Multi-Pathotype Resistance to Black Spot in Roses Conferred By the Rdr1 R-Gene-Family

The first resistance gene in roses is the Rdr1 gene a member of a multigene TNL gene family with 20 sequence characterised members in roses. Originating from Rosa multiflora TNLs of similar structure are found at a syntenic locus in Fragaria but not in Prunus, Malus and model species from the Fabaceae. This indicates a relatively recent origin of the family at their current genomic position. First studies in analysing the functions of individual members via transient gene expression have now been extended by the analysis of transgenic roses expressing two of the Rdr1 family members. Inoculation experiments with a larger set of single conidial isolates of the pathogen as well as mixed inoculum from various field sites indicate that the Rdr1 gene acts on a large number of pathotypes. A second gene from the cluster which does not confer sufficient resistance to inhibit sporulation of the fungus however slows down pathogen spread in the infected tissue indicating that more than one member of the Rdr1 gene family plays a role in the defense against black spot.