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Chloroplast DNA (cpDNA) was extracted from composite needle samples, representing ten individuals from each of twelve populations of Sitka spruce ( Picea sitchensis (Bong.) Carr.) from Alaska. Needle material used for the study was collected from an Icelandic provenance trial. Restriction analysis of cpDNA, followed by heterologous hybridization to psbA probe, indicated the presence of white spruce (Picea glauca (Moench) Voss) species-specific cpDNA restriction fragments in many of these samples. Sitka spruce specific restriction fragments were, however, dominant in all composite samples analyzed. We interpret this finding as evidence of widespread penetration of white spruce into many Sitka spruce populations of the Kenai peninsula region of Alaska. We draw the further conclusion that the Sitka spruce used for afforestation in Iceland represents, to a large extent, a product of introgressive hybridization between white and Sitka spruce.
by Alfred E. Szmidt