title: EST-derived SSR markers used as anchor loci for the construction of a consensus linkage map in ryegrass (Lolium spp.).
abstract: BACKGROUND
  Genetic markers and linkage mapping are basic prerequisites for marker-assisted selection and map-based cloning. In the case of the key grassland species Lolium spp., numerous mapping populations have been developed and characterised for various traits. Although some genetic linkage maps of these populations have been aligned with each other using publicly available DNA markers, the number of common markers among genetic maps is still low, limiting the ability to compare candidate gene and QTL locations across germplasm.
  
  
  RESULTS
  A set of 204 expressed sequence tag (EST)-derived simple sequence repeat (SSR) markers has been assigned to map positions using eight different ryegrass mapping populations. Marker properties of a subset of 64 EST-SSRs were assessed in six to eight individuals of each mapping population and revealed 83% of the markers to be polymorphic in at least one population and an average number of alleles of 4.88. EST-SSR markers polymorphic in multiple populations served as anchor markers and allowed the construction of the first comprehensive consensus map for ryegrass. The integrated map was complemented with 97 SSRs from previously published linkage maps and finally contained 284 EST-derived and genomic SSR markers. The total map length was 742 centiMorgan (cM), ranging for individual chromosomes from 70 cM of linkage group (LG) 6 to 171 cM of LG 2.
  
  
  CONCLUSIONS
  The consensus linkage map for ryegrass based on eight mapping populations and constructed using a large set of publicly available Lolium EST-SSRs mapped for the first time together with previously mapped SSR markers will allow for consolidating existing mapping and QTL information in ryegrass. Map and markers presented here will prove to be an asset in the development for both molecular breeding of ryegrass as well as comparative genetics and genomics within grass species.
authors: Department of Genetics and Biotechnology, Faculty of Agricultural Sciences, Research Centre Flakkebjerg, Aarhus University, Forsøgsvej 1, 4200 Slagelse, Denmark. bruno.studer@agrsci.dk
authors: Bruno
authors: B
authors: Studer
authors: Roland
authors: R
authors: Kölliker
authors: Hilde
authors: H
authors: Muylle
authors: Torben
authors: T
authors: Asp
authors: Ursula
authors: U
authors: Frei
authors: Isabel
authors: I
authors: Roldán-Ruiz
authors: Philippe
authors: P
authors: Barre
authors: Céline
authors: C
authors: Tomaszewski
authors: Helena
authors: H
authors: Meally
authors: Susanne
authors: S
authors: Barth
authors: Leif
authors: L
authors: Skøt
authors: Ian P
authors: IP
authors: Armstead
authors: Oene
authors: O
authors: Dolstra
authors: Thomas
authors: T
authors: Lübberstedt
mesh_terms: D002874:Chromosome Mapping; D018744:DNA, Plant / Q000235:genetics; D020224:Expressed Sequence Tags; D008040:Genetic Linkage; D005819:Genetic Markers; D018745:Genome, Plant; D005838:Genotype; D008129:Lolium / Q000235:genetics*; D018895:Microsatellite Repeats; D011110:Polymorphism, Genetic; D040641:Quantitative Trait Loci
chemical_list: D018744:DNA, Plant; D005819:Genetic Markers