Genetic effects of rooting ability and early growth traits in loblolly pine clones

Loblolly pine is the most important commercial tree species in the southern United States with over 1.1 billion seedlings planted annually. With elite genotypes becoming available, several forest industry companies in the southeastern United States are developing rooted cutting and somatic embryogenesis programs aiming towards deployment of tested clones or families. However, before clones can be deployed, sufficient data need to be collected on the population in order to have reliable information about the clones for deployment decisions.;This dissertation reports on the genetic effects of rooting ability and early growth traits in nearly 2,200 clones of loblolly pine from 70-full-sib families. More than 239,000 stem cuttings were set in five rooting trials over two years. Overall rooting success across the five trials was 43%, and significant seasonal effects were observed. Heritability of rooting ability was estimated both on the observed binary scale and on the transformed underlying normal scale.;Rooted cuttings from these trials along with seedlings from the same full-sib families were established at several sites, and early growth traits through age two were compared between propagule types. All growth traits demonstrated genetic variation, and parental and full-sib family rankings were similar for both propagule types. However, estimates of dominance genetic variance in the seedling population appear to be inflated at the expense of additive effects due to a lack of randomization of seedlings prior to field establishment. Little genotype x environment interaction was observed across sites for all traits.;A successful clonal forestry program for loblolly pine based on rooted cutting technology needs to consider selection for both rooting ability and subsequent growth. There was a positive genetic correlation between rooting ability and 2nd year height at the parental, full-sib family, and clonal levels indicating that selection for one trait will also lead to improvement of the other. The genetic gains in rooting ability and 2 nd year height associated with several selection and deployment strategies are discussed. Moderate to high family and clonal mean heritabilities, moderate to high type B correlations, and substantial among-family and among-clone genetic variation indicate the potential for increasing rooting efficiency and improving growth.