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Research project (§ 26 & § 27)
Duration : 2018-07-01 - 2022-06-30

Extreme climatic events are main triggers of pest outbreaks, and an improved mechanistic understanding of drought effects on interactions of the Eurasian spruce bark beetle (Ips typographus) and its host Norway spruce is highly demanded. The proposed drought manipulation study deals with the problem of resource allocation in Norway spruce with specific regard to secondary metabolism. To what extent is constitutive and induced defence against bark beetle attack, such as resin flow and hypersensitive reaction on blue stain fungus inoculation, influenced by tree drought stress? In particular, patterns in the composition and concentration of monoterpenes in spruce bark as well as in volatile emissions are addressed. Response of bark beetles in terms of tree attack is tested in the field, in terms of direct repellent or attractive effects of different bouquets on male beetles in the lab. The in situ drought manipulation experiment will provide novel empirical evidence of effects of water deficiency on Norway spruce secondary metabolism important for risk assessment. Study results will be incorporated in a previously developed, comprehensive model framework addressing the complex interplay between drought stress intensity, induced and constitutive defence responses, and insect infestation. At the drought manipulation site, sample trees are embraced by rain-out shelters in the size of 5x5 m, further trees are chosen for control. Climate parameters and tree water status in terms of pre-dawn twig water potentials are recorded. Constitutive and induced defence is examined by resin flow, hypersensitive reaction on blue-stain fungus inoculation, and jasmonic acid concentrations in the bark. Volatile compounds emitted from the tree stems and bark extracts are analysed by Gas Chromatography and Mass Spectrometry. Using the novel attack box approach, bark beetle attack under controlled test conditions is regularly observed. Local bark beetle activity is checked by pheromone-baited flight-barrier traps and trap trees outside the forest stand. By use of an olfactometer, behavioural response is tested for various blends of monoterpenes identified in the course of the field experiment.
Research project (§ 26 & § 27)
Duration : 2015-12-02 - 2019-12-01

Ash dieback caused by the ascomycete Hymenoscyphus fraxineus has spread recently all over Austria. This disease has caused severe damage on ash trees, and can cause yield loss, dieback and even dieback of affected trees. This disease is currently causing major changes in the composition and ecology of hardwood forests in Austria. The management of ash has more or less stopped, as only old trees are harvested but regeneration is absent. However, also in highly affected stands apparently resistant trees are detected regularly. These trees usually show only few or no symptoms of the disease and probably have a high level of resistance against the pathogen. Up to 5% of the clones in Austrian seed orchards appear to be resistant to the disease to a certain degree. International research has provided evidence that a large part of this resistance has a genetic basis. Based on these results efforts to select resistant clones seem very promising to maintain ash as one of the main hardwood species in Austria. The basis for such an endeavour is the collection of a large number of resistant clones from all over Austria, both to be able to select the best clones, but also to maintain genetic diversity in the species. The goal of the proposed project is the selection of several hundred resistant mother clones to conserve the genetic diversity of the species. The breeding value of the selected mother trees will be calculated based on the performance of single tree offspring in a common garden experiment. In a further step male trees (putative father) of these offspring will be identified by paternity analysis to be able also to select male ash trees for a future seed orchard. Both the best mother and father trees are to be propagated by grafting and cuttings, to preserve their genetic information. This selection of highly resistant clones with superior resistance against ash dieback will enable the set-up of new ash clone seed orchards. Vegetatively propagated plants shall also be provided to end users, to provide resistant reproductive material to forest managers, as a direct output of the project.
Research project (§ 26 & § 27)
Duration : 2016-05-10 - 2017-02-05

Speciation is a fundamental evolutionary process responsible for the great diversity of life on Earth. Main factors contributing to the evolution of reproductive isolation are geographic and ecological isolation. However, oft-forgotten and controversially discussed players in the speciation process of insects are reproduction-manipulating endosymbiotic bacteria of the genus Wolbachia that can form pre- and postzygotic barriers in infected insect populations. The multiply infected Rhagoletis fruit flies are an excellent system to study such effects as the evolutionary history of this genus involves a number radiations with different geographic modes, ranging from classic allopatric divergence to sympatric speciation via host plant shifting. Aim of this proposal is to evaluate the contribution of Wolbachia to speciation in different Rhagoletis species utilizing on-site research at the highly complex structured North American fruit fly populations. The research objective will be accomplished by analyzing Wolbachia strains from different Rhagoletis species groups that have undergone allopatric (e.g., R. suavis group) vs. sympatric (e.g., R. pomonella group) speciation. Following the broadly accepted theory that bacterial reproductive isolation almost always evolves in allopatry, I hypothesize that sympatrically derived species with extant gene flow will share the same strains of Wolbachia while allopatric species will possess different strains. I will test this hypothesis by the characterization of different Rhagoletis populations. Further, Wolbachia strains in parasitoid wasps attacking Rhagoletis flies will be characterized as possible vector of horizontal Wolbachia transmission between Rhagoletis species. This will give new insights into routes of horizontal transmission between different species and the evolution of Wolbachia in geographically separated populations with possible influences into speciation. Going beyond the capabilities of the established MLST system for strain discrimination, a combination of Sanger and next generation high throughput sequencing will be adapted to perform a high resolution characterization of this bacteria. Additionally the Rhagoletis species and their parasitoids will be screened for other bacterial endosymbionts influencing the host’s reproduction. Verifying an active role of Wolbachia in reproductive isolation and Rhagoletis speciation will ultimately require breeding of flies that are depleted of the bacteria to determine the extent that fertility is restored between flies. Thus, a secondary objective of the current proposal is to develop and establish protocols for curing Rhagoletis of Wolbachia, allowing follow-up manipulative studies in the future to confirm a direct connection of Wolbachia with fly reproductive isolation.

Supervised Theses and Dissertations