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Disease Detection and Losses

Response of Potato Cultivars to Infection by the Potato Spindle Tuber Viroid. M. A. Pfannenstiel, Research assistant, Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706; S. A. Slack, associate professor, Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706. Phytopathology 70:922-926. Accepted for publication 25 March 1980. Copyright The American Phytopathological Society. DOI: 10.1094/Phyto-70-922.

Symptom severity of potato spindle tuber disease was evaluated with respect to potato cultivar, inoculation method, and the strain of potato spindle tuber viroid (PSTV). Potatoes were inoculated by rubbing foliage with infectious Rutgers tomato sap (mechanical inoculation), by striking (switching) the potato foliage with an infected Rutgers tomato plant, or by mechanical inoculation followed 1 wk later by switching (combination inoculation). Switching inoculations and combination inoculations infected more plants and induced more severe symptoms than did mechanical inoculations. Fourteen potato cultivars were inoculated with a strain of PSTV that caused severe symptoms in Rutgers tomato (PSTV-S) and symptom severity was assessed by measuring various foliage and tuber parameters. Disease severity caused by PSTV-S ranged from mild to severe, depending upon the potato cultivar. Three cultivars were tolerant. It is suggested that PSTV-tolerant cultivars may be important to PSTV perpetuation. Tolerant and susceptible potato cultivars were inoculated with PSTV-S and three strains of PSTV causing mild symptoms on Rutgers tomatoes (PSTV-M). In first-year infections, cultivars developed milder symptoms with the PSTV-M strains than with PSTV-S, and tolerant cultivars were less affected than were susceptible cultivars by PSTV-M.