Fitness costs associated with evolved herbicide resistance alleles in plants

Abstract

Summary: Predictions based on evolutionary theory suggest that the adaptive value of evolved herbicide resistance alleles may be compromised by the existence of fitness costs. There have been many studies quantifying the fitness costs associated with novel herbicide resistance alleles, reflecting the importance of fitness costs in determining the evolutionary dynamics of resistance. However, many of these studies have incorrectly defined resistance or used inappropriate plant material and methods to measure fitness. This review has two major objectives. First, to propose a methodological framework that establishes experimental criteria to unequivocally evaluate fitness costs. Second, to present a comprehensive analysis of the literature on fitness costs associated with herbicide resistance alleles. This analysis reveals unquestionable evidence that some herbicide resistance alleles are associated with pleiotropic effects that result in plant fitness costs. Observed costs are evident from herbicide resistance‐endowing amino acid substitutions in proteins involved in amino acid, fatty acid, auxin and cellulose biosynthesis, as well as enzymes involved in herbicide metabolism. However, these resistance fitness costs are not universal and their expression depends on particular plant alleles and mutations. The findings of this review are discussed within the context of the plant defence trade‐off theory and herbicide resistance evolution. Contents Summary 751 I. Introduction 752 II. Methods for the detection and estimation of herbicide resistance fitness costs 753 III. Fitness costs associated with AHAS target site resistance 756 IV. Fitness costs associated with ACCase target site resistance 757 V. Fitness costs associated with resistance to phenoxy herbicides 758 VI. Arabidopsis thaliana as a model plant to understand pleiotropic effects of herbicide target‐site based resistance alleles 759 VII. Fitness costs associated with herbicide resistance endowed by enhanced rates of herbicide metabolism catalysed by P450 enzymes 760 VIII. Fitness costs associated with glyphosate resistance 760 IX. Discussion 761 X. Conclusion 762 Acknowledgements 763 References 763