Patterns of genetic variation in a prairie wildflower, Silphium integrifolium, suggest a non-prairie origin and locally adaptive variation.

Abstract

AO_SCPLOWBSTRACTC_SCPLOWO_ST_ABSPremiseC_ST_ABSUnderstanding the relationship between genetic structure and geography provides information about a species evolutionary history and can be useful to breeders interested in de novo domestication. The North American prairie is especially interesting because of its relatively recent origin and subsequent dramatic fragmentation and degradation. Silphium integrifolium is an iconic perennial American prairie wildflower targeted for domestication as an oilseed crop. Germplasm in the existing breeding program is derived from accessions collected in restricted geographic regions. We present the first application of population genetic data in this species to address the following goals (1) improve breeding programs by characterizing genetic structure and (2) identify the species geographic origin and potential targets and drivers of selection during range expansion. MethodsWe developed a reference transcriptome as a genotyping reference for samples from throughout the species range. Population genetic analyses were used to describe the distribution of genetic variation and demographic modeling was used to characterize potential processes that shaped variation. Outlier scans for selection and associations with environmental variables were used to identify loci linked to putative targets and drivers of selection. Key resultsGenetic variation partitions samples into three geographic clusters. Patterns of variation and demographic modeling suggest that the species origin is in the American southeast. Breeding program accessions are from the region with lowest observed genetic variation. ConclusionsThis iconic prairie species did not originate within the modern prairie. Breeding programs can be improved by including accessions from outside of the germplasm founding region, which has relatively little variation. The geographic structuring coupled with the identified targets and drivers of adaptation can guide collecting efforts towards populations with beneficial agronomic traits.