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Candido Ribeiro, Rafael

University of British Columbia

There is an urgent need to better understand how populations of trees will respond to changes in climate and the intensification of extreme weather events. Characterizing the amount of genetic variation and genetic architecture of climate-adaptive traits is important for developing management approaches that mitigate the effects of climate change on forests. In this dissertation, I combined three large-scale common garden experiments (~6,000 seedlings) with population genomic approaches to investigate phenotypic and genomic variation across the natural ranges of the two main varieties of Douglas-fir (Pseudotsuga menziesii var. menziesii and var. glauca), as well as within breeding zones in British Columbia. Seedlings from 74 natural and 14 selected breeding populations were assessed for drought tolerance, cold hardiness, growth, phenology, and plastic responses to drought. I also used a case-control genome-wide association approach to identify single nucleotide polymorphisms (SNPs) associated with drought tolerance and cold hardiness within populations, and tested for repeated evolution between varieties, pleiotropy between traits, and allelic clines along environmental gradients. Finally, I tested the effects of selection for growth in tree breeding programs on climate adaptive phenotypes, and on the frequency of SNPs associated with cold hardiness and drought tolerance, by comparing selected seedlots with their wild counterparts. Signals of local adaptation to drought were weak within var. glauca and nearly absent within var. menziesii. Genetic variation for drought tolerance in seedlings is maintained primarily within rather than among populations. The complex polygenic architectures and genomic redundancy controlling climate adaptation make it challenging to use genomic information in management of Douglas-fir. Selection for faster growth reduced cold hardiness in var. menziesii, but had weaker effects in var. glauca. Drought tolerance was not affected by selection for faster growth. There is potential to increase drought tolerance through selection within breeding populations. These results collectively can inform adjustments to assisted gene flow in Douglas-fir.

Text

2025-07-07

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/91529

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/