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Browsing by Person "Kaiser, Yasmin"

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    Integrated management, analysis of mechanisms and early detection of resistant populations of Alopecurus myosuroides HUDS. and Apera spica-venti L. Beauv.
    (2015) Kaiser, Yasmin; Gerhards, Roland
    The control of pests is one of the major challenges in agricultural production worldwide. Especially weeds cause severe yield losses by competing with crops for light, space, water and nutrients. Due to the relatively low costs for acquisition and application of herbicides and a high control efficacy, chemical measures are predominantly applied to control weeds. In Europe, Alopecurus myosuroides HUDS. (blackgrass) and Apera spica-venti L. Beauv. (silky windgrass) are major weeds especially in winter wheat. The occurrence at high population densities in combination with a consequent use of herbicides with the same modes of action has resulted in the selection of resistant populations. Populations with target-site resistance (TSR) as well as non-target-site resistance (NTSR) could be confirmed for A. myosuroides and A. spica-venti. In contrast to the mechanisms of TSR, NTSR mechanisms are less investigated. Due to the steadily increasing number of putative herbicide resistant weed populations, the demand for rapid resistance tests is rising. The papers of the dissertation focus on the integrated management, the investigation of resistance mechanisms and the detection of herbicide resistant weed populations. The following research objectives have been examined within the four work packages (papers): – To develop a new methodology for a rapid detection of herbicide resistance and to confirm that results are comparable with classical greenhouse approaches – To investigate metabolism of herbicides in sensitive and resistant populations of A. myosuroides to gain comprehensive knowledge on resistance mechanisms – To evaluate the influence of agronomic factors on the probability of resistance occurrence and to develop a geo-referenced database for mapping the spread of herbicide-resistant A. spica-venti populations across Europe – To assess the influence of crop rotation and herbicide strategies on population development and herbicide resistance of A. myosuroides and crop yield The four papers come to the following results regarding the main research objectives: 1st paper: A laboratory test was developed to accelerate the detection of herbicide resistance. Therefore, A. myosuroides was cultivated in wellplates containing nutrient agar and herbicides. The evaluation of herbicide resistance was conducted by a sensor, measuring chlorophyll fluorescence. The results of the developed test corresponded well to the standard whole-plant pot tests in the greenhouse. In both tests sensitive and resistant populations were identified, however results of the Chlorophyll Fluorescence Imaging were available earlier. 2nd paper: Metabolism of herbicides was investigated in populations of A. myosuroides by using liquid chromatography - tandem mass spectrometry (LC-MS/MS) to gain comprehensive knowledge on mechanisms of herbicide resistance. NTSR populations differed from sensitive and TSR A. myosuroides in form of an enhanced degradation of the active ingredient or metabolite, depending on the investigated herbicide. For the investigated herbicides (inhibition of ACCase and ALS) it was shown that herbicide metabolism plays an important role regarding herbicide resistance in A. myosuroides. 3rd paper: To evaluate the influence of agronomic factors on the probability of resistance occurrence in A. spica-venti, numerous populations were screened in the greenhouse. The corresponding field history obtained from questionnaires and the results of greenhouse assays were used to develop a GIS-database in which herbicide-resistant A. spica-venti populations were mapped. The statistical analysis revealed that a high percentage of winter crops in the crop rotation, together with conservation tillage, early sowing dates and high population density increased the occurrence of herbicide resistance in A. spica-venti. 4th paper: To assess the impact of crop rotation and herbicide strategies on A. myosuroides, field studies at two locations in Southern Germany have been carried out. Results show that densities of A. myosuroides increased in continuous winter wheat. The introduction of spring crops significantly reduced densities, even without using herbicides. Furthermore it has been shown that the risk of herbicide resistance was reduced when performing a consequent change of herbicide mode of action. The use of herbicides with only one mode of action increased the number of herbicide resistant plants. Crop yield was notably influenced by A. myosuroides in winter wheat. The overall results of this dissertation showed the great impact of agricultural measures on herbicide resistance in A. myosuroides and A. spica-venti and demonstrated opportunities for prevention and management. The developed resistance quick test provides an accelerated detection of herbicide resistance and therefore the chance to initiate resistance management strategies much earlier.