Comparative mapping in grasses. Oat relationships

The development of RFLP linkage maps in hexaploid and diploid oat allows us to study genetic relationships of these species at the DNA level. In this report, we present the extension of a previously developed diploid oat map (Avena atlantica x A. hirtula) and its molecular-genetic relationships with wheat, rice and maize. Examination of 92–99% of the length of the oat genome map with probes common to Triticeae species, rice or maize showed that 84, 79 and 71%, respectively, was conserved between these species and oat. Generally, the orders of loci among chromosomes homoeologous to oat chromosomes A and D were the most conserved and those of chromosomes homoeologous to oat chromosome G were the least conserved. Conservation was observed for blocks ranging from whole chromosomes 101 cM long to small segments 2.5 cM long containing two loci. Comparison of the homoeologous segments of Triticeae, rice and maize relative to oat indicated that certain regions have been maintained in all four species. The relative positions of major genes governing traits such as seed storage proteins and resistance to leaf rusts have been conserved between cultivated oat and Triticeae species. Also, the locations of three vernalization/or photo-period response genes identified in hexaploid oat correspond to the locations of similar genes in homoeologous chromosomes of wheat, rice or maize. The locations of the centromeres for six of the seven oat chromosomes were estimated based on the homoeologous segments between oat and Triticeae chromosomes.     

Structural and functional organization of the '1S0.8 gene-rich region' in the Triticeae

Wheat genes are present in physically small, gene-rich regions, interspersed by gene-poor blocks of retrotransposon-like repetitive sequences. One of the largest gene-rich regions is present around fraction length (FL) 0.8 of the short arm of wheat homoeologous group 1 chromosomes and is called `1S0.8 region'. The objective of this study was to reveal the structural and functional organization of the `1S0.8 region' in various Triticeae and other Poaceae species. Consensus genetic linkage maps of the `1S0.8 region' were constructed for wheat, barley, and rye by combining mapping information from 16, 11, and 12 genetic linkage maps, respectively. The consensus genetic linkage maps were compared with each other and with a consensus physical map of wheat homoeologous group 1. Comparative analyses localized 75 agronomically important genes to the `1S0.8 region'. This high-resolution comparison revealed exceptions to the rule of conserved gene synteny, established using low-resolution marker comparisons. Small rearrangements such as duplications, deletions, and inversions were observed among species. Proportion of chromosomal recombination occurring in the `1S0.8 region' was very similar among species. Within the gene-rich region, the extent of recombination was highly variable but the pattern was similar among species. Relative recombination among markers was similar except for a few loci where drastic differences were observed among species. Chromosomal rearrangements did not always change the extent of recombination for the region. Differences in gene order and relative recombination were the least between wheat and barley, and were the highest between wheat and oat.     

The physical relationship of barley chromosome 5 (1H) to the linkage groups of rice chromosomes 5 and 10

 Using a recently developed polymerase chain reaction (PCR)-mediated approach for physical mapping of single-copy DNA sequences on microisolated chromosomes of barley, sequence-tagged sites of DNA probes that reveal restriction fragment length polymorphisms (RFLP) localized on the linkage maps of rice chromosomes 5 and 10 were allocated to cytologically defined regions of barley chromosome 5 (1H). The rice map of linkage group 5, of about 135 cM in size, falls into two separate parts, which are related to the distal portions of both the short and long arms of the barley chromosome. The markers on the rice map of chromosome 5 were found to be located within regions of the barley chromosome which show high recombination rates. The map of rice chromosome 10, of about 75 cM in size, on the other hand, is related to an interstitial segment of the long arm of chromosome 5 (1H) which is highly suppressed in recombination activity. For positional cloning of genes of this homoeologous region from the barley genome, the small rice genome will probably prove to be a useful tool. No markers located on rice chromosomes were detected within the pericentric Giemsa-positive heterochromatin of the barley chromosome, indicating that these barley-specific sequences form a block which separates the linkage segments conserved in rice. By our estimate approximately half of the barley-specific sequences of chromosome 5 (1H) show a dispersed distribution, while the other half separates the conserved linkage segments. Received: 29 February 1996 / Accepted: 28 June 1996     

Comparison of wheat physical maps with barley linkage maps for group 7 chromosomes

Comparative genetic maps among the Triticeae or Gramineae provide the possibility for combining the genetics, mapping information and molecular-marker resources between different species. Dense genetic linkage maps of wheat and barley, which have a common array of molecular markers, along with deletion-based chromosome maps of Triticum aestivum L. will facilitate the construction of an integrated molecular marker-based map for the Triticeae. A set of 21 cDNA and genomic DNA clones, which had previously been used to map barley chromosome 1 (7H), were used to physically map wheat chromosomes 7A, 7B and 7D. A comparative map was constructed to estimate the degree of linkage conservation and synteny of chromosome segments between the group 7 chromosomes of the two species. The results reveal extensive homoeologies between these chromosomes, and the first evidence for an interstitial inversion on the short arm of a barley chromosome compared to the wheat homoeologue has been obtained. In a cytogenetically-based physical map of group 7 chromosomes that contain restriction-fragment-length polymorphic DNA (RFLP) and random amplified polymorphic DNA (RAPD) markers, the marker density in the most distal third of the chromosome arms was two-times higher than in the proximal region. The recombination rate in the distal third of each arm appears to be 8–15 times greater than in the proximal third of each arm where recombination of wheat chromosomes is suppressed.     

Comparative mapping in grasses. Wheat relationships

Conventionally, the genetics of species of the family Gramineae have been studied separately. Comparative mapping using DNA markers offers a method of combining the research efforts in each species. In this study, we developed consensus maps for members of the Triticeae tribe (Triticum aestivum, T. tauschii, andHordeum spp.) and compared them to rice, maize and oat. The aneuploid stocks available in wheat are invaluable for comparative mapping because almost every DNA fragment can be allocated to a chromosome arm, thus preventing erroneous conclusions about probes that could not be mapped due to a lack of polymorphism between mapping parents. The orders of the markers detected by probes mapped in rice, maize and oat were conserved for 93, 92 and 94% of the length of Triticeae consensus maps, respectively. The chromosome segments duplicated within the maize genome by ancient polyploidization events were identified by homoeology of segments from two maize chromosomes to regions of one Triticeae chromosome. Homoeologous segments conserved across Triticeae species, rice, maize, and oat can be identified for each Triticeae chromosome. Putative orthologous loci for several simply inherited and quantitatively inherited traits in Gramineae species were identified.Communicated by H. Saedler     

Molecular genetic maps of the group 6 chromosomes of hexaploid wheat (Triticum aestivum L. em. Thell.).

Restriction fragment length polymorphism (RFLP) maps of chromosomes 6A, 6B, and 6D of hexaploid wheat (Triticum aestivum L. em. Thell.) have been produced. They were constructed using a population of F7-8 recombinant inbred lines derived from a synthetic wheat x bread wheat cross. The maps consist of 74 markers assigned to map positions at a LOD >= 3 (29 markers assigned to 6A, 24 to 6B, and 21 to 6D) and 2 markers assigned to 6D ordered at a LOD of 2.7. Another 78 markers were assigned to intervals on the maps. The maps of 6A, 6B, and 6D span 178, 132, and 206 cM, respectively. Twenty-one clones detected orthologous loci in two homoeologues and 3 detected an orthologous locus in each chromosome. Orthologous loci are located at intervals of from 1.5 to 26 cM throughout 70% of the length of the linkage maps. Within this portion of the maps, colinearity (homosequentiality) among the three homoeologues is strongly indicated. The remainder of the linkage maps consists of three segments ranging in length from 47 to 60 cM. Colinearity among these chromosomes and other Triticeae homoeologous group 6 chromosomes is indicated and a consensus RFLP map derived from maps of the homoeologous group 6 chromosomes of hexaploid wheat, tetraploid wheat, Triticum tauschii, and barley is presented. Key words : RFLP, wheat, linkage maps, molecular markers.     

Analysis of recombination and gene distribution in the 2L1.0 region of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.)

Both wheat and barley belong to tribe Triticeae and are closely related. High-density detailed comparison of physical and genetic linkage maps revealed that wheat genes are present in physically small gene-rich regions (GRRs). One of the largest GRRs is located around fraction length 1.0 of the long arm of wheat homoeologous group 2 chromosomes termed the "2L1.0 region." The main objective of this study was to analyze the structural and functional organization of the 2L1.0 region in barley in comparison to wheat. Using the 29 physically mapped RFLP markers for the region, wheat and barley consensus genetic linkage maps of the 2L1.0 region were generated by combining information from 18 wheat and 7 barley genetic linkage maps. Comparative analysis using these consensus maps and other available wheat and barley mapping resources identified 227 DNA markers and ESTs for the region. The region accounted for 58% of the genes and 68% of the arm's recombination in wheat. However, the corresponding region in barley accounted for about 42% of the genes and 81% of the recombination. The kb/cM ratio for the region was 122 in barley compared to 244 in wheat. Distribution of genes and recombination varied between the two species even though the gene order and density were similar.     

Comparison of genetic and physical maps of group 7 chromosomes from Triticum aestivum L.

We present a high density physical map of homoeologous group 7 chromosomes from Triticum aestivum L. using a series of 54 deletion lines, 6 random amplified polymorphic DNA (RAPD) markers and 91 cDNA or genomic DNA clones from wheat, barley and oat. So far, 51 chromosome segments have been distinguished by molecular markers, and 54 homoeoloci have been allocated among chromosomes 7A, 7B and 7D. The linear order of molecular markers along the chromosomes is almost identical in the A- B- and D-genome of wheat. In addition, there is colinearity between the physical and genetic maps of chromosomes 7A, 7B and 7D from T. aestivum, indicating gene synteny among the Triticeae. However, comparison of the physical map of chromosome 7D from T. aestivum with the genetic map from Triticum tauschii some markers have been shown to be physically allocated with distortion in more distal chromosome regions. The integration of genetic and physical maps could assist in estimating the frequency and distribution of recombination in defined regions along the chromosome. Physical distance did not correlate with genetic distance. A dense map facilitates the detection of multiple rearrangements. We present the first evidence for an interstitial inversion either on chromosome arm 7AS or 7DS of Chinese Spring. Molecularly tagged chromosome regions (MTCRs) provide landmarks for long-range mapping of DNA fragments.     

Comparative mapping of homoeologous group 1 regions and genes for resistance to obligate biotrophs in Avena, Hordeum, and Zea mays.

The colinearity of markers linked with resistance loci on linkage group A of diploid oat, on the homoeologous groups in hexaploid oat, on barley chromosome 1H, and on homoeologous maize chromosomes was determined. Thirty-two DNA probes from homoeologous group 1 chromosomes of the Gramineae were tested. Most of the heterologous probes detected polymorphisms that mapped to linkage group A of diploid oat, two linkage groups of hexaploid oat, barley chromosome 1H, and maize chromosomes 3, 6, and 8. Many of these DNA markers appeared to have conserved linkage relationships with resistance and prolamin loci in Avena, Hordeum, and Zea mays. These resistance loci included the Pca crown rust resistance cluster in diploid oat, the R203 crown rust resistance locus in hexaploid oat, the Mla powdery mildew resistance cluster in barley, and the rp3, wsm1, wsm2, mdm1, ht2, and htn1 resistance loci in maize. Prolamin encoding loci included Avn in diploid oat and Hor1 and Hor2 in barley. A high degree of colinearity was revealed among the common RFLP markers on the small chromosome fragments among these homoeologous groups. Key words : disease resistance, colinearity, Gramineae, cereals.     

Molecular linkage mapping in rye (Secale cereale L.)

A rye linkage map containing clones from rye, wheat, barley, oat and rice genomic and cDNA libraries, known-function genes and microsatellite markers, was created using an F₂ population consisting of 110 F₂-derived F₃ families. Both co-dominant and dominant markers were added to the map. Of all probes screened, 30.8% were polymorphic, and of those polymorphic 79.3% were mapped. The current map contains 184 markers present in all seven linkage groups covering only 727.3 cM. This places a marker about every 3.96 cM on average throughout the map; however, large gaps are still present. The map contains 60 markers that have been integrated from previous rye maps. Surprisingly, no markers were placed between the centromere and C1–1RS in the short arm of 1R. The short arm of chromosome 4 also lacked an adequate number of polymorphic markers. The population showed a remarkable degree of segregation distortion (72.8%). In addition, the genetic distance observed in rye was found to be very different among the maps created by different mapping populations. Received: 10 January 2000 / Accepted: 26 May 2000     

A linkage map of meadow fescue (<Emphasis Type="Italic">Festuca pratensis</Emphasis> Huds.) and comparative mapping with other Poaceae species

A genetic linkage map has been constructed for meadow fescue (Festuca pratensis Huds.) (2n=2x=14) using a full-sib family of a cross between a genotype from a Norwegian population (HF2) and a genotype from a Yugoslavian cultivar (B14). The two-way pseudo-testcross procedure has been used to develop separate maps for each parent, as well as a combined map. A total number of 550 loci have been mapped using homologous and heterologous RFLPs, AFLPs, isozymes and SSRs. The combined map consists of 466 markers, has a total length of 658.8 cM with an average marker density of 1.4 cM/marker. A high degree of orthology and colinearity was observed between meadow fescue and the Triticeae genome(s) for all linkage groups, and the individual linkage groups were designated 1F–7F in accordance with the orthologous Triticeae chromosomes. As expected, the meadow fescue linkage groups were highly orthologous and co-linear with Lolium, and with oat, maize and sorghum, generally in the same manner as the Triticeae chromosomes. It was shown that the evolutionary 4AL/5AL translocation, which characterises some of the Triticeae species, is not present in the meadow fescue genome. A putative insertion of a segment orthologous to Triticeae 2 at the top of 6F, similar to the rearrangement found in the wheat B and the rye R genome, was also observed. In addition, chromosome 4F is completely orthologous to rice chromosome 3 in contrast to the Triticeae where this rice chromosome is distributed over homoeologous group 4 and 5 chromosomes. The meadow fescue genome thus has a more ancestral configuration than any of the Triticeae genomes. The extended meadow fescue map reported here provides the opportunity for beneficial cross-species transfer of genetic knowledge, particularly from the complete genome sequence of rice.Communicated by P. Langridge     

Identification and High-Density Mapping of Gene-Rich Regions in Chromosome Group 1 of Wheat

We studied the distribution of genes and recombination in wheat (Triticum aestivum) group 1 chromosomes by comparing high-density physical and genetic maps. Physical maps of chromosomes 1A, 1B, and 1D were generated by mapping 50 DNA markers on 56 single-break deletion lines. A consensus physical map was compared with the 1D genetic map of Triticum tauschii (68 markers) and a Triticeae group 1 consensus map (288 markers) to generate a cytogenetic ladder map (CLM). Most group 1 markers (86%) were present in five clusters that encompassed only 10% of the group 1 chromosome. This distribution may reflect that of genes because more than half of the probes were cDNA clones and 30% were PstI genomic. All 14 agronomically important genes in group 1 chromosomes were present in these clusters. Most recombination occurred in gene-cluster regions. Markers fell at an average distance of 244 kb in these regions. The CLM involving the Triticeae consensus genetic map revealed that the above distribution of genes and recombination is the same in other Triticeae species. Because of a significant number of common markers, our CLM can be used for comparative mapping and to estimate physical distances among markers in many Poaceae species including rice and maize.     

Comparison of homoeologous group-6 short arm physical maps of wheat and barley reveals a similar distribution of recombinogenic and gene-rich regions

Eighty two new loci, mapped with 51 DNA clones, were added to the earlier deletion maps of the homoeologous group-6 short arms of hexaploid wheat ( Triticum aestivum L. em Thell., 2n = 6 x = 42, AABBDD). There are now 41, 56 and 52 loci mapped on deletion maps of 6AS, 6BS and 6DS, respectively. The linear order of orthologous loci in all three arms appears to be identical. The majority of the loci are located in the distal one-half of the three arms. There seems to be an increased marker/gene density from the centromeric to the telomeric regions in each arm, and the marker density in comparable physical regions is similar on all three maps. Recombination is not uniformly distributed along the chromosome arms; 60% of recombination occurs in the distal one-third of each arm. Recombination increases from the proximal region to the distal end in a nonlinear pattern. The distribution of loci and recombination along each of the three chromosome arms is highly correlated. Comparison of the 6BS deletion map from this study and a 6HS physical map of barley ( Hordeum vulgare L., 2n = 2 x = 14, HH) reveals a remarkably similar distribution of recombinogenic and gene-rich regions between the two chromosome arms, suggesting that the distribution patterns of genes may be conserved in the homoeologous group-6 chromosome short arms of wheat and barley. A consensus map of wheat group-6 short arms containing 46 orthologous loci was constructed. Comparison of the consensus map with published linkage maps of Triticeae group-6 chromosome short arms indicates that the linear order of the loci on the maps has been largely conserved. Evidence from this study does not support the existence of a 2BS-6BS reciprocal terminal translocation.     

A molecular linkage map of rye

A genetic map of six chromosomes of rye, (all of the rye chromosomes except for 2R), was constructed using 77 RFLP and 12 RAPD markers. The map was developed using an F₂ population of 54 plants from a cross between two inbred lines. A rye genomic library was constructed as a source of clones for RFLP mapping. Comparisons were made between the rye map and other rye and wheat maps by including additional probes previously mapped in those species. These comparisons allowed (1) chromosome arm orientation to the linkage groups to be given, (2) the corroboration of several evolutionary translocations between rye chromosomes and homoeologous chromosomes of wheat; (3) an increase in the number of available markers for target regions of rye that show colinearity with wheat. Inconsistencies in the location of markers between the wheat and rye maps were mostly detected by multi-copy probes.     

A chromosome bin map of 2148 expressed sequence tag loci of wheat homoeologous group 7

The objectives of this study were to develop a high-density chromosome bin map of homoeologous group 7 in hexaploid wheat (Triticum aestivum L.), to identify gene distribution in these chromosomes, and to perform comparative studies of wheat with rice and barley. We mapped 2148 loci from 919 EST clones onto group 7 chromosomes of wheat. In the majority of cases the numbers of loci were significantly lower in the centromeric regions and tended to increase in the distal regions. The level of duplicated loci in this group was 24% with most of these loci being localized toward the distal regions. One hundred nineteen EST probes that hybridized to three fragments and mapped to the three group 7 chromosomes were designated landmark probes and were used to construct a consensus homoeologous group 7 map. An additional 49 probes that mapped to 7AS, 7DS, and the ancestral translocated segment involving 7BS also were designated landmarks. Landmark probe orders and comparative maps of wheat, rice, and barley were produced on the basis of corresponding rice BAC/PAC and genetic markers that mapped on chromosomes 6 and 8 of rice. Identification of landmark ESTs and development of consensus maps may provide a framework of conserved coding regions predating the evolution of wheat genomes.     

Molecular mapping of wheat. Homoeologous group 3.

A prerequisite for molecular level genetic studies and breeding in wheat is a molecular marker map detailing its similarities with those of other grass species in the Gramineae family. We have constructed restriction fragment length polymorphism maps of the A-, B-, and D-genome chromosomes of homoeologous group 3 of hexaploid wheat (Triticum aestivum L. em. Thell) using 114 F7-8 lines from a synthetic x bread wheat cross. The map consists of 58 markers spanning 230 cM on chromosome 3A, 62 markers spanning 260 cM on 3B, and 40 markers spanning 171 cM on 3D. Thirteen libraries of genomic or cDNA clones from wheat, barley, and T. tauschii, the wheat D genome donor, are represented, facilitating the alignment and comparison of these maps with maps of other grass species. Twenty-four clones reveal homoeoloci on two of the three genomes and the associated linkages are largely comparable across genomes. A consensus sequence of orthologous loci in grass species genomes is assembled from this map and from existing maps of the chromosome-3 homoeologs in barley (Hordeum spp.), T. tauschii, and rice (Oryza spp.). It illustrates the close homoeology among the four species and the partial homoeology of wheat chromosome 3 with oat (Avena spp.) chromosome C. Two orthologous red grain color genes, R3 and R1, are mapped on chromosome arms 3BL and 3DL.     

An enhanced molecular marker based genetic map of perennial ryegrass (Lolium perenne) reveals comparative relationships with other Poaceae genomes.

A molecular-marker linkage map has been constructed for perennial ryegrass (Lolium perenne L.) using a one-way pseudo-testcross population based on the mating of a multiple heterozygous individual with a doubled haploid genotype. RFLP, AFLP, isoenzyme, and EST data from four collaborating laboratories within the International Lolium Genome Initiative were combined to produce an integrated genetic map containing 240 loci covering 811 cM on seven linkage groups. The map contained 124 codominant markers, of which 109 were heterologous anchor RFLP probes from wheat, barley, oat, and rice, allowing comparative relationships between perennial ryegrass and other Poaceae species to be inferred. The genetic maps of perennial ryegrass and the Triticeae cereals are highly conserved in terms of synteny and colinearity. This observation was supported by the general agreement of the syntenic relationships between perennial ryegrass, oat, and rice and those between the Triticeae and these species. A lower level of synteny and colinearity was observed between perennial ryegrass and oat compared with the Triticeae, despite the closer taxonomic affinity between these species. It is proposed that the linkage groups of perennial ryegrass be numbered in accordance with these syntenic relationships, to correspond to the homoeologous groups of the Triticeae cereals.     

Genetic Map of Diploid Wheat, Triticum Monococcum L., and Its Comparison with Maps of Hordeum Vulgare L

A genetic map of diploid wheat, Triticum monococcum L., involving 335 markers, including RFLP DNA markers, isozymes, seed storage proteins, rRNA, and morphological loci, is reported. T. monococcum and barley linkage groups are remarkably conserved. They differ by a reciprocal translocation involving the long arms of chromosomes 4 and 5, and paracentric inversions in the long arm of chromosomes 1 and 4; the latter is in a segment of chromosome arm 4L translocated to 5L in T. monococcum. The order of the markers in the inverted segments in the T. monococcum genome is the same as in the B and D genomes of T. aestivum L. The T. monococcum map differs from the barley maps in the distribution of recombination within chromosomes. The major 5S rRNA loci were mapped on the short arms of T. monococcum chromosomes 1 and 5 and the long arms of barley chromosomes 2 and 3. Since these chromosome arms are colinear, the major 5S rRNA loci must be subjected to positional changes in the evolving Triticeae genome that do not perturb chromosome colinearity. The positional changes of the major 5S rRNA loci in Triticeae genomes are analogous to those of the 18S-5.8S-26S rRNA loci.     

Molecular and physical mapping of a barley gene on chromosome arm 1 HL that causes sterility in hybrids with wheat.

Addition of the long arm of barley chromosome 1H (1HL) to wheat causes severe meiotic abnormalities and complete sterility of the plants. To map the barley gene responsible for the 1H-induced sterility of wheat, a series of addition lines of translocated 1H chromosomes were developed from the crosses between the wheat 'Shinchunaga' and five reciprocal translocation lines derived from the barley line St.13559. Examination of the seed fertility of the addition lines revealed that the sterility gene is located in the interstitial 25% region of the 1HL arm. The genetic location of the sterility gene was also estimated by physically mapping sequence-tagged site (STS) markers and simple-sequence repeat (SSR) markers with known map locations. The sterility gene is designated Shw (sterility in hybrids with wheat). Comparison of the present physical map of 1HL with two previously published genetic maps revealed a paucity of markers in the proximal 30% region and non-random distribution of SSR markers. Two inconsistencies in marker order were found between the present physical map and the consensus genetic map of group 1 chromosomes of Triticeae. On the basis of the effects on meiosis and chromosomal location, the relationship of the present sterility gene with other fertility-related genes of Triticeae is discussed.     

Chromosomal rearrangements differentiating the ryegrass genome from the Triticeae, oat, and rice genomes using common heterologous RFLP probes

An restriction fragment length polymorphism (RFLP)-based genetic map of ryegrass (Lolium) was constructed for comparative mapping with other Poaceae species using heterologous anchor probes. The genetic map contained 120 RFLP markers from cDNA clones of barley (Hordeum vulgare L.), oat (Avena sativa L.), and rice (Oryza sativa L.), covering 664 cM on seven linkage groups (LGs). The genome comparisons of ryegrass relative to the Triticeae, oat, and rice extended the syntenic relationships among the species. Seven ryegrass linkage groups were represented by 10 syntenic segments of Triticeae chromosomes, 12 syntenic segments of oat chromosomes, or 16 syntenic segments of rice chromosomes, suggesting that the ryegrass genome has a high degree of genome conservation relative to the Triticeae, oat, and rice. Furthermore, we found ten large-scale chromosomal rearrangements that characterize the ryegrass genome. In detail, a chromosomal rearrangement was observed on ryegrass LG4 relative to the Triticeae, four rearrangements on ryegrass LGs2, 4, 5, and 6 relative to oat, and five rearrangements on ryegrass LGs1, 2, 4, 5, and 7 relative to rice. Of these, seven chromosomal rearrangements are reported for the first time in this study. The extended comparative relationships reported in this study facilitate the transfer of genetic knowledge from well-studied major cereal crops to ryegrass.