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Screening Commercial Onion Cultivars for Resistance to White Rot. R. S. Utkhede, Research Associate, Pestology Centre, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6; J. E. Rahe, associate professor, Pestology Centre, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6. Phytopathology 68:1080-1083. Accepted for publication 5 December 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1080.

Sixty-four North American and European cultivars of dry-bulb, sweet Spanish, pickling, and bunching onions were evaluated in a simple lattice design for resistance to Sclerotium cepivorum, the causal agent of white rot. The trial was conducted in Burnaby, British Columbia on organic muck soil with uniform high levels of added inoculum. Percent white rot infection, weights of total and healthy bulbs harvested, downy mildew infection levels, and sprouting during storage were measured. Significant differences in susceptibility and yield occurred. A correlation between low levels of downy mildew infection in the field and sprouting in storage was found. The same 64 cultivars also were evaluated for percent infection by white rot in a laboratory trial. There was an overall correlation (P = 0.06, r = 0.26) between percent infection in the field and laboratory trials, and this was significant at P = 0.01 (r = 0.39) when the 45 dry-bulb cultivars were analyzed separately. Percent infection in the field trial was significantly least (P = 0.05) for the cultivars Ailsa Craig. Dako, and Wolska. These three cultivars also were among those least infected in the laboratory trial.