Alterations in amount of chlorophyll as indicator of resistance for Chenopodium album L. and Amaranthus retroflexus L. to atrazine

Resistance in weeds, as a natural phenomenon or caused by herbicide application, is a major challenge for science and agricultural production. Nevertheless, a small number of plants is naturally resistant or has developed a resistance caused by a natural selection process. Stress factors such as the use of herbicides results in development of resistant species by selection pressure. Slow uptake and translocation of herbicides, faster metabolization and/or the isolation of "foreign" molecules in certain tissues, structural changes in the target sites and others influencing factors are mechanisms of survival. Many research projects have been trying to find adequate physiological or morphological parameters for the determination of weed resistance to herbicides. For herbicides inhibiting photosynthesis, the most reliable parameters for the determination of weed resistance are bleaching effects as well as changes in plant dry mass and chlorophyll fluorescence. Therefore, the main objective of this study was to test the validity of measuring changes in the amount of chlorophyll as an indicator for the sensitivity/resistance of Chenopodium album L. and Amaranthus retroflexus L. to atrazine. The resistance was investigated using susceptible weed populations from Great Britain as well as weed populations from Great Crljeni and Belgrade. The total amount of chlorophyll was determined by a non-destructive method (SPAD meterchlorophyll readings obtained with the Minolta-502 SPAD meter) and a destructive methode (extraction by dimethylphormamide). The validity of both methods was evaluated and the amount of chlorophyll and its fluorescence was correlated. Results showed that by measuring the amount of chlorophyll in both ways it was possible to distinguish between sensitive and resistant weed populations. A correlation between the amount of chlorophyll and changes in fluorescence could not be not confirmed