Philosophiae Doctor - PhD / Self-incompatibility (SI) is a major mechanism that prevents inbreeding in ow-ering plants, which was identi ed in Rosaceae, Solanaceae and Scrophulariace. In these families, SI is gametophytic and retains inter-speci c genetic variations by out-crossing promotion. Self-incompatibility is genetically controlled by an S- locus where both male (pollen) and female (pistil) S-determinants are encoded. The female determinant (SRNase) has been extensively studied, whereas its male counterpart (SLF/SFB) has only recently been characterized as a pollen-expressed protein, which encodes for an F-box domain. However, the exact mechanism of in- teraction between SLF/SFB and SRNase is still largely unclear in Rosaceae. This study takes a closer look at the mechanism of self-incompatibility to gain a clearer understanding of the ligand-receptor binding mechanism of SI using molecular evolutionary analysis, structure prediction and binding speci city characteriza- tion, the outcome of which, will translate into a guideline for future studies. The major aims of this study were to derive an evolutionary pattern for GSI in Rosaceae subfamilies and to further assess the collaborative non-self recognition in Malus domestica Borkh.. The evolutionary analysis suggests a di erence in the evolution- ary pattern of Prunoideae and Maloideae S-genes, hence proposing a di erence in their GSI systems. Furthermore, sites responsible for this divergence are identi ed as critical amino acids in GSI function. To maintain GSI it is expected that the S-genes must be linked and co-evolve as a genetic unit. The results of this study show that these genes have co-existed, while SRNase have experienced a higher rate of evolution compared to SLF, thus rejecting the co-evolution of these genes in Maloideae. Furthermore, positively selected sites of S-locus pistil and pollen genes were identi ed that are likely to be responsible for speci city determination. Di erent numbers of these sites are found for both S-genes, while SRNase holds a larger number of positively selected sites. Additionally a model of speci city is introduced that supports the collaborative non-self recognition in Malus GSI, while critical sites responsible for such speci city are proposed and mapped to the predicted ancestral tertiary structure of SRNase and SLF/SFB. The identi cation of regions determining pollen pistil speci city as well as proposing a Collaborative Non-self Recognition model for Malus domestica Borkh. provide greater in-sight into how pollen-pistil communication system works in Maloideae (Rosaceae subfamily).

The genus Restrepia is well known to orchid enthusiasts but its micromorphology has not been described, and its pollination and breeding systems have not been investigated. The aim of this investigation was, therefore, to add to existing knowledge so that the resultant data could be used to facilitate ex situ conservation initiatives. A detailed electron microscopy study (SEM) of the floral organs was performed. This confirmed the structure of the dorsal sepal and lateral petal osmophores, their secretory nature together with that of the synsepal and the labellum. It was postulated how, by manipulating different labellar surface textures, the flower might use these ‘tactile guides’ to steer the insect (fly) through the flower. The cirrhi were postulated to help by destabilising the pollinator in flight, trapping it and bringing about pollination. The papillate structure of the calli was established and their optical properties investigated. Media comparison investigations established that Western medium supported the highest germination rates and, with the addition of banana supplement, the highest rates for seedling growth and development. This represented the first protocol for axenic germination of Restrepia in the literature (Millner et al., 2008) and provided a tested methodology for investigating breeding systems and producing Restrepia plant material for both scientific and horticultural purposes. Self-pollinations were found to produce fewer embryos compared to cross-pollinations. The operation of self-incompatibility (SI) was confirmed by the study of pollen tube growth which further confirmed the time interval between pollination and fertilisation. A time line from pollination/fertilisation to flowering was established. The type of SI in operation was best explained by gametophytic incompatibility. This demonstrated that it was possible to raise Restrepia hybrids and species from seed, by performing intraspecific crosses so helping to preserve them for posterity and relieve pressure on wild populations. Narrow endemic Restrepia species face combined threats from habitat loss, habitat degradation and problems of viable seed production due to the effects of SI and inbreeding depression (ID). Recently developed online resources, such as GeoCAT, were used to perform a Red List assessment in order to identify the degree of threat individual species faced, both globally and nationally. All species were classified as facing substantial levels of threat; although this was lessened for populations in protected habitats. Conservation is needed for cultivated collections as well as these wild populations by keeping alive existing knowledge and expertise in growing these species.

Marker assisted selection in hybrid breeding of oil seed rape