Application of somatic embryogenesis in high-value clonal forestry: Deployment, genetic control, and stability of cryopreserved clones

Summary The most important advantage of cloning conifers by somatic embryogenesis (SE) is that the embryogenic tissue can be cryopreserved without changing its genetic make-up and without loss of juvenility. This offers an opportunity to develop high-value clonal varieties by defrosting and repropagating cryopreserved clones after genetic testing has shown which clones are the best performers. In the current absence of cost-effective automated embling handling systems or artificial seed technology, the deployment of the high-value clones in clonal forestry can be achieved inexpensively by mass serial rooting of cuttings from juvenile donor plants produced from cryopreserved embryogenic cultures. In a genetic analysis of the SE process in white sprucePicea glauca, we found that induction of SE was under strong genetic control. Although the dominance variance diminished rapidly as the zygotic embryos matured, the additive variance remained relatively large during the induction phase. The genetic effects in the subsequent maturation and germination phases were less strong. Furthermore, genetic variation at the different phases of SE was not correlated. Thus, it is the induction phase of SE that can be manipulated by breeding. Most of the embryogenic clones were cryopreserved easily, i.e., there was no apparent genotype effect. To determine stability of cryopreserved clones, a set of 12 clones was retrieved after 3 and 4 years, respectively, from cryopreservation and repropagated by SE. An assessment of morphologicalin vitro development andex vitro survival and growth characters demonstrated general stability of the cryopreserved clones of white spruce. Based on a presentation at the Joint Meeting of the IUFRO Working Parties on Somatic Cell Genetics and Molecular Genetics of Trees held in Quebec City, Canada, August 12–16, 1997.