Allozyme diversity of selected and natural loblolly pine populations
1999
Schmidtling, R.C. | Carroll, E. | Lafarge, T.
Loblolly pine (Pinus taeda L.) megagametophytes and embryos were examined electrophoretically to compare the extent and distribution of genetic variability in allozymes of selected and wild populations. Range-wide collections of three different types were investigated in this study. These consisted of seed sampled from, 1. a provenance test established in 1953, 2. bulk seed sampled from collections obtained from natural stands, and 3. seed harvested from clones used to produce improved seed in a tree improvement program. All 18 loci tested were found to be polymorphic. The average number of alleles overall (N-a) was 3.8. Expected heterozygosities (H-e) varied from 0.193 in the 70-year old orchard clones, to 0.174 in the 40-year-old provenance test samples, to 0.163 in the embryos of the bulk collections. The maximum F-ST was 0.066 for the provenance test populations, which indicates that only a small proportion (6.6 %) of the total variation in allozymes was attributed to population differences. In spite of this, the populations were well differentiated in multivariate analysis. In controlled-pollinated progeny tests of the orchard selections, there was a negative association between growth and the presence of rare alleles in the parent. A rare allele at the IDH locus was associated with slower growth, probably because it indicated hybridization with the slower- growing shortleaf pine (P. echinata MILL.). Allozyme variation as well as variation in cortical monoterpenes and fusiform rust resistance suggests that loblolly pine resided in two refugia during the Pleistocene; one in south Texas / northeast Mexico and one in south Florida / Caribbean. The two populations migrated to the northern Gulf Coastal Plain at the beginning of the Holocene and merged just east of the Mississippi River.
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