Abstract

The quantitative determination of ametryn, atrazine and prometryn as well as their metabolites in the culture medium of herbicide-treated Scenedesmus vacuolatuswas undertaken using high-performance liquid chromatography (HPLC). Resistant biotype metabolized about 60% of biologically active herbicides tested into two metabolites for ametryn and three metabolites for atrazine and prometryn.  Chromatographic analysis data of the three herbicides tested were strongly correlated with their inhibitory effects on algal growth and reproduction. Susceptible culture of S. vacuolatus was able to metabolize about 5% of the applied concentration of ametryn and atrazine into one metabolite (for ametryn) and two metabolites (for atrazine).  However, the same biotype was better able to metabolize 15% of applied concentration of prometryn into two metabolites.  The bioassay and biochemical data confirmed the role of herbicide metabolic degradation as a main mechanism of resistance toward herbicides.  In addition, surface area of resistant cell was about four times greater than susceptible cell; however, no clear difference in the thickness of cell was achieved.  Weed resistance toward herbicides could be managed by adding suitable synergists to herbicide formulations and also by integrating herbicides with negative cross resistance in rotation with non-chemical means of weed control.

Key words: Triazine herbicides, resistance phenomenon, resistance metabolic mechanism.