Mu. Stoehr et Ya. Elkassaby, LEVELS OF GENETIC DIVERSITY AT DIFFERENT STAGES OF THE DOMESTICATION CYCLE OF INTERIOR SPRUCE IN BRITISH-COLUMBIA, Theoretical and Applied Genetics, 94(1), 1997, pp. 83-90
Concerns over the reductionist nature of the domestication of forest-t
ree species focus on the possibility of potential genetic erosion duri
ng this process. To address these concerns, genetic diversity assessme
nts in a breeding zone the Province of British Columbia ''interior'' s
pruce (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 cro
ps produced from the same breeding zone's seed orchard. The natural po
pulation sample consisted of a total of 360 trees representing three s
tands 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). Consequen
tly, the sum of these nine populations was considered as a baseline fo
r the genetic variation present in the breeding zone. The comparisons
between the seed orchard and the breeding zone produced a similar perc
entage of polymorphic loci (%P = 64.7%) while the expected hetrozygosi
ty (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 popula
tions 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 select
ion in the nursery. Simulated roguing in the orchard did not drastical
ly reduce H-e even if up to 50% of the orchard's clones were rogued. H
owever, roguing was associated with a reduction in the average number
of alleles per locus (i.e., sampling effect).