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.
2006
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2005
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In spring 2002, extensive damages were recorded in southeast Norway on nursery-grown Norway spruce seedlings that had either wintered in nursery cold storage or had been planted out in autumn 2001. The damages were characterised by leader shoot dieback and necroses on the upper or lower part of the 2001-year-shoot. Gremmeniella abietina and Phomopsis sp. were frequently isolated from the diseased seedlings. RAMS (random amplified microsatellites) profiling indicated that the G.abietina strains associated with diseased nursery seedlings belonged to LTT (large-tree type) ecotype, and inoculation tests confirmed their pathogenicity on Norway spruce. Based on sequence analysis of the internal transcribed spacer (ITS) regions of ribosomal DNA, the Phomopsis strains associated with diseased seedlings do not represent any characterized Phomopsis species associated with conifers. Phomopsis sp. was not pathogenic in inoculation tests, this implying it may be a secondary colonizer. ITS-based real-time PCR assays were developed in order to detect and quantify Gremmeniella and Phomopsis in the nursery stock. We describe here the Gremmeniella - associated shoot dieback symptoms on Norway spruce seedlings and conclude that the unusual disease outburst was related to the Gremmeniella epidemic caused by the LTT type on large pines in 2001.
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Rhizoctonia solani was frequently isolated in the Italian Alps from ursery-grown European beech (Fagus sylvatica) seedlings displaying symptoms of cotyledon rot. Koch?s postulates were verified and mode of infection of the associated isolates was investigated with light and scanning electron microscopy. Population structure of the pathogen was investigated by scoring the anastomosis reaction type in pairings between different isolates from the same seedbed. One pathogen genotype showed a large distribution area within the seedbed, this implying that the inoculum had been building up in the seedbed over a longer time period. Hyphal anastomosis tests and sequence analysis of the internal transcribed spacer (ITS) region of ribosomal DNA indicated that the pathogen belongs to AG 2-1 of R. solani. ITS sequence analysis indicates that the isolates from beech are closely related to R. solani isolates causing a disease on tulip. The striking similarities between the two diseases are discussed.
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In field experiments, clones of Norway spruce [Picea abies (L.) Karst.] showed different degrees of resistance against pathogenic fungi inoculated into the bark that correlate with differences in polyphenolic parenchyma (PP) cells of the bark. Cells of spruce callus cultures, particularly towards the callus surface, resemble PP cells and this study looks at changes in callus cells during infection and the relative resistance of cultures from clones of low (weak) or high (strong) resistance to fungal infection. Callus cultures, initiated from trees with different resistance, were co-inoculated with Ceratocystis polonica (Siem.) C. Moreau and Heterobasidion annosum (Fr.) Bref. Callus cells from strong clones resemble PP cells of bark tissue from strong clones, having more polyphenolic bodies, while callus cells from weak clones are more similar to PP cells from those clones, which have less extensive phenolic bodies. Callus cultures from trees with weak resistance were more quickly overgrown by both species of pathogenic fungi than cultures from trees with strong resistance. Callus cells of infected cultures showed changes similar to activated PP cells of bark, including enhanced accumulation of polyphenolics. Phenolic bodies were more numerous and more extensive (larger and denser) in callus cells of strong versus weak clones under all conditions. Thus, callus cells may perform similar functions in defense as PP cells in the bark. Callus from trees of varying resistance seem to reflect the relative resistance of the trees from which they are derived, and this study indicates that some mechanisms of resistance can be studied using callus from trees of different resistance.
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This paper describes the use of quantitative real-time PCR for monitoring colonization of birch wood (Betula pubescens) by the white-rot fungus Trametes versicolor in an EN113 decay experiment. The wood samples were harvested after 4, 8, 12, 16 and 20 weeks of incubation.The mass loss was in the range of 440%. Chitin and ergosterol assays were conducted for comparison. Second-order polynomial fits of the mass loss of decayed wood versus chitin, ergosterol and DNA gave correlations (r2) of 0.87, 0.61 and 0.84, respectively. Compared to the other two assays employed, real-time PCR data correlated best with the relative mass loss of decayed samples 48 weeks after inoculation, while the saturation and decline of DNA-based estimates for fungal colonization 1620 weeks after inoculation indicated that the DNA assay is not suited for quantification purposes in the late stages of decay.The impact of conversion factors, extraction efficiency, inhibitory compounds and background levels in relation to the three detection assays used is discussed.