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Disease Note Root Necrosis Caused by Fusarium oxysporum on 2-Year-Old Douglas-fir Seedlings in Oregon. P. B. Hamm, Department of Botany, Oregon State University, Corvallis 97331. A. Kanaskie, P. Morgan, and S. J. Cooley. Oregon Department of Forestry, Salem 97310; Oregon Department of Forestry, Elkton 97436; and USDA Forest Service, Portland, OR 97208. Plant Dis. 71:651. Accepted for publication 7 April 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0651C. Root necrosis was observed for two consecutive years on 2-yr-old
bare-root-grown Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)
in an Oregon forest nursery. Damage was conspicuous but generally
confined to wet bed ends and, overall, accounted for <1% loss.
Aboveground symptoms included stunting, chlorosis, and necrosis.
Below the ground, one or more lateral roots were killed but not decayed
and red-brown elongate lesions were found on the taproot, originating
at the points of attachment of the killed lateral roots. Most infections
occurred 5-7 cm below the cotyledon scar. Enlargement of the taproot
lesion(s) eventually killed the seedlings. Ninety-five percent of the
isolations from symptomatic lateral roots and taproots yielded Fusarium oxysporum Schlecht.; 53% of the symptomless roots yielded
F. oxysporum. No other fungi were isolated in high numbers. Isolates of
F. oxysporum caused similar symptoms on 2-yr-old root-inoculated
Douglas-fir. This is the first report of root necrosis caused by F.
oxysporum in the Pacific Northwest on 2-yr-old seedlings; the organism
was previously restricted to mortality of younger seedlings. One other
report describes a similar disease in New York State (1). |