Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2018
Sammendrag
Yunnan pine is the most important tree species in SW China in both economical and ecological terms, but it is often killed by pine shoot beetles (Tomicus spp.). Tomicus beetles are secondary pests in temperate regions and the aggressiveness of the beetles in SW China is considered to be due to the warm subtropical climates as well as the beetles’ virulent fungal associates. Here, we assessed the virulence of three blue-stain fungi (Leptographium wushanense, L. sinense and Ophiostoma canum) associated with pine shoot beetles to Yunnan pine (Pinus yunnanensis) in SW China. Following fungal inoculation, we measured necrotic lesion lengths, antioxidant enzyme activities and monoterpene concentrations in the stem phloem of Yunnan pine. Leptographium wushanense induced twice as long lesions as L. sinense and O. canum, and all three fungi induced significantly longer lesions than sterile agar control inoculations. The activity of three tested antioxidant enzymes (peroxidase, polyphenol oxidase, and superoxide dismutase) increased after both fungal inoculation and control inoculation. However, L. wushanense and L. sinense generally caused a greater increase in enzyme activities than O. canum and the control treatment. Fungal inoculation induced stronger increases in six major monoterpenes than the control treatment, but the difference was significant only for some fungus-monoterpene combinations. Overall, our results show that L. wushanense and L. sinense elicit stronger defense responses and thus are more virulent to Yunnan pine than O. canum. The two Leptographium species may thus contribute to the aggressiveness of their beetle vectors and could damage Yunnan pine across SW China if they spread from the restricted geographical area they have been found in so far.
Forfattere
Paal KrokeneSammendrag
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Forfattere
Paal KrokeneSammendrag
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Forfattere
Tao Zhao Dineshkumar Kandasamy Paal Krokene Jingyuan Chen Jonathan Gershenzon Almuth HammerbacherSammendrag
The bark beetle Ips typographus carries numerous fungi that could be assisting the beetle in colonizing live Norway spruce (Picea abies) trees. Phenolic defenses in spruce phloem are degraded by the beetle's major tree-killing fungus Endoconidiophora polonica, but it is unknown if other beetle associates can also catabolize these compounds. We compared the ability of five fungi commonly associated with I. typographus to degrade phenolic compounds in Norway spruce phloem. Grosmannia penicillata and Grosmannia europhioides were able to degrade stilbenes and flavonoids faster than E. polonica and grow on minimal growth medium with spruce bark constituents as the only nutrients. Furthermore, beetles avoided medium amended with phenolics but marginally preferred medium colonized by fungi. Taken together our results show that different bark beetle-associated fungi have complementary roles in degrading host metabolites and thus might improve this insect's persistence in well defended host tissues.
Sammendrag
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Forfattere
May Bente BrurbergSammendrag
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Sammendrag
Acetylation of wood can provide protection against wood deteriorating fungi, but the exact degradation me- chanism remains unclear. The aim of this study was to determine the effect of acetylation of Pinus radiata wood (weight percent gain 13, 17 and 21%) on the expression of genes involved in decay by brown-rot fungus Rhodonia placenta. Gene expression analysis using qRT-PCR captured incipient to advanced decay stages. As expected the initiation of decay was delayed as a result the degree of acetylation. However, once decay was established, the rate of degradation in acetylated samples was similar to that of unmodi fied wood. This suggests a delay in decay rather than an absolute protection threshold at higher acetylation levels. In accordance with previous studies, the oxidative system of R. placenta was more active in wood with higher degrees of acetylation and expression of cellulose active enzymes was delayed for acetylated samples compared to untreated samples. The reason for the delay in the latter might be because of the slower diffusion rate in acetylated wood or that partially acetylated cellobiose may be less effective in triggering production of saccharification enzymes. Enzymes involved in hemicellulose and pectin degradation have previously not been focused on in studies of degradation of acetylated wood. Surprisingly, CE16 carbohydrate esterase, assumed to be involved in deace- tylation of carbohydrates, was expressed significantly more in untreated samples compared to highly acetylated samples. We hypothesise that this enzyme might be regulated through a negative feedback system, where acetic acid supresses the expression. The up-regulation of two expansin genes in acetylated samples suggests that their function, to loosen the cell wall, is needed more in acetylated wood due the physical bulking of the cell wall. In this study, we demonstrate that acetylation affects the expression of specific target genes not previously re- ported, resulting in delayed initiation of decay. Thus, targeting these degradation mechanisms can contribute to improving wood protection systems.
Sammendrag
The apple fruit moth Argyresthia conjugella (Lepidoptera, Yponomeutidae) is a seed predator of rowan (Sorbus aucuparia) and is distributed in Europe and Asia. In Fennoscandia (Finland, Norway and Sweden), rowan fruit production is low every 2–4 years, and apple (Malus domestica) functions as an alternative host, resulting in economic loss in apple crops in inter-mast years. We have used Illumina MiSeq sequencing to identify a set of 19 novel tetra-nucleotide short tandem repeats (STRs) in Argyresthia conjugella. Such motifs are recommended for genetic monitoring, which may help to determine the eco-evolutionary processes acting on this pest insect. The 19 STRs were optimized and amplified into five multiplex PCR reactions. We tested individuals collected from Norway and Sweden (n = 64), and detected very high genetic variation (average 13.6 alleles, He = 0.75) compared to most other Lepidoptera species studied so far. Spatial genetic differentiation was low and gene flow was high in the test populations, although two non-spatial clusters could be detected. We conclude that this set of genetic markers may be a useful resource for population genetic monitoring of this economical important insect species.
Sammendrag
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