RT Dissertation/Thesis
T1 Distribution, detection and genetic background of herbicide-resistant Alopecurus myosuroides (Huds.) in Germany
A1 Rosenhauer,Maria
WP 2015/09/14
AB Weed control is an important part in agricultural practice. Since selective herbicides were introduced, the labour-intensive mechanical weed control was replaced by chemicals. The use of chemicals for weed control has become increasingly problematic due to the evolution of herbicide-resistant weeds. In Germany, Alopecurus myosuroides (Huds.) is one of the most problematic weeds concerning herbicide resistance. The first resistant black-grass biotype in Germany was found in 1982.
More than 30 years after the first resistant black-grass was found in Germany (1982), there are still numerous unsolved questions and challenges concerning the problem of herbicide resistance. Further knowledge about the distribution, the detection, and the genetic background of different resistance mechanisms is needed to find comprehensive solutions for the future. Knowledge about the occurrence and distribution of herbicide-resistant black-grass in Germany, and the herbicides primarily affected may provide more detailed information for farmers to quickly react on upcoming resistances. Moreover, if the genetic background of resistance is better understood, practical conclusions regarding the choice of herbicides and management tools can be drawn. Furthermore, a reliable and easy-to-handle test system for the detection of resistances would enable farmers to react faster and in a more targeted manner.
The aim of the present study was to investigate these aspects addressing herbicide-resistant black-grass in Germany.
How widespread is TSR in Germany? Did the amount of TSR change over the years? Are there “TSR-hot spots” in Germany? 
The first paper addressed ACCase and ALS-resistant black-grass samples in Germany. It dealt with the distribution and development of TSR in Germany over a period of nine years. It could be demonstrated that TSR was more widespread than expected. The frequency of ACCase-TSR increased from 4.0% in 2004 to 38.5% in 2012. ALS-TSR rose from 0.8% in 2007 to 13.9% in 2012. Both TSRs significantly increased over time within a standing number of seed samples over the years. 
How many genes are involved in NTSR? Are there differences between the plants and can we detect cross-resistances? 
The second paper dealt with the inheritance of NTSR conferring resistance to chlorotoluron, fenoxaprop-P-ethyl, pinoxaden, mesosulfuron + iodosulfuron, and flufenacet in six different black-grass plants. Segregation analyses of the quantitative trait showed a minimum of five loci conferring specific resistances. The resistances against chlorotoluron and fenoxaprop-P-ethyl were mostly conferred by one locus, whereas resistances against pinoxaden and mesosulfuron + iodosulfuron were mostly conferred by a minimum of two loci. A minimum of one to three loci explained resistance to flufenacet. The accumulation of resistance loci in individual plants could be achieved by the study. Furthermore, the number of loci was shown to be herbicide- and plant-specific which further confirms the complexity of NTSR. 
How is it possible to test pre-emergence herbicides in black-grass? Which test system is the most reliable? 
The aim of the third paper was to find a reliable test system to monitor pre-emergence herbicide resistance in black-grass. It is widely known that diverse sites of action can be affected by NTSR. Moreover, resistance against pre-emergence herbicides belonging to the HRAC groups N, K3, and C2 occur. The outcomes of the study indicate that a soil-based greenhouse test with pre-germinated seeds is most suitable for resistance detection. Discriminating herbicide rates which were able to distinguish between the resistant and susceptible black-grass biotypes were found for all of the herbicides tested. This enables a reliable, quick, and easy way to identify pre-emergence resistance. 
In conclusion, herbicide-resistant black-grass has become an increasing problem in Germany. The high frequency of nearly 40% ACCase TSR on resistance suspected sites highlights the importance of changes in agricultural practices. The aim should be to avoid the repeated use of single site of action herbicides in short term crop-rotations with large quantities of winter cereals. The accumulation of NTSR loci in single plants increases the risk of biotypes with broad resistances against many different modes of action. Resistance linkages were found to be plant-specific which may result in unpredictable resistance situations in the field. Even pre-emergence herbicides can be affected by NTSR. An option to detect these resistances is provided by a soil-based greenhouse bioassay with pre-germinated seeds.

K1 Resistenz
K1 Herbizid
K1 Ackerfuchsschwanzgras
K1 Vorauflaufherbizide
PP Hohenheim
PB Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
UL http://opus.uni-hohenheim.de/volltexte/2015/1109