Screening resistance against Sclerotinia sclerotiorum in Brassica crops with use of detached stem assay under controlled environment

Sclerotinia sclerotiorum is a major pathogen that infects stem tissue, causing yield loss and poor seed quality in rapeseed (Brassica napus). Here we report a reliable detached stem inoculation method for evaluating resistance under controlled environment. Two sets of Brassica materials were employed, including 17 genotypes from five Brassica crops in experiment 1, and 71 F2 lines derived from a cross between susceptible and resistant lines of B. oleracea in experiment 2. High correlations were detected between stem and branch for lesion length in both experiments and between stem and sections of stem in experiment 1. Although the lesion length of detached stem inoculation under controlled environment was positively correlated with that of toothpick inoculation in the field, the variation of lesion length in the detached stem inoculation was lower than that in toothpick inoculation in experiment 2. Moreover, no significant association was detected between lesion length and the diameter of stem or branch. These findings suggest that the detached stem inoculation under controlled conditions is a large-scale, flexible and reliable method of screening for resistance against S. sclerotiorum in Brassica crops. The application of detached stem inoculation is discussed in resistance breeding programs against S. sclerotiorum in Brassica crops.