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    Author(s): Robert L. James; R. Kasten Dumroese
    Date: 2007
    Source: In: Guyon JC, compiler. Proceedings of the 53rd Western International Forest Disease Work Conference. Ogden (UT): USDA Forest Service, Intermountain Region. p 3–11.
    Publication Series: Miscellaneous Publication
    PDF: View PDF  (579 KB)

    Description

    Fusarium spp. cause important diseases that limit production of seedlings in forest nurseries worldwide. Several aspects of these diseases have been investigated for many years within Inland Pacific Northwest nurseries to better understand disease etiology, pathogen inoculum sources, and epidemiology. Investigations have also involved improving disease control efforts to limit impacts. Major diseases caused by Fusarium spp. include pre- and post-emergence damping-off, root disease, stem cankers, and top blight. The major Fusarium pathogen of bareroot nurseries is F. oxysporum. It is a common soilborne species with pathogenic and nonpathogenic strains readily isolated from conifer seeds, diseased and healthy seedlings, and nursery soil. Pathogenic strains appear to be genetically distinct from common saprophytic strains. The major Fusarium pathogen of container nurseries is F. proliferatum. This species is especially adapted for rapid spread throughout greenhouses. Most tested isolates of F. proliferatum are highly virulent. Other Fusarium species commonly associated with seedling diseases include F. solani, F. acuminatum, F. sporotrichioides, F. sambucinum, and F. avenaceum. Several other Fusarium spp. are encountered infrequently. Most other Fusarium spp. are less virulent on conifer seedlings than F. oxysporum and F. proliferatum. Improved disease control has been obtained by reducing pathogen inoculum on seeds, reused containers, greenhouse environments, and within nursery soil. Biological control has not yet proven as effective as fungicides in reducing disease severity. Pathogens colonizing roots of seedlings are usually replaced by other mycoflora following outplanting on forest sites. Efforts to reduce dependence on pre-plant soil fumigation have been successful in some, but not all bareroot nurseries. Keeping fallow fields free of plants with periodic cultivation for at least one year may often be as effective as fumigation. Conversely, growing cover crops, incorporating organic amendments into soil, and rotating seedling production with Brassica green manure crops have usually proven unsuccessful because of stimulation of Fusarium populations following addition of organic matter to soil. Future research efforts should involve using molecular probes to quantify pathogenic Fusarium populations to allow better prediction of requirements for implementation of disease controls.

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    Citation

    James, Robert L.; Dumroese, R. Kasten. 2007. Investigations of Fusarium diseases within Inland Pacific Northwest forest nurseries. In: Guyon JC, compiler. Proceedings of the 53rd Western International Forest Disease Work Conference. Ogden (UT): USDA Forest Service, Intermountain Region. p 3–11.

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