RT Dissertation/Thesis
T1 Consequences for weed management in crop rotations by introducing imidazolinone-tolerant oilseed rape varieties
A1 Krato,Christoph
WP 2013/01/08
AB OSR (Brassica napus L.) is one of the most important arable oil crops globally and is grown on an area of 31,680,945 ha as winter- and spring-sown varieties. The harvest is mainly used in human nutrition, animal feeding and as a renewable resource for the production of paints, varnishes and biodiesel.
OSR can be considered a quite competitive crop but nonetheless weed control is carried out on the vast majority of the grown area. The most common treatments are done PRE-E or early POST-E, mainly as prophylactic treatments without exact knowledge of the weed species or their densities. In order to facilitate a more targeted weed control in OSR, IT varieties combined with the corresponding imidazolinone herbicide imazamox (target-site is ALS) + metazachlor/quinmerac (ClearfieldŽ production system) were developed for the European market by BASF SE and several breeding companies. 
By integrating IT plants into cropping systems, herbicide-tolerance genes will appear in agricultural ecosystems. Unless the tolerance is achieved by non-transgenic breeding methods, the introduction creates concerns regarding spreading the herbicide-tolerance in space and time causing unwanted changes for volunteer OSR management. 
The aim of the present study was to investigate important aspects, which are likely to arise with a commercial introduction and cultivation of IT OSR in Europe: 
POST-E weed control was successful using IT varieties. The total herbicide efficacy of imazamox/metazachlor/quinmerac was about 90 % in the field trials. Good results were achieved against volunteer cereals, Thlaspi arvense, Chenopodium album, Matricaria inodora, Papaver rhoeas, Capsella bursa-pastoris and Apera spica-venti but a lack of efficacy was observed regarding control of Agropyron repens and Viola arvensis. Yield was increased significantly in treated plots compared to untreated ones by up to 50 %. IT OSR can be a tool for the use of damage thresholds in integrated weed management in OSR.
Outcrossing between IT and IS OSR varieties was confirmed with outcrossing frequencies between 0.57 and 2.05 % between pollen donors and acceptors that were directly adjacent. 
Outcrossing declined significantly with increasing distance but was still found 45 m from IT plants. The transfer of both tolerance genes and heterozygosity was shown by 84 % of analysed F1-plants. 
A cross-tolerance of IT OSR to SUs, TPs and SCTs was shown in greenhouse bioassays and field trials with calculated resistance factors between 5 and 775. Furthermore, homozygous IT plants expressed a much higher tolerance level compared to heterozygous ones. 
Herbicides with alternative modes of action other than HRAC B (ALS-inhibition) were found to be effective to control IT volunteers in subsequent crops. Pendimethalin, picolinafen, isoproturon, diflufenican, florasulam, flufenacet and flurtamone controlled IT volunteers in WW. In sugar beet, herbicide combinations with metamitron, desmedipham, phenmedipham, ethofumesate, chloridazon and lenacil were able to control IT volunteers but single active ingredients were not.
Significant negative correlations were detected for the independent variable volunteer OSR density and the wheat yield parameters heads m-2, HW and yield. In contrast, moisture content of wheat and percentage of dockage increased with increasing volunteer density. The highest volunteer density of 261 plants m-2 caused a maximum yield loss of 68 % in WW. Based on a non-linear regression analysis, a single volunteer OSR plant per m2 causes a yield loss of between 0.74 and 1.61 %. 
In conclusion, the use of IT OSR varieties can substitute the herbicide clomazone in the future and provide POST-E weed control with detailed knowledge of the weed spectrum. This can promote integrated weed management, the use of damage thresholds in weed control and working management benefits for growers.
Clearly, difficulties in volunteer management are a drawback of IT OSR, but with conducting an accurate, delayed tillage after OSR harvest and adjusting herbicide regimes in subsequent crops, IT volunteers should not cause more harm compared to IS OSR volunteers. 
Based on the assumption that innovations in development of new active ingredients for weed control cannot be expected, the use of HT crops has to be seen as a major tool to solve issues in weed management.

K1 Imidazolinone
K1 Ausfallraps
K1 Clearfield
K1 Herbizidtoleranz
PP Hohenheim
PB Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
UL http://opus.uni-hohenheim.de/volltexte/2013/793