Sclerotinia stem rot (SSR, Sclerotinia sclerotiorum) is a damaging disease of oilseed brassicas world-wide. Host resistance is urgently needed to achieve control, yet the factors that contribute to stem resistance are not well understood.
Uloth et al. show that S. sclerotiorum invades the vascular system of highly susceptible Brassica genotypes, which ensures lesions extend rapidly along the stem. In contrast, resistant Brassica genotypes restrict growth of the fungus by a combination of strategies that impede pathogen progress towards stem vascular tissues, including the hypersensitive reaction, more cell layers in the cortex, and rapid lignification within the cortex, endodermis and surrounding lesions. These complex pathogen–host interactions explain variable expressions of resistance observed in the field.