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. / Doctor of Philosophy / 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, a fungal disease (Cryphonectria parasitica) decimated chestnut populations, resulting in the loss of billions of trees. The American Chestnut Foundation developed disease-resistant American chestnut backcross trees by breeding American chestnut trees with Chinese chestnut trees (Castanea mollissima). These trees will need additional breeding with wild American chestnut trees so that their offspring will have both the disease-resistant traits and the adaptations to the local environment where they will be replanted. This is important, because trees that are both disease-resistant and locally adapted will be most likely to survive and thrive in their replanting location. However, a comprehensive evaluation of the genomic basis for local adaptation in American chestnut populations is lacking. 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, number of unique populations, and population size changes over time in wild American chestnut; 2) revealed the genes related to local adaptation in American chestnut, developed a novel method to make tree sampling estimates for conserving wild American chestnut diversity, and defined unique seed zones (areas within the species range that have unique adaptations to environment) for American chestnut based on climate (ie, precipitation and temperature values) and genotype (DNA), and 3) determined the amount of wild genomic diversity related to local adaption captured by the backcross breeding program and made recommendations for their replanting region. These results will inform the development of a breeding plan of wild American chestnut with backcross and transgenic chestnut populations to create locally adapted and disease-resistant chestnut populations for reintroduction.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115874 |
| Date | 27 July 2023 |
| Creators | Sandercock, Alexander M. |
| Contributors | Genetics, Bioinformatics, and Computational Biology, Holliday, Jason A., Kim, Inyoung, Westbrook, Jared, Haak, David C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution-NonCommercial 4.0 International, http://creativecommons.org/licenses/by-nc/4.0/ |
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