Attack and defence in the Brassica–Sclerotinia pathosystem

Resistant Brassica genotypes restrict growth of the fungus by a combination of strategies that impede pathogen progress towards stem vascular tissues.

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.

Light and scanning electron micrographs showing disease progression caused by Sclerotinia sclerotiorum MBRS-1 (A–C) and WW-3 (D) on the stems of Brassica carinata following inoculation using colonized filter paper discs.
Light and scanning electron micrographs showing disease progression caused by Sclerotinia sclerotiorum MBRS-1 (A–C) and WW-3 (D) on the stems of Brassica carinata following inoculation using colonized filter paper discs. Full details in Uloth et al.

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.

Reference List

Uloth, M. B., Clode, P. L., You, M. P., & Barbetti, M. J. (2015). Attack modes and defence reactions in pathosystems involvingSclerotinia sclerotiorum,Brassica carinata,B. junceaandB. napus. Annals of Botany, 117(1), 79–95. http://dx.doi.org/10.1093/aob/mcv150