Genetic control of somatic embryogenesis initiation in loblolly pine and implications for breeding

Major advances have been achieved in somatic embryogenesis (SE) of loblolly pine, making it a promising method for the implementation of clonal forestry. However, the frequency of initiation of SE cultures, which is highly variable among loblolly pine families, needs improvement to further advance the implementation of this technology in conjunction with tree breeding. Genetic control of SE initiation was investigated using a diallel mating design with six parent trees. The results showed that SE initiation is under the control of strong genetic additive effects, as 42% of the total variance was explained by the variation due to general combining ability effects. The variation due to maternal effects explained a moderate proportion of the total variance, whereas other components of variance had small but significant effects. The conclusions regarding the strong genetic control of SE initiation were drawn from two independent experiments in which consistent results were obtained with seed from the same controlled pollinations but using entirely different procedures. Practical implications for breeding and clonal propagation were tested in independent experiments with targeted matings. Our results indicated that large improvement in SE culture initiation could be achieved in a predictable manner by selecting the most favorable female parent, or in some cases, a favorable male parent.