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.
2008
Abstract
No abstract has been registered
Authors
Halvor SolheimAbstract
Climate change may influence in a worse manner for the forests in various ways. Some pathogens may increase their importance and new may arrive. Root and butt rot is the most serious problem in Norway spruce forests. In mean more than every fourth tree is infested when harvested. Dryer summers may give increased frequency of rot caused by Heterobasidion. In addition Armillaria spp may gain change in weather condition both as root rot and in connection with a syndrome together with drought and bark beetles. More unstable winter climate may give increase of Gremmeniella attack on Scots pine. Longer and warmer growth season will give many pathogens better condition. Among those is Ophiostoma novo-ulmi causing Dutch elm disease which is lasting in south eastern Norway at a rather low frequency and the volume of elm is not lower than for 15 years ago. In which way the newly introduced Chalara fraxinea will behave in Norway is uncertain, but a better growth season will probably also influence on the possibility to be spread all over Norway where ash are growing.
Abstract
Ips typographus is economically most important insect pest of mature spruce in Eurasia. Normally, it prefers to reproduce in dead and/or dying trees, but following large-scale storm disturbances, its outbreaks kill waste areas of living stands. One factor triggering such epidemics is a surplus of broken and uprooted trees with non-existent, or weak, defence....
Abstract
Induced reactions in the phloem is a basic mechanism of conifer resistance to bark beetle and their associated fungi (1,2). Previous research has proved that certain doses of Ceratocystis polonica infection or methyl jasmonate (MeJA) application could induce acquired resistance and decrease subsequent fungal or bark beetle colonization (3,4,5). To study the induced chemical changes after fungal infection and MeJA application in the phloem of mature Norway spruce, three groups, each of 24 P. abies trees of similar size, were chosen in Tönnersjöheden, southern Sweden, in May 2006. The three groups were then inoculated with C. polonica, sprayed with MeJA, or used as untreated control, respectively. Phloem samples were taken twice from each tree: on the same day as treatment and 1 mo later. The terpene composition of all the samples was analyzed by GC-MS, and the enantiomeric compositions of α-pinene, β-pinene, and limonene were analyzed by 2D-GC (6). The result indicated that both MeJA application and C. polonica infection had certain effects on the terpene composition. C. polonica infection significantly increased the biosynthesis of 3-carene, sabinene, and terpinolene. Both mean absolute amounts and relative amounts of these monoterpenes increased in samples from fungus inoculated trees, similar to what is observed in Scots pine after Leptographium wingfieldii inoculation (7). MeJA application increased the absolute amount of α-pinene, β-pinene, limonene, and some other major terpenes, but it did not change the relative amount of these terpenes. However, neither MeJA application nor fungal infection changed the enantiomeric compositions of α-pinene, β-pinene, and limonene in the phloem of Norway spruce.
Abstract
The root-rot causing fungus Heterobasidion annosum sensu lato is the most devastating pathogen of conifers in Europe. This pathogen enters Norway spruce through the roots and can colonize the tree from within, growing as a saprophyte when established within the dead heartwood and acting as a necrotroph when in contact with living host tissue. Despite the high incidence of damage, trees have defences against this pathogen in the bark and living wood. Furthermore, spruce has a defense against internal attack by forming a reaction zone, in this case the host defense is directed inwardly by the still living sapwood toward the central colonized heartwood. We have studied the host responses to infection in Norway spruce clones at the transcriptional level and found that the speed of recognition and that spatial defense signalling appears to be the hallmarks of trees with high degree of resistance...
Abstract
No abstract has been registered
Abstract
Due to the great economic losses caused by the root and butt-rot pathogen Heterobasidion annosum, developments of efficient control measures are warranted. H. annosum a necrotroph colonize the Norway spruce from inside and is responsible of 10-13 millions Euros losses in Norway alone. Considerable clonal variation has been recorded for Norway spruce in resistance towards H. annosum, but the defence mechanisms contributing to host resistance remain poorly understood. The recent genome sequencing of Populus has made the genus a model to facilitate tree genetics. Genome-wide transcript profiling of Populus tremula upon pathogen attack will now be used, and homologues of Norway spruce genes to defence genes up-regulated in Populus will be identified. Populus-Phellinus tremula pathosystem is selected as P. tremula behaves like H. annosum.
Abstract
No abstract has been registered
Abstract
Many bacteria produce antimicrobial substances such as nonribosomally synthesized antibiotics and ribosomally synthesized proteinaceous compounds referred to as bacteriocins. Secretion of antimicrobials is generally thought to contribute to the competitiveness of the producing organism, but there are indications that these compounds in some cases may have regulatory roles too. Bacteriocins most often act on closely related species only and are thus of interest for application as targeted narrow-spectrum antimicrobials with few side effects. Although the application of bacteriocins in plant disease control is an attractive option, very little is known about the occurrence and roles of these compounds in plant pathogenic bacteria and their natural competitors occurring in the same biotopes. This study presents an overview of current knowledge of bacteriocins from plant pathogenic bacteria.
Abstract
The Gram-positive bacterium Clavibacter michiganensis subsp. sepedonicus is the causal agent of bacterial wilt and ring rot of potato. So far, only two proteins have been shown to be essential for virulence, namely a plasmid-encoded cellulase CelA and a hypersensitive response-inducing protein. We have examined the relative expression of CelA and eight putative virulence factors during infection of potato and in liquid culture, using quantitative real-time PCR. The examined putative virulence genes were celB, a cellulase-encoding gene and genes encoding a pectate lyase, a xylanase and five homologues of the Clavibacter michiganensis subsp. michiganensis pathogenicity factor Pat-1 thought to encode a serine protease. Six of the nine assayed genes were up-regulated during infection of potato, including celA, celB, the xylanase gene, and two of the pat genes. The pectate lyase gene showed only slightly elevated expression, whereas three of the five examined pat genes were down-regulated during infection in potato. Interestingly, the two up-regulated pat genes showed a noticeable sequence difference compared to the three down-regulated pat genes. These results reveal several new proteins that are likely to be involved in Clavibacter michiganensis subsp. sepedonicus pathogenicity.