Improving germination in white spruce somatic embryos with desiccation and/or cold treatments

Clonal propagation of white spruce (Picea glauca (Moench) Voss) through somatic and will embryogenesis (SE) has important applications in tree improvement programs help the forest industry to achieve maximum sustainable yield. The level of induction of embryogenic tissue and the yield of mature embryos through SE has reached acceptable levels using current protocols. However, a large percentage of these embryos produce abnormal seedlings. This problem needs to be assessed and this was done in the work described in this thesis.; My study looked at the effects of controlled partial and complete desiccation of white spruce somatic embryos at four stages of development on subsequent germinant quality. Both slow desiccation at 5°C and flash desiccation at ambient temperature were examined. The effect of temperature treatments as an alternate means of improving germinant quality and its effect on desiccation tolerance were also examined. Dried somatic embryos are likely to suffer imbibitional damage. Therefore, the effects of various rehydration methods were also examined.; Large numbers of mature embryos were required for our desiccation experiments. Therefore, a method of squashing the embryogenic tissue into a polypropylene mesh was developed. This method allowed embryogenic tissue to be easily transferred to fresh medium and produced a flat mat of mature embryos that were more accessible for harvesting.; The tolerance of the embryos to desiccation, and the level of desiccation required to improve germinant quality, increased as the embryos matured. A temperature treatment of 5 and 10°C also improved germinant quality, producing 70--80% normal germinants. The 5°C treatment can be used as a short-term storage method. A 5°C temperature treatment for 4-8 weeks significantly improved the tolerance of 39--51 d embryos to flash desiccation. This has important applications in the development of synthetic seed.; Rehydration experiments showed that slowly and rapidly desiccated embryos responded differently to the method of rehydration. Slowly desiccated embryos suffered less imbibitional damage if they were indirectly rehydrated at 100% RH. Flash desiccated embryos suffered less damage if they were rehydrated directly on germination medium.; The above treatments have significantly improved germinant quality. (Abstract shortened by UMI.)...