Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2010
Authors
Kristin Kaspersen Therese With Berge Steve Goldberg Jan Netland Øyvind Overskeid Trygve StølanAbstract
No abstract has been registered
Abstract
Development of ontogenic resistance to powdery mildew (Podosphaera aphanis) on strawberry leaves has been reported, however, the components of resistance have not been elucidated. Five developmental stages of strawberry leaves were identified and assigned numerical values from newly emerged and unexpanded (S1) to fully expanded and dark green (S5) of cvs. Korona and Senga Sengana. The upper and lower surface of the leaves were inoculated from each of the five leaf developmental stages and incubated under controlled conditions. The effect of leaf age on germination, infection efficiency, latency period, and sporulation were later evaluated. All responses were significantly (p = 0.05) affected by leaf age. Germination percentage, infection efficiency, and sporulation were highest, and latent periods were shortest on S1 leaves of both cultivars. On Senga Sengana, germinating conidia produced fewer secondary hyphae during infection. Conidia produced very few secondary hyphae and did not sporulate on S3 leaves, and no infections established on S4 or S5 leaves. The high success of infection and colonization of P. aphanis on S1 leaves indicates that disease is established preferentially on emergent and expanding leaves and these should be the target of management strategies.
Authors
Arild Andersen Trond Hofsvang May Bente Brurberg Christer Magnusson Trond Rafoss Brita Toppe Anne Marte Tronsmo Bjørn Økland Leif SundheimAbstract
No abstract has been registered
Authors
Arild Andersen Trond Hofsvang May Bente Brurberg Christer Magnusson Trond Rafoss Brita Toppe Anne Marte Tronsmo Bjørn Økland Leif SundheimAbstract
No abstract has been registered
Authors
Arild Andersen Trond Hofsvang May Bente Brurberg Christer Magnusson Trond Rafoss Anne Marte Tronsmo Bjørn Økland Leif SundheimAbstract
No abstract has been registered
Abstract
The Pasvik River valley is the easternmost part of Norway, and borders to Finland and Russia. In Norway it is known for its wilderness and taiga forests. During the 1960-1970s most of the mature pine forests were harvested, and large areas of pine stands have been naturally regenerated. In addition, large areas are covered with birch. The Pasvik River valley and the adjoining areas are therefore important both as an area for growing timber resources and for recreation. However, these areas have also been exposed to air pollution from Russian smelting industry since the 1930s. In addition to sulphur dioxide, emissions consist of various heavy metals which contaminate the surroundings. The main pollution source is the huge nickel plant in the Russian city Nikel, located only 10 km from the Norwegian border. For a long time there was general concern for the quality of the forest ecosystems in these areas. This concern accelerated in the mid-1980s.
Abstract
Plants use an array of responses to pathogenic infection. Understanding of the underlying defence mechanisms may lead to new strategies for reducing the damage. Our objective here was to study histological and cytological responses in Norway spruce of different ages (from seedlings to mature trees) to infection with several pathogenic organisms (Pythium dimorphum, Ceratocystis polonica and Heterobasidion annosum) and compared them to effects of mechanical wounding. To visualize the reaction on infection/wounding we used different histological staining techniques followed by laser confocal microscopy and TEM. Primary roots of Norway spruce seedlings were infected with P. dimorphum, while mature trees (about 30 years old) were infected with C. polonica, H. annosum and wounded. In seedling roots the hyphae of P. dimorphum penetrated the tissue rapidly and colonized the root within 24 hours. In the infected tissue the lignin concentration doubled within 6 days compared to non infected roots. General response to infection by C. polonica and H. annosum in mature trees was the production of lignosuberised wound periderm, accumulation of polyphenolic aggregates in living parenchyma cells in the phloem and development of traumatic resin ducts in the xylem. Upon wounding, we observed a similar, but less intense response. In conclusion, although we tested fungi belonging to different taxonomical and ecological groups, the responses were similar, differing in intensity and timing of the defence response mainly. The response seems to be similar but dependent on the degree of susceptibility in the individual trees and clones.
Authors
Nadeem Yaqoob Jan Karlsson Benedicte Riber Albrectsen Halvor Solheim Carl Gunnar FossdalAbstract
Plants are exposed to a variety of pathogens in their natural habitats. To understand the key processes of defense responses in aspen (Populus tremulae) at the transcript level two clones C72 and C23 with differential level of resistance from the SwAsp collection were inoculated with a foliar rust (Melampsora magnusiana Wagnar). Leaf samples were collected from adjacent areas of the inoculation site to examine the long distance (systemic) defense responses at day1, day3 and day14 post treatments. We performed microarray experiments on the biothrophic interaction, on comparison with the healthy controls we found that the two clones respond in a widely different fashion to the rust. Clone C23 showed almost no response to biotroph after 24 hours while clone 72 gave a clear defense response to the pathogen. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) showed a significant differential expression patterns in susceptible and resistant colnes. Chitinase, cinnamic acid reductase and the iaa genes showed signification up-regulation in resistant clone. The level of expression was 5.9 delta threshold cycles in chitinase gene at day14. Data analysis from extracted total phenolics and condensed tannins verify the results of cDNA arrays and qRT-PCR.
Abstract
Today the spruce bark beetle Ips typographus is always univoltine in Northern Europe including Norway and completes development from egg to adult between May and August. Further south in Europe, development is bivoltine with the completion of two generations in most years. A temperature-driven developmental model suggests that by 2070-2100 the voltinism of I. typographus will change dramatically in Norway. If summers become only 2.5°C warmer than today bivoltinism can be expected every single year in the major spruce growing areas in S-Norway. This is likely to have dramatic effects on forestry since two generations per year will give two, instead of one, attack periods each summer. In addition to increasing the number of attacked trees the effect of the attacks may also be more severe, as Norway spruce is more susceptible to beetle attacks later in the summer. However, climate change will probably also change the phenology of Norway spruce and thus its susceptibility to attack by I. typographus and its phytopathogenic fungal associates. We are currently modelling how tree resistance varies with temperature and tree phenology in order to provide more well-founded advice to forest managers on the interaction between bark beetles and tree in a future climate.
Authors
Paal KrokeneAbstract
The interaction between conifers, ophiostomatoid fungi and bark beetles is a key factor in conifer ecosystems worldwide, since combined beetle-fungus attacks may cause massive tree mortality, huge economical losses and landscape-level ecological changes. For more than a century researchers have been arguing about who is responsible for tree mortality in bark beetle attacked trees - the beetles themselves or their associated fungi. As in many such polarized debates the best answer probably lies somewhere in between the extremes. The beetles are obviously central in tree killing, as they are actively selecting suitable host trees, short-circuiting tree defenses by boring straight into the relatively defenseless cambial area, and causing mechanical damage to the phloem. However, ophiostomatoid fungi are equally obvious contributors to tree death since nearly all tree-killing bark beetles are associated with such fungi, these fungi are able to colonize and kill healthy phloem and sapwood far beyond the beetle tunnels, and many fungi can kill healthy trees in experimental mass-inoculations. Thus, the trees are facing a beetle-fungus complex that probably acts synergistically to overwhelm tree defenses. The beetles’ mass-attack strategy is central to the success of the beetle-fungus complex, since multiple attacks deplete tree defenses and speed up tree-killing.