USING CHLOROPHYLL FLUORESCENCE INDUCTION FOR A QUANTITATIVE DETOXIFICATION ASSAY WITH METRIBUZIN AND CHLOROTOLURON IN EXCISED WHEAT (TRITICUM-AESTIVUM AND TRITICUM-DURUM) LEAVES

Chlorophyll fluorescence induction was used as a probe to detect herbi cide detoxification in tolerant or susceptible wheat cultivars. Experi mental conditions have been carefully examined for establishing detoxi fication kinetics of chlorotoluron and metribuzin, two photosystem-II- inhibiting herbicides. After a root treatment, leaves were cut, placed in glass tubes and maintained in the dark. The fluorescence induction rise was examined repeatedly and detoxification kinetics were establi shed from these data for the same position on the individual leaves. T he herbicide-dependent fluorescence rise decreased within hours in chl orotoluron-tolerant but not in susceptible Triticum aestivum cultivars . In contrast, no significant reversion could be detected after metrib uzin application in both tolerant and susceptible cultivars of Triticu m durum. Near the fluorescence-determined half-inhibition of photosyst em II, linear detoxification kinetics were obtained in individual leav es, thus providing an accurate measurement of relative detoxification rates.