An investigation of inter-family competition in loblolly pine

Typescript (photocopy).Three inter-related experiments were used to evaluate the role of inter-family competition in the growth and development of loblolly pine (Pinus taeda L.). In the first study, five 20-year-old progeny tests of loblolly pine were utilized to examine changes in genetic parameters over time. Patterns of parameter development were unique to each test. There was no evidence to indicate that competition was influencing the change that occurred in each test. Five families common to two of the above tests were re-established in a juvenile competition study in a greenhouse bench. Again no discernible pattern developed; competition appeared to have little influence on changing genetic parameters. In addition, juvenile genetic parameter development did not duplicate mature genetic parameter development. From within the juvenile competition study the relationships between specific family combinations did reveal significant competitive interactions. Family S2PT10 was highly sensitive to adjacent family performance. In combination with S3PT7, S2PT10 produced the best family height growth. When grown with S4PT6, S2PT10 was one of the poorest height producers. Further competitive interactions among family combinations were displayed for diameter at the cotyledons, hypocotyl length, and root and shoot dry weight. Specific family combinations representing overyielding, underyielding, and complementary competitive effects were then established in the root:shoot competition study. Among the family combinations root and shoot competition appeared to influence seedling growth equally. Family rankings remained the same across treatments. Inter-family root competition had the same effect on overyielding seedlings as it did on underyielding seedlings. The same was true for inter-family shoot competition. Family combination rankings were consistent with the rankings in the juvenile competition study