IMPACT OF SELECTION AND BREEDING ON THE GENETIC DIVERSITY IN DOUGLAS-FIR

Genetic changes following domestication of Douglas-fir were studied us ing isozyme data derived from two generations of seed orchards and the ir 49 wild progenitor populations. In addition, the breeding, producti on, and infusion populations used in the seed orchards were compared t o their wild counterparts. Several parameters of gene diversity were m easured (number of alleles per focus N-a, per cent of polymorphic loci PLP, and expected heterozygosity H, and population divergence D). The se measures were similar or higher in the domesticated populations com pared to their natural progenitors, indicating that early selection an d breeding of a highly polymorphic species does not significantly redu ce genetic variation. The two generations of seed orchards also did no t differ, indicating that genetic variation may remain stable over fut ure generations of forest plantations. Interestingly, compared to the natural populations, heterozygosity was higher in the seed orchards, p robably due to pooling of widely distributed natural populations; howe ver, rare localized or private alleles seemed to be less frequent in t he domesticated populations. Differentiation values were not significa nt between the first generation orchards and the natural populations, but significant differences were observed between the second generatio n orchards and the wild progenitor populations, probably due to the in terbreeding that forms the advanced generation seed orchards.