Propagating Trees using Somatic Embryogenesis
By Emmanuelle Brière and Aude Tousignant
November 2012
Somatic embryogenesis, a tissue culture method that allows the production of genetically identical trees, can replicate the favourable natural traits of the species.
Imagine you have found a tree with exceptional characteristics for wood quality and pest resistance. It has perfect tapering, good vigour and desirable growth traits. It is such a perfect specimen that you want to make exact copies of it. Somatic embryogenesis (SE) from seed explants, a vegetative propagation technology, makes this possible.
Stage 1: Initiation and proliferation
An embryo excised from a seed is placed on a Petri dish containing a medium that supplies the nutrients required for embryo development. After about six weeks, some of the growing tissue becomes embryogenic tissue. This proliferation process marks the initiation of somatic embryogenesis. During this phase, embryogenic tissue proliferates continuously and can be cryopreserved in liquid nitrogen for future use or for germplasm conservation.
Stage 2: Maturation of embryos
Clumps of embryogenic tissue are transferred onto a maturation medium
containing a plant hormone that promotes formation of the somatic embryos.
Stage 3: Germination of embryos
The mature somatic embryos germinate to form roots and shoots, similar to plants germinating from seeds. The resulting plants are called “somatic seedlings.”
Stage 4: Greenhouse culture and field planting
The somatic seedlings are transplanted into soil for further growth and acclimatization. After a greenhouse culture period, the seedlings can be planted in the field.
Vegetative reproduction is a process that creates copies of trees that have the same genetic make-up as the original seed. Somatic embryogenesis, a type of vegetative reproduction, results in the production of an unlimited number of somatic embryos from a single seed that grow into genetically identical trees.
The most important advantage of tree propagation by SE is that embryogenic tissue can be stored indefinitely by cryopreservation. Cryopreservation is a process by which embryogenic tissue is stored indefinitely in liquid nitrogen. This allows long term storage during field testing. Twins from embryogenic tissues that behaved best during field testing can be retrieved from storage, and used for mass production of planting stock.
Origins and Development
Natural Resources Canada’s Canadian Forest Service (CFS) was one of the first research organizations in the world to discover the SE in conifers and apply it to several tree species. Since 1985, CFS researchers have worked on reproducing economically and ecologically important trees in Canada, including spruce, pine, and larch species.
Once the technology had been developed sufficiently, the intent was to make the technology available for applications outside the laboratory. To achieve this, the National Network of Somatic Embryogenesis Laboratories (NNSEL) was founded by Dr. Yill Sung Park, a researcher at the Canadian Wood Fibre Centre at Natural Resources Canada. “Our goal is to build competency in SE of all commercially and ecologically important Canadian conifers through collaboration, research and development,” says Yill Sung. “Collaborative efforts by all forestry stakeholders (governments, universities, industry, etc.) are essential for the operational implementation of SE on a large scale.”
Applications of Somatic Embryogenesis
The current application of SE in combination with cryopreservation is to implement it in multi-varietal forestry, which is the use of several tested tree varieties in plantation while maintaining diversity. The use of high-value tree varieties in plantations would have a major economic impact by delivering a product with desirable wood quality attributes, increasing its value. This would provide the Canadian forest industry with a competitive advantage in the global market.
Somatic embryogenesis can also be used for conservation and restoration of endangered or threatened tree species. For example, whitebark pine growing at high elevations in western Canada is an ecologically important tree but is threatened due to a lack of sufficient seed production and infestation by disease and insects. Some available seeds are used to develop embryogenic lines and cryopreserved while disease and insect resistance testing is conducted. Once resistant lines are identified, they can be thawed from cryopreservation, propagated by SE, and used for restoration.
For more information, visit the CFS site.
To read about related articles, see Forestry Industry.
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