Empirical investigation of de novo mutations conferring herbicide resistance
In a predictable natural selection process, herbicides select for adaptive alleles that allow weed populations to survive. These resistance alleles may be available immediately from the standing genetic variation within the population, as well as, may immigrate via pollen or seeds from other populations. Moreover, because all natural populations are constantly subject to new mutant genotypes by de novo mutations, resistant mutants may arise spontaneously in any herbicide-sensitive weed population. Recognizing that the relative contribution of each of these three sources deeply affect what strategies should be applied to counteract herbicide resistance evolution, we aimed to provide experimental information to the resistance evolutionary framework. In this sense, the objective of this experiment was to calculate the de novo mutation rate conferring herbicide resistance in a natural plant population, and, specifically, test the hypothesis that the mutation rate increases when plants are stressed by sub-lethal exposure to herbicides. For this purpose, we used a method to discover spontaneous herbicide-resistant mutants by screening millions of plants using grain amaranth and resistance to ALS herbicides as a model system. After screening 70,000,000 plants, no spontaneous resistant genotypes were detected, determining the probability to find a spontaneous ALS-resistant mutant in a given sensitive plant population as lower than 2 x 10-8. This is lower than expected from theoretical calculations based on previous studies, setting a higher limit for the probability of herbicide-resistant mutants to arise spontaneously in natural plant populations. In addition, we found no evidence that herbicide stress increased the mutation rate. The results found in this study imply that de novo mutations conferring herbicide resistance do not appear to occur at high frequency in plant populations.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign