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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).

Reference: (1) W. A. Sinclair and G. W. Hudler. Plant Dis. 64:590, 1980.