Herbicide sensitivity of transgenic multiple herbicide-tolerant oilseed rape

Glyphosate and glufosinate-ammonium herbicide tolerance traits were combined into both winter and spring lines of Brassica napus L. This allowed the study of possible interactions between these transgenes in two genetic backgrounds when treated with a variety of herbicides. Selective herbicides that are commonly used within Brassica crops showed no adverse effects on the transgenic plants or their null controls. Lines containing both glyphosate and glufosinate transgenes remained tolerant to their respective herbicides, regardless of the presence of the second tolerance transgene. Lines containing only a single transgene retained tolerance to the encoded trait and did not show cross-tolerance to the second. Null lines were killed by either herbicide. All plant lines, regardless of their transgene content, were found to be equally susceptible to three herbicides (paraquat, metsulfuronmethyl and mecoprop), commonly used to remove volunteer B napus from succeeding crops and set-a-side land.     

Modelling the effect of crop and weed on herbicide efficacy in wheat

Recommended field application rates of herbicides have to give effective weed control in every situation and are, thus, often higher than that required for specific fields. An understanding of the interaction between crop:weed competition and herbicide dose may, in many cases, allow herbicide application rates to be reduced, important both environmentally and economically. We have developed a model of the interaction between crop:weed competition and herbicide dose, using an empirical model of the relationship between crop yield and weed biomass (related to weed density), and an empirical model of the relationship between weed biomass and herbicide dose. The combined model predicts crop yield, given herbicide dose and weed biomass at an interim assessment date. These crop yield loss predictions may be used to quantify the herbicide dose required to restrict yield loss to a given percentage. Parameters of the model were estimated and the model tested, using results from experiments, which used cultivated oats ( Avena sativa ) or oilseed rape ( Brassica napus ) as model weeds in a crop of winter wheat ( Triticum aestivum ).For the crop:weed:herbicide combinations investigated there was little increase in crop yield for herbicide dose rates above 20% of recommended field rates, in broad agreement with the model predictions. There may still be potential for further reduction below this level on economic grounds; the model could be used to estimate the `break-even' herbicide dose.     

Modelling spatio-temporal dynamics of herbicide resistance

A mathematical model has been developed for the risk assessment of the spread of genes conferring herbicide resistance in plant populations. The model combines an age-and-stage-structured population dynamic model, a population genetic model and a model of spatial spread. This is achieved by embedding a local matrix population model into a cellular automaton model with raster cells as spatial units. The dynamics of each cell is determined by both its local dynamics and the interaction with neighbouring cells. The model is applied to the evaluation of management strategies to delay or even to prevent long-term evolution of resistance in an annual grass weed. The results show that the appearance and spread of resistant genes is a highly non-linear process exhibiting threshold phenomena, which occur for a wide range of parameters. The properties of the seed survival curve constitute the `genetic memory' of the system and thus determine its long-term dynamics. It is possible to delay the evolution of resistance by suspension of treatment, reduction in herbicide application rate and introducing fallow periods. Spatial spread from an infested plot is inhibited by leaving untreated strips between adjacent fields.     

除草剂对蚕豆、油菜田小籽虉草的防除效果和安全性评价

小籽虉草Phalaris minor是近年来危害云南中西部地区冬季作物田的恶性杂草。云南冬季作物以阔叶作物为主, 有必要开展在阔叶作物田小籽虉草的化学防除效果研究。本研究在室内和田间测试了108 g/L高效氟吡甲禾灵EC、150 g/L精吡氟禾草灵EC、10%精喹禾灵EC、69 g/L精噁唑禾草灵EW、240 g/L烯草酮EC、12.5%烯禾啶EC、5%唑啉草酯EC等7种阔叶作物田茎叶处理剂对小籽虉草的防效以及对油菜和蚕豆的安全性。室内研究结果表明, 药后30 d, 5%唑啉草酯EC、12.5%烯禾啶EC、10%精喹禾灵EC在推荐剂量作用下对小籽虉草的鲜重防效超过90%, 杂草植株表现明显枯死症状, 并且安全性指数均大于2; 240 g/L烯草酮EC的株防效较差, 鲜重防效也低于50%; 其他药剂的鲜重防效为80%左右。田间药效试验表明, 5%唑啉草酯EC防效最优, 接近95%, 108 g/L高效氟吡甲禾灵EC和12.5%烯禾啶EC等防效能达到90%, 其他药剂的防效也超过80%, 所有药剂对油菜和蚕豆均安全。以上结果表明, 当前大多数阔叶作物田禾本科杂草除草剂对小籽虉草高效, 对作物安全, 控制小籽虉草的备选除草剂品种较多。     

Fates of Setaria faberi and Abutilon theophrasti seeds in three crop rotation systems

Weed seeds in and on the soil are the primary cause of weed infestations in arable fields. Previous studies have documented reductions in weed seedbanks due to cropping system diversification through extended rotation sequences, but the impacts of different rotation systems on additions to and losses from weed seedbanks remain poorly understood. We conducted an experiment in Iowa, USA, to determine the fates of Setaria faberi and Abutilon theophrasti seeds in 2‐, 3‐ and 4‐year crop rotation systems when seed additions to the soil seedbank were restricted to a single pulse at the initiation of the study. Over the course of the experiment, seedlings were removed as they emerged and prevented from producing new seeds. After 41 months, seed population densities dropped >85% for S. faberi and >65% for A. theophrasti, but differences between rotation systems in the magnitude of seedbank reductions were not detected. Most of the reductions in seedbank densities took place from autumn through early spring in the first 5 months following seed deposition, before seedling emergence occurred, suggesting that seed predation and/or seed decay was important. For S. faberi, total cumulative seedling emergence and total seed mortality did not differ between rotation systems. In contrast, for A. theophrasti, seedling emergence was 71% lower and seed mortality was 83% greater in the 3‐ and 4‐year rotation systems than in the 2‐year system. Results of this study indicate that for certain weed species, such as A. theophrasti, crop rotation systems can strongly affect life‐history processes associated with soil seedbanks.     

Combined effects of wheat competition and 2,4-D amine on phenoxy herbicide resistant Raphanus raphanistrum populations

Phenoxy herbicides are integral to the control of Raphanus raphanistrum populations in Australian crop production systems, but the development of phenoxy resistant R. raphanistrum populations poses a major threat to the sustainability of these systems. In dose–response pot studies, phenoxy herbicide resistant R. raphanistrum populations, WARR12 and WARR20, suffered large biomass reductions following treatment with recommended or higher application rates of phenoxy herbicides. This indicates the presence of a weak resistance mechanism where treated plants, although surviving, are affected by these herbicides. Subsequently, the competitive ability of 2,4-D amine treated or untreated WARR12 and WARR20 populations with wheat was assessed using a target-neighbourhood experiment. The combination of wheat competition and 2,4-D amine application resulted in control of the resistant WARR12 population, but not the WARR20 population. Wheat crop competition alone resulted in large (>40%) biomass reductions of WARR12 and WARR20 populations. However, the application of the recommended rate of 2,4-D amine caused a large (>75%) reduction in WARR12 biomass, but had a reduced effect on WARR20 biomass. These studies possibly explain the largely successful control of R. raphanistrum populations being achieved with phenoxy herbicides in cropping systems across the Western Australia wheatbelt. However, the results also indicated that the strategy of combining crop competition with phenoxy herbicides for the control of this weed is likely to be an effective option in the short-term only.     

The metabolism of a novel herbicide ZJ0273 in oilseed rape and crickweed

Experiments were conducted to investigate the metabolism of a novel herbicide ZJ0273 in the seedlings of the susceptible crickweed and tolerant oilseed rape. Six metabolites of ZJ0273 were identified in crickweed seedlings, compared to 8 metabolites in oilseed rape. Among these metabolites, the metabolite M7, with the chemical name of 2-(4,6-dimethoxypyrimidin-2-yloxy) benzoic acid, was found to be the most herbicidally effective molecule with significant inhibition to acetolactate synthase. The differences in the amount and rate of ZJ0273 transformation to M7, and its metabolic detoxification, contributed to the primary mechanism of herbicidal selectivity of ZJ0273.     

Mechanism of resistance to bensulfuron-methyl in Alisma plantago-aquatica biotypes from Portuguese rice paddy fields

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.     

Distribution and metabolism of D/L-, L- and D-glufosinate in transgenic, glufosinate-tolerant crops of maize (Zea mays L ssp mays) and oilseed rape (Brassica napus L var napus)

The aim of the present study was to determine whether post-emergence application of glufosinate to transgenic crops could lead to an increase in residues or to the formation of new, hitherto unknown metabolites. Transgenic oilseed rape and maize plants were treated separately with L-glufosinate, D-glufosinate or the racemic mixture. Whereas about 90% of the applied D-glufosinate was washed off by rain and only 5-6% was metabolised, 13-35% of the applied L-glufosinate remained in the form of metabolites and unchanged herbicide in both transgenic maize and oilseed rape. The main metabolite was N-acetyl-L-glufosinate with total residues of 91% in oilseed rape and 67% in maize, together with small amounts, of 5% in oilseed rape and 28% in maize, of different methylphosphinyl fatty acids. These metabolites were probably formed from L-glufosinate by deamination and subsequent decarboxylation. The residues were distributed in all fractions of the plants, with the highest contents in treated leaves and the lowest in the grains (0.07-0.3% in maize and 0.4-0.6% in oilseed rape). There was no indication of an accumulation of total residues or of residue levels above the official tolerances for glufosinate.     

Response of Alopecurus myosuroides Huds. to varying intensities of acetolactate synthase-inhibiting herbicides in a crop rotation including imidazolinone-tolerant oilseed rape

Journal of Plant Diseases and Protection - Herbicide-tolerant winter oilseed rape (OSR) varieties offer the opportunity of using imazamox for weed control, an active ingredient belonging to the...     

Herbicides used in combination can reduce the probability of herbicide resistance in finite weed populations

A simulation study was conducted to examine the effect of pattern of herbicide use on development of resistance to two herbicides with different modes of action in finite weed populations. The effects of the size of the treatment area (analogous to initial weed population), germination fraction and degree of self‐pollination in the weed were investigated. The results indicate that the probability of developing resistance to one or both herbicides decreases as the size of the area/initial population decreases. For treatment areas of 100 ha or less with an initial weed seedbank of 100 seeds m^?2 and initial frequencies of the resistance genes of 10^?6, development of resistance to both herbicides (double‐resistance) is uncommon within 50 years for all types of weeds if both herbicides are used in all years (used in combination). If herbicides are used in alternate years (rotated) double‐resistance almost always occurs in 100 ha areas but is uncommon in areas of 1 ha or less. The results suggest that adoption of practices that limit movement of weeds in conjunction with using herbicides in combination rather than in rotation can substantially delay development of herbicide resistance.     

The impact of altered herbicide residues in transgenic herbicide-resistant crops on standard setting for herbicide residues

The global area covered with transgenic (genetically modified) crops has rapidly increased since their introduction in the mid-1990s. Most of these crops have been rendered herbicide resistant, for which it can be envisaged that the modification has an impact on the profile and level of herbicide residues within these crops. In this article, the four main categories of herbicide resistance, including resistance to acetolactate-synthase inhibitors, bromoxynil, glufosinate and glyphosate, are reviewed. The topics considered are the molecular mechanism underlying the herbicide resistance, the nature and levels of the residues formed and their impact on the residue definition and maximum residue limits (MRLs) defined by the Codex Alimentarius Commission and national authorities. No general conclusions can be drawn concerning the nature and level of residues, which has to be done on a case-by-case basis. International residue definitions and MRLs are still lacking for some herbicide-crop combinations, and harmonisation is therefore recommended.     

The adverse impact of the neonicotinoid seed treatment ban on crop protection in oilseed rape in the United Kingdom

This paper describes the consequences of the ban on neonicotinoid seed treatments on pest management in oilseed rape. Since the ban was implemented in December 2013, there have been serious crop losses in 2014, 2015 and 2016 owing to cabbage stem flea beetles, Psylliodes chrysocephala, and aphids, Myzus persicae, which have developed resistance to the alternative pyrethroid sprays that were employed to control them. This has resulted in increased crop losses, decreased yields and a substantial decrease in the area grown, leading to fewer flowering crops available in the spring, especially in the eastern region of the United Kingdom. This is likely to have an adverse effect on bees locally. © 2016 Society of Chemical Industry     

The use of cytochrome P450 genes to introduce herbicide tolerance in crops: a review

Mechanisms of herbicide resistance include (1) modified target site, (2) enhanced detoxification or delayed activation, and (3) alterations in the uptake, translocation, or compartmentalization of a herbicide. The first two mechanisms have mainly been identified in plants. Herbicide resistance genes were isolated for several herbicides of different modes of action. Genes that coded for herbicide target or detoxification enzymes were transferred into crop plants. The transgenic plants expressing these genes were tolerant of the active ingredients of herbicides. Before commercialization, the transgenic plants were tested in the field for risk assessment. In the case of crops with herbicide detoxification enzymes, including cytochrome-P450-species-metabolizing xenobiotics, the substrate specificity of the enzymes as well as the toxicological properties of the herbicide metabolites and the pattern of secondary metabolites in plants must be evaluated. © 1999 Society of Chemical Industry