Laying a genetic foundation for Silphium integrifolium domestication

Abstract

Silphium integrifolium, a member of the Asteraceae family native to the central United States, has been proposed as a candidate for domestication as a new perennial oilseed crop. If successfully domesticated, S. integrifolium has the potential to provide growers with a profitable crop while improving pollinator habit and reducing soil erosion, nutrient leaching, and reliance on irrigation. As breeding work towards this goal was initiated relatively recently, a number of questions still remain which will need to be answered to facilitate the domestication process. This dissertation fills some of these knowledge gaps, and in so doing contributes to a foundation which may be built on by future breeding work. My first study described phenotypic variation available for breeding in S. integrifolium and developed selection targets. I evaluated a set of 380 diverse S. integrifolium genotypes in six locations, ranging from northwest Minnesota to southeast Texas, measuring a number of architecture, yield, and phenology traits over the course of several years. I then use this data to identify traits which were relatively heritable, and traits which were highly influenced by within- and between-environment variation, as well as to identify patterns of change across time. Selection targets were then identified based on correlations and relationships among traits of interest. In my second study, I measured the prevalence of inbreeding depression in S. integrifolium, expressed both as embryo lethal alleles and as reductions in biomass and yield traits. Both of these phenomena have the potential to negatively impact S. integrifolium breeding efforts, and I recommend several strategies that could be used to mitigate this problem. In my third study, I developed the first linkage map for S. integrifolium. I then was able to successfully map the S. integrifolium self-incompatibility locus by developing a novel experimental design and collaborating with another researcher to develop an analysis method for the design. This finding represented one of the first times a self-incompatibility locus has been mapped in the Asteraceae family, and has implications both for the breeding of S. integrifolium, and for better understanding self-incompatibility in the Asteraceae family. Finally, in my concluding chapter, I discuss some of the breeding progress which was made over the course of my graduate school career, and identify ways in which my findings could be used in future efforts.