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Research project (§ 26 & § 27)
Duration : 2018-10-01 - 2021-09-30

Ash dieback is a serious disease of ash (Fraxinus) species caused by the ascomycete fungus Hymenoscyphus fraxineus, which is native to East Asia and an invasive alien species in Europe. In Austria, symptoms of ash dieback were first recorded in 2005, and due to the successive spread of the causative agent, the disease now occurs in entire Austria. Besides the highly susceptible common ash (Fraxinus excelsior), which is severely damaged throughout most of its distribution range in Europe, narrow-leaved ash (Fraxinus angustifolia), which is in Austria mainly distributed in floodplain forests along the river March, is highly susceptible to the ash dieback pathogen. As observed for F. excelsior, there are individual F. angustifolia trees in young and mature forest stands which are only slightly affected by the disease. Such trees possibly possess a genetically heritable high resistance towards H. fraxineus. In order to preserve the autochthonous occurrence of F. angustifolia in floodplain forests along the March, which is threatened by ash dieback, undamaged or only slightly damaged ash trees across all age classes will be selected in the natural distribution range of the species. These trees will be incorporated in a clonal collection and in a progeny trial, in which their disease resistance levels will be evaluated. Heavily damaged afforestations of narrow-leaved ash which have been established during the last 10 to 15 years will be inspected, and undamaged or slightly damaged plants will be selected and vegetatively propagated, first by grafting and later by rooted cuttings. For the older age classes, seeds will be collected from undamaged or slightly damaged ash trees, from which plants will be grown. With the vegetatively and generatively propagated plant material two field trials will be established. In these trials, the level of resistance of the various genotypes will be tested. Simultaneously, the experimental sites shall serve for the ex situ preservation of narrow-leaved ash. Thereby, the present project will in the long-term lay the foundation for the establishment of seed orchards with disease resistant specimens of this ash species.
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.

Supervised Theses and Dissertations