Abstract

Herbicide-resistant weeds pose a serious threat to weed management across the globe. Weeds evolve resistance to herbicides as a result of herbicide selection pressure. Under continuous herbicide selection, the resistant individuals dominate in a population. Understanding the genetics of herbicide resistance will help assess frequency and spread of herbicide resistance allele(s) in a population, which will assist in formulating prudent weed management practices to delay the evolution of resistance. Herbicide resistance, inherited by nuclear genes evolves quicker and spreads rapidly as the trait can be transmitted via pollen as opposed to maternally-inherited resistance. Dominant expression of the resistance allele also accelerates the process. Target-site resistance (TSR) is determined by a single gene, and is more likely a result of strong selection pressure. Although, non-target site resistance (NTSR) usually results under moderate selection pressure accumulating multiple alleles with minor effects imparting resistance, it may also involve a single gene when evolved under high selection pressure. Such monogenic resistances evolve and spread quickly, especially when the resistance is dominant and nuclear-inherited. Herbicide mixtures with different modes of action when applied at recommended doses can effectively delay the evolution of both TSR and NTSR.