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    The genetic architecture of the divaricate growth form : a QTL mapping approach in Sophora (Fabaceae) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Biology at Massey University, Manawatu, New Zealand
    (Massey University, 2019) Pilkington, Kay
    Divarication is a plant growth form described, in its simplest form, as a tree or shrub with interlaced branches, wide branch angles and small, widely spaced, leaves giving the appearance of a densely tangled shrub. This growth form is a unique feature in the New Zealand flora that is present in ~ 10% of the woody plant species, a much higher frequency than that of other regional floras. While several hypotheses have been developed to explain why this growth form has evolved multiple times within New Zealand, to our knowledge, no work has addressed the genetic basis of the divaricating form. Sophora is one of several genera in New Zealand that possesses divaricate species. Among the factors making this an ideal system for a genetic investigation of divarication is an existing F₂ population formed from reciprocal crosses between the divaricating S. prostrata and the non-divaricating S. tetraptera. Using this segregating population and newly developed molecular markers, the first linkage maps for Sophora were generated, providing a new genetic resource in Sophora. These linkage maps allowed for quantitative trait locus (QTL) mapping for traits associated with the divaricate form in the segregating population. Multiple QTL were mapped to seven of the divaricate traits with many QTL co-locating for multiple traits, indicating that the divaricate growth form is genetically controlled by many loci, potentially including pleiotropic loci, that each contribute to the overall divaricate phenotype in Sophora. The strigolactone biosynthesis and perception pathway is a good candidate for involvement in control of the divaricate form based on mutant phenotypes in Pisum that display similarities to the divaricate growth form, such as increased branching, shorter plant height and smaller leaves. QTL, for multiple traits, were mapped to two candidate genes investigated, RMS1 and RMS4. An amino acid replacement was identified in RMS1, in S. prostrata, that is predicted to be deleterious suggesting it may be non-functional in S. prostrata. These results support RMS1 as a strong candidate gene for future work on divarication. This study is the first to investigate the genetic architecture of the divaricate growth form and contributes to further understanding of this unique feature in the New Zealand flora and of plant architecture generally.
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    The biogeography and origin of New Zealand Sophora (Leguminosae) : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Plant Molecular Genetics at Massey University, New Zealand
    (Massey University, 1996) Hurr, Kathryn Ann
    The application of DNA sequencing to studies of the biogeography and origin of New Zealand plant groups is illustrated by evolutionary relationships of kowhai (Sophora spp.; sect. Edwardsia; Sophoreae: Papilionoideae: Leguminosae). DNA sequences from an intergene region of the chloroplast atpB-rbcL were determined for l2 species by the use of the polymerase chain reaction. Signals in the molecular data were evaluated using phylogenetic algorithms to reconstruct the evolutionary history of the species. The extremely high genetic similarity between Edwardsia Sophora resulted in an inability to fully resolve the phylogenetic tree. Three hypotheses are presented to account for the patterns of sequence differences between the New Zealand Edwardsia. One proposes a recent origin of Sophora section Edwardsia in New Zealand (4-10 million years ago), with subsequent dispersal of buoyant Sophora microphylla seeds to offshore and oceanic islands, where they might occasionally colonise. A second hypothesis suggests a recent radiation of Sophora microphylla and Sophora prostrata populations during the Pleistocene (0.1 - 1.6 million years ago), but is not well supported by the available sequence data. A third hypothesis proposes that the Lord Howe Island and New Zealand Sophora are derived from a Miocene (5-16 million years ago) oceanic migration of a Chilean ancestor of Sophora section Edwardsia. Predictions of the three hypotheses and strategies to test them are discussed. Some of the conclusions derived from analyses of the chloroplast DNA sequences conflict with those obtained from morphological and chemotaxonomical studies. Analyses of all data sets indicates that the variations in morphology and secondary metabolitic constituents between Sophora prostrata and Sophora microphylla obscures a small amount of genetic diversity. The question of hybrid origins for Sophora microphylla is not supported by tree reconstructions from the molecular data set, and further genetic and ecological studies are required to investigate this.