Fine mapping of the Rpi-rzc1 gene conferring broad-spectrum resistance to potato late blight

The Rpi-rzc1 gene originates from Solanum ruiz-ceballosii, a wild diploid relative of the cultivated potato. It provides high levels of resistance to late blight both in detached leaflet and in tuber slice tests. Here, we present evidence on the broad-spectrum of this resistance using detached leaflet assays and 509 diverse Polish Phytophthora infestans isolates of which only seven (1.4 %) were virulent on plants with the Rpi-rzc1 gene. In a previous mapping study genetic distance between the Rpi-rzc1 gene and locus F conferring violet flower colour was 3.4 cM, while on the other side the gene was flanked by marker T1521 located in the distance of 6.1 cM. Adding new RenSeq markers changed the map order and slightly decreased these distances. To further increase the precision of the genetic map we expanded the mapping population with another 240 individuals originating from the same cross. These individuals were assessed for resistance to P. infestans in detached leaflet tests and their flower colours were evaluated. Ten sequence-specific PCR markers were scored in the enlarged mapping population: two were derived directly from the NBS-LRR homologs from the potato genome sequence, two were identified by the Resistance Gene Enrichment Sequencing (RenSeq) approach, and the remaining six from other mapping studies. On the resulting map the Rpi-rzc1 gene is flanked by markers located 0.4 cM from it. Narrowing down the chromosome sector containing the Rpi-rzc1 gene to 1 cM improves the efficiency of marker-assisted selection and will be useful for studies aiming at cloning the gene.