No abstract

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.

During 2002During -2004, three laboratories in Canada and France collaborated to improve initiation of somatic embryogenesis (SE) in jack pine (Pinus banksiana Lamb.), eastern white pine (P. strobus L.), maritime pine (P. pinaster Ait.), and Scots pine (P. sylvestris L.), giving particular attention to the effects of (1) N-(2-chloro-4-pyridyl)-N¢-phenylurea (CPPU) versus various concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and benzyladenine (BA), (2) differences in basal nutrient media, i.e., macro-and microelements, and (3) gelling agent concentration. The work was carried out separately at each laboratory, but the details of media compositions were shared and tested on their respective species. Results indicate that the developmental stage of the zygotic embryo (ZE) and genotype effects had a large influence on SE initiation, and that genetic effects were consistent over time. Different species responded differently to PGR types and concentration, basal nutrient media, trace elements, and their combinations. Currently, our best initiation rates based on a selected group of genotypes, optimal development stage of ZE, and medium are 3.9% for jack pine, 54.6% for eastern white pine, 76.2% for maritime pine, and 19.7% for Scots pine.