyphosate‐susceptible horseweed population absorbed 6–13% more 14C‐glyphosate than the glyphosate‐resistant population. The addition of saflufenacil reduced 14C‐glyphosate translocation in both the glyphosate‐resistant and the glyphosate‐susceptible horseweed populations by at least 6%; however, due to the exceptional efficacy of saflufenacil, these reductions did not reduce the level of control. Saflufenacil holds great potential as an alternative control option for glyphosate‐resistant horseweed and is a valuable tool in the management of resistant weeds.  相似文献   

10.
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   

11.
BACKGROUND: In a large cropping area of northern Argentina, Sorghum halepense (Johnsongrass) has evolved towards glyphosate resistance. This study aimed to determine the molecular and biochemical basis conferring glyphosate resistance in this species. Experiments were conducted to assess target EPSPS gene sequences and 14C‐glyphosate leaf absorption and translocation to meristematic tissues. RESULTS: Individuals of all resistant (R) accessions exhibited significantly less glyphosate translocation to root (11% versus 29%) and stem (9% versus 26%) meristems when compared with susceptible (S) plants. A notably higher proportion of the applied glyphosate remained in the treated leaves of R plants (63%) than in the treated leaves of S plants (27%). In addition, individuals of S. halepense accession R2 consistently showed lower glyphosate absorption rates in both adaxial (10–20%) and abaxial (20–25%) leaf surfaces compared with S plants. No glyphosate resistance endowing mutations in the EPSPS gene at Pro‐101–106 residues were found in any of the evaluated R accessions. CONCLUSION: The results of the present investigation indicate that reduced glyphosate translocation to meristems is the primary mechanism endowing glyphosate resistance in S. halepense from cropping fields in Argentina. To a lesser extent, reduced glyphosate leaf uptake has also been shown to be involved in glyphosate‐resistant S. halepense . Copyright © 2011 Society of Chemical Industry  相似文献   

12.
Annual ryegrass (Lolium rigidum) is the only weed species to have evolved resistance to the broad‐spectrum herbicide glyphosate in Australia. A population that had failed to be controlled by glyphosate was collected from a vineyard in the Adelaide Hills region of South Australia. Dose–response experiments on this population (SLR 77) showed that it was glyphosate resistant, with an LD50 that was 1.9–3.4 times higher than that of a susceptible population (VLR 1). The movement of radiolabelled glyphosate within SLR 77 plants showed that this population did not have the differential glyphosate translocation mechanism of resistance common to several other Australian glyphosate‐resistant populations. Subsequent analysis of shikimic acid accumulation within the plant after glyphosate treatment showed that this population accumulated significantly less shikimic acid than a susceptible population, but more than a glyphosate‐resistant population with the translocation mechanism, indicating the possible involvement of another mechanism of resistance. Sequencing of a portion of the SLR 77 5‐enolpyruvylshikimate‐3‐phosphate synthase gene was carried out and a mutation causing an amino acid change at position 106 from proline to threonine was identified. This mutation is likely to be responsible for glyphosate resistance in this population, as mutations in this position have been found to be responsible for glyphosate resistance in goosegrass (Eleusine indica) from Malaysia. This paper represents the first report of target‐site glyphosate resistance in L. rigidum and provides evidence that this species has at least two mechanisms of glyphosate resistance present in Australia.  相似文献   

13.
BACKGROUND: Resistance to glyphosate in weed species is a major challenge for the sustainability of glyphosate use in crop and non‐crop systems. A glyphosate‐resistant Italian ryegrass population has been identified in Arkansas. This research was conducted to elucidate its resistance mechanism. RESULTS: The investigation was conducted on resistant and susceptible plants from a population in Desha County, Arkansas (Des03). The amounts of glyphosate that caused 50% overall visual injury were 7 to 13 times greater than those for susceptible plants from the same population. The EPSPS gene did not contain any point mutation that has previously been associated with resistance to glyphosate, nor were there any other mutations on the EPSPS gene unique to the Des03 resistant plants. The resistant plants had 6‐fold higher basal EPSPS enzyme activities than the susceptible plants, but their I50 values in response to glyphosate were similar. The resistant plants contained up to 25 more copies of EPSPS gene than the susceptible plants. The level of resistance to glyphosate correlated with increases in EPSPS enzyme activity and EPSPS copy number. CONCLUSION: Increased EPSPS gene amplification and EPSPS enzyme activity confer resistance to glyphosate in the Des03 population. This is the first report of EPSPS gene amplification in glyphosate‐resistant Italian ryegrass. Other resistance mechanism(s) may also be involved. Copyright © 2012 Society of Chemical Industry  相似文献   

14.
BACKGROUND: Glyphosate‐resistant (GR) weed species are now found with increasing frequency and threaten the critically important GR weed management system. RESULTS: The reported 31P NMR experiments on glyphosate‐sensitive (S) and glyphosate‐resistant (R) horseweed, Conyza canadensis (L.) Cronq., show significantly more accumulation of glyphosate within the R biotype vacuole. CONCLUSIONS: Selective sequestration of glyphosate into the vacuole confers the observed horseweed resistance to glyphosate. This observation represents the first clear evidence for the glyphosate resistance mechanism in C. canadensis. Copyright © 2010 Society of Chemical Industry  相似文献   

15.
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   

16.
Paraquat resistance in a biotype of Vulpia bromoides (L.) S. F. Gray   总被引：1，自引：0，他引：1  
A biotype of Vulpia bromoides from a lucerne field in Elmhurst, Victoria, Australia was shown to be resistant to paraquat in pot trials. Application of paraquat at 50 g a.i. ha?1 killed all of the plants of a susceptible Vulpia bromoides biotype but only 6% of the resistant biotype. The LD50 for paraquat of the resistant biotype was five- to sixfold higher than for the susceptible biotype. The resistant biotype was also resistant to the bipyridyl herbicide diquat, but was susceptible to glyphosate and metribuzin. Application of 100 g a.i. ha?1 paraquat at anthesis completely suppressed seed set of the susceptible biotype and reduced that of the resistant biotype by 95%. Seed set by the paraquat-treated resistant biotype, however, showed little reduction in germination. This is the fourth species to have been found to be resistant to bipyridyl herbicides in this field, the others being Hordeum glaucum, H. leporinum and Arctotheca calendula. Résistance au paraquat d'un biotype de Vulpia bromoides (L.) S. F. Gray Un biotype de Vulpia bromoides issu d'un champ de luzerne à Elmhurst, Victoria, Australie s'est révélé résistant au paraquat lors d'essais en pots. Des traitements au paraquat 50 g m.a. ha?1 détruisaient toutes les plantes d'un biotype sensible de V. bromoides mais seulement 6% du biotype résistant. La DLV50 du paraquat pour ce biotype était 5 à 6 fois plus élevée que pour le biotype sensible. Le biotype résistant l'était aussi à l'herbicide bipyridyle diquat, mais était sensible au glyphosate et à la métribuzine. Des traitements au paraquat 100 g m.a. ha?1 au stade anthèse supprimaient complètement la production de graines du biotype sensible et réduisait de 95% celle du biotype résistant. Cependant, le pouvoir germinatif des graines issues du biotype résistant traité, n'était que peu réduit. Après Hordeum glaucum, Hordeum leporinum et Arctotheca calendula, c'est la quatrième espèce trouvée dans ce même champ résistante aux herbicides bipyridyles. Paraquatresistenz eines Biotyps von Vulpia bromoides (L.) S. F. Gray Ein Biotyp von Vulpia bromoides von einem Luzernefeld in Elmhurst, Victoria, Australien, erwies sich in Topfversuchen als paraquatresistent. Mit 50 g AS ha?1 wurden Pflanzen eines empfindlichen Biotyps abgetötet, jedoch nur 6% des resistenten. Die LD50 des resistenten Biotyps für paraquat war 5- bis 6mal höher als die des empfindlichen Biotyps. Der resistente Biotype war auch gegenüber dem Bipyridylherbizid Deiquat résistent, gegenüber Glyphosat und Metribuzin jedoch empfindlich. Nach Anwendung von 100 g AS ha?1 Paraquat vor der Blüte bildeten sich bei dem empfindlichen Biotyp keine Samen aus, bei dem resistenten waren sie um 95% vermindert; die dennoch gebildeten Samen keimten etwas weniger. Dies ist die vierte Pflanzenart, bei der eine Resistenz gegenüber Bipyridylherbiziden beobachtet wurde, die anderen sind Hordeum glaucum. Hordeum leporinum und Arctotheca calendula.  相似文献   

17.
Primisulfuron‐resistant (AR and MR) and ‐susceptible (AS and MS) Bromus tectorum biotypes were collected from a Poa pratensis field at Athena, Oregon, and in research plots at Madras, Oregon. Studies were conducted to characterize the resistance of the B. tectorum biotypes. Whole plant bioassay and acetolactate synthase (ALS) enzyme assay revealed that the AR biotype was highly resistant to the sulfonylurea (SU) herbicides, primisulfuron and sulfosulfuron and to a sulfonylaminocarbonyltriazolinone (SCT) herbicide, propoxycarbazone‐sodium. However, the AR biotype was not resistant to imazamox, an imidazolinone (IMI) herbicide. Results of the whole plant bioassay studies showed that the MR biotype was moderately resistant to all ALS inhibitors tested. However, there were no differences in ALS sensitivities between the MR and MS biotypes. The nucleotide and amino acid sequence analysis of the als gene demonstrated a single‐point mutation from C to T, conferring the exchange of the amino acid proline to serine at position 197 in the AR biotype. However, this mutation was not found in the MR biotype. Results of this research indicate that: the resistance of the AR biotype to SU and SCT herbicides is based on an altered target site due to a single‐point mutation; resistance in the MR biotype is not due to a target site mutation.  相似文献   

18.
The intensive use of the acetolactate synthase (ALS)‐inhibiting herbicides, imazethapyr, penoxsulam and bispyribac‐sodium, in imidazolinone‐resistant (Clearfield) rice increases the risk of the evolution of ALS‐resistant barnyardgrass. In 2009, imazethapyr failed to control barnyardgrass that was collected from a field in Arkansas, USA, following the failure of the herbicide in 2008. A greenhouse experiment was conducted to confirm and document the level of resistance of the biotype against three ALS‐inhibiting herbicides that currently are labeled in rice. The level of control of the resistant biotype at the labeled rate of bispyribac‐sodium of 35 g ai ha?1 was 10%, penoxsulam at 22 g ai ha?1 was 0% and imazethapyr at 70 g ai ha?1 was 25%. The level of mortality of the susceptible biotype was 100% with all the herbicides at the labeled rate. The dose needed to kill 50% of the resistant plants was 49 g ha?1 of bispyribac‐sodium, 254 g ha?1 of penoxsulam and 170 g ha?1 of imazethapyr. For the susceptible biotype, bispyribac‐sodium at 6 g ha?1, penoxsulam at 10 g ha?1 and imazethapyr at 12 g ha?1 killed 50% of the treated plants. Based on these findings, it was confirmed that a barnyardgrass population has evolved cross‐resistance to three ALS‐inhibiting herbicides in rice culture in Arkansas. Furthermore, an experiment was conducted to determine if the ALS‐resistant biotype could be controlled using other mechanisms of action. The results indicated that propanil, a photosystem II inhibitor, and quinclorac, a synthetic auxin, failed to control the resistant biotype at the labeled rates, whereas all the other evaluated herbicides provided effective control of both biotypes.  相似文献   

19.
Resistance to glyphosate and paraquat has evolved in some populations of Conyza spp. from California, USA. This study evaluated whether herbicide absorption and translocation were involved in the mechanism of resistance to both herbicides. Three lines of each species were used: glyphosate‐paraquat‐susceptible (GPS), glyphosate‐resistant (GR) and glyphosate‐paraquat‐resistant (GPR). Radiolabelled herbicide was applied to a fully expanded leaf, and absorption and movement out of the treated leaf were monitored for up to 24 h for paraquat and 72 h for glyphosate. Plants treated with paraquat were incubated in darkness for the first 16 h and then subjected to light conditions. More glyphosate was absorbed in C. bonariensis (52.9–58.3%) compared with C. canadensis (28.5–37.6%), but no differences in absorption were observed among lines within a species. However, in both species, the GR and GPR lines translocated less glyphosate out of the treated leaf when compared with their respective GPS lines. Paraquat absorption was similar among lines and across species (71.3–77.6%). Only a fraction of paraquat was translocated in the GPR lines (3% or less) when compared with their respective GPS or GR lines (20% or more) in both species. Taken together, these results indicate that reduced translocation is involved in the mechanism of resistance to glyphosate and paraquat in C. bonariensis and C. canadensis.  相似文献   

20.
Recent reports of weed‐control failures after the use of glyphosate led to suspicion about the selection of resistant biotypes of Conyza at locations in west and north Paraná, Brazil. Plants were collected, identified as Conyza sumatrensis and subsequently evaluated for possible resistance to glyphosate in four stages of weed development. The experiments were carried out in a greenhouse by combining biotypes, stages of development and a range of glyphosate doses. All the suspected biotypes were collected from locations in Cascavel, Toledo, Assis Chateaubriand, Tupãssi and Campo Mourão with a history of glyphosate use in burndown and in glyphosate‐resistant soybean for at least the four previous years and were compared to a susceptible biotype (São Jorge do Ivaí) with no previous history of herbicide use. The doses of glyphosate ranged from 0 to 5760 g ae ha?1. The biotypes were considered as resistant if two combined criteria were present (resistance factor > 1 and the rate required to achieve 80% control is >720 g ha?1). The results provided evidence that there is a marked difference in the level of control of older plants and also confirmed the presence of some resistant biotypes. For applications at the first stage of development, two biotypes that were resistant to glyphosate were identified (Cascavel‐1 and Tupãssi‐6). For applications in the second stage of development, beyond the biotypes that were found in the first stage, three other biotypes were considered as resistant: Toledo‐5, Assis Chateaubriand‐7 and Floresta‐10. However, for applications at the third and fourth stages, all the biotypes were considered as resistant.  相似文献   

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