Differences Between Rose Cultivars in Susceptibility to Infection byBotrytis cinerea

Differences in the susceptibility of rose flowers to blossom blight caused by Botrytis cinerea were investigated. Rose flowers, cvs. Supra and Royalty, were inoculated with various concentrations of B. cinerea conidia and incubated in humidified chambers at 21 C. Disease severity was quantified 2 days later as the number of lesions that had developed on each flower. The slope of the inoculum concentration/disease severity (IC/DS) regression line was used as a measure of susceptibility. Supra was more susceptible than Royalty, but the susceptibility of each cultivar and the difference between them varied among sampling dates. In experiments using isolated petal disks, there was no difference between cultivars in the number of B. cinerea conidia that germinated on the petal surfaces