2019 ASHS Annual Conference

The fungal pathogen, Diplocarpon rosae Wolf, infects only roses (Rosa spp.) and leads to rose black spot disease. Rose black spot is the most problematic disease of outdoor grown roses worldwide due to the potential for rapid leaf yellowing and defoliation. Plants repeatedly defoliated from black spot become weakened and may eventually die from lack of energy reserves. Eleven races of the pathogen were previously characterized from isolates collected in North America and Europe. Isolates of D. rosae obtained from infected leaves of Brite Eyes^TM (‘RADbrite’; isolate BEP; collected in West Grove, PA) and Paprika^TM (‘CHEwmaytime’; isolate PAP; collected in Minneapolis, MN) proved to have unique infection patterns using the established host differential and Lemon Fizz^TM (‘KORlem’). The new races are designated race 12 (BEP) and 13 (PAP), respectively. A differential infection pattern on Lemon Fizz^TM is what distinguished race 12 from the previously characterized race 7. Expanding the collection of D. rosae races provides an ever more valuable resource for ongoing efforts to identify and characterize unique race-specific resistance genes in Rosa and virulence genes in the pathogen as well as for supporting rose breeding programs.