ABSTRACT
The next and most important phase after the confirmation of herbicide resistance in a weed population is the deciphering of the underlying resistance mechanism(s). The majority of research studies investigating differential absorption, translocation, and metabolism are based on availability and application of C-labeled herbicides. Herbicide sequestration, especially, sequestration of glyphosate, as a resistance mechanism has been investigated and reported on extensively. This chapter aims to summarize current understanding of metabolic resistance in weeds by providing a history of related research, reporting recent advances, and identifying future research opportunities. In general, five modes of herbicide resistance have been identified in weeds: (1) altered target site due to a mutation at the site of herbicide action resulting in complete or partial lack of inhibition; (2) metabolic deactivation; (3) reduced absorption and/or translocation; (4) sequestration/compartmentation by which a herbicide is immobilized away from the site of action; and (5) gene amplification/over-expression of the target site.
