Nitrogen levels can modulate the effectiveness of clubroot resistance in an isolate- and host-specific manner. While the same QTL were detected under high and low nitrogen, their effects were altered.

Clubroot, caused by the obligate biotrophic soil-borne pathogen Plasmodiophora brassicae Woron., is one of the most damaging diseases of Brassica crops worldwide. The development of resistant cultivars is considered as a need in the control of this disease for all Brassica species. The study of the organisation and the characterization of the genetic factors involved in clubroot resistance as well as the characterization of the transcriptional changes during the P. brassicae/Brassicaceae interaction has been undertaken in the three species B. oleracea, B. napus and Arabidopsis thaliana. Isolate-specific and broad-spectrum major genes and/or QTLs are involved in the control of clubroot resistance in B. oleracea and B. napus. Genes differentially expressed during P. brassicae/resistant B. oleracea, B. napus and A. thaliana interactions have been identified through differential transcriptome analyses.

Clubroot, caused by Plasmodiophora brassicae, is one of the most damaging diseases of vegetable Brassica crops in the world. In this study, genetic control and mapping of loci implied in quantitative resistance against five isolates of P. brassicae were studied in the F-1 and F-2/3 progenies of the cross C10 (resistant kale)xHDEM (susceptible broccoli). A genetic map was constructed using RFLP, random and specific PCR-based markers. The 199 loci were assembled into nine linkage groups covering 1,226.3 cM. The F-3 families were assessed for resistance under controlled conditions with four single-spore isolates and one field isolate. A total of nine genomic regions were detected for clubroot resistance. Depending on the isolate, two to five QTLs were identified. The total phenotypic variation accounted for by QTLs ranged from 70% to 88% depending on the isolate. One of the QTLs (Pb-Bo1) was detected in all isolates and explained 20.7-80.7% of the phenotypic variation. Pb-Bo1 had a major effect on three isolates but this effect was weaker for the last two. Five QTLs with minor effect were identified in only one isolate. To construct clubroot resistant varieties, the existence of both broad-spectrum and isolate-specific QTLs should be taken into account for the choice of genomic regions to use in a marker-assisted selection strategy.