Characterization of Black Spot Resistance in Hybrid Populations of Rosa spp

Black spot disease, caused by the fungus Diplocarpon rosae Wolf, is the most serious disease of landscape roses (Rosa hybrid L.) worldwide. Although partial resistance has been documented, the responsible QTLs remain unidentified. In this project, responses to D. rosae of eight hybrid populations of roses were characterized with a detached leaf assay (DLA). Diploid parents that are either partially resistant (PR) or susceptible (S) to D. rosae were used for generating hybrid populations. Data collected from the populations that shared the same parent combination was pooled together. Results from DLA indicated that the transgressive segregation were observed in all populations with progenies that fall beyond their parental performances. Responses to pathogen of progenies are skewed toward partial resistance. Selfing might interfere with the genotypes of progenies since the PR lines were used as female parents in several hybrid populations. Strong effect QTL(s) that respond to PR might also influence the phenotypes. Hybrid populations which segregate for partial resistance could be utilized for mapping and PR related QTL(s) identification. Molecular markers that are associated with the QTL(s) can also be generated for future breeding work as an efficient method of selecting PR progenies.