Using QTL and GBS SNPs to Study the Contemporary Evolution of Introduced Wild Oats in California

Avena barbata (slender wild oat) is a tetraploid (AB genome, 2n=4x=28) oat introduced and widespread in California.  Allozyme studies in the 1970's identified two multilocus genotypes associated with contrasting moist and dry habitats, suggesting divergently adapted ecotypes.  However, QTL mapping of recombinant inbred lines have since revealed no evidence of local adaptation. Instead, the same high fitness alleles, mostly originating from the moist allozyme genotype, are consistently favoured by natural selection across field gardens and these results predict the spread of favoured genotypes.  Genotype by Sequencing of RILs using a two-enzyme library yielded over 3000 high-quality SNPs.  This increased both the coverage and density of the earlier AFLP map, and connected the 19 AFLP linkage groups into 14 chromosomes.  Seven of these chromosomes cross-mapped to linkage groups in an A-genome diploid map. I also screened a preliminary diversity panel of wild A. barbata accessions from throughout California using a single enzyme (PstI) GBS system.  This yielded fewer SNPs, but these could be placed on the higher density map.  Although southern California is still virtually monomorphic for a single GBS genotype matching the dry allozyme ecotype, many other areas formerly occupied by the dry ecotype now contain the moist adapted ecotype, or recombinant hybrids.  A third introduction in Northern California has added new genetic variation to the system.  Many Northern California populations exhibit new SNP alleles that are not segregating in the moist by dry mapping cross.