IMPACT OF SELECTION ON GENETIC-VARIABILIT Y OF THE WHITE SPRUCE IN QUEBEC

The genetic structure and variability of two natural white spruce (Pic ea glauca (Moench) Voss.) populations from southern Quebec were compar ed by isoenzymatic analysis with those observed from three superior pr ovenances of the Great Lakes and St. Lawrence regions. Twenty 15- to 2 0-year-old trees, selected within the provenances and integrated into a diallel cross plan, were also studied. The analysis of seven enzymat ic systems demonstrates, in an overall fashion, the consistency of var iability within provenances when these are compared with natural popul ations. It indicates that the selection of a restricted number of indi viduals in these populations does not cause a significant loss of vari ability. The level of heterozygosity for the selected individuals inte grated into the diallel cross plan appears very high and no loss of al leles is recorded when compared with the original provenances, despite the sizeable reduction in numbers. This result suggests that the seco nd selection, in favour of individuals demonstrating a strengthened vi gour, favored the most polymorph genotypes.