This thesis is an investigation into the genetic diversity, genetic structure and phenotypic differentiation of the rare plant Melampyrum sylvaticum L. (Orobanchaceae) in the United Kingdom, in the context of habitat fragmentation. Habitat fragmentation is of conservation concern as it may result in reduced population sizes, reduced genetic diversity and gene flow, and altered environmental and ecological conditions. Seven polymorphic microsatellite markers were developed and revealed that M. sylvaticum is highly inbreeding (FIS = 0.90). Ten populations in a fragmented landscape in Scotland had significantly less genetic diversity than eight large populations from Scandinavia where the species’ habitat is more continuously distributed. Overall, genetic differentiation between populations was very high (F’ST = 0.892). Furthermore, the use of a replicated, spatially explicit sampling scheme revealed that ‘fragmented’ Scottish sites had much stronger spatial genetic structure (Sp = 0.267 – 0.311), per unit area, than more continuously distributed sites (Sp = 0.026 – 0.096) in Sweden. These genetic data indicate that the fragmented populations of M. sylvaticum have low genetic diversity and that gene flow is very low. To quantify morphological differences among populations, plant phenotypes were described using a novel method based on count and architectural position data of ecologically-relevant fitness-related traits. Four populations in the UK were phenotypically differentiated in their whole-plant, vegetative and reproductive phenotypes. Vegetative phenotypes correspond to traditionally recognised ‘seasonal variants’ in the Orobanchaceae and are likely to represent ecotypic local adaptation. The number of ‘unsuccessful’ and ‘potentially successful’ reproductive traits was significantly different among populations. It is not possible to say whether this is due to site-specific resource effects or population-specific inbreeding depression. Horticultural protocols were developed to enable conservation actions to be carried out with greater success. Recommendations for the conservation management of the species are to focus on site-based management, local expansions and ex-situ conservation.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 119-125). Also available in electronic version.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 92-99). Also available in electronic version.

Thesis (Ph. D.)--Ohio State University, 2007.

No description available.

This study describes the effect of the root hemi-parasitic angiosperm Rhinanthus minor on the structure of the communities in which it lives and seeks to elucidate a mechanism through which the parasite acts to effect these changes in the community. Field manipulations reveal that R. minor suppressed the growth of grasses and legumes in a newly sown meadow whilst promoting the forbs within one growing season. In contrast the removal of R. minor from mature meadow plots did not influence their composition. After an additional growing season the parasite did not further influence the composition of the new meadows but removal did begin to benefit the biomass of mature plots. In isolation the parasite caused most damage to grasses whilst leaving legumes and forbs undamaged. Moreover, the parasite performed worst in terms of growth and photosynthesis when attached to the forbs. Consequently the parasite was able to moderate intra-specific competition between grasses and forbs. I thus hypothesised that forbs were able to prevent the parasite form abstracting resources where as grasses could not. Tracer experiments using isotopically e5N) labelled potassium nitrate confirmed this hypothesis showing that more of the resources taken up by the host were stolen by the parasite from grasses than from forbs. There was much variability in the translocation of resources from the legume studied. The reasons underlying the differential uptake of resources were highlighted using histological studies which showed that all of the forbs possessed successful resistance mechanisms to the parasite whilst no successful resistance was observed in the grasses or legumes. Two different resistance mechanisms were observed in the forbs; hypersensitive cell-death at the host-parasite interface and host lignification. I therefore propose that differential host resistance may underlie this parasite's community level effects as forbs possess a resistance capacity that other potential hosts do not.

Evolution, physiology and ecology of root-parasitic Rhinanthoid Orobanchaceae was investigated with special emphasis on understanding biology of hemiparasitism. The research was based on a wide range of methods including molecular hylogenetics, cultivation experiments, stable isotope analysis, electron icroscopy, geometric morphometrics and flow-cytometry.

No description available.

Parasitic weeds of the family Orobanchaceae attach to the roots of host plants via haustoria capable of drawing nutrients from host vascular tissue. Species in this family span the spectrum of host nutrient dependency, allowing comparisons that provide insight into parasite adaptation. A key aspect of this is the relationship between parasite metabolism and the metabolite profile of its host. To what extent does the metabolite profile of the parasite depend on that of the host? Do parasites that differ in host-dependency also differ in their metabolism or do they use common metabolic strategies? These questions were addressed using comparative profiling of primary metabolites to gain insight into carbon and nitrogen assimilation by the obligate holoparasite Phelipanche aegyptiaca and the facultative hemiparasite Triphysaria versicolor. First, metabolite profiles of these parasites and their hosts were compared during the key life stages before and after haustorial attachment. Second, the impact of specific variations in host metabolism was analyzed for P. aegyptiaca growing on Arabidopsis thaliana hosts that had mutations in amino acid metabolism but otherwise identical genetic backgrounds. Comparison of P. aegyptiaca and T. versicolor metabolite profiles identified substantial differences in the stages spanning the transition from pre-haustorial development through post-haustorial feeding. Each parasite species is distinct from the other and from their hosts. For parasites growing on host lines that differ in amino acid content, the size of P. aegyptiaca tubercles decreased when grown on the aap6 mutant line, which has decreased levels of asparagine in the phloem sap compared to the wild type. However, altered amino acid levels in other lines did not impact P. aegyptiaca growth, indicating that this parasite has ability to compensate for variation in host metabolic composition. This research highlights the importance of aspartate and asparagine to early post-attachment metabolism in both P. aegyptiaca and T. versicolor and through host deficiencies possibly associated with decreased growth in P. aegyptiaca. Overall, this work provides insights both into the metabolism of parasitic plants and lays the foundation for the development of new metabolism-based control strategies. / Ph. D. / Parasitic weeds of the plant family Orobanchaceae attach to the roots of host plants via haustoria. Parasite haustoria embed into the host plant and are capable of drawing nutrients from host vascular tissue. Species in this family span the spectrum of the extent to which a parasitic plant may depend on its host for nutrients. This allows comparisons that provide insight into the ways in which parasites adapt. A key aspect of this is the relationship between the metabolite profile of the parasite and the metabolite profile of the host. To what extent does the metabolite profile of the parasite depend on that of the host? Do parasites that differ in host-dependency also differ in their metabolism or do they use common metabolic strategies? These questions were addressed using comparative profiling of primary metabolites to gain insight into carbon and nitrogen assimilation by the obligate parasite Phelipanche aegyptiaca (which cannot perform photosynthesis) and the facultative parasite Triphysaria versicolor (which can perform photosynthesis). First, metabolite profiles of these parasites and their hosts were compared during the key life stages before and after haustorial attachment. Second, the impact of specific variations in host metabolism was analyzed for P. aegyptiaca growing on Arabidopsis thaliana hosts. These hosts had mutations in enzymes related to amino acid metabolism but otherwise identical genetic backgrounds. Comparison of P. aegyptiaca and T. versicolor metabolite profiles identified substantial differences in the stages spanning the transition from pre-haustorial development through post-haustorial feeding. Each parasite species is distinct from the other and from their hosts. For parasites growing on host lines that differ in amino acid content, the size of P. aegyptiaca tubercles decreased when grown on the aap6 mutant line, which has decreased levels of asparagine in the phloem sap compared to the wild type. However, altered amino acid levels in other lines did not impact P. aegyptiaca growth, indicating that this parasite has ability to compensate for variation in host metabolic composition. Overall, this work provides insights both into the metabolism of parasitic plants and lays the foundation for the development of new metabolism-based control strategies.

Ph. D.