Molecular characterisation of defence of Brassica napus (Oilseed rape) to Rhizoctonia solani AG2-1 confirmed by functional analysis in Arabidopsis thaliana

Rhizoctonia solani is a necrotrophic, soil-borne fungal pathogen associated with significant establishment losses in Brassica napus (Oilseed Rape; OSR). The Anastomosis Group (AG) 2-1 of R. solani is most virulent to OSR, causing damping-off, root and hypocotyl rot, and seedling death. Resistance to R. solani AG2-1 in OSR has not been identified, and the regulation of OSR defence to its adapted pathogen, AG2-1, has not been investigated. In this work, we used confocal microscopy to visualise the progress of infection by sclerotia of AG2-1 on B. napus varieties with contrasting disease phenotypes. We defined their defence response using gene expression studies and functional analysis with Arabidopsis thaliana mutants. Our results showed existing variation in susceptibility to AG2-1 and plant growth between OSR varieties, and differential expression of genes of hormonal and defence pathways related to auxin, ethylene, jasmonic acid, abscisic acid, salicylic acid, and reactive oxygen species regulation. Auxin, abscisic acid signalling, and the MYC2 branch of jasmonate signalling contributed to susceptibility to AG2-1, whilst induced systemic resistance was enhanced by NAPDH RBOHD, ethylene signalling and the ERF/PDF branch of jasmonate signalling. These results pave the way for future research, which will lead to the development of Brassica crops that are more resistant to AG2-1 of R. solani and reduce dependence on chemical control options.