Genetic Gains of Full-Sib Families from Disconnected Diallels in Loblolly Pine

Breeding values for the 2^nd-cycle of the loblolly pine (Pinus taeda L.) breeding program were analyzed with the NCSUIndustry Tree Improvement Cooperative database to estimate genetic gains and compare different strategies for full-sib deployment. In the disconnected half-diallel mating design used for loblolly pine, six parents within each diallel were crossed to generate 15 full-sib families for general combining ability (GCA) and specific combining ability (SCA) estimates. Parents among disconnected diallels were never crossed, and the SCA and full-sib family breeding values cannot be estimated directly. Using the GCA and SCA estimates from 60 diallels in the Atlantic Coastal region of loblolly pine, genetic gains were estimated in this study for full-sib families within the disconnected diallels and then compared with the potential gains that would be expected if we select parents for full-sib families based on GCA values for all parents within a geographic region. As the dominance variance was found to be much less than the additive variance, the SCA contribution to the full-sib genetic gain was relatively small. Higher full-sib genetic gains were obtained by crossing the best GCA parents from different diallels within a geographic region than selecting only those within diallels. The difference increased with increasing number of selected full-sibs. Results from different selection scenarios, with various selection intensities and relatedness managements, suggest that selection based on GCA from all parents within a geographic region would result in a higher genetic gain for full-sib families in loblolly pine. The deployment of full-sib families are very important for achieving higher genetic gains in a loblolly pine breeding program. But they were not due to the SCA contribution, but rather due to high GCA of best parents in creating these full-sib crosses. The strategies for family and clonal deployment are very attractive based on the data from this study.