Identification of five physiological races of blackspot, Diplocarpon rosae, Wolf on roses

Differentiation into physiological races of Diplocarpon rosae, which causes blackspot on wild and cultivated roses, was investigated with single conidial isolates of the pathogen. Infection experiments with a simple excised leaf assay demonstrated differential interactions between single isolates and a set of 10 test rose genotypes. Differential reactions could be observed among rose varieties as well as between and within a wild rose species. Accordingly, five different physiological races can be identified among the 15 isolates tested. A breeding line and one genotype of the wild species Rosa wichuraiana were found to be resistant against all isolates tested. These data will be employed in further investigations on the genetics of blackspot resistance in roses and for resistance breeding programmes.