Allozyme diversity of selected and natural loblolly pine populations
| Authors: | Ronald C. Schmidtling, E. Carroll, T. LaFarge |
| Year: | 1999 |
| Type: | Scientific Journal |
| Station: | Southern Research Station |
| Source: | Silvae Genetica. 48(1): 35-45. |
Abstract
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 (Na) was 3.8. Expected heterozygosities (He) 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 FST was 0.066 for the provenance test populations, which indicates that only a small proportion (6.6 percent) 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.