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.
2009
Forfattere
Lena Lie NymoenSammendrag
Det er ikke registrert sammendrag
Forfattere
Lena Lie NymoenSammendrag
Det er ikke registrert sammendrag
Forfattere
Arne Stensvand David M. Gadoury Håvard Eikemo Andrew Dobson M. Catherine Heidenreich Robert C. SeemSammendrag
Field trials at Ås, Norway and Geneva, NY, USA revealed a substantial impact of initial levels of powdery mildew (Podosphaera macularis) upon disease development in strawberry (Fragaria × ananassa). Five-row plots of 50 to 100 mildew-free plants (planting distance 0.45 × 1.2 m) were established each year within large grain fields with a minimum distance of 90 m between plots and were left untreated with fungicides. Beginning each season, plants at the center of each plot were inoculated with 0, 1, 10, or 100 mildew-infected leaflets. Uninoculated plots developed only trace levels of powdery mildew, despite nearby diseased plots and wild strawberries in both Norway and NY trials over 3 years. More rapid and severe disease development was observed in the inoculated plots; e.g., mildew was observed on 31, 36, 311, and 912 leaflets in the 0, 1, 10, and 100 plots, respectively, in Norway in year 1 of the trial, and reached only 6 leaves per plot in the 0 plot in year 2. Spatiotemporal analyses were subsequently performed, but the practical impact of the trials was to demonstrate long-lasting benefits of clean, mildew-free planting stock in commercial strawberry production, even in areas where the pathogen is endemic and the environment is very conducive to disease.
Sammendrag
Colletotrichum acutatum is the causal agent of bitter rot in fruit crops (cherry, plum, apple, pear) and black spot in strawberry (Fragaria × ananassa). C. acutatum has also been isolated from a number of other cultivated and non-cultivated plant species; to date the fungus has been found on more than 25 different host species in Norway. The wide host range of C. acutatum necessitates research on the possibility of cross infection between alternative hosts and the potential of isolates of different origin to cause disease in strawberry. Planting healthy strawberry transplants adjacent to infected sweet cherry (Prunus avium) trees resulted in latent C. acutatum infections in the strawberry plants, indicating that cross infections between host species readily occur under field conditions. Molecular analyses (AFLP) have shown that isolates collected in Norway could be separated into three major phylogenetic groups in which isolates collected from either Prunus spp., Malus domestica or Fragaria × ananassa predominated. Two isolates from each of these groups were selected for experiments in vitro and in the field. Preliminary results indicate that isolates from all these groups are able to cause disease in strawberry, but that there may be differences in aggressiveness. In a field trial carried out in 2009 all six isolates caused symptoms in strawberry fruits when spore suspensions were applied three times during fruit development. The isolates from the Prunus group resulted in black spot on 42 and 53% of the strawberry fruits at harvest, while the corresponding numbers were 22 and 54% for the isolates from the Malus group, and 90 and 98% for the isolates from the Fragaria group.
Forfattere
David M. Gadoury Belachew Asalf M. Catherine Heidenreich Maria Luz Herrero Mary Jean Welser Robert C. Seem Anne Marte Tronsmo Arne StensvandSammendrag
A collection of clonal isolates of Podosphaera aphanis was heterothallic, and was composed of two mutually exclusive mating types. Cleistothecial initials approximately 30 µm were observed within 7 to 14 days after pairing of compatible isolates and developed into morphologically mature ascocarps within 4 weeks on both potted plants maintained in isolation and in field plantings in New York, USA and southern Norway. Ascospores progressed through a lengthy maturation process over winter, during which (i) the conspicuous epiplasm of the ascus was absorbed, (ii) the osmotic potential of the ascospore cytoplasm increased, resulting in bursting of prematurely-freed spores in water, and finally (iii) the development of physiologically mature, germinable, and infectious ascospores. Release of overwintered ascospores from field collections was coincident with renewed plant growth in spring. Overwintered cleistothecia readily dehisced when wetted, and released ascospores onto glass slides, detached strawberry leaves, and leaves of potted plants. Plant material so exposed to discharged ascospores developed macroscopically-visible mildew colonies within 7 to 10 days while non-inoculated controls remained mildew free. Scanning electron and light microscopy studies revealed that cleistothecia of P. aphanis were enmeshed within a dense mat of hyphae on the persistent leaves of field-grown strawberry plants, and were highly resistant to removal by rain while these leaves remained alive. In contrast, morphologically mature cleistothecia on leaves of 11 deciduous perennial plant species were readily detached by simulated rain and seemed adapted for passive dispersal by rain to other substrates. Contrary to many previous reports, cleistothecia appear to be a functional source of primary inoculum for strawberry powdery mildew. They furthermore differ substantially from cleistothecia of powdery mildews of many deciduous perennial plants in their propensity to remain attached to the persistent leaves of their host during the intercrop period.
Sammendrag
Crown rot caused by Phytophthora cactorum is an important disease in commercial strawberry production worldwide. The level of resistance varies greatly between cultivars, and many of the most commonly grown cultivars are quite susceptible to P. cactorum. Adequate soil drainage, clean planting material and use of highly resistant cultivars are the most important measures against crown rot. Previous work at our institute has involved evaluation of methods to screen for resistance, cultivar and progeny screening, and use of induced resistance against the disease. That work also included a genetic study of P. cactorum isolates from various host plants and different geographic origins. P. cactorum has many host plants, but it turned out that isolates causing crown rot of strawberry differs genetically from those with other host origin. A project was recently initiated, where one of the main goals has been to identify molecular markers for resistance against P. cactorum in strawberry. Genotypes of diploid Fragaria species have been screened for resistance, and the progeny from a cross between a susceptible and a resistant genotype will be evaluated by the end of this year. Commercially grown strawberry is very heterozygous and octoploid. Diploid Fragaria species are therefore useful as model organisms. The Fragaria genus has a conserved organisation, and hopefully information obtained from the study of diploid genotypes can be transferred to cultivated Fragaria x ananassa and possibly to other important crop plants in Rosaceae.
Sammendrag
Red stele in strawberry is caused by the oomycete Phytophthora fragariae. To prevent the introduction of the pathogen to Norway, it has been prohibited to import planting material of Fragaria spp. to the country since 1986. During 1995 to 1997 the Food Authority had a country-wide survey to reveal if P. fragariae was present. The pathogen was found in three separate regions: (i) Hedmark County, along the Mjøsa lake; (ii) Aust-Agder and Vest-Agder Counties, in coastal areas; (iii) Rogaland and Hordaland Counties, along the western border between the two counties. In the latter area there were clear indications of spread of infected plant material from a small certified nursery where P. fragariae was detected. All strawberry farms that had received plants from the nursery were thoroughly investigated and further sales of planting material was stopped. All other incidences in the 1995-97 survey were among strawberry fruit producers. In 2006 and 2007 there were two new detections of red stele in Vest-Agder, and one of the growers had produced and forwarded non-certified planting material to other strawberry growers. In 2008, a new country-wide survey was initiated, and the pathogen was found at a few new production sites for strawberry fruits in Hedmark and at one site in Vestfold County (in south eastern Norway). In 2009, red stele was also discovered at one site in Møre og Romsdal County (in western Norway). Totally, red stele has been found at 19 production sites in Norway. Since the mid 1990"s there have been no discoveries of red stele among certified plant producers. Sites where P. fragariae has been detected may continue to produce strawberry fruit for sale, but all production of strawberry plants or other planting material for further distribution is prohibited. For strawberry production on soil infested with P. fragariae, buffer zones to neighboring fields and creeks/rivers are required. No strawberry production can take place in the buffer zones, and normally the zones should be at least 100 m wide, but topographic and other conditions locally may increase or decrease the width of the zones. There are also restrictions on sharing machinery and equipment with other farms, and soil from infested farms may not be moved out of the farm. Testing of plant material is done by a root tip bait test and PCR.
Forfattere
Belachew Asalf Arne Stensvand David M. Gadoury Robert C. Seem Andrew Dobson Anne Marte TronsmoSammendrag
Development of ontogenic resistance to powdery mildew (Podosphaera aphanis) in strawberry fruit has not been quantified, and thus cannot be exploited in disease management programs. Four commercially-relevant strawberry cultivars were evaluated for ontogenic resistance to powdery mildew. Fruits were inoculated at one of the four growth stages: flowering, green, white and early pink fruit. There was a significant difference between and within cultivars at the bloom and green stage of inoculations (P ≤ 0.05) for both disease incidence and severity. On average 16.4, 39.5, 48.7, and 60.3 % of the fruits inoculated at bloom developed powdery mildew in cultivars Elan, Korona, Frida and Inga, respectively. None of the cultivars developed powdery mildew when inoculated at the pink stage. It may be concluded that flowers and green fruits of strawberry were much more susceptible to powdery mildew infection than white and pink fruits. The high susceptibility of cultivars at the flower and early green stages seemed coincident with the succulent nature of the fruits at these stages, making it easy for penetration and establishment of mildew. Control measures targeting at these critical windows of fruit susceptibility are likely to reduce yield loss.
Forfattere
Robert C. Seem Arne Stensvand David M. Gadoury Håvard Eikemo Andrew Dobson M. Catherine HeidenreichSammendrag
The objective of this work was to investigate how primary disease levels of powdery mildew (Podosphaera aphanis) in strawberry (Fragaria × ananassa) influence disease development in time and space. Experiments were repeated over two seasons in field trials in Norway (Ås, cv. Korona) and USA (Geneva, NewYork, cvs. Earliglow and Elan). Five-row plots of 50 to 100 mildew-free plants (planting distance 0.45 x 1.2 m) were established each year within large grain fields, with a minimum distance of 90 m between plots, and no fungicide treatments. At start of the experiments, plants at the center of each plot were inoculated with 0, 1, 10, or 100 mildew-infected leaflets. Uninoculated plots developed only trace levels of powdery mildew, despite nearby diseased plots. More rapid and severe disease development was observed in the inoculated plots; e.g., mildew was observed on 31, 36, 311, and 912 leaflets in the 0, 1, 10, and 100 plots, respectively, in Norway in year 1 of the trial. Within the plots, disease development was highest close to the inoculum source and downwind from the prevailing wind. It may be concluded that in the absence of nearby sources of contamination, disease severity in strawberry plantings is determined by the dose of initial inoculum resident within the planting. The practical impact of the trials was to demonstrate long-lasting benefits of clean, mildew-free planting stock in commercial strawberry production, even in areas where the pathogen is endemic and the environment is very conducive to disease.
Forfattere
Venche TalgøSammendrag
Det er ikke registrert sammendrag