Seedling evaluation of Atlantic coastal and piedmont sources of loblolly pine and their hybrids for height growth

Seedlings of 60 loblolly pine (Pinus taeda L.) polycross families representing four populations, Atlantic Coastal (CxC) Piedmont (PxP), Coastal x Piedmont (CxP), and Piedmont x Coastal (PxC) were evaluated for first-year seedling height growth in an outdoor site in Raleigh, North Carolina. The CxP hybrids grew as well as the pure Coastal loblolly source, and the PxC hybrids were not significantly taller than the pure Piedmont population. The hybrid populations were intermediate between the parental populations and did not exhibit heterosis for height. However, the hybrids were 4-10% taller than the PxP population, which is the population currently used for forestation in the Piedmont region. There was an advantage for early seedling height growth in having the female parent from the Coastal plain, which appeared to be related to length of the growing season as measured by bud set time. There were strong family differences for seedling height within populations, indicating the potential for selecting the best families within the best populations. The implication is that the hybrid populations of CxP and PxC with improved growth may be better planting stock for the Piedmont than the pure Piedmont populations on some sites. Before implementing such a plan, cold-hardiness and long-term growth and adaptability should be evaluated.