Pathogenic Seedborne Fusarium oxysporum from Douglas-Fir. J. H. Graham, Oregon State University, Corvallis 97331. R. G. Linderman, USDA, ARS, Horticultural Crops Research Laboratory, Corvallis, OR 97330. Plant Dis. 67:323-325. Accepted for publication 1 October 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/PD-67-323.

Fusarium oxysporum was isolated from 1–5% of the seed from two of six Douglas-fir seed sources examined. Isolates were recovered both from seed washed but not surface-sterilized and from seed treated with hydrogen peroxide. In addition, isolates were obtained from roots of diseased seedlings where infection occurred on random individual seedlings, some of which were grown in growth chambers, indicating that the pathogen had been introduced with the seed. Soaking Douglas-fir seed in spore suspensions of either seed or root isolates caused significant preemergence damping-off or seed rotting compared with uninoculated controls. Seedling root isolates caused more postemergence damping-off than seed isolates. Two isolates from sugar pine caused preemergence damping-off on Douglas-fir, but only one caused postemergence damping-off. Some preemergence and postemergence damping-off occurred in uninoculated controls from which F. oxysporum was recovered; the latter was the result of either seedborne inoculum or cross-contamination. We observed significant sporulation by F. oxysporum on aboveground infected stems or cotyledons and seed coats as well as on the medium surface that could readily have been air-blown or water-splashed to other seedlings. Implications regarding seedborne pathogenic F. oxysporum on Douglas-fir seed as a means of introduction into fumigated nursery beds or into container nurseries with subsequent spread from sporulation on aboveground plant parts or seed coats are discussed.