Date of Award


Document Type


Degree Name

Master of Science (MS)


Plant and Soil Science

First Advisor

Eric J. Bishop-von Wettberg


There are many mechanisms by which landraces evolve in a contemporary agricultural setting; however, the influence of forced human migration on landrace redistribution and evolution has received little attention in comparison to the stochastic effects of drift, mutation, and gene flow in the centers of origin. Although the seed systems of forcedly-displaced people remain poorly understood, evidence suggests that refugees often continue to grow traditional crops after resettlement. From a genetics perspective, the crops that are transported to highly disparate environments provide an interesting opportunity to study adaptation.

This research addresses how forced human migration has impacted contemporary landrace evolution in a specific case study of African maize being grown by new American farmers in Vermont and New Hampshire. We utilize a whole genome sequencing approach and methods in population genetics to investigate the origin, genetic diversity, and potential adaptation in these crops. Our findings suggest that maize grown by new American farmers in the study does in fact originate from Africa and that each farmer is growing a genetically distinct crop, although we are unable to link origin of the crop to immigration history of the farmer. We also found that genetic diversity is remarkably high across all samples, even compared to landrace panels assembled from the U.S. National Plant Germplasm System. Lastly, we found numerous signatures of positive selection across all farmer samples, and through Gene Ontology analysis, we identified two significant biological processes enriched by positive selection, (1) cinnamoyl-CoA reductase biosynthesis and (2) glutathione synthase activity, that may indicate recent adaptation and be correlated to increased cold tolerance. Overall, through this case study we show a specific example of how forced human migration has affected landrace redistribution, subsequent evolution, and potential adaptation to a disparate environment. We believe these findings hold interesting implications towards agrobiodiversity conservation and suggest the potential of refugee seed systems to promote contemporary adaptation in traditional crops.



Number of Pages

64 p.