Oilseed rape is economically affected by stem rot caused by 'Sclerotinia sclerotiorum' worldwide. Glucosinolates are the specific secondary metabolites of Brassica plants that appear in different profiles of each species. Their hydrolysis products have biocidal activity and may play a role in resistance against plant pathogenic fungi. The resistance of oilseed rape ('Brassica napus') cultivars and two other Brassica species ('B. nigra' and 'Sinapis alba') was evaluated employing leaf disc inoculation, and oxalic acid and fungal inoculums on leaves of intact plants under controlled conditions. By using leaf disc inoculation, three plant ages were used to compare their reactions against the pathogen. No significant differences between genotypes were observed in this method. However, results demonstrated significant differences in main effects of wounding and plant age. The two intact plant inoculation techniques (oxalic acid and fungal mycelium) resulted in significant differences between genotypes in reaction to the disease. Furthermore, the oxalic acid assay followed the same pattern as fungal inoculations. Among the oilseed rape cultivars, AV-Sapphire and AG-Castle were the most resistant and susceptible genotypes, respectively. Brassica species differed significantly in their reaction to disease, in both wounded and non-wounded leaves with fungal mycelium inoculation and oxalic acid. Overall, non-significant differences between Brassica genotypes showed the unreliability of the leaf disc assay, whereas leaf inoculation of intact plants by means of either oxalic acid or fungal mycelium demonstrated significant differences in lesion size among Brassica cultivars and species.