THE IMPACT OF STROBILURINS ON THE PLANT PHYSIOLOGY OF WHEAT
J HABERMEYER, M GERHARD and V ZINKERNAGEL
Technical University of Munich, Freising-Weihenstephan, Germany
Background and objectives
Materials and methods
The possibly altered phytohormone level was measured with the parameter ethylene production by aid of gas chromatography. As Grossmann and Retzlaff  proposed for controlled conditions, a change in the carbon dioxide compensation point after applying kresoxim-methyl gas exchange and chlorophyll fluorescence measurements were carried out in the field. The possibly changed photosynthetic activity on biomass production and stress tolerance of wheat plants should be investigated. The above-ground biomass production after strobilurin use was assessed weekly. The nitrogen and carbon content as well as translocation proceedings were studied by using an elementary analyser and mass spectrometer.
Results and conclusions
No significant correlation between the intensity of ethylene production in GS 75 on flag leaves and the timing of strobilurins (varying between GS 30 and GS 59) was remarkable, i.e. ethylene formation was reduced (compared to convential sprayed plants) to the same level independant from application timing. This 'memory-effect' resulted in corresponding yield responses.
Chlorophyll fluorescence studies showed greater stress tolerance of strobilurin treated plants especially concerning draught stress. Stomatal regulation is significantly changed in strobilurin plots over a whole day measuring period.
In conclusion, kresoxim-methyl or azoxystrobin induce severe physiological changes in field wheat plants. In combination they seem to enable plants for better adaption to environment. In most cases this leeds to an average yield increase up to 5-10%.