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.
2014
Forfattere
Halvor SolheimSammendrag
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Sammendrag
Nematodes as limiting factors in potato production in Norway Plant parasitic nematodes associated with potato feeds on roots and/or tubers. At least 68 species, representing 24 genera of have been found associated with potato. Since nematodes generally attack underground plant parts, there are no reliable foliar symptoms to show that nematodes may be the major cause of poor growth and reduced tuber yields. Potato roots damaged by nematodes may show the presence of lesions, females/cysts or galls. After a few weeks, however, roots may be attacked by other pathogens such as bacteria and fungi, and the original damage by nematodes may not be obvious. Therefore, nematode damage often may have been attributed to other factors. There are no estimations for potatoes yield losses in Scandinavia due to nematodes, however, in the United Kingdom, it is estimated that 9 % of the potato crop is lost annually because of the potato cyst nematodes (PCN), Globodera rostochiensis and G. pallida, and it is reasonable to assume that this percentage is also applicable to Scandinavia. However, if we consider the possible additional effects of other nematode species occurring in Norway, yield reductions could be as high as 20%. Besides direct yield losses, some nematodes affect tuber quality. Yield losses depend on the pathogenicity of the species of nematode, the nematode population density at planting, the susceptibility and tolerance of the host and by a range of environmental factors. In Norway, potato cyst nematodes (G. rostochiensis and G. pallida) are by far the most important nematodes in potato. Other important nematodes include root-lesion nematodes (Pratylenchus spp.), stubby root nematodes (Trichodorus spp. and Paratrichodorus spp.) and stem and tuber nematodes (Ditylenchus spp.). Nematodes considered less important include root knot nematode (Meloidogyne hapla) and needle nematodes (Longidorus spp.). In Norway, potato cyst nematodes (Globodera rostochiensis and G. pallida) are quarantine pests subjected to regulations. PCN infestations result in costly production systems and loss in sales value of farms. Their occurrences restrict acreage available for potato production as in some cases legislative regulations forbid potato production or make the production more difficult and more expensive. Furthermore societal consequences by far exceed yield losses. It is also compulsory to sample the soil for seed potato production to document freedom from PCN. When PCN is present in the field complete eradication is not possible. Effective management requires reliable information on virulence, decline rates of population densities and infectivity in soil. It is also crucial to know what conditions or practices increase these decline rates. Today in Norway, non-virulent G. rostochiensis is managed by crop rotation, while infestations by G. pallida or virulent G. rostochiensis pathotypes capable of breaking the resistance in potato cultivars in current use results in a 40-years prohibition for growing potato in the infected field. Root-lesion nematodes (Pratylenchus spp.) cause damage to the roots and induce scabby to sunken lesions on tubers. Stubby root nematodes (Trichodorus spp. and Paratrichodorus are nematode vectors of Tobacco Rattle Virus they causes the symptom called “Spraing” in tubers. Occasionally stem and tuber nematodes (Ditylenchus spp.), have been reported as problems both in field and storage, especially when weeds are not well controlled. Management strategies aim to prevent nematode multiplication and hence protect the potato crop from damage. An efficient method of controlling nematodes as Ditylenchus spp. and root-lesion nematodes is black fallow, but this may be difficult to achieve in many cases.
Sammendrag
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Sammendrag
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Forfattere
Erik J. JonerSammendrag
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Sammendrag
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Sammendrag
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Ari M. Hietala, Volkmar Timmermann, Isabella Børja & Halvor Solheim Norwegian Forest and Landscape Institute. PO Box 115, 1431 Ås, Norway: ari.hietala@skogoglandskap.no Owing to the Gulf Stream, the northernmost European populations of several tree species are found in Norway. Common ash (Fraxinus excelsior), the only native ash species in Norway, is present in the lowlands in the southeastern part with continental climate and in southern and southwestern coastal regions with North Atlantic climate up to Central Norway. The current standing volume of ash in Norway is ca 3 mill m3 (broadleaved trees in total 220 mill m3). The first documentation of Ash Dieback (ADB) is from 2008 from a nursery in the southeastern part of the country. A survey later that year showed that dieback symptoms were present over a distance of nearly 400 km in the southeastern region. In addition to nurseries and forests, ADB symptoms were observed on roadside, alley, garden and park trees. Based on the presence of old ADB-like stem lesions detected in 2008, the pathogen must have arrived to Norway no later than 2006. In 2008, the Norwegian Food Safety Authority laid down regulations with the aim of preventing further spread of ADB. These regulations divide the country into quarantine, observation and infection-free zones, and prohibit the export of ash seedlings, seed and wood from the quarantine zone. Despite of these regulations, the disease spread rapidly along the western coast in the period between 2009 and 2013, and currently only the ash stands in Central Norway are free of the disease. The rapid spread of the disease in Norway is obviously due to airborne dispersal of pathogen ascospores. In our experimental stand in SE Norway the number of pathogen fruit bodies can be as high as 10,000 per m2 in the peak season, mid-July to mid-August. During the early morning hours the amount of pathogen ascospores at a diseased stand can exceed 100,000 ascospores per m3 air. The first symptoms of the disease, necrotic lesions on leaf blade and petiole, appear typically during the first two weeks of August in SE Norway. To observe long-term impacts of ADB, eight monitoring plots have been established in continental and North Atlantic climate zones. In SE Norway with the oldest disease history, above 60 % of the trees with a breast height diameter (BHD) below 12.5 cm have so far died or suffer from severe defoliation, 1/3 of the larger trees being affected to a similar degree. The proportions of healthy (no signs of defoliation) small and larger trees are 20% and 37%, respectively. In SW Norway with more recent disease history a similar trend is observed but the proportion of dead trees is still small. As a consequence of ADB, the Norwegian nurseries no longer grow ash seedlings. There are currently no practical control options for the disease in forestland. Several European countries have reported that even at heavily diseased ash stands there are often some ash trees that show little symptoms. This may be due to genetic variation between trees in disease resistance, a hypothesis that is currently being investigated in several European projects. Thus implementation of forest management practices that eliminate ash could have a negative effect as survival of the tree ultimately depends on selection of trees with increased disease resistance. Bibliography for Ari M. Hietala Ari M. Hietala is a Senior Forest Pathologist at the Norwegian Forest and Landscape Institute, which is a primarily government funded organisation providing scientific research and services to government, non-governmental and commercial organisations. He has worked with a range of fungal root and shoot diseases occurring on broadleaved trees and conifers indigenous to the Nordic countries. Ari and the rest of the group participate currently in several European consortia engaged in ash dieback research.
Forfattere
Peder GjerdrumSammendrag
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