Marker-assisted pyramiding of potato late blight resistance genesRpi-rzc1andRpi-phu1on di- and tetraploid levels

Late blight is a disease with the biggest economic impact on potato cultivation worldwide. Pyramiding of the resistance genes originating from potato wild relatives is a breeding strategy that has a potential to produce potato cultivars durably resistant to late blight. Growing such cultivars would allow limiting the intensive chemical control of the disease. The goal of this work was to transfer the late blight resistance geneRpi-rzc1fromSolanum ruiz-ceballosiito the tetraploid level of cultivated potato and to pyramid it with theRpi-phu1gene.We obtained two diploid and, through 4x-2x cross, a tetraploid potato population segregating for theRpi-rzc1presence, as well as one diploid and one tetraploid population where both genes were introgressed. In total, 754 progeny clones were tested for resistance to late blight in detached leaflet assays. Pathogen isolates avirulent on plants with both genes and virulent on plants with theRpi-phu1were used. The selection was assisted by two PCR markers flanking theRpi-rzc1gene and a newly designed, highly specific intragenic marker indicating theRpi-phu1gene presence. We obtained 26 diploid and 49 tetraploid potato clones with pyramid of both genes that should enhance the durability and spectrum of their late blight resistance and that can be exploited in potato breeding. The specificity of the marker for theRpi-phu1gene and the precision of theRpi-rzc1mapping were improved in this work.