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Australian sunflower oil is often low in polyunsaturated fatty acids due to high temperature depression of linoleic acid synthesis during seed development. With existing cultivars the selection of favourable sowing areas and times cannot reliably overcome this problem. To fully solve the problem new sunflower genotypes are needed that have the capacity for high levels of linoleic acid synthesis independent of the temperature experienced during seed development. The aim of this thesis is to examine the genetic variability that exists in the sunflower for the selection of such a genotype and also to examine methods that would aid this selection. It was thought that the use of embryo culture could help the selection of the desired genotype, but before this could be investigated it was necessary to precisely define the phases of development of the embryo and to determine at which stage of development oil synthesis was most sensitive to the influence of high temperature. The phase of rapid oil synthesis was found to occur between 200 to 500 day-degrees after pollination. The final oil composition of the seed was found to be most influenced by high temperature during this phase, especially between 300 to 500 day-degrees. Therefore sunflower embryos were taken for culturing during this phase. ... The work in this thesis indicates that genetic variability of oil composition in sunflowers does exist. The culturing technique offers a tool to aid the selection of genotypes with the desired oil composition at high temperatures. Therefore the selection of a sunflower genotype with the ability to produce high levels of linoleic acid over the range of growing conditions experienced in Australia seems a feasible objective. |
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