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Etiology

Stress and Stimulus Modifications of Disease Severity in the Wart Disease of Potato. M. C. Hampson, Research scientist, Agriculture Canada, Research Station, P.O. Box 7098, St. John's West, Newfoundland A1E 3Y3; Janet W. Coombes, research technician, Agriculture Canada, Research Station, P.O. Box 7098, St. John's West, Newfoundland A1E 3Y3. Phytopathology 75:817-820. Accepted for publication 1 March 1985 . Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-817.

Sprouted potato tubers were inoculated with Synchytrium endobioticum in soil and aqueous suspension. During subsequent growth, watering was adjusted to develop stress or nonstress conditions. Among 30 weekly trials of nonstressed plants, fresh wart tissue mass was generally about 1.5% of fresh green plant top mass irrespective of variations in individual weights. When, however, wart tissue mass exceeded 1.5% of fresh green plant top mass, wart weights were observed to increase and associated green top weights to decrease. Under moisture stress conditions, both types of tissue demonstrated weight decrease. Healthy plants were little affected by the changes in levels of moisture stress. Plants grown in earthworm-infested soil showed increase in top green weight but no change in wart tissue weight. Results indicate that plant vigor was affected by the fungus, and that wart tissue appeared to grow at the expense of the host.