Variation in American beech (Fagus grandifolia Ehrh.): isozyme analysis of genetic structure in selected stands.

Abstract

The genetic structure of Fagus grandifolia Ehrh. stands in Massachusetts (MA) and West Virginia (WV) was studied by analysis of isozyme variation at nine loci. The stands were found to be substructured into mosaics of putative clones and trees of seedling origin. The level of genetic diversity was high: observed per locus heterozygosities averaged 0.382; number of alleles per locus averaged 2.9. Significant deviations from Hardy-Weinberg equilibrium were detected for up to five of the nine loci studied. Deviations resulted from an excess of heterozygotes at the 6PG-2, MDH-1, and CTO-1 (MA only) loci, and a deficiency of heterozygotes at the CTO-2 and PER-3 loci. Overall, positive mean F IS values indicated slight deficits (2.3%) of heterozygotes within populations. Positive assortative mating, as a result of crossing within clonal and/or family patches in stands, may be responsible. A mean F ST value of 0.064 provided evidence for moderate differentiation between the two populations. Clonal structure had a small effect on the computation of population genetic statistics for these two stands