Browsing by Subject "Herbicide"

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Adaptation of model organisms and environmental bacilli to glyphosate gives insight to species-specific peculiarities of the shikimate pathway
(2024) Schwedt, Inge; Commichau, Fabian M.
Glyphosate (GS), the active ingredient of the popular herbicide Roundup, inhibits the 5-enolpyruvyl shikimate-3-phosphate (EPSP) synthase of the shikimate pathway, which is present in archaea, bacteria, Apicomplexa, algae, fungi, and plants. In these organisms, the shikimate pathway is essential for de novo synthesis of aromatic amino acids, folates, quinones and other metabolites. Therefore, the GS-dependent inhibition of the EPSP synthase results in cell death. Previously, it has been observed that isolates of the soil bacteria Burkholderia anthina and Burkholderia cenocepacia are resistant to high amounts of GS. In the framework of this PhD thesis, it could be demonstrated that B. anthina isolates are not intrinsically resistant to GS. However, B. anthina rapidly adapts to the herbicide at the genome level and the characterization of GS-resistant suppressor mutants led to the discovery of a novel GS resistance mechanism. In B. anthina, the acquisition of loss-of-function mutations in the ppsR gene increases GS resistance. The ppsR gene encodes a regulator of the phosphoenolpyruvate (PEP) synthetase PpsA. In the absence of a functional PpsR protein, the bacteria synthesize more PEP, which competes with GS for binding in the active site of the EPSP synthase, increasing GS resistance. The EPSP synthase in B. anthina probably does not allow changes in the amino acid sequence as it is the case in other organisms. Indeed, the Gram-negative model organism Escherichia coli evolves GS resistance by the acquisition of mutations that either reduce the sensitivity of the EPSP synthase or increase the cellular concentration of the enzyme. Unlike E. coli, the EPSP synthase is also critical for the viability of Gram-positive model bacterium Bacillus subtilis. This observation is surprising because the enzyme belongs to the class of GS-insensitive EPSP synthases. In fact, the EPSP synthase is essential for growth of B. subtilis. The determination of the nutritional requirements allowing the growth of B. subtilis and E. coli mutants lacking EPSP synthase activity revealed that the demand for shikimate pathway intermediates is higher in the former organism. This finding explains why laboratory as well as environmental Bacilli exclusively adapt to GS by the mutational inactivation of glutamate transporter genes. Here, it was also shown that a B. subtilis mutant lacking EPSP synthase activity grows in minimal medium only when additional mutations accumulate in genes involved in the regulation of aerobic/anaerobic metabolism and central carbon metabolism. The characterization of these additional mutants will help to elucidate the peculiarities of the shikimate pathway in B. subtilis. Moreover, the mutants could be useful to identify the aromatic amino acid transporters that still await their discovery.
Development and testing of a precision hoeing system for re-compacted ridge tillage in maize
(2024) Alagbo, Oyebanji O.; Saile, Marcus; Spaeth, Michael; Schumacher, Matthias; Gerhards, Roland
Ridge tillage (RT) is a conservation practice that provides several benefits such as enhanced root growth and reduced soil erosion. The objectives of this study were to develop an autosteered living mulch seeder and hoeing prototype for RT systems using RTK-GNSS (real-time kinematic global navigation satellite systems) created ridges as a guide. It was also aimed to compare weed control efficacy and crop response of ridge-hoeing compared to conventional hoeing in flat tillage (FT). It was further aimed to investigate the impact of a new RT technology (with ridge re-compaction) on maize root development, yield, soil temperature, and moisture compared to FT. Field experiments were conducted with maize in 2021 and 2022 in a two-factorial split-plot design with tillage (RT and FT) as main treatment and weed control (untreated, herbicide, twice hoeing, hoeing + living mulch) as sub-treatment factors. Weed density, coverage, biomass, crop density, weed control efficacy (WCE) and maize silage yield were assessed. Temperature loggers were installed within RT and FT to take temperature readings at 20 min. Soil moisture and root penetrability were measured every two weeks in each plot using soil samples and a penetrometer. The WCE and yield did not differ significantly between the tillage systems. Twice hoeing resulted in 71–80 % WCE, which was equal to herbicide treatment. Hoeing + living mulch achieved 70–72 % WCE. Different from previous studies with ridge tillage, temperatures in the compacted ridges did not consistently differ from the ridge valleys and flat seedbeds. Root penetration (against 1.4 MPa penetrometer cone index) was 40 % higher in RT than in FT. On average, RT maize produced more (53.6 g m−2) root biomass compared to FT. In summary, re-compacted ridges built along RTK-GNSS lines can allow post-emergent hoeing and living mulch seeding along ridges and also provide good growing conditions for maize.
Integrating perennial biomass crops into crop rotations: How to remove miscanthus and switchgrass without glyphosate
(2023) Lewin, Eva; Kiesel, Andreas; Magenau, Elena; Lewandowski, Iris
Perennial energy grasses have gained attention in recent years as a promising resource for the bioeconomy because of their benign environmental profile, high stress tolerance, high biomass yields and low input requirements. Currently, strong breeding efforts are being made to extend the range of commercially available miscanthus and switchgrass genotypes. In order to foster farmers' acceptance of these crops, and especially of novel hybrids, more information is required about how they can be efficiently integrated into cropping rotations, how they can be removed at the end of their productive lifespan, and what effect they have on subsequently grown crops. Farmers in Europe are meanwhile increasingly constrained in the methods available to them to remove these crops, and there is a risk that the herbicide glyphosate, which has been used in many studies to remove them, will be banned in coming years. This study looks at the removal of seven‐year‐old stands of miscanthus and switchgrass over 1 year at an experimental site in Southern‐Germany. Three novel miscanthus genotypes were studied, alongside one variety of switchgrass, and the impact of each crop's removal on the yield of maize grown as a follow‐on crop was examined. A combination of soil tillage and grass herbicides for maize cultivation was successful in controlling miscanthus regrowth, such that yields of maize grown after miscanthus did not differ significantly from yields of maize grown in monoculture rotation (18.1 t dry biomass ha−1). Yields of maize grown after switchgrass (14.4 t dry biomass ha−1) were significantly lower than maize in monoculture rotation caused by insufficient control of switchgrass regrowth by the applied maize herbicide. Although some regrowth of miscanthus and switchgrass was observed in the follow‐on crop maize, complete eradication of both crops was achieved by subsequent winter wheat cultivation.