VIEW ARTICLE

Ecology and Epidemiology

Soil Temperature and Rate of Colonization of Ceratocystis wageneri in Douglas-Fir. P. F. Hessburg, Former graduate research assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902, Present address: USDA Forest Service, Forest Pest Management, 319 S.W. Pine St., P.O. Box 3623, Portland, OR 97208; E. M. Hansen, associate professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902. Phytopathology 76:627-631. Accepted for publication 22 January 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-627.

The effect of soil temperature on infection success and rate of colonization of Ceratocystis wageneri in Douglas-fir (Pseudotsuga menziesii) seedling roots was studied in growth chambers, greenhouse, and field. In growth chambers at 10 and 17 C, 92 and 97% of the seedlings became infected; at 28 C, only 19% of the seedlings were infected. Vertical growth rate of C. wageneri in seedling xylem was two to three times faster at 17 than at 10 C; growth rate at 28 C was intermediate. Growth rates varied predictably with soil temperature fluctuations in the greenhouse. Increases in the proportion of days when soil temperatures were 15-18 C produced increases in fungal growth rate in xylem; conversely, increases in the proportion of days when soil temperatures were > 18 C or < 15 C depressed growth rate. Soil temperatures > 15 C generally favored faster growth of C. wageneri in xylem. Growth rate of C. wageneri in roots of 20-yr-old trees averaged 2.2 m/yr, with a maximum of 3.6 m/yr; an average of eight successive annual rings were colonized within 3 mo. Results from these experiments indicate that fungal growth rate in roots is sufficient to explain observed radial spread of the disease in infection centers.