Different methods for recording morphological and physiological parameters were used to define the level of susceptibility/resistance of Abutilon theophrasti populations to atrazine, in the period between 2002 and 2003. Three different populations of A. theophrasti from the fields near Belgrade were investigated. Total leaf weight and fresh
and dry shoot weight among morphological parameters as well as transpiration, water vapour diffusion, chlorophyll fluorescence and total amount of chlorophyll among physiological parameters were measured. Minor differences to atrazine application between the tested populations of A. theophrasti were observed. There are some differences in all morphological parameters, but the most informative ones were the total fresh and dry shoot weight. Although the
measurements of chlorophyll fluorescence caused lower differences between tested populations, this method proved itself as most sensitive among physiological methods. Calculated resistance indexes based on different parameters ranged from 2.2 to 15.9.
