Genetic gain from selection for rooting ability and early growth in vegetatively propagated clones of loblolly pine

A successful clonal forestry program for loblolly pine based on rooted cutting technology needs to consider selection for both rooting ability and subsequent field growth. Rooting ability and second-year height were assessed in more than 2,000 clones from 70 full-sib families of loblolly pine. The bivariate analysis of rooting ability from five rooting trials and field growth from six field trials allowed for estimation of the genetic covariance between rooting ability and second-year height for parental effects, full-sib family effects, and the total genetic value of clones within full-sib family. There was a positive genetic relationship between rooting ability and second-year height at all three genetic levels. The genetic correlation at the parental level between rooting ability and second-year height was 0.32. At the full-sib family level, the genetic correlation between traits was 0.39. The correlation of total genetic values of clones for rooting ability and second-year height was 0.29. The genetic gain in rooting ability and second-year height was estimated for a number of deployment options based on various selection scenarios using the best linear unbiased prediction (BLUP) values from the bivariate analysis. The deployment strategies compared were (1) half-sib family deployment, (2) full-sib family deployment, and (3) clonal deployment. Moderate to high family and clonal mean heritabilities, moderate to high type B genetic correlations, and substantial among-family and among-clone genetic variation indicate the potential for increasing rooting efficiency and improving growth.