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.

A high-density, multi-parental SNP genetic map on apple validates a new mapping approach for outcrossing species

Quantitative trait loci(QTL)mapping approaches rely on the correct ordering of molecular markers along the chromosomes,which can be obtained from genetic linkage maps or a reference genome sequence.For apple(Malus domestica Borkh),the genome sequence v1 and v2 could not meet this need;therefore,a novel approach was devised to develop a dense genetic linkage map,providing the most reliable marker-loci order for the highest possible number of markers.The approach was based on four strategies:(i)the use of multiple full-sib families,(ii)the reduction of missing information through the use of HaploBlocks and alternative calling procedures for single-nucleotide polymorphism(SNP)markers,(iii)the construction of a single backcross-type data set including all families,and(iv)a two-step map generation procedure based on the sequential inclusion of markers.The map comprises 15417 SNP markers,clustered in 3 K HaploBlock markers spanning 1267 cM,with an average distance between adjacent markers of 0.37 cM and a maximum distance of 3.29 cM.Moreover,chromosome 5 was oriented according to its homoeologous chromosome 10.This map was useful to improve the apple genome sequence,design the Axiom Apple 480 K SNP array and perform multifamily-based QTL studies.Its collinearity with the genome sequences v1 and v3 are reported.To our knowledge,this is the shortest published SNP map in apple,while including the largest number of markers,families and individuals.This result validates our methodology,proving its value for the construction of integrated linkage maps for any outbreeding species.