Seedling Evaluation of Atlantic Coastal and Piedmont Sources of Pinus taeda L. and Their Hybrids for Cold Hardiness

Seedlings of 59 loblolly pine (Pinus taeda L.) polycross families representing four populations (Atlantic Coastal, Piedmont, Coastal x Piedmont, and Piedmont x Coastal) were evaluated for cold hardiness. Seedlings were preconditioned in phytotron environments and then subjected to a freezing treatment. Freezing injury, mortality, and size of seedlings were assessed. Significant differences in cold injury were found among populations and families within each population. The Piedmont families and hybrid seedlings with a Piedmont maternal parent had less injury and higher survival relative to those of the other populations. Most families with high cold injury had a Coastal maternal parent, whereas most families with the least cold injury had a Piedmont maternal parent. The large observed among- and within-population variations in cold injury suggested that family or individual-within-family selection could improve cold hardiness in loblolly pine. Based on the results of seedling growth and cold injury, there may be an advantage to deploying Piedmont x Coastal hybrids or Piedmont families on more adverse sites, e.g., cold sites. On the milder sites, deployment of Coastal x Piedmont hybrids or hardy Coastal families seems appropriate.