High-density SNP-based genetic maps for the parents of an outcrossed and a selfed tetraploid garden rose cross, inferred from admixed progeny using the 68k rose SNP array

Dense genetic maps create a base for QTL analysis of important traits and future implementation of marker-assisted breeding.In tetraploid rose,the existing linkage maps include<300 markers to cover 28 linkage groups(4 homologous sets of 7 chromosomes).Here we used the 68k WagRhSNP Axiom single-nucleotide polymorphism(SNP)array for rose,in combination with SNP dosage calling at the tetraploid level,to genotype offspring from the garden rose cultivar‘Red New Dawn’.The offspring proved to be not from a single bi-parental cross.In rose breeding,crosses with unintended parents occur regularly.We developed a strategy to separate progeny into putative populations,even while one of the parents was unknown,using principle component analysis on pairwise genetic distances based on sets of selected SNP markers that were homozygous,and therefore uninformative for one parent.One of the inferred populations was consistent with self-fertilization of‘Red New Dawn’.Subsequently,linkage maps were generated for a bi-parental and a self-pollinated population with‘Red New Dawn’as the common maternal parent.The densest map,for the selfed parent,had 1929 SNP markers on 25 linkage groups,covering 1765.5 cM at an average marker distance of 0.9 cM.Synteny with the strawberry(Fragaria vesca)genome was extensive.Rose ICM1 corresponded to F.vesca pseudochromosome 7(Fv7),ICM4 to Fv4,ICM5 to Fv3,ICM6 to Fv2 and ICM7 to Fv5.Rose ICM2 corresponded to parts of F.vesca pseudochromosomes 1 and 6,whereas ICM3 is syntenic to the remainder of Fv6.

In the name of the rose:a roadmap for rose research in the genome era

The recent completion of the rose genome sequence is not the end of a process,but rather a starting point that opens up a whole set of new and exciting activities.Next to a high-quality genome sequence other genomic tools have also become available for rose,including transcriptomics data,a high-density single-nucleotide polymorphism array and software to perform linkage and quantitative trait locus mapping in polyploids.Rose cultivars are highly heterogeneous and diverse.This vast diversity in cultivated roses can be explained through the genetic potential of the genus,introgressions from wild species into commercial tetraploid germplasm and the inimitable efforts of historical breeders.We can now investigate how this diversity can best be exploited and refined in future breeding work,given the rich molecular toolbox now available to the rose breeding community.This paper presents possible lines of research now that rose has entered the genomics era,and attempts to partially answer the question that arises after the completion of any draft genome sequence:‘Now that we have“the”genome,what’s next?’.Having access to a genome sequence will allow both(fundamental)scientific and(applied)breeding-orientated questions to be addressed.We outline possible approaches for a number of these questions.