Eighteen isolates of Fusarium comprising four species (F. oxysporum, E. avenaceum, E. acuminatum, and F. sambucinum) isolated from diseased conifer seedlings from nurseries were tested for pathogenicity on Douglas-fir germlings. Three of the most pathogenic F. oxysporum isolates on Douglas-fir germlings were also tested on ponderosa pine germlings and older Douglas-fir seedlings; three of the most pathogenic F. gamPucinum isolates on Douglas-fir germlings were likewise tested on older Douglas-fir seedlings. Most F. oxysporum isolates and all the other fusaria were highly pathogenic to germlings. Level of virulence on germlings was best measured by rate of infection and tissue degradation. All inoculated older Douglas-fir seedlings became infected, although foliar disease symptoms were rare. Based on extent of root system colonization, isolates of F. oxysporum were generally more pathogenic to older Douglas-fir seedlings than F. sambucinum. These tests confirm the wide range of pathogenicity of fusaria commonly isolated from diseased seedlings.
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