Genetic diversity and population structure in pitch pine (Pinus rigida Mill.)

Guries, Raymond; Ledig, F.

Gene frequencies for 21 enzymatic loci were studied in 11 populations from Quebec and NE USA. Sixteen of the loci were polymorphic in at least one population; av. individual heterozygosity was 14.6%. Only a small proportion of the observed genic diversity was due to differences between populations, the remainder being due to differences between individual trees. For the allozyme loci studied, the dwarf forest populations of the New Jersey Pine Plains were essentially identical in genetic constitution to tall forest of the New Jersey Pine Barrens. Genic diversity and the organization of genetic variability in pitch pine were examined in 11 populations across the species range. Pitch pine is genetically variable; 76.2% of the loci studied were polymorphic and the average individual heterozygosity was 14.6%, but this is less than that exhibited by several other woody species. The contrast may reflect differences among species in their evolutionary history, or may be an artifact relating to the choice of enzyme systems analyzed. Only a small percent of the observed genic diversity in pitch pine appears to be interpopulation, the remainder is due to differences between individuals within populations, in agreement with results for other tree species. Analysis of F-statistics indicates that populations of pitch pine simulate panmixis with an F̄IS of 0.009. Populations are only weakly differentiated, and genetic and geographic distance are only weakly correlated. Central populations seem to be more variable than those near the species border. An isolated population at the northern extreme of the species range has a heterozygosity of 11.7%, compared to the species average of 13.8% and an average of 15.0% for central populations from New Jersey. The dwarf forest populations of the New Jersey Pine Plains are essentially identical in genic constitution to tall forest of the New Jersey Pine Barrens, at least for the allozyme loci we sampled. Whatever factors are responsible for the dwarf stature of these populations, they have not resulted in detectable changes in allozyme frequencies among populations. In general, results of allozyme analysis are not in agreement with previously reported patterns for morphological and growth traits, emphasizing the need to sample several types of loci to adequately understand the genetic structure of populations.

Genetic diversity and population structure in pitch pine (Pinus rigida Mill.)

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