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UBC Theses and Dissertations
The genetics of selective breeding in western hemlock Tsuga heterophylla Wellman, Hugh Francis
Abstract
Rates of genetic diversity were inferred from allozyme allelic variation and used to compare differing seed crops that had originated from seed orchards under various seed production conditions with natural stands of western hemlock (Tsuga heterophylla (Raf.) Sarg). The supplemental mass pollination (SMP) technique was found to maximize both Ht and H0 when compared with unimproved wind pollinated seed crops and controlled full-sib crosses. This was identified as being the result of minimized self-fertilization and an improved parental balance. It also can be noted that 8 private alleles were lost in the seed orchard populations when compared with natural populations. Results of an inbreeding analysis have suggested that when compared with natural populations, inbreeding decreased in the wind pollinated unimproved and controlled fullsib seed crops of first generation seed orchard. The SMP treatment also showed lower values of inbreeding and when compared with controlled crosses had the highest genetic diversity. These finding suggest that the SMP technique best maintains genetic diversity and minimizes inbreeding while retaining the required selection intensity for genetic gains. Fifteen microsatellite markers were isolated from western hemlock genomic DNA and six of these markers were optimized for use in mountain hemlock [Tsuga mertensiana (Bong) Carr.]. The developed SSR's were then implemented in a test of the Heterozygosity-Fitness Correlation (HFC) in western hemlock elite families. In general no significant relationship was identified between the genetic distance/relatedness of top western hemlock families and the fitness of their progeny based on phenotypic indicators. One exception were the MKL and STV progeny trials which were found to be significantly correlated at 9 5 % . They both showed negative slope indicating that as genetic distance increase, height decreases which is indicative of outbreeding depression. Reasons that may have lent to the null result include limited parental lines, concluding in too little distance variation, a low degree of relatedness resulting in very little inbreeding depression and very little evidence for linkage disequilibrium, a cause of associative overdominance. The lack of structure identified in Western hemlock populations may not have allowed for strong heterosis therefore resulting in the poor predictive power of genetic distance.
Item Metadata
Title |
The genetics of selective breeding in western hemlock Tsuga heterophylla
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2004
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Description |
Rates of genetic diversity were inferred from allozyme allelic variation and used
to compare differing seed crops that had originated from seed orchards under various
seed production conditions with natural stands of western hemlock (Tsuga heterophylla
(Raf.) Sarg). The supplemental mass pollination (SMP) technique was found to
maximize both Ht and H0 when compared with unimproved wind pollinated seed crops
and controlled full-sib crosses. This was identified as being the result of minimized self-fertilization
and an improved parental balance. It also can be noted that 8 private alleles
were lost in the seed orchard populations when compared with natural populations.
Results of an inbreeding analysis have suggested that when compared with natural
populations, inbreeding decreased in the wind pollinated unimproved and controlled fullsib
seed crops of first generation seed orchard. The SMP treatment also showed lower
values of inbreeding and when compared with controlled crosses had the highest genetic
diversity. These finding suggest that the SMP technique best maintains genetic diversity
and minimizes inbreeding while retaining the required selection intensity for genetic
gains.
Fifteen microsatellite markers were isolated from western hemlock genomic DNA
and six of these markers were optimized for use in mountain hemlock [Tsuga
mertensiana (Bong) Carr.]. The developed SSR's were then implemented in a test of the
Heterozygosity-Fitness Correlation (HFC) in western hemlock elite families. In general
no significant relationship was identified between the genetic distance/relatedness of top
western hemlock families and the fitness of their progeny based on phenotypic indicators.
One exception were the MKL and STV progeny trials which were found to be
significantly correlated at 9 5 % . They both showed negative slope indicating that as
genetic distance increase, height decreases which is indicative of outbreeding depression.
Reasons that may have lent to the null result include limited parental lines, concluding in
too little distance variation, a low degree of relatedness resulting in very little inbreeding
depression and very little evidence for linkage disequilibrium, a cause of associative
overdominance. The lack of structure identified in Western hemlock populations may
not have allowed for strong heterosis therefore resulting in the poor predictive power of
genetic distance.
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Extent |
10736001 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-11-27
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0091736
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2004-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.