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Standing Genetic Variation Behind Blackgrass Resistance to Herbicides, Study Shows

A chromosome-level reference genome for blackgrass (Alopecurus myosuroides), the most economically damaging herbicide-resistant weed in Europe, is reported in the Proceedings of the National Academy of Sciences this week, revealing that standing genetic variation is responsible for the plant's rapid evolution of herbicide resistance. The agricultural use of herbicides has led to the selection of many herbicide-resistant grass weeds over the past several decades, among them blackgrass. This selection pressure, while problematic for farmers, presents the opportunity for investigating how organisms rapidly respond to strong selection, especially the role newly arising mutations play versus mutations that are already present in a population. To that end, a team led by Max Planck Institute for Biology scientists generated a high-quality A. myosuroides reference genome, then combined analyses of known herbicide-resistant loci with forward-in-time simulations to show that target-site resistance mutations likely often predate the application of herbicides. The findings, the study's authors write, indicates that "with the diversity of resistance mechanisms available, a large fraction of A. myosuroides populations is likely to have the genetic prerequisites not only for rapid evolution of resistance to currently used herbicide modes of action but also to potential new future modes of action.