Abstract
Laboratory and field experiments assessed the relative resistance of sunflower lines to diseases caused by Sclerotinia sclerotiorum and S. minor. Resistance was measured in terms of the percentage of plants that developed disease symptoms, the time after inoculation when wilting and basal stem lesions became apparent, and the linear rate of lesion development. The linear rate of lesion development of basal stem lesions was considered to be a good measure of relative resisance to basal stem rots under laboratory and field conditions because lines with a high rate of lesion enlargement had a high incidence of basal stem lesions under field conditions and vice versa. The ranking of sunflower lines for disease resistance was similar for both S. sclerotiorum and S. minor.