Localized origins of herbicide resistance in Alopecurus myosuroides

The process of evolution of resistance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides was investigated in four distinct patches of Alopecurus myosuroides Huds. (black-grass) that occur within adjacent fields on a cereal farm in Nottinghamshire, UK. In one field, there was a `main' patch containing 96% resistant plants and two `satellite' patches containing ≈2.9% and 4.4% resistant plants, and in an adjacent field another patch contained 25% resistant plants. Genome fingerprinting by simple sequence repeat (SSR)-anchored polymerase chain reaction (PCR) was used to analyse variation at 30 genetic loci in at least 20 resistant and 20 sensitive individual plants from each patch, from additional resistant populations from Essex and Lincolnshire, and from a sensitive reference population. Banding patterns were found to be highly repeatable. Each patch contained a high level of genetic diversity, regardless of its resistance status, and there was evidence for genetic differences between the patches (Gst = 0.14, Nei's distances up to 0.26). There was no evidence that resistance had spread from the `main' patch to the others, as resistant and sensitive plants in the same patch were more closely related on average than were resistant plants from neighbouring patches. The most likely explanations of this distribution, and their implications, are discussed.     

The survival of Alopecurus myosuroides Huds. seeds in soil

The survival of Alopecurus myosuroides seeds was studied in soil under arable cropping and short term grass leys in which seed return was prevented. At two winter wheat sites, where weed seeds were sown, the mean annual seed decline was 73–83% over a 2- or 3-year period. The rate of decline was similar with all the cultivation systems studied: ploughing, tine cultivation and direct drilling. Seeds buried initially by ploughing, and then not disturbed by cultivation, were slightly more persistent. At five arable sites with natural populations of A. myosuroides, seed numbers declined to an average of 3% of the original amount present after 3 years, and to 1% after 4 years. Initial populations of over 50 000 seeds m^?2 were recorded. Plant populations were not always proportional to the total seed content of the soil, especially on ploughed land. Seed decline in two grass fields was similar to that under arable cropping. A. myosuroides plants were recorded in a wheat crop following a 2-year grass ley. Weed plants did not persist in the vegetative state in grass used for conservation and grazing. At all sites, appreciable quantities of seeds were still present in the soil after 2–4 years. Although a relatively small proportion of seeds survived, the actual number of seeds surviving was substantial. For this reason, it was concluded that any eradication policy is unlikely to be effective in a cropping system dominated by winter cereals.     

Inscribing Workplaces: The Spatiality of the Production Process

ABSTRACT In this paper, the social being in the spatiality of the production process is addressed. Spatiality, following Soja (1989), means the ceaseless and recursive dialectical interplay amongst time, space, and the social being. The production process, as a specific set of social relations, comprises both the tasks associated with productive labor and the regulations that organize the extraction of surplus value. The social being as worker is located within the various sets of power relations in the workplace, and workers as social beings position themselves within and amongst the numerous sets of social relations that are part of the production process. Distributions of power are negotiated through labor and mediated by other sets of social relations in specific places as well as the historical and material conditions of the lives of individual workers and their employment at a firm. This conceptual argument is demonstrated by drawing on information gathered in multiple-depth interviews with women employed as franchise housekeepers, personal experience as a franchise housekeeper, and structured interviews with managers, owners, and head office personnel in housekeeping services franchises.     

The lack of effect of inoculation with equine influenza vaccine on theophylline pharmacokinetics in the horse

Several studies conducted during the past few years have shown that the pharmacokinetics of a variety of drugs may be altered following viral infection or vaccination. The elimination of drugs which are extensively metabolized, such as theophylline, may be prolonged, especially following exposure to RNA viruses such as Type A influenza or similar orthomyxoviruses. The purpose of this study was to determine whether vaccination of horses with equine influenza virus affected pharmacokinetic parameters describing the distribution and elimination of intravenously administered theophylline. Three thoroughbred horses and three ponies were vaccinated with a trivalent vaccine containing inactivated strains of A/Equi 1 (Prague), A/Equi 2 (Miami) and A/Equi 2 (Kentucky 81). Antibody titre, serum interferon concentrations, and the pharmacokinetic parameters t1/2 beta, Vc, Vd(ss), Vd(area) and ClB were measured at various intervals after vaccination. Antibody titre increased substantially in only two animals, while plasma interferon was detectable in low concentrations in four subjects. There was no significant change in any parameter describing the pharmacokinetics of theophylline when measured 2, 6, or 12 days after vaccination. It is suggested that the failure of vaccination to substantially increase plasma interferon concentrations, and thereby alter theophylline elimination, was related to the use of an inactivated viral vaccine, the only type available for vaccination of horses against infection with equine influenza. Regular use of such vaccines, as is required by most Racing Authorities, is therefore unlikely to affect drug withdrawal times.     

A COMPARISON OF POTASSIUM-ACTIVITY RATIOS DERIVED FROM EQUILIBRATION PROCEDURES AND FROM MEASUREMENTS ON DISPLACED SOIL SOLUTION

Direct and indirect methods of determining cation ratios of natural soil solutions are reviewed. The problems of comparing their results are discussed. K activity ratios derived from measurements on ethyl alcohol-displaced soil solutions and values determined for the same soils by the Q/I equilibration procedure were in excellent agreement. An approximate rapid Q/I procedure using two K-Ca solutions whilst less precise in its determination of activity ratio would be useful for routine purposes. The use of a proportionality constant to calculate activity ratios is acceptable.     

A SNaPshot assay for the rapid and simple detection of known point mutations conferring resistance to ACCase‐inhibiting herbicides in Lolium spp.

Evolution of resistance to herbicides in weeds is becoming an increasing problem worldwide. To develop effective strategies for weed control, a thorough knowledge of the basis of resistance is required. Although non‐target‐site‐based resistance is widespread, target site resistance, often caused by a single nucleotide change in the gene encoding the target enzyme, is also a common factor affecting the efficacies of key herbicides. Therefore, fast and relatively simple high‐throughput screening methods to detect target site resistance mutations will represent important tools for monitoring the distribution and evolution of resistant alleles within weed populations. Here, we present a simple and quick method that can be used to simultaneously screen for up to 10 mutations from several target site resistance‐associated codons in a single reaction. As a proof of concept, this SNaPshot multiplex method was successfully applied to the genotyping of nine variable nucleotide positions in the CT domain of the chloroplastic ACCase gene from Lolium multiflorum plants from 54 populations. A total of 10 nucleotide substitutions at seven of these nine positions (namely codons 1781, 1999, 2027, 2041 2078, 2088 and 2096) are known to confer resistance to ACCase‐inhibiting herbicides. This assay has several advantages when compared with other methods currently in use in weed science. It can discriminate between different nucleotide changes at a single locus, as well as screening for SNPs from different target sites by pooling multiple PCR products within a single reaction. The method is scalable, allowing reactions to be carried out in either 96‐ or 384‐well plate formats, thus reducing work time and cost.     

Influence of growth stage and season on the energy value of fresh herbage. 1. Changes in metabolizable energy content

The energy value and chemical composition of 70 herbages harvested over two years as either spring primary growths of increasing maturity (n= 32), summer regrowths (n= 14) or autumn regrowths of increasing maturity (n= 24) are reported. The herbages, which were dominated by perennial ryegrass, were harvested from commercial grassland on four sites in England in1986 (year 1) and 1987 (year 2). Digestibility and energy values were determined in vivo using wether sheep. In year 1, autumn regrowths had significantly (P < 0·05) lower neutral detergent fibre concentrationsthan summer regrowths, and lignin was lower (P < 0·05) in spring than in summer herbages. In year 2, autumn herbages had significantly(P < 0·05) higher concentrations of crude protein and hemicellulose than summer and autumn herbages. Spring herbages had higher concentrations of water-soluble carbohydrates than summer (P 0·01) and autumn (P < 0·001) herbages. A higher (P < 0·05) metabolizable energy (ME) concentration was observed in spring compared with summer herbages in year 2 and in general there was considerably more variability in the values for the spring growths, ME content fell with increasing maturity in spring growths(0·046 and 0·035 MJ kg^-1 DM per day; years 1and 2 respectively) and this decline was 3–4 times faster than for autumn-harvested material (0·012 and 0·017 MJ kg^-1 DM per day; years 1 and 2 respectively). In both years only immature spring herbages consistently produced ME contents in excess of 11·9 MJ kg^-1 DM. For 15 of the herbages the proportion of gross energy intake (GEI) lost as methane was measured directly using respiration chambers. The mean methane energy loss was 0·07 of GEI (range 0·057–0·082). A commonly used publish equation for predicting methane energy loss was shown not to be appropriate, although no relationships could be established between methane energy loss and either energy digestibility in vivo or chemical composition.