Rpp1, a dominant gene providing race-specific resistance to rose powdery mildew ( Podosphaera pannosa): molecular mapping, SCAR development and confirmation of disease resistance data.

We have previously demonstrated that in the diploid rose population 97/9 resistance to the powdery mildew race 9 is controlled by a major dominant resistance gene, Rpp1. In the study reported here, we isolated several molecular markers closely linked to Rpp1 via bulked segregant analysis, with the gene being tagged in an interval of 5 cM between the two most adjacent markers. It was possible to convert the most closely linked amplified fragment length polymorphic (AFLP) marker into a sequence-characterised amplified region (SCAR) segregating in the same manner. Indirect mapping of Rpp1 in relation to the black spot resistance gene Rdr1 revealed no linkage between the two R genes. Furthermore, the genetic model based on a single dominant resistance gene was supported by the marker data.