Developing resistance to powdery mildew (Podosphaera pannosa (Wallr.: Fr.) de Bary): A challenge for rose breeders

Powdery mildew is the major fungal pathogen of roses in greenhouses and also an important disease on field-grown roses. In the past decade different tools have been developed allowing breeders to develop resistant roses in a more efficient way. Different pathotypes of the fungus, important for resistance testing, were detected. Resistance mechanisms in rose leaves were found and characterized. Screening techniques to evaluate powdery mildew resistance are available. These methods allow pathotype specific inoculation on detached leaves or can be used for the selection of resistant genotypes within a population of thousands of seedlings. New information on the genetic background of powdery mildew resistance became available. Genetic maps providing information on resistance markers are currently being developed and integrated. Marker-assisted selection is expected to be ready soon for use in rose breeding programs for powdery mildew resistance among other traits. This review aims to provide an overview on fundamental information and methodology available and necessary to make progress in breeding for powdery mildew resistance in roses.