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Five plus‐trees in natural stands and the same genotypes grafted in seed orchards were compared with respect to mating system. Selfing rates were estimated with rare isozyme markers. Selfing rates in natural stands and in seed orchards were 0.12±0.11 and 0.08±0.07, respectively. Correspondingly, the seed orchard progenies were slightly more heterozygous than those from natural stands. The bearing of these findings on performance differences is discussed.

Eleven populations of Picea abies in Sweden were analysed for isozyme variation in four polymorphic loci. Genetic differentiation between geographically isolated populations could be demonstrated, the major part of genic differences occurring in the esterase‐A and acid phosphatase‐A loci. When populations originating from foreign seeds are involved in comparisons with indigenous populations, higher values of genetic differentiation are found. Genic variability within populations was estimated from “average heterozygosity”, a measure which is based upon the observed gene frequencies. An increase in “average heterozygosity” was found in two populations of foreign origin, which to a certain extent may be due to intercrossing between genomes of different origin.