PgmNr P2017: The evolution of herbicide resistance in an agricultural weed, Capsella bursa-pastoris.

Authors:
Julia Kreiner; John Stinchcombe; Stephen Wright


Institutes
University of Toronto, Toronto, Ontario, CA.


Abstract:

How much is adaptive evolution driven by local de novo mutation, selection on standing variation, or gene flow from other populations? Weed populations regularly sprayed with herbicides generally experience stronger and more predictable selection than natural populations, and have well-characterized target loci subject to selection, making them an interesting model for understanding the population genomics of adaptation. Here we investigate the population genomics of resistance to acetolactate synthase (ALS) inhibitor herbicides in the agricultural weed Capsella bursa-pastoris across a broad geographic range in Alberta and Saskatchewan, Canada. We genotyped 96 individuals via genotype-by-sequencing (GBS) and sequenced whole genomes from 192 individuals distributed among two pools collected from low and high resistance geographic regions. We compared the number of independent resistance mutations and the frequency of resistance mutations from our pooled-seq data to population structure estimates from our GBS data.  We infer the extent to which herbicide resistance adaptation was driven by local vs. global selective sweeps, and/or from selection on standing genetic variation.  The evolution of resistant agricultural weeds in response to single target herbicides is becoming increasingly common since reports were first made in 1968 (Jasieniuk et al., 1996) and underlines the importance of understanding how the evolutionary rescue of populations proceeds under increasing levels of stress. The origins and spread of herbicide resistance alleles is important for contemporary weed management, food security, and conservation.