Stability of juvenile wood specific gravity of loblolly pine in diverse geographic areas

The stability of wood specific gravity for 12-year-old loblolly pine (Pinus taeda L.) was evaluated for 18 open-pollinated families and four bulked seed lots representing provenances from the eastern shore of Maryland; Marion County, Florida; Gulf Hammock, Florida; and Livingston Parish, Louisiana. Wood samples were collected from seven plantings chosen to provide a north-south and east-west sample distribution essentially encompassing an area spanning the natural range of loblolly pine. There was significant genotype x environment interaction, and 4 of the 18 families were classified as unstable for specific gravity. These four families accounted for 49.5% of the genotype x environment interaction sum of squares. However, the loss in potential gain in a breeding program for specific gravity due to the presence of a significant genotype x environment interaction was estimated to be only 1%. Loblolly pine from the Florida provenances and from the widely planted Livingston Parish provenance consistently displayed low specific gravity and ranked at or near the bottom at all test locations, including the southernmost plantings.