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.
2008
Forfattere
Margarita Novoa Garrido Cristina L. Marolda Miguel A. Valvano Henning SørumSammendrag
Organic acids are promising candidates as substitutes for antibiotic growth promoters, as they show positive effects on weight gain and control of pathogens. Their addition to the litters as sanitizers, are being suggested. Organic acids affect bacteria in different ways depending on the type of organic acid molecule, external factors such as pH, and the type of bacterial strain. A better understanding of the effects organic acids cause on normal intestinal bacterial flora is needed to make an optimal use of organic acids and avoid possible negative long-term consequences. To investigate the response of a normal intestinal commensal bacterium to continuous mild acid stress, a wild type Escherichia coli strain was submitted to serial passages in buffered medium containing 0,03% formic acid (FA) at mild acidic conditions (pH 5.25 and 6.1) for 20 months. Three morphologically distinctive colony variants (mucoid, non-mucoid and parental) appeared after two months of serial culture in FA. The mucoid colonies formed a long thread that could be up to three meters long when they were picked with a loop. The non-mucoid showed a very dry appearance and irregular shape. The third type of colony variant resembled the parental E. coli strain. Cultivation on Congo red agar and calcofluor suggested the production of fimbriae and/or cellulose or another similar linear extracellular polymer on the surface of the mucoid and non-mucoid variants. In a biofilm assay on glass surfaces the mucoid and non-mucoid variants showed pellicle- and biofilm-forming properties. The parental strain did not show any of the multicellular behaviour features. Phase contrast microscopy demonstrated that the bacterial cells from the mucoid colonies were notorious long, forming "spaghetti"-like structures containing clear vacuoles and pycnotic areas. The SEM examination demonstrated that the cells from the non-mucoid colonies were connected by filament-like structures, probably curli fimbriae, that created a net-like matrix between the bacterial cells which were not observed in colonies from the parental strain or from the mucoid colonies. By LPS extraction and immunoblot analysis we have also shown that the expression of O antigen of the E. coli strain r17 was reduced after several months of weekly passages in the presence of FA. Thus, we also examined the LPS profile of the two colony variants. While the mucoid colonies displayed a normal LPS profile, the non-mucoid variant had an anomalous O antigen profile characteristic of strains lacking the wzz gene, which is responsible for the regulation of the length of the O antigen chains. The development of the parental strain r17 into these morphologically different colonies is likely to be a response of the strain to the environmental stress that the mild acidic pH and the presence of FA in the medium represent. The changes suffered by the parental strain cause biofilm formation. One may speculate whether a selection towards a more invasive and/or biofilm producing bacterial flora is taking place when organic acids are used as feed additives in animal husbandry with the potential consequences for the animal health and hygiene this could represent. Screening of the normal intestinal bacterial microflora of animals fed with these feed additives and their environment could bring more light to this concern. This study has been funded by a grant from the Norwegian Research Council.
Sammendrag
Det er ikke noe nytt at norske gårder i gjennomsnitt blir større og færre over tid. Strukturrasjonaliseringa ser imidlertid ut til å gå enda raskere innen økologisk landbruk fordi relativt mindre gårder melder seg ut av Debio-ordningen, mens relativt større blir meldt inn. Helt siden 2002 har det gjennomsnittlige jordbruksarealet på Debio-sertifiserte gårder vært større enn gjennomsnittet for norske gårder. For 2007 er forskjellen i areal 255 vs 213 dekar, og trenden ser ut til å holde seg.
Sammendrag
Etter sine dyrkingsmessige egenskaper blir våre dyrkete hagejordbær inndelt i engangsbærende og flergangsbærende (remonterende) sorter. Mens blomstringen hos de vanlige engangsbærende sortene har vært gjenstand for omfattende undersøkelser og er kjent for å være indusert av kort dag (KD), har det vært betydelig forvirring i litteraturen om daglengde-reaksjonen for de flergangsblomstrende sortene. I et nylig avslutta forskningsprosjekt har vi imidlertid kunnet fastslå at danningen av blomsterknopper hos disse sortene er indusert av langdags (LD)-forhold. Ved høy temperatur (> 25 ºC) er disse plantene obligatoriske LD-planter, mens de ved midlere temperaturer (15 - 20 ºC) også vil blomstre under KD-forhold, men da er blomstringen sterkt forsinket. Ved lave temperaturer (< 10 ºC) er imidlertid også disse sortene dagnøytrale i likhet med flere av de engangsbærende sortene.
Forfattere
Anita Sønsteby Ola M. HeideSammendrag
Det er ikke registrert sammendrag
Forfattere
Helge SjursenSammendrag
Flikbrønsle tilhører den biologiske gruppen sommerettårige ugras. Planten har en greinet pålerot, og kan bli 20-90 cm høy. Stengelen er opprett, vanligvis brungrønn til rødbrun og sterkt greinet. Bladene er motsatte, glatte, tre-fem-fliket med stor midtflik som er dypt sagtagget. Fargen er mørkgrønn. De nedre bladene er tydelig skaftet. Planten har blomsterkorger, enslige eller i kvast, formet som en halvskjerm. Frukten er en fnokkløs nøtt, langstrakt, med stivhårete ribber langs midten på begge sider av kantene, som kan lett feste seg i pelsen på dyr, og bli spredd på den måten. Forekommer i dyrket og udyrket mark, langs grøfter og kanaler, på vassjuk og sur jord. Opptrer som ugras i fuktig åker, eng og beite. Bekjempelse: Grøfting av fuktig mark, og ellers tiltak som mot andre sommerettårige ugras.
Sammendrag
A field fertilizer trial planted in late August was used to study effects of fertilizer timing and application method on flowering and ripening in strawberry cv. Korona. In treatment 1 (T1), fertilization in August prior to planting was followed by fertigation with low nutrient rate from May to August in the first harvest year. In treatment 2 (T2) all nutrients were applied as nutrient solution from May to August the first harvest year. By August in the first harvest year, the total amount of fertilizer applied was similar for both treatments (80 kg N ha(-1)). Equal amounts of water were also applied in both treatments. In the second harvest year, all the fertilizer was applied using fertigation from May to August. Both treatments were given the same fertilizer rate (80 kg N ha(-1)) to study after-effects of T1 and T2. In the first harvest year, preplant fertilized plants flowered earlier and required a higher number of days and day-degrees from anthesis to berry ripening than did T2 plants which were not fertilized until spring the first harvest year. Significant differences were found in yield but not in the number of berries, as berry size was significantly higher in T1. No significant differences were found between fertilizer treatments in the second harvest year, although T2 tended to yield the maximum number of berries later in the season than T1.
Sammendrag
The environmental control of flowering in five populations of Fragaria virginiana ssp. glauca and three populations of F virginiana ssp. virginiana (henceforth referred to as F virginiana), obtained as seed from the National Plant Germplasm Repository, Corvallis, OR, USA, has been studied under controlled environment conditions. Except for the F virginiana ssp. glauca population PI 551648 from the Wasatch Mountains in Utah, which was truly day-neutral across a 9 degrees - 27 degrees C temperature range, all the other populations of both sub-species behaved as quantitative (facultative) short-day (SD) plants with earlier and more abundant flowering under SD than under long-day (LD) conditions. Flowering of the remaining F virginiana ssp. glauca populations was governed by a significant interaction of photoperiod and temperature. The SD dependence for flowering increased with increasing temperature from 9 degrees C to 27 degrees C. The optimum temperature for the SD flowering response was 15 degrees - 21 degrees C. While SD promotion of flowering was more pronounced in the F virginiana populations, temperature had no significant main effect on flowering in this sub-species, demonstrating a wide temperature tolerance for flowering. Vigorous runner formation was observed in all populations, in both SD and LD, with a highly significant advancement effect of increasing temperature. The flowering and runnering responses of these E virginiana populations are discussed in relation to their putative paternity of perpetual-flowering F. X ananassa cultivars. It is concluded that, with the complex inheritance in these octoploid plants, the flowering responses of the populations studied here are not reflected in the LD flowering response of cultivated everbearing strawberries.
Sammendrag
Det er ikke registrert sammendrag
Forfattere
Jens KøhlerSammendrag
Det er ikke registrert sammendrag
Forfattere
Nils-Otto KitterødSammendrag
Det er ikke registrert sammendrag