Levels of genetic diversity at different stages of the domestication cycle of interior spruce in British Columbia.
Concerns over the reductionist nature of the domestication of forest-tree species focus on the possibility of potential genetic erosion during this process. To address these concerns, genetic diversity assessments in a breeding zone the Province of British Columbia "interior" spruce (Picea glauca x engelmanni) program was conducted using allozyme markers. Genetic-variation comparisons were made between natural and production (seed orchard) populations as well as seed and seedling crops produced from the same breeding zone's seed orchard. The natural population sample consisted of a total of 360 trees representing three stands within each of three watersheds present in the Shuswap-Adams low-elevation zone of interior British Columbia. Small amounts of genetic differentiation were observed among the nine natural populations (4%) and this was attributable to extensive gene flow (N(m) = 7). Consequently, the sum of these nine populations was considered as a baseline for the genetic variation present in the breeding zone. The comparisons between the seed orchard and the breeding zone produced a similar percentage of polymorphic loci (%P = 64.7%) while the expected hetrozygosity (H(e)) (0.207 vs 0.210) and the average number of alleles per locus (2.7 vs 2.4) were slightly lower in the seed orchard. A total of seven natural populations' rare alleles (P < 0.007) were not present in the orchard population, while one allele was unique to the orchard. The %P increased to 70.6% in the seedlot, but dropped to the natural populations level (64.7%) in the plantation. The observed increase in %P was a result of pollen contamination in the orchard. It is suspected that the reduction in the plantation was caused by an unintentional selection in the nursery. Simulated roguing in the orchard did not drastically reduce H(e) even if up to 50% of the orchard's clones were rogued. However, roguing was associated with a reduction in the average number of alleles per locus (i.e., sampling effect).
Glyn Road Research Station, Ministry of Forests, 1320 Glyn Road, V8W 3E7, Victoria, B.C., Canada.
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El-Kassaby