Marker assisted background selection for the introgression of black spot resistance into cultivated roses

Abstract

Summary In a model breeding program Rdr1 , a gene conferring resistance to black spot ( Diplocarpon rosae Wolf) was introduced from a wild rose species into the genetic background of cultivated tetraploid roses. The chromosomal set of the original diploid donor genotype, a Rosa multiflora hybrid, was doubled via colchicine treatment and crossed to a tetraploid hybrid tea variety. The resulting hybrid genotype, 91/100-5, was crossed to a Floribunda garden rose and the resulting progeny was tested for black spot resistance. AFLP markers were then used to screen a subset of the resistant progeny for the fraction of donor genome, which segregates from 32 to 84% in this population. The genotype with the smallest number of donor-specific markers was further backcrossed to the Floribunda parent and the hybrid tea grandparent, and the analyses conducted in the previous generation were repeated. The BC 2 population segregated for the fraction of the original donor genome, ranging from 12.3% to 32%. A parallel screen for morphological markers in the BC 1 demonstrated the superiority of the molecular markers for the reduction of the genetic background of wild rose species in introgression programs allowing a more efficient utilization of wild rose germplasm.