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.     

Mapping of three self-fertility mutations in rye (Secale cereale L.) using RFLP, isozyme and morphological markers

 Three mutations determining self-fertility at the S, Z and S5 self-incompatibility loci on chromosomes 1R, 2R and 5R of rye, respectively, were mapped using three different F₂ populations. There was a close linkage of one isozyme and four RFLP markers, and no recombinant plants were detected. These markers are Prx7, Xiag249 and Xpsr634 for the S locus (1R), Xbcd266 for the Z locus (2R) and Xpsr100 for the S5 locus (5R). Linkage data for markers associated to the self-fertility mutations at the S, Z and S5 loci were calculated and compared with genetic maps computed by MAPMAKER multipoint analysis. Received: 8 October 1997 / Acepted: 26 November 1997     

Placement of loci for avenins and resistance to Puccinia coronata to a common linkage group in Avena strigosa.

Alcohol-soluble seed storage proteins of oat (avenins) were extracted from two diploid accessions representing the A genome and separated by high-resolution acid polyacrylamide gel electrophoresis. Polymorphisms were detected for three clearly resolved protein bands. Linkage analysis of 88 F2:3 families mapped the three bands to a single locus. Integration of avenin segregation data with an RFLP linkage map constructed from the same population, mapped the avenin locus to a linkage group containing a locus conferring resistance to nine isolates of Puccinia coronata. Linkage between genes encoding alcohol-soluble seed proteins and genes for resistance to Puccinia species was also observed for the homoeologous group 1 chromosomes of barley (1H), rye (1R), wheat (1A, 1B, 1D), and chromosomes 4 and 10 of maize.     

A genetic map of rye (Secale cereale L.) combining RFLP, isozyme, protein, microsatellite and gene loci

Among the cereals, rye (Secale cereale L.) can be grown under extreme climatic and poor soil conditions and, is a major crop in North Europe. In the present paper, we report the development of a genetic linkage map of rye using a pooled F₂ mapping population created from a reciprocal cross of two self-fertile inbred lines. The 183 mapped markers consist 139 RFLPs, 19 isozyme and protein markers, 13 microsatellites, 10 known function sequences and two morphological genes. The markers are randomly distributed on the seven chromosomes with a maximum of 38 on chromosome 5R and a minimum of 19 on chromosome 3R. In addition, 23 gene loci and 25 quantitative trait loci were aligned to chromosome regions. For some of the mapped or aligned genes comparable loci are present in other cereals. The homoeologous relationships of these loci are discussed. The potential of the new map for further genetic studies is outlined. Received: 11 May 2000 / Accepted: 12 July 2000     

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.     

Mapping of genes for male-fertility restoration in ’Pampa’ CMS winter rye (Secale cereale L.)

Hybrid rye breeding and seed production is based on the cytoplasmic male sterility (CMS)-inducing Pampa (P)-cytoplasm. For restoring male fertility in the hybrids, dominant, nuclear restorer genes are necessary. However, current pollinator lines are only partial restorers. Effective restorers were recently detected in the German inbred line L18 and in materials originating from the Argentinian rye cultivar Pico Gentario and an Iranian primitive rye accession called IRAN IX. F₂ populations were developed for each of these three restorer sources to map the responsible genes by means of RFLP (restriction fragment length polymorphism) markers. For this purpose, homo- and heterologous DNA probes were used leading to 101 polymorphic marker loci in total. For phenotypic evaluation, 100 to 134 randomly chosen plants from each of the populations were cloned and grown at two or three locations with two plants each. Segregation ratios of pollen fertility in the F₂ populations with L18 and IRAN IX were in accordance with a monogenic dominant inheritance. The segregation pattern for Pico Gentario indicated complementary gene action. Major dominant restorer genes were detected on chromosomes 1RS (L18) and 4RL (Pico Gentario, IRAN IX). The gene on 1RS explained 54% of the phenotypic variation and that on 4 RL 59% and 68% in the Pico Gentario and IRAN IX populations, respectively. Additionally, three minor genes from L18 were identified on chromosomes 3RL, 4RL and 5R. In the Pico Gentario population, a dominant modifier gene contributed by the female parent was found on chromosome 6R. This gene significantly enhanced the expression of the major restorer gene but on its own was not able to restore any degree of fertility. The map-distances between the major restorer loci and at least one flanking marker were small in all three F₂ populations (5–6 cM). In Pico Gentario an unfavorable linkage exists between the major restorer gene and a QTL for plant height. Since highly effective restorers are scarce in actual breeding populations, the major restorer genes detected on chromosomes 1 RS and 4RL should be introgressed into actual restorer lines. This is facilitated by using the closely linked molecular markers described. Received: 10 February 2000 / Accepted: 31 March 2000<@head-com-p1a.lf>Communicated by G. Wenzel     

RFLP maps of rye chromosomes 6R and 7R including terminal C-bands.

A F2 mapping population was created from a cross between 'UC-90' and E-line ryes (Secale cereale L.), two lines that showed polymorphism for eight C-band loci. Clones from rye, as well as other grasses, were used as probes. RFLP maps of rye chromosomes 6R and 7R were generated that include the 6RS and 6RL terminal C-bands and the 7RS terminal C-band. The 6R map spans 230 cM and includes 9 loci. The 7R map covers 225 cM and includes 21 loci. Segregation distortion was detected for several chromosomal regions. Heterochromatic C-bands did not appear to be responsible for the distortion.     

Inheritance and linkage relationships of seed peroxidase loci in hexaploid oat (Avena sativa L.).

Polyacrylamide gel electrophoresis has been used to investigate the inheritance and linkage relationships between anodal (PXA) and cathodal (PXC) seed peroxidases in hexaploid oat (Avena sativa L.). A total of 12 seed peroxidase loci (5 loci of PXA and 7 loci of PXC) were identified in three crosses. Only two Pxc loci (Pxc5 and Pxc7) were not linked to any peroxidase loci; the others were scored in three linkage groups. The order of the three loci assigned to one of the linkage groups was Pxc1-Pxa5-Pxc2. The order of loci in the other two linkages were Pxc4-Pxa1-Pxa3 and Pxc3-Pxa4-Pxa2. Also, the Pxc6 locus was shown to be linked to the Pxc3 locus. Considering that A. sativa is an allohexaploid, it can be proposed that the three peroxidase linkages represent homoeologous chromosomes.     

Characterization of ‘Sun II’ oat monosomics through C-banding and identification of eight new ‘Sun II’ monosomics

 Monosomics are a powerful tool for genetic mapping in allopolyploid plant species such as oat (Avena sativa L., 2n=6x=42). A C-banded karyotype of the oat cultivar Sun II was compared with previously described oat karyotypes and was used to identify the missing chromosome in each line of Sun II aneuploids. These included new aneuploids, isolated among derivatives of oat haploids obtained from Sun II oat×maize crosses, along with the original Sun II aneuploid set which had been obtained by cytological screening of a Sun II population for spontaneous aneuploids. Eight new Sun II monosomics were identified among the derivatives of haploids from the oat×maize crosses, to give a total of 18 unique Sun II monosomic/nullisomic lines. All seven C-genome chromosomes are represented by Sun II monosomics. Chromosomes 13, 14 and 17 are not represented by Sun II aneuploids but are found in the Kanota monosomic series. Therefore, monosomics of some form are now available for all 21 oat chromosomes. A reciprocal translocation involving chromosomes 3C and 14, found in a portion of the original set of Sun II monosomic lines, was also described. No new translocations were detected in the Sun II×maize crosses. Received: 11 December 1996 / Accepted: 15 July 1997     

Generation of a Restriction Fragment Length Polymorphism Linkage Map for Toxoplasma Gondii

We have constructed a genetic linkage map for the parasitic protozoan, Toxoplasma gondii, using randomly selected low copy number DNA markers that define restriction fragment length polymorphisms (RFLPs). The inheritance patterns of 64 RFLP markers and two phenotypic markers were analyzed among 19 recombinant haploid progeny selected from two parallel genetic crosses between PLK and CEP strains. In these first successful interstrain crosses, these RFLP markers segregated into 11 distinct genetic linkage groups that showed close correlation with physical linkage groups previously defined by molecular karyotype. Separate linkage maps, constructed for each of the 11 chromosomes, indicated recombination frequencies range from approximately 100 to 300 kb per centimorgan. Preliminary linkage assignments were made for the loci regulating sinefungin resistance (snf-1) on chromosome IX and adenine arabinoside (ara-1) on chromosome V by linkage to RFLP markers. Despite random segregation of separate chromosomes, the majority of chromosomes failed to demonstrate internal recombination events and in 3/19 recombinant progeny no intramolecular recombination events were detected. The relatively low rate of intrachromosomal recombination predicts that tight linkage for unknown genes can be established with a relatively small set of markers. This genetic linkage map should prove useful in mapping genes that regulate drug resistance and other biological phenotypes in this important opportunistic pathogen.     

A consensus linkage map of rye (Secale cereale L.) including 374 RFLPs, 24 isozymes and 15 gene loci

 Consensus linkage maps were constructed for all seven rye chromosomes using 12 basic RFLP maps. The maps presented contain a total of 413 markers. The number of markers per chromosome varies from 41 (chromosome 3R) to 83 (chromosome 1R). In addition to 374 RFLP and 24 isozyme markers 15 gene loci were incorporated, determining the traits reduced plant height, self fertility, male sterility restoration, vernalization response, resistance against powdery mildew, chlorophyll deficiency, hairy leaf sheath, hairy peduncle, waxy endosperm, waxless plant and absence of ligules. The maps presented allow the selection of markers for the fine mapping of certain regions of the rye genome. In terms of the known chromosomal rearrangements within the Triticeae its utilization can also be extended for mapping in wheat and barley. Received: 13 February 1998 / Accepted: 26 May 1998     

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.     

Assignment of RFLP linkage groups to chromosomes using monosomic F1 analysis in hexaploid oat

The availability of molecular genetic maps in oat (Avena spp.) and improved identification of chromosomes by C-banding are two recent developments that have made locating linkage groups to chromosomes possible in cultivated hexaploid oat, 2n=6x=42. Monosomic series derived from Avena byzantina C. Koch cv Kanota and from Avena sativa L. cv Sun II were used as maternal plants in crosses with the parents, Kanota-1 and Ogle-C, of the oat RFLP mapping population. Monosomic F₁ plants were identified by root-tip cell chromosome counts. For marker analysis, DNAs of eight F₂ plants from a monosomic F₁ were combined to provide a larger source of DNA that mimicked that of the monosomic F₁ plant. Absence of maternal alleles in monosomic F₁s served to associate linkage groups with individual chromosomes. Twenty two linkage groups were associated with 16 chromosomes. In seven instances, linkage groups that were independent of each other in recombination analyses were associated with the same chromosome. Five linkage groups were shown to be associated with translocation differences among oat lines. Additionally, the results better-characterized the oat monosomic series through the detection of duplicates and translocation differences among the various monosomic lines. The F₁ monosomic series represents a powerful cytogenetic tool with the potential to greatly improve understanding of the oat genome. Received: 24 April 2000 / Accepted: 10 May 2000     

A linkage map of rye

A linkage map of rye (Secale cereale L.) is presented which comprises 60 loci including RFLPs, RAPDs, isozyme, morphological and physiological markers. The genetics and linkage relationships of these markers were investigated in several inbred lines of rye. For the RFLP mapping a genomic library of PstI-digested DNA was constructed from which 50 size-selected clones were analysed. The portion of single-copy and multi-copy DNA and the frequency of polymorphic DNA was determined. The markers are unequally distributed over the seven chromosomes of rye. Many of them exhibit a distorted segregation. The main region of deviating segregation ratios could be localized near the self-incompatibility loci.     

Linkage group-chromosome correlation in Podospora anserina

Summary Two reciprocal translocations have been studied in an attempt to establish a one-to-one assignment of the seven linkage groups of P. anserina to specific chromosomes. Genetical data demonstrated clearly the relationships of the two translocations with three linkage groups. Cytological observations at meiosis in crosses heterozygous for the chromosomal interchanges showed the characteristic cross-like figures and confirmed the fact that the two translocations had one chromosome in common. The correspondence of the three largest chromosomes, including the one bearing the nucleolar organizer, with three well known linkage groups has thus been established. Evidence is also given that loci exhibiting a percentage of second division segregation as high as 98% are not at the end of the chromosomes.     

Detection and effects of a homeologous reciprocal transposition in Brassica napus

A reciprocal chromosomal transposition was identified in several annual oilseed Brassica napus genotypes used as parents in crosses to biennial genotypes for genetic mapping studies. The transposition involved an exchange of interstitial homeologous regions on linkage groups N7 and N16, and its detection was made possible by the use of segregating populations of doubled haploid lines and codominant RFLP markers. RFLP probes detected pairs of homeologous loci on N7 and N16 for which the annual and biennial parents had identical alleles in regions expected to be homeologous. The existence of an interstitial reciprocal transposition was confirmed by cytological analysis of synaptonemal complexes of annual x biennial F1 hybrids. Although it included approximately one-third of the physical length of the N7 and N16 chromosomes, few recombination events within the region were recovered in the progenies of the hybrids. Significantly higher seed yields were associated with the parental configurations of the rearrangement in segregating progenies. These progenies contained complete complements of homeologous chromosomes from the diploid progenitors of B. napus, and thus their higher seed yields provide evidence for the selective advantage of allopolyploidy through the fixation of intergenomic heterozygosity.     

RFLP-based mapping of three mutant loci in rye (Secale cereale L.) and their relation to homoeologous loci within the Gramineae

 Three mutant loci of rye determining absence of ligules (al), waxless plant (wa1) and waxy endosperm (Wx) characters were mapped in a single F₂ population, comprising 84 individual plants. The three loci could be clearly tagged in relation to 7 (al on chromosome 2R), 4 (wa1 on chromosome 7R) or 6 (Wx on chromosome 4R) RFLP markers. The mapping data are compared with existing data for homoeologous regions containing equivalent mutants of wheat, barley, rice and maize. It is shown that the loci analysed are highly conserved across the cereal species, including rye. Received: 14 March 1997 / Accepted: 21 March 1997     

Chromosomal assignment of the nine linkage groups of sugar beet (Beta vulgaris L.) using primary trisomics

 Twenty-four marker loci representing each of the nine linkage groups of sugar beet (Beta vulgaris) have been assigned to the nine primary trisomics of Butterfass (1964). Single-copy RFLP probes were hybridized with filter-bound DNA of the trisomics. The autoradiographs were scanned and analyzed by densitometric methods. Statistics on the integrated optical densities of the RFLP bands revealed a clear relationship of each linkage group to a distinct trisomic type. For the first time each of the linkage groups could unequivocally be assigned to one sugar beet chromosome. A standard nomenclature of the 9 chromosomes of sugar beet is suggested and discussed with respect to previous numbering systems. Received: 27 February 1997/Accepted: 7 March 1997     

Mapping QTLs for submergence tolerance in rice by AFLP analysis and selective genotyping

By combining the amplified fragment length polymorphism (AFLP) technique with selective genotyping, we constructed a linkage map for rice and assigned each linkage group to a corresponding chromosome. The AFLP map, consisting of 202 AFLP markers, was generated from 74 recombinant inbred lines (RIL) which were selected from both extremes of the population (250 lines) with respect to the response to complete submergence. Map length was 1756 cM, with an average interval size of 8.5 cM. To assign linkage groups to chromosomes, we used 50 previously mapped AFLP markers as anchor markers distributed over the 12 chromosomes. Other AFLP markers were then assigned to specific chromosomes based on their linkage to anchor markers. This AFLP map is equivalent to the RFLP/AFLP map constructed previously as the anchors were in the same order in both maps. Furthermore, tests with two restriction fragment length polymorphism (RFLP) markers and two sequence-tagged site (STS) markers showed that they mapped in the expected positions. Using this AFLP map, a major gene for submergence tolerance was localized on chromosome 9. Quantitative trait loci (QTL) associated with submergence tolerance were detected on chromosomes 6, 7, 11, and 12. We conclude that the combination of AFLP mapping and selective genotyping provides a much faster and easier approach to QTL identification than the use of RFLP markers. Received: 20 December 1996 / Accepted: 21 January 1997