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
Abstract
Three unsprayed coffee farms (farm 1, 2 and 3) were studied for the natural occurrence of the insect pathogenic fungus Beauveria bassiana in Hypothenemus hampei populations throughout the rainy season of 2004 (July-November) and 2005 (July-December). B. bassiana infections were found during most sampling dates in both years, on all three farms. The B. bassiana infection levels were higher in 2005 than in 2004 with mean prevalence of 12.1 % and 2.7%, respectively. No consistent significant differences in infection level between farms were found in any of the years. B. bassiana infection levels fluctuated widely throughout the season, and peaked at 13.5% on farm 3 in 2004 and at 44.0% on farm 1 in 2005. The H. hampei population was significantly higher in 2004 than in 2005, with 6.9% of the berries infested in 2004 and only 0.7% in 2005. In both years, the H. hampei infestation level was significantly higher on farm 2. No consistent significant differences in H. hampei infestation levels were found between sampling dates on any of the farms. H. hampei infestation levels fluctuated throughout both seasons, and peaked at 15.3% on farm 2 in 2004 and 2.2% on farm 2 in 2005. No consistent density dependent correlation between H. hampei infestation level and B. bassiana infection level was found. Correlations between climatic conditions and R bassiana or H. hampei were not found. (C) 2007 Elsevier Inc. All rights reserved.
Abstract
A possible cost-effective real-time patch spraying implementation against seed-propagated broad-leaved weeds in cereals is a camera mounted in front of the tractor taking images at feasible distances in the direction of travel, on-board image analysis software and entire boom switched on and off. To assess this implementation, manual weed counts (0.25 m(2) quadrats) in a 1.5 m x 2 m grid, were used to simulate camera outputs. Each quadrat was classified into 'spray' and 'not spray' decisions based on a threshold model, and the resulting map defined the 'ground truth'. Subsequently, 'on/off' spraying at larger control areas where sizes were given by the boom width and image distance, and spraying decision controlled by weed status at the single quadrat simulating the camera's view, were simulated. These coarser maps were compared with 'ground truth', to estimate mapping error (area above threshold not sprayed), spraying error (area below threshold sprayed), total error (sum of mapping and spraying error) and the herbicide reduction. Three levels of the threshold model were tested. Results were used to fit models that predict errors from boom width and image distance. Size of control area did not on average affect the magnitude of the simulated herbicide reductions, but the bigger the control area the higher the risk that the simulated herbicide reduction deviate from the reduction in 'ground truth'. Mean simulated herbicide reductions were 42-59%, depending on threshold level. Only minor differences due to threshold level were seen for mean mapping and spraying errors at given spraying resolutions. Using original threshold level and image distance 2 m, predicted total errors for boom widths 2 m, 6 m, 20 m and 40 m would be 6%, 10%, 16% and 17%, respectively. Results indicate that control area should not exceed about 10 m 2 if acceptable total error is maximum 10%.
Abstract
Lack of automatic weed detection tools has hampered the adoption of site-specific weed control in cereals. An initial object-oriented algorithm for the automatic detection of broad-leaved weeds in cereals developed by SINTEF ICT (Oslo, Norway) was evaluated. The algorithm ("WeedFinder") estimates total density and cover of broad-leaved weed seedlings in cereal fields from near-ground red-green-blue images. The ability of "WeedFinder" to predict 'spray'/'no spray' decisions according to a previously suggested spray decision model for spring cereals was tested with images from two wheat fields sown with the normal row spacing of the region, 0.125 m. Applying the decision model as a simple look-up table, "WeedFinder" gave correct spray decisions in 65-85% of the test images. With discriminant analysis, corresponding mean rates were 84-90%. Future versions of "WeedFinder" must be more accurate and accommodate weed species recognition.
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.
Abstract
To evaluate overwintering strategies of the fungus Neozygites floridana, an important natural enemy of Tetranychus urticae, hibernating T. urticae females were investigated for the presence of fungal structures throughout one winter (October 12, 2006 to February 19, 2007) in field-grown strawberries in a cold climate in Norway ( min. ambient temp -15.3 degrees C). Neozygites floridana was present as hyphal bodies inside live, hibernating females in T. urticae populations throughout the sampling period. The lowest percentages of hibernating females with hyphal bodies were found at the two first dates of sampling at 5.5 and 0% on October 12 and 19, respectively. The prevalence then increased and peaked at 54.4% on January 14. Resting spores (immature) were also found in live hibernating females at some dates, but at lower prevalence than for hyphal bodies and predominantly only until November 8. Prevalence of resting spores in live hibernating females ranged from 2.5 to 13.8%. Total number of T. urticae was also recorded, and most mites of all four categories (nymphs, males, non-hibernating and hibernating females) were found at the first sampling date. At this date non-hibernating females were the most abundant. A sharp decrease in non-hibernating females, nymphs and males was, however, seen from mid-October to mid-November; also numbers of hibernating females decreased, but not as fast. The relative abundance of hibernating females compared to non-hibernating females increased from 32.2% at the first collection (October 12) to 97.7% at the last collection (February 2). This study confirms that N.floridana survives the winter as a semi-latent hyphal body infection, protected inside live hibernating females. It is therefore ready to develop and sporulate as soon as climatic conditions permit, resulting in early season infection of T. urticae.
Abstract
An infectious cDNA clone of a Norwegian isolate of Poinsettia mosaic virus (PnMV) was generated. It consisted of 6,098 nucleotides and encoded a polyprotein of 219.5 kDa. Sequence comparisons indicated that this isolate shared 98.6% (nucleotide) and 97.1% (amino acid) identity with the previously sequenced isolate from Germany. RNA transcripts derived from this cDNA were infectious in Nicotiana benthamiana. However, plants did not present typical PnMV symptoms. Furthermore, RNA transcripts from this cDNA clone were not infectious in poinsettia. Serial propagation of this cDNA clone in N. benthamiana plants restored symptom induction in this host but did not re-establish infectivity in poinsettia.
Authors
Abdelhameed Elameen Siri Fjellheim Arild Larsen Odd Arne Rognli Leif Sundheim Susan Msolla Esther Masumba Kiddo Mtunda Sonja KlemsdalAbstract
Sweet potato (Ipomoea batatas L.) is the fifth most important crop in the developing countries after rice, wheat, maize and cassava. The amplified fragment length polymorphism (AFLP) method was used to study the genetic diversity and relationships of sweet potato accessions in the germplasm collection of Sokoine University of Agriculture, Morogoro and Sugarcane Research Institute, Kibaha, Tanzania. AFLP analysis of 97 sweet potato accessions using ten primer combinations gave a total of 202 clear polymorphic bands. Each one of the 97 sweet potato accessions could be distinguished based on these primer combinations. Estimates of genetic similarities were obtained by the Dice coefficient, and a final dendrogram was constructed with the un-weight pair-group method using arithmetic average. AFLP-based genetic similarity varied from 0.388 to 0.941, with a mean of 0.709. Cluster analysis using genetic similarity divided the accessions into two main groups suggesting that there are genetic relationships among the accessions. Principal Coordinate analysis confirmed the pattern of the cluster analysis. Analysis of molecular variance revealed greater variation within regions (96.19%) than among regions (3.81%). The results from the AFLP analysis revealed a relatively low genetic diversity among the germplasm accessions and the genetic distances between regions were low. A maximally diverse subset of 13 accessions capturing 97% of the molecular markers diversity was identified. We were able to detect duplicates accessions in the germplasm collection using the highly polymorphic markers obtained by AFLP, which were found to be an efficient tool to characterize the genetic diversity and relationships of sweet potato accessions in the germplasm collection in Tanzania.
Authors
Geir Kjølberg Knudsen Maria Bengtsson Sverre Kobro Gunnhild Jaastad Trond Hofsvang Peter WitzgallAbstract
Apple fruit moth Argyresthia conjugella is a specialist seed predator of rowan Sorbus aucuparia. Large-scale synchronous fluctuation of seed production in rowan (i.e. named masting) drives the apple fruit moth to seek alternative host plants such as apple, during years when rowan berries are not available for oviposition. The role of plant volatile compounds in the attraction of gravid apple fruit moth females is studied in a laboratory wind tunnel. Volatiles from rowan branches with green berries stimulate female moths to fly upwind and to land at the odour source. By contrast, females are not attracted to rowan branches without green berries, and they are not attracted to apple, demonstrating that the chemical stimulus from rowan berries is required for attraction. Attraction to synthetic compounds identified from rowan, anethole and 2-phenyl ethanol confirms the role of plant volatiles in host finding. These two compounds, however, show a discrepant behavioural effect in wind tunnel and field tests. Field traps baited with 2-phenyl ethanol capture female moths but anethole does not produce significant captures. Wind tunnel tests produce the opposite results: moths fly upwind towards the anethole lure, whereas 2-phenyl ethanol is not attractive at all. Wind tunnel attraction to 2-phenyl ethanol is achieved by adding odour from a rowan branch without berries, which is not attractive on its own. This finding demonstrates that interaction with the background odour contributes to the behavioural effect of plant volatile stimuli in the field.
Authors
I. A. Yakolev Daniel Kwaku Addo Asante Carl Gunnar Fossdal Jouni Partanen Olavi Junttila Øystein JohnsenAbstract
Det er ikke registrert sammendrag
Abstract
Det er ikke registrert sammendrag