Identification of a polymorphism within the Rosa multiflora muRdr1A gene linked to resistance to multiple races of Diplocarpon rosae W. in tetraploid garden roses (Rosa × hybrida).

A QTL for resistance to several races of black spot co-located with the known Rrd1 locus in Rosa. A polymorphism in muRdr1A linked to black spot resistance was identified and molecular markers were designed. Black spot, caused by Diplocarpon rosae, is one of the most serious foliar diseases of landscape roses that reduces the marketability and weakens the plants against winter survival.