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 d
ata were analyzed statistically using a threshold model for ordered ca
tegorical data. Bulb weight measurements were modeled as weight change
of plants cultivated in Fusarium-infested soil relative to weight cha
nge of control plants, and further analyzed by ANOVA. Results of both
observations were highly correlated. For disease ratings, six categori
es provided more information than two or three categories. Variation i
n resistance amongs the cultivars was demonstrated. The threshold anal
ysis with six categories showed at least four groups of cultivars that
differed in resistance. Disease ratings provided reproducible results
and a practical experimental design.