CHLOROPHYLL FLUORESCENCE MICROSCREENING AS A RAPID DETECTION METHOD FOR HERBICIDE RESISTANCE IN GRASS WEEDS IN NORTH CHINA PLAIN WINTER WHEAT PRODUCTION SYSTEMS AND BEYOND

The North China Plain (NCP) is one of the most important winter wheat production areas in the world. A double cropping system of winter wheat followed by summer maize in one year is the most common cropping practice in the NCP. However new crops and agricultural practices including chemical weed control measures were recently introduced in this area. Alopecurus spp., Aegilops squarrosa L. and Bromus japonicus Thunb. were found to be the most abundant grass weeds in the NCP winter wheat production system. In 2008 and 2009, A. japonicus seeds were collected from different locations in the NCP to conduct herbicide efficacy studies. Besides conventional glasshouse bioassays a rapid herbicide resistance test has been developed and tested. This new resistance test is based on chlorophyll fluorescence microscreenings for evaluation of the efficacy of herbicides on grass weeds grown in tissue culture plates filled with an agar-herbicide solution. In glasshouse bioassays for chlorotoluron a resistance factor of 3.5 was found for one of the NCP biotypes compared to the sensitive control biotype. The chlorophyll fluorescence microscreening clearly verified this result. Further studies showed that this method is also suitable for other herbicide modes of action like ALS and ACC inhibitors. Furthermore this method is easily transferable to other important grass weeds. Using the chlorophyll fluorescence assay, it becomes possible to evaluate efficacy for a large number of biotypes with a minimum requirement of time and space. Therefore it is well suited for high throughput resistance screenings, especially at locations where glasshouse space is a limiting factor. An accelerated identification of resistant grass weed biotypes and thus a prompt resistance management plan for the field will be of great importance for the North China Plain and other intensive agricultural areas in the world.