Uptake, Translocation and Metabolism of ¹⁴C-lsoproturon in Susceptible and Resistant Biotypes of Little Seed Canary Grass (Phalaris minor) and Wheat (Triticum aestivum)

Studies with one biotype each of isoproturon resistant (R) and susceptible (S) Phalaris minor and wheat were carried out to investigate the physiological basis of their tolerance to the herbicide. Resistant population of P. minor and wheat recorded 13 and 15 times higher GR₅₀values (a dose required for 50% reduction in the biomass). In a time-course activity study where plants were exposed to 5 µg ml⁻¹ isoproturon for different durations, it was noticed that the dry weight reductions in R- P. minor and wheat with 24 h exposure were equivalent to a mere 4 h exposure for S- P. minor. The resistant population of P. minor recovered faster in herbicide-free nutrient solution following a 4 h pulse treatment with 5 µg m⁻¹ isoproturon compared to their susceptible counterparts. This demonstrated the presence of an enhanced detoxification mechanism in R-biotypes of P. minor. Detailed studies made with ¹⁴C-isoproturon revealed that there was no major difference with regard to the uptake of the herbicide or its translocation to the foliage between the plant species. However, the accumulation of the herbicide in roots of wheat was significantly lower than with both biotypes of P. minor. The metabolism studies following a pulse treatment with isoproturon revealed that the rate of detoxification was faster in R- biotype and in wheat than in S- biotype. At 96 h after treatment, wheat and R- P. minor metabolized 87.6 and 92.3% of applied isoproturon, respectively, compared to 67.7% in S-biotype. The metabolites were not identified but there appeared to be difference in metabolism participants between wheat and R-biotype of P. minor.