Late blight resistance gene from Solanum ruiz-ceballosii is located on potato chromosome X and linked to violet flower colour

A major resistance gene, Rpi-rzc1, against P. infestans originating from Solanum ruiz-ceballosii was mapped to potato chromosome X using Diversity Array Technology (DArT) and sequence-specific PCR markers. The gene provided high level of resistance in both detached leaflet and tuber slice tests. It was linked, at a distance of 3.4 cM, to violet flower colour most likely controlled by the previously described F locus. The marker-trait association with the closest marker, violet flower colour, explained 87.1% and 85.7% of variance, respectively, for mean detached leaflet and tuber slice resistance. A genetic linkage map that consisted of 1,603 DArT markers and 48 reference sequence-specific PCR markers of known chromosomal localization with a total map length of 1204.8 cM was constructed.The Rpi-rzc1 gene described here can be used for breeding potatoes resistant to P. infestans and the breeding process can be expedited using the molecular markers and the phenotypic marker, violet flower colour, identified in this study. Knowledge of the chromosomal localization of Rpi-rzc1 can be useful for design of gene pyramids. The genetic linkage map constructed in this study contained 1,149 newly mapped DArT markers and will be a valuable resource for future mapping projects using this technology in the Solanum genus.Domestication of crop plants involving selection through many generations has brought yield and quality improvement but also narrowed the gene pools of cultivated species [1]. Therefore, for the last hundred years, modern plant breeders have searched wild relatives of crop plants for valuable genes, alleles and Quantitative Trait Loci (QTL) encoding desirable phenotypic characters. In potato, more than 210 wild and cultivated species [1] provide a good chance of finding useful traits. However, till date only a limited number has been used in breeding programs. Exploitation of wild Solanum species has focused on those resistant to pests and pathogens. Among potato p