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Determination of Resistance to Fusarium oxysporum in Lilium. Th. P. Straathof, Centre for Plant Breeding and Reproduction Research (CPRO-DLO), P.O. Box 16, 6700 AA Wageningen, The Netherlands; J. Jansen, and H. J. M. Löffler. Centre for Plant Breeding and Reproduction Research (CPRO-DLO), P.O. Box 16, 6700 AA Wageningen, The Netherlands. Phytopathology 83:568-572. Accepted for publication 1 February 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-568.

A screening test for determination of resistance to Fusarium oxysporum f. sp. lilii in Lilium was developed. Under standardized conditions, 16 Asiatic lily cultivars were tested for resistance. Disease rating data were analyzed statistically using a threshold model for ordered categorical data. Bulb weight measurements were modeled as weight change of plants cultivated in Fusarium-infested soil relative to weight change of control plants, and further analyzed by ANOVA. Results of both observations were highly correlated. For disease ratings, six categories provided more information than two or three categories. Variation in resistance among the cultivars was demonstrated. The threshold analysis with six categories showed at least four groups of cultivars that differed in resistance. Disease ratings provided reproducible results and a practical experimental design.