Genome-wide genotyping-by-sequencing data provide a high-resolution view of wild Helianthus diversity, genetic structure, and interspecies gene flow

Premise: Wild sunflowers harbor considerable genetic diversity and are a major resource for improvement of the cultivated sunflower, Helianthus annuus. The Helianthus genus is also well known for its propensity for gene flow between taxa.

Methods: We surveyed genomic diversity of 292 samples of wild Helianthus from 22 taxa that are cross-compatible with the cultivar using genotyping by sequencing. With these data, we derived a high-resolution phylogeny of the taxa, interrogated genome-wide levels of diversity, explored H. annuus population structure, and identified localized gene flow between H. annuus and its close relatives.

Key results: Our phylogenomic analyses confirmed a number of previously established interspecific relationships and indicated for the first time that a newly described annual sunflower, H. winteri, is nested within H. annuus. Principal component analyses showed that H. annuus has geographic population structure with most notable subpopulations occurring in California and Texas. While gene flow was identified between H. annuus and H. bolanderi in California and between H. annuus and H. argophyllus in Texas, this genetic exchange does not appear to drive observed patterns of H. annuus population structure.

Conclusions: Wild H. annuus remains an excellent resource for cultivated sunflower breeding effort because of its diversity and the ease with which it can be crossed with cultivated H. annuus. Cases of interspecific gene flow such as those documented here also indicate wild H. annuus can act as a bridge to capture alleles from other wild taxa; continued breeding efforts with it may therefore reap the largest rewards.