Insights into the genetic basis of the pre-breeding potato clones developed at the Julius Kuhn Institute for high and durable late blight resistance

Due to the high yield losses caused by late blight in potato cultivation, the development of resistant pre-breeding material is of great importance for cultivar breeding. The gene pool of the Julius Kuhn Institute (JKI) includes a large collection of resistant clones whose resistance has not yet been analysed in detail with markers for relevant resistance genes. A panel of 52 pre-breeding potato clones developed at the JKI via interspecific crosses and highly resistant to late blight were tested for the presence of seven resistance genes (Rpi-blb1/Rpi-sto1, Rpi-blb2, Rpi-blb3/R2/Rpi-abpt, R1, R3a, R3b, Rpi-phu1) and one QTL allele (QTL_ phu-stn) from Solanum species S. bulbocastanum, S. demissum, S. phureja and S. stoloniferum, respectively. Molecular marker assays based on sequence-specific primers revealed that 36 of the 52 pre-breeding clones carried either 1, 2, 3 or 4 resistance genes introgressed from these wild Solanum species. Results indicate that these resistance genes were retained over generations of breeding. Although highly resistant to late blight, 16 pre-breeding clones did not carry any of these resistance genes. Resistance in the gene pool may, thus, be based not only on individual resistance genes but also on QTL effects. Results help to better understand both inheritance and expression of late blight resistance of this unique gene pool and may be used for breeding programmes.