Evaluating the Adaptive Genomic Landscape of Remnant and Backcross American Chestnut Populations to Inform Germplasm Conservation

The American chestnut tree (Castanea dentata) is a deciduous tree that largely exists in the eastern United States along the Appalachian Mountain range. Approximately 100 years ago, a fungal pathogen (Cryphonectria parasitica) decimated chestnut populations, resulting in the loss of billions of trees. Disease-resistant American chestnut populations have been developed, but the introgression of wild adaptive diversity into these breeding populations will be necessary to develop locally adapted and disease resistant chestnut trees for reintroduction. In this dissertation, I presented our findings which addressed previous gaps in knowledge regarding the population genomics of wild and backcross American chestnut populations. I 1) estimated the genomic diversity, population structure, and demographic history of remnant wild American chestnut populations; 2) revealed the genomic basis of local climate adaptation in American chestnut, developed a novel method to make tree sampling estimates for germplasm conservation, and defined unique seed zones for American chestnut based on climate and genotype, and 3) determined the amount of wild adaptive diversity captured by the backcross breeding program and made recommendations for their replanting region. These results will inform the development of a breeding plan for the introgression of adaptive diversity into backcross and transgenic chestnut populations.