Mapping Black Spot Resistance in Autotetraploid Rose Using Genotyping-by-Sequencing

The black spot pathogen, Diplocarpon rosae, creates significant damage to landscape roses.  Once infection has occurred the leaves of affected plants become colonized by unsightly black patches which can be followed by significant defoliation and the eventual death of the plant.  Control of this endemic pathogen is difficult particularly as industry phases-out the use of fungicides.  Rose breeding programs around the world could benefit from molecular markers for black spot resistance but the complex history and genetics of rose combined with under-developed genomics resources has limited efforts.

Here we present our work to map two races of black spot in autotetraploid rose.  Using genotyping-by-sequencing (GBS) we constructed parental maps from 350 hybrids from a cross between accession 564 and Gentle Giant®.  Using a detached leaf assay we phenotyped resistance to both races, each of which mapped as a single dominant gene.  The GBS SNPs were converted to high resolution DNA melting assays and have been deployed to our cold hardy landscape rose breeding program.  This project will serve as a framework for future development of markers across a number of traits important for developing superior roses.