Weed resistance to herbicides–mechanisms and molecular basis

Abstract

 Herbicide resistance is increasing througout the world in a rapid and threatening pace. Resistance is usually associated with high selection pressure imposed on the weed population by using high rates of residual herbicides, monoculture and minimum tillage. As an answer to such a strong selection impact and due to the fact that one herbicide or those having the same mechanism of impact are successively used, the genetic composition of weed populations changes in that the frequency of resistant allells and individuals increases. Re–use of the same herbicide or of that with the same impact mode disrupts the sensitive and makes the resistant populations viable so that the characteristics of resistance may further be transferred to the next generation.

This review summarises information from the literature and experimental experience of the authors in research on weed resistance to herbicides. Factors conditioning the origin of resistance are described. The origin of resistant weeds to nine active ingredients with a different mode of action is presented chronologically and the distribution of resistant weeds around the world outlined. The fundamental modes of action: reduction of the target site sensitivity, so–called „target site resistance“, and the mode by which a herbicide is metabolised into inactive products, are listed. Function and genetic modifications of target sites of selected herbicides are described.