Project description:Resistance to herbicides in weeds can be due to alteration(s) in the gene encoding the herbicide target site, or to herbicide degradation via a deviation in plant general metabolism. If target-site-based resistance is easy to study, the multigenic control of metabolism-based resistance renders it much more complex to study. Metabolism-based resistance to herbicides represents the major part of herbicide resistance in black-grass. Its most likely basis is an overexpression of genes encoding enzymes degrading herbicides. We thus seek to identify such overexpressed genes by comparing the transcriptomes of resistant and sensitive black-grass individuals belonging to an F2 line segregating for two resistance genes. Given there are no genomic tools developed for black-grass, this approach will use heterologous hybridisation onto a wheat Affymetrix microarray. Comparison using heterologous hybridisation onto a wheat whole-genome microarray of transcriptome of three pools of black-grass plants obtained 2h30 after herbicide spraying at field rate. The three pools correspond to: · Sensitive plants (killed by herbicide). · Moderately resistant plants (growth impaired by herbicide but plants still alive) · Resistant plants (growth unimpaired by herbicide) 6 arrays - wheat
Project description:Resistance to herbicides in weeds can be due to alteration(s) in the gene encoding the herbicide target site, or to herbicide degradation via a deviation in plant general metabolism. If target-site-based resistance is easy to study, the multigenic control of metabolism-based resistance renders it much more complex to study. Metabolism-based resistance to herbicides represents the major part of herbicide resistance in black-grass. Its most likely basis is an overexpression of genes encoding enzymes degrading herbicides. We thus seek to identify such overexpressed genes by comparing the transcriptomes of resistant and sensitive black-grass individuals belonging to an F2 line segregating for two resistance genes. Given there are no genomic tools developed for black-grass, this approach will use heterologous hybridisation onto a wheat Affymetrix microarray. Comparison using heterologous hybridisation onto a wheat whole-genome microarray of transcriptome of three pools of black-grass plants obtained 2h30 after herbicide spraying at field rate. The three pools correspond to: · Sensitive plants (killed by herbicide). · Moderately resistant plants (growth impaired by herbicide but plants still alive) · Resistant plants (growth unimpaired by herbicide)
Project description:Alopecurus myosuroides Huds. is an important pinoxaden-resistant grass weed in many countries of Europe. Recently, the low efficacy of pinoxaden was reported in winter cereals in Croatia, but a preliminary dose-response trial showed no herbicide resistance for the investigated weed population. Therefore, a two-year experiment was conducted under greenhouse conditions to determine the efficacy of various pinoxaden doses (20, 40 and 80 g a.i. ha-1) on weed visual injuries and biomass reduction after herbicide application at different growth stages. As expected, the maximum weed biomass reduction (97.3%) was achieved by applying the highest dose (80 g a.i. ha-1) at the earliest growth stage (ZCK 12-14). A pinoxaden dose of 20 g a.i. ha-1 resulted in satisfactory weed biomass reduction (88.9%) only when applied at ZCK 12-14. The recommended dose (40 g a.i. ha-1) also provided sufficient weed control up to the growth stage ZCK 21-25. Slightly delayed (ZCK 31-32) application of the recommended dose brought about a low weed biomass reduction (60.1%). Double than the recommended dose also failed to provide satisfactory weed control at the advanced weed growth stages (ZCK 31-32 and ZCK 37-39). Thus, reported low efficacy of pinoxaden is most likely because of delayed herbicide application when A. myosuroides is overgrown.
Project description:Identification of the mechanisms that led to two different subtypes of multiple herbicide resistance in blackgrass using RNA-Seq data.
Project description:The distribution of Alopecurus myosuroides (black-grass) in fields is patchy. The locations of these patches can be influenced by the environment. This presents an opportunity for precision management through patch spraying. We surveyed five fields on various types of soil using a nested sampling design and recorded both A. myosuroides seedlings in autumn and seed heads in summer. We also measured soil properties at those sampling locations. We found that the patches of seed heads within a field were smaller than the seedling patches, suggesting that techniques for patch spraying based on maps of heads in the previous season could be inherently risky. We also found that the location of A. myosuroides patches within fields can be predicted through their relationship with environmental properties and that these relations are consistent across fields on different soil types. This improved understanding of the relations between soil properties and A. myosuroides seedlings could allow farmers to use pre-existing or suitably supplemented soil maps already in use for the precision application of fertilisers as a starting point in the creation of herbicide application maps.
Project description:The evolution of resistance to herbicides is a classic example of rapid contemporary adaptation in the face of a novel environmental stress. Evolutionary theory predicts that selection for resistance will be accompanied by fitness trade-offs in environments where the stress is absent. Alopecurus myosuroides, an autumn-germinating grass weed of cereal crops in North-West Europe, has evolved resistance to seven herbicide modes-of-action, making this an ideal species to examine the presence and magnitudes of such fitness costs. Here, we use two contrasting A. myosuroides phenotypes derived from a common genetic background, one with enhanced metabolism resistance to a commercial formulation of the sulfonylurea (ALS) actives mesosulfuron and iodosulfuron, and the other with susceptibility to these actives (S). Comparisons of plant establishment, growth, and reproductive potential were made under conditions of intraspecific competition, interspecific competition with wheat, and over a gradient of nitrogen deprivation. Herbicide dose response assays confirmed that the two lines had contrasting resistance phenotypes, with a 20-fold difference in resistance between them. Pleiotropic effects of resistance were observed during plant development, with R plants having a greater intraspecific competitive effect and longer tiller lengths than S plants during vegetative growth, but with S plants allocating proportionally more biomass to reproductive tissues during flowering. Direct evidence of a reproductive cost of resistance was evident in the nitrogen deprivation experiment with R plants producing 27% fewer seed heads per plant, and a corresponding 23% reduction in total seed head length. However, these direct effects of resistance on fecundity were not consistent across experiments. Our results demonstrate that a resistance phenotype based on enhanced herbicide metabolism has pleiotropic impacts on plant growth, development and resource partitioning but does not support the hypothesis that resistance is associated with a consistent reproductive fitness cost in this species. Given the continued difficulties associated with unequivocally detecting costs of herbicide resistance, we advocate future studies that adopt classical evolutionary quantitative genetics approaches to determine genetic correlations between resistance and fitness-related plant life history traits.
Project description:Acetyl-CoA carboxylase (ACCase) alleles carrying one point mutation that confers resistance to herbicides have been identified in arable grass weed populations where resistance has evolved under the selective pressure of herbicides. In an effort to determine whether herbicide resistance evolves from newly arisen mutations or from standing genetic variation in weed populations, we used herbarium specimens of the grass weed Alopecurus myosuroides to seek mutant ACCase alleles carrying an isoleucine-to-leucine substitution at codon 1781 that endows herbicide resistance. These specimens had been collected between 1788 and 1975, i.e., prior to the commercial release of herbicides inhibiting ACCase. Among the 734 specimens investigated, 685 yielded DNA suitable for PCR. Genotyping the ACCase locus using the derived Cleaved Amplified Polymorphic Sequence (dCAPS) technique identified one heterozygous mutant specimen that had been collected in 1888. Occurrence of a mutant codon encoding a leucine residue at codon 1781 at the heterozygous state was confirmed in this specimen by sequencing, clearly demonstrating that resistance to herbicides can pre-date herbicides in weeds. We conclude that point mutations endowing resistance to herbicides without having associated deleterious pleiotropic effects can be present in weed populations as part of their standing genetic variation, in frequencies higher than the mutation frequency, thereby facilitating their subsequent selection by herbicide applications.