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Patterns of variation in Pacific silver fir (Abies amabilis [Dougl.] Forbes) on Vancouver Island Davidson, Roberta H.


This thesis describes patterns of variation in several cone, seed and seedling characteristics of Pacific silver fir (Abies amabilis [Doug.] Forbes) sampled from Vancouver Island, B.C. Cone collections kept separate by tree were made at eight locations during the fall of 1983 to provide material for the study. The inheritance patterns of 13 enzyme loci were determined from seed tissues of 87 trees, and seven loci were found to possess at least two allozyme variants. These loci conformed to the assumptions of Mendelian-type inheritance, although AAT-2 displayed marked segregation distortion. No linkage groups could be established at the sampling intensity available (20 seeds per tree). Significant levels of inbreeding, based on a multilocus estimate of outcrossing, were detected in five of seven populations and indirect evidence suggests related matings other than selfing may be occurring. Variation among populations in outcrossing rate was evident (0.725 < tm ≤ 1.0) and appears positively correlated with seed size (measured by 1000-seed weight). High levels of allozyme variation were found to exist within populations (95-98%) and estimates of the extent of population differentiation were shown to differ depending upon the particular analytic method employed. Maternal (extant) trees appeared more heterozygous than did viable embryos and populations sampled on southern Vancouver Island appeared more genetically diverse than did populations sampled on northern Vancouver Island. A sub-sample consisting of two populations, each with seven trees, from northern, mid and southern Vancouver Island provided material for a germination test and open-pollinated progeny study. Seed dormancy was not pronounced among populations. Large family differences in germination responses were detected, irrespective of pregermination treatment, suggesting a high degree of genetic control of germination in Pacific silver fir. Anomalous germination behavior in one population was attributed to sub-optimal stratification conditions and proliferation of mold. Improvement in production of seedlings of Pacific silver fir may be achieved by collecting and germinating seeds on a family-by-family basis. Germinants from the first count of the germination test provided open-pollinated progeny for measurement of growth variables. Seedlings were grown in a greenhouse alongside production Abies stock for 29 weeks. Population differences accounted for a considerable part of variance in cone and seed size. The effect of population on height of seedlings at eight weeks was significant but declined to virtually zero by the end of the test. Populations had negligible influence on growth rate of seedlings as well. Variation in growth rate among open-pollinated families was statistically significant but accounted for only 20% of the total variation. Significant population differences were detected in root weight of harvested seedlings. Family differences in this and other biomass variables were at most 20%, with the majority of variation in seedling growth traits residing within families.

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