Whole genome mapping in a wheat doubled haploid population using SSRs and TRAPs and the identification of QTL for agronomic traits

Genetic maps are useful for detecting quantitative trait loci (QTL) associated with quantitative traits and for marker-assisted selection (MAS) in breeding. In this research, we used the wheat × maize method to develop a doubled haploid (DH) population derived from the synthetic hexaploid wheat (SHW) line TA4152-60 and the North Dakota hard red spring wheat line ND495. The population consisted of 213 lines, of which a subset of 120 lines was randomly selected and used to construct linkage maps of all 21 chromosomes and for QTL detection. The whole genome maps consisted of 632 markers including 410 SSRs, 218 TRAPs, 1 RFLP, and 3 phenotypic markers, and spanned 3,811.5 cM with an average density of one marker per 6.03 cM. Telomere sequence-based TRAPs allowed us to define the ends of seven linkage groups. Analysis revealed major QTLs associated with the traits of days to heading on chromosomes 5A and 5B, plant height on chromosomes 4D and 5A, and spike characteristics on chromosomes 3D, 4A, 4D, 5A and 5B. The DH population and genetic map will be a useful tool for the identification of disease resistance QTL and agronomically important loci, and will aid in the identification and development of markers for MAS. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Populations of doubled haploids for genetic mapping in hexaploid winter triticale

To create a framework for genetic dissection of hexaploid triticale, six populations of doubled haploid (DH) lines were developed from pairwise hybrids of high-yielding winter triticale cultivars. The six populations comprise between 97 and 231 genotyped DH lines each, totaling 957 DH lines. A consensus genetic map spans 4593.9 cM is composed of 1576 unique DArT markers. The maps reveal several structural rearrangements in triticale genomes. In preliminary tests of the populations and maps, markers specific to wheat segments of the engineered rye chromosome 1R (RM1B) were identified. Example QTL mapping of days to heading in cv. Krakowiak revealed loci on chromosomes 2BL and 2R responsible for extended vernalization requirement, and candidate genes were identified. The material is available to all parties interested in triticale genetics.     

High-density genetic map of durum wheat × wild emmer wheat based on SSR and DArT markers

A genetic linkage map of tetraploid wheat was constructed based on a cross between durum wheat [Triticum turgidum ssp. durum (Desf.) MacKey] cultivar Langdon and wild emmer wheat [T. turgidum ssp. dicoccoides (K?rn.) Thell.] accession G18-16. One hundred and fifty-two single-seed descent derived F(6) recombinant inbred lines (RILs) were analyzed with a total of 690 loci, including 197 microsatellite and 493 DArT markers. Linkage analysis defined 14 linkage groups. Most markers were mapped to the B-genome (60%), with an average of 57 markers per chromosome and the remaining 40% mapped to the A-genome, with an average of 39 markers per chromosome. To construct a stabilized (skeleton) map, markers interfering with map stability were removed. The skeleton map consisted of 307 markers with a total length of 2,317 cM and average distance of 7.5 cM between adjacent markers. The length of individual chromosomes ranged between 112 cM for chromosome 4B to 217 cM for chromosome 3B. A fraction (30.1%) of the markers deviated significantly from the expected Mendelian ratios; clusters of loci showing distorted segregation were found on chromosomes 1A, 1BL, 2BS, 3B, and 4B. DArT markers showed high proportion of clustering, which may be indicative of gene-rich regions. Three hundred and fifty-two new DArT markers were mapped for the first time on the current map. This map provides a useful groundwork for further genetic analyses of important quantitative traits, positional cloning, and marker-assisted selection, as well as for genome comparative genomics and genome organization studies in wheat and other cereals.     

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.     

Genetic map of triticale compiling DArT, SSR, and AFLP markers

A set of 90 doubled haploid (DH) lines derived from F(1) plants that originated from a cross between × Triticosecale Wittm. 'Saka3006' and ×Triticosecale Wittm. 'Modus', via wide crossing with maize, were used to create a genetic linkage map of triticale. The map has 21 linkage groups assigned to the A, B, and R genomes including 155 simple sequence repeat (SSR), 1385 diversity array technology (DArT), and 28 amplified fragment length polymorphism (AFLP) markers covering 2397 cM with a mean distance between two markers of 4.1 cM. Comparative analysis with wheat consensus maps revealed that triticale chromosomes of the A and B genomes were represented by 15 chromosomes, including combinations of 2AS.2AL#, 2AL#2BL, 6AS.6AL#, and 2BS.6AL# instead of 2A, 2B, and 6A. In respect to published maps of rye, substantial rearrangements were found also for chromosomes 1R, 2R, and 3R of the rye genome. Chromosomes 1R and 2R were truncated and the latter was linked with 3R. A nonhomogeneous distribution of markers across the triticale genome was observed with evident bias (48%) towards the rye genome. This genetic map may serve as a reference linkage map of triticale for efficient studies of structural rearrangements, gene mapping, and marker-assisted selection.     

Synthesizing double haploid hexaploid wheat populations based on a spontaneous alloploidization process

Doubled haploid (DH) populations are useful to scientists and breeders in both crop improvement and basic research. Current methods of producing DHs usually need in vitro culture for extracting haploids and chemical treatment for chromosome doubling. This report describes a simple method for synthesizing DHs (SynDH) especially for allopolyploid species by utilizing meiotic restitution genes. The method involves three steps: hybridization to induce recombination, interspecific hybridization to extract haploids, and spontaneous chromosome doubling by selfing the interspecific F1s. DHs produced in this way contain recombinant chromosomes in the genome(s) of interest in a homogeneous background. No special equipment or treatments are involved in the DH production and it can be easily applied in any breeding and/or genetic program. Triticum turgidum L. and Aegilops tauschii Coss, the two ancestral species of common wheat (Triticum aestivum L.) and molecular markers were used to demonstrate the SynDH method.     

小麦A/B染色体组SSR标记在新小麦合成前后的比较研究

微卫星分子标记已广泛用于普通小麦遗传和进化研究。由于人工合成小麦与小麦品种之间存在高的遗传多样性,人工合成小麦已被大量应用于小麦分子标记工作中。但是,目前还缺乏人工合成小麦的异源六倍化过程对微卫星影响的研究。本研究直接比较了四倍体小麦与节节麦远缘杂交并经染色体加倍获得人工合成小麦前后,位于普通小麦A/B染色体组不同染色体臂上的66个特异引物揭示的微卫星位点的保守性和可转移性。结果表明,除了一个引物在新合成小麦中扩增出供体亲本没有的新带,一个引物在节节麦扩增出的产物在新合成小麦中消失,其他的所有微卫星引物的扩增产物在小麦合成前后是保守的,没有变异发生。所有的引物能够在四倍体小麦中扩增出微卫星产物,四倍体小麦中的扩增产物也出现在新的人工合成小麦中;有70%的引物能够在节节麦扩增出产物,其中的绝大多数产物也出现在新的人工合成小麦中。因此,普通小麦A/B染色体组的这些微卫星引物除了在人工合成小麦的A/B染色体组中扩增出产物,还能在其D染色体组中扩增出产物,也就是说,这些引物对人工合成小麦而言,并非是A/B染色体组特异的。根据该研究结果,讨论了小麦微卫星的可转移性和特异性问题,重点讨论了在应用人工合成小麦构建的遗传群体进行微卫星分子标记中的应用价值及其应该注意的问题。     

Extension of the Messapia x dicoccoides linkage map of Triticum turgidum (L.) Thell

A set of recombinant inbred lines (RIL) derived from a cross between the cultivar Messapia of durum wheat (Triticum turgidum var. durum) and the accession MG4343 of T. turgidum var. dicoccoides was analysed to increase the number of assigned markers and the resolution of the previously constructed genetic linkage map. An updated map of the durum wheat genome consisting of 458 loci was constructed. These loci include 261 Restriction Fragment Length Polymorphisms (RFLPs), 91 microsatellites (Simple Sequence Repeats, SSRs), 87 Amplified Fragment Length Polymorphisms (AFLPs), two ribosomal genes, and nine biochemical (seven seed storage proteins and two isozymes) and eight morphological markers. The loci were mapped on all 14 chromosomes of the A and B genomes, and covered a total distance of 3038.4 cM with an average distance of 6.7 cM between adjacent markers. The molecular markers were evenly distributed between the A and the B genomes (240 and 218 markers, respectively). An additional forty loci (8.8%) could not be assigned to a specific linkage group. A fraction (16.4%) of the markers significantly deviated from the expected Mendelian ratios; clusters of loci showing distorted segregation were found on the 1B, 2A, 2B, 3A, 4A, 7A and 7B chromosomes. The genetic lengths of the chromosomes range from 148.8 cM (chromosome 6B) to 318.0 cM (chromosome 2B) and approximately concur with their physical lengths. Chromosome 2B has the largest number of markers (47), while the chromosomes with the fewest markers are 3A and 6B (23). There are two gaps larger than 40 cM on chromosomes 2A and 3B. The durum wheat map was compared with the published maps of bread and durum wheats; the order of most common RFLP and SSR markers on the 14 chromosomes of the A and B genomes were nearly identical. A core-map can be extracted from the high-density Messapia x dicoccoides map and a subset of uniformly distributed markers can be used to detect and map quantitative trait loci.     

High segregation distortion in maize B73 x teosinte crosses

Two genetic linkage maps of cultivated maize inbred lines and teosinte species were constructed. One population comprised 81 F(2) individuals derived from a cross between maize inbred line B73 and Zea mays ssp parviglumis, while the second consisted of 63 backcross individuals from a cross of maize inbred line B73 with Z. mays ssp diploperennis. In the B73 x Z. mays ssp parviglumis F(2) population, 172 simple sequence repeat (SSR) markers were mapped to 10 chromosomes, which covered 2210.8 cM. In the B73 x Z. mays ssp diploperennis backcross population, 258 SSR markers were mapped to 10 chromosomes, covering 1357.7 cM. Comparison of the two maps revealed that the total map length of Z. mays ssp diploperennis covers 1357.7 cM, which is about 61.4% of that of Z. mays ssp parviglumis (2210.8 cM). Extensive segregation distortion regions were found on chromosomes 1, 2, 3, 5, 6, 7, and 10 in the B73 x Z. mays ssp parviglumis F(2) population and on chromosomes 1-5 and 8-10 in the B73 x Z. mays ssp parviglumis backcross population. Segregation distortion analysis confirmed that the segregation distortion ratio in the interspecific population B73 x Z. mays ssp diploperennis was higher than in B73 x Z. mays ssp parviglumis. We found that the recombination distances are highly variable in these genetic crosses between cultivated and wild species of maize.     

水稻籼粳杂种生殖障碍的基因定位分析

籼稻(Oryza sativa L.ssp.indica)与粳稻(O.sativa ssp.japonica)杂交优势明显但存在生殖隔离。生殖障碍主要表现为胚囊败育、花粉败育、开花时花药不开裂和雌雄异熟。应用具有137个标记位点的籼、粳杂交(“窄叶青8号”/“京系17”)F_1花药培养获得的127个双单倍体(DH)群体构建的RFLP图谱,对控制籼、粳杂种小穗败育的基因座位进行了定位研究。结果在第1、3、4、5、6、7、8、12染色体上检测到10个基因座位,其中第3、12染色体上的2个不育基因位点stj-3和stj-12与同一杂交组合F_2分离群体中发现的异常分离热点处于相同的染色体区段。Ssj-6的基因加性效应为负值,有增加籼、粳亲和性的作用;其余的不育基因座位皆有增加籼、粳杂种不育性的作用。     

Development of a high density integrated reference genetic linkage map for the multinational Brassica rapa Genome Sequencing Project

We constructed a high-density Brassica rapa integrated linkage map by combining a reference genetic map of 78 doubled haploid lines derived from Chiifu-401-42?× Kenshin (CKDH) and a new map of 190 F2 lines derived from Chiifu-401-42?× rapid cycling B. rapa (CRF2). The integrated map contains 1017 markers and covers 1262.0 cM of the B. rapa genome, with an average interlocus distance of 1.24 cM. High similarity of marker order and position was observed among the linkage groups of the maps with few short-distance inversions. In total, 155 simple sequence repeat (SSR) markers, anchored to 102 new bacterial artificial chromosomes (BACs) and 146 intron polymorphic (IP) markers were mapped in the integrated map, which would be helpful to align the sequenced BACs in the ongoing multinational Brassica rapa Genome Sequencing Project (BrGSP). Further, comparison of the B. rapa consensus map with the 10 B. juncea A-genome linkage groups by using 98 common IP markers showed high-degree colinearity between the A-genome linkage groups, except for few markers showing inversion or translocation. Suggesting that chromosomes are highly conserved between these Brassica species, although they evolved independently after divergence. The sequence information coming out of BrGSP would be useful for B. juncea breeding. and the identified Arabidopsis chromosomal blocks and known quantitative trait loci (QTL) information of B. juncea could be applied to improve other Brassica crops including B. rapa.     

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.     

QTL analysis: unreliability and bias in estimation procedures

Several statistical methods which employ multiple marker data are currently available for the analysis of quantitative trait loci (QTL) in experimental populations. Although comparable estimates of QTL location and effects have been obtained by these methods, using simulated and real data sets, their accuracy and reliability have not been extensively investigated. The present study specifically examines the merit of using F₂ and doubled haploid populations for locating QTL and estimating their effects. Factors which may affect accuracy and reliability of QTL mapping, such as the number and position of the markers available, the accuracy of the marker locations and the size of the experimental population used, are considered. These aspects are evaluated for QTL of differing heritabilities and locations along the chromosome.A population of 300 F₂ individuals and 150 doubled haploid lines gave estimates of QTL position and effect which were comparable, albeit extremely unreliable. Even for a QTL of high heritability (10%), the confidence interval was 35 cM. There was little increase in reliability to be obtained from using 300, rather than 200, F₂ individuals and 100 doubled haploid lines gave similar results to 150. QTL estimates were not significantly improved either by using the expected, rather than the observed, marker positions or by using a dense map of markers rather than a sparse map. A QTL which was asymmetrically located in the linkage group resulted in inaccurate estimates of QTL position which were seriously biassed at low heritability of the QTL. In a population of 300 F₂ individuals the bias increased from 4 cM to 20 cM, for a QTL with 10% and 2% heritability respectively.     

Characterization of quantitative trait loci controlling genetic variation for preharvest sprouting in synthetic backcross-derived wheat lines

Aegilops tauschii, the wild relative of wheat, has stronger seed dormancy, a major component of preharvest sprouting resistance (PHSR), than bread wheat. A diploid Ae. tauschii accession (AUS18836) and a tetraploid (Triticum turgidum L. ssp. durum var. Altar84) wheat were used to construct a synthetic wheat (Syn37). The genetic architecture of PHS was investigated in 271 BC(1)F(7) synthetic backcross lines (SBLs) derived from Syn37/2*Janz (resistant/susceptible). The SBLs were evaluated in three environments over 2 years and PHS was assessed by way of three measures: the germination index (GI), which measures grain dormancy, the whole spike assay (SI), which takes into account all spike morphology, and counted visually sprouted seeds out of 200 (VI). Grain color was measured using both Chroma Meter- and NaOH-based approaches. QTL for PHSR and grain color were mapped and their additive and epistatic effects as well as their interactions with environment were estimated by a mixed linear-model approach. Single-locus analysis following composite interval mapping revealed four QTL for GI, two QTL for SI, and four QTL for VI on chromosomes 3DL and 4AL. The locus QPhs.dpiv-3D.1 on chromosome 3DL was tightly linked to the red grain color (RGC) at a distance of 5 cM. The other locus on chromosome 3D, "QPhs.dpiv-3D.2" was independent of RGC locus. Two-locus analysis detected nine QTL with main effects and 18 additive x additive interactions for GI, SI, and VI. Two of the nine main effects QTL and two epistatic QTL showed significant interactions with environments. Both additive and epistatic effects contributed to phenotypic variance in PHSR and the identified markers are potential candidates for marker-assisted selection of favorable alleles at multiple loci. SBLs derived from Ae. tauschii proved to be a promising tool to dissect, introgress, and pyramid different PHSR genes into adapted wheat genetic backgrounds. The enhanced expression of PHS resistance in SBLs enabled us to develop white PHS-resistant wheat germplasm from the red-grained Ae. tauschii accession.     

Isolation and mapping of microsatellite markers specific for the D genome of bread wheat.

The potential of Aegilops tauschii, the diploid progenitor of the D genome of wheat, as a source of microsatellite markers for hexaploid bread wheat was investigated. By screening lambda phage and plasmid libraries of Ae. tauschii genomic DNA, dinucleotide microsatellites containing GA and GT motifs were isolated and a total of 65 functional microsatellite markers were developed. All primer pairs that were functional in Ae. tauschii amplified well in hexaploid wheat. Fifty-five loci amplified by 48 primer sets were placed onto a genetic framework map of the reference population of the International Triticeae Mapping Initiative (ITMI) 'Opata 85' x 'W7984'. The majority of microsatellite markers could be assigned to the chromosomes of the D genome of wheat. The distribution of the markers along the chromosomes is random. Chromosomal location of 22 loci nonpolymorphic in the reference population was determined using nullitetrasomic lines of Triticum aestivum 'Chinese Spring'. The results of this study demonstrate the value of microsatellite markers isolated from Ae. tauschii for the study of bread wheat. The microsatellite markers developed improve the existing wheat microsatellite map and can be used in a wide range of genetic studies and breeding programs.     

Mapping of QTLs for androgenetic response based on a molecular genetic map of x Triticosecale Wittmack.

Quantitative trait loci (QTLs) for androgenetic response were mapped in a doubled haploid (DH) population derived from the F1 hybrid of 2 unrelated varieties of triticale, 'Torote' and 'Presto'. A molecular marker linkage map of this cross was previously constructed using 73 DH lines. This map contains 356 markers (18 random amplified 5 polymorphic DNA, 40 random amplified microsatellite polymorphics, 276 amplified fragment length polymorphisms, and 22 simple sequence repeats) and was used for QTL analysis. The genome was well covered, and of the markers analysed, 336 were located in 21 linkage groups (81.9%) identified using SSR markers. The map covered a total length of 2465.4 cM with an average of 1 marker for each 6.9 cM. The distribution of the markers was not homogeneous across the 3 genomes, with 50.7% detected in the R genome. Several QTLs were found for the following variables related to the androgenetic response: number of embryos/100 anthers; plants regenerated from 100 embryos; number of green plants/total number of plants; and number of green plants/1000 anthers. Two were detected on chromosome 6B and 4R, which together had a 30% total influence on the induction of embryos. Another was found on 6B and on the unidentified LG1; these influenced the production of total plants from haploid embryo cultures. One QTL on chromosome 3R determined the photosynthetic viability of the haploid plantlets regenerated from microspores. Other QTLs were found on chromosomes 1B, 1R, 4R, and 7R, which helped the control of the final androgenetic response (the number of plantlets obtained for every 1000 anthers cultured).     

Retention of D genome chromosomes in pentaploid wheat crosses

The transfer of genes between Triticum aestivum (hexaploid bread wheat) and T. turgidum (tetraploid durum wheat) holds considerable potential for genetic improvement of both these closely related species. Five different T. aestivum/T. turgidum ssp. durum crosses were investigated using Diversity Arrays Technology (DArT) markers to determine the inheritance of parental A, B and D genome material in subsequent generations derived from these crosses. The proportions of A, B and D chromosomal segments inherited from the hexaploid parent were found to vary significantly among individual crosses. F(2) populations retained widely varying quantities of D genome material, ranging from 99% to none. The relative inheritance of bread wheat and durum alleles in the A and B genomes of derived lines also varied among the crosses. Within any one cross, progeny without D chromosomes in general had significantly more A and B genome durum alleles than lines retaining D chromosomes. The ability to select for and manipulate this non-random segregation in bread wheat/durum crosses will assist in efficient backcrossing of selected characters into the recurrent durum or hexaploid genotype of choice. This study illustrates the utility of DArT markers in the study of inter-specific crosses to commercial crop species.     

Molecular mapping of wheat. Homoeologous group 2.

A molecular-marker map of bread wheat having many markers in common with other grasses in the Gramineae family is a prerequisite for molecular level genetic studies and breeding in this crop species. We have constructed restriction fragment length polymorphism maps of the A-, B-, and D-genome chromosomes of homoeologous group 2 of hexaploid wheat (Triticum aestivum L. em. Thell) using 114 F7 lines from a synthetic x bread wheat cross and clones from 11 libraries. Chromosomes 2A, 2B, and 2D comprise 57, 60, and 56 markers and each spans about 200 cM. Comparisons between chromosomes are facilitated by 26 sets of homoeoloci. Genes mapped include a heterologous abscisic acid responsive locus cloned as pBS128, the epidermal waxiness inhibitor W21, and two presumed leaf rust and stem rust resistance genes. Anomalies suggesting ancestral rearrangements in chromosome 2B are pointed out and features of wheat group 2 chromosomes that are common to barley (Hordeum vulgare L.), rice (Oryza spp.), and T. tauschii are discussed.     

The construction of a genetic linkage map of non-heading Chinese cabbage （Brassica campestris ssp. chinensis Makino）

Non-heading Chinese cabbage （Brassica carnpestris ssp. chinensis Makino） is one of the most important vegetables in eastern China. A genetic linkage map was constructed using 127 doubled haploid （DH） lines, and the DH population was derived from a commercial hybrid ＂Hanxiao＂ （lines SW-13 x L-118）. Out of the 614 polyrnorphic markers, 43.49% were not assigned to any of the linkage groups （LGs）. Chi-square tests showed that 42.67% markers were distorted from expected Mendelian segregation ratios, and the direction of distorted segregation was mainly toward the paternal parent L-118. After sequentially removing the markers that had an interval distance smaller than 1 cM from the upper marker, the overall quality of the linkage map was increased. Two hundred and sixty-eight molecular markers were mapped into 10 LGs, which were anchored to the corresponding chromosome of the B. rapa reference map based on com- mon simple sequence repeat （SSR） markers. The map covers 973.38 cM of the genome and the average interval distance between markers was 3.63 cM. The number of markers on each LG ranged from 18 （R08） to 64 （R07）, with an average interval distance within a single LG from 1.70 cM （R07） to 6.71 cM （R06）. Among these mapped markers, 169 were sequence-related amplified polymorphism （SRAP） molecular markers, 50 were SSR markers and 49 were random amplification polymorphic DNA （RAPD） markers. With further saturation to the LG9 the current map offers a genetic tool for loci analysis for important agronomic traits.     

An intervarietal molecular marker map in Triticum aestivum L. Em. Thell. and comparison with a map from a wide cross

 An intervarietal molecular marker map covering most of the nuclear genome was developed in Triticum aestivum. One hundred and six androgenetic-derived doubled haploid lines obtained from the F₁ between monosomics of ‘Chinese Spring’ and ‘Courtot’ were analysed for genetic mapping. The map covered 18 of the 21 chromosomes with an identical distribution of markers in the A and B genome, and only small segments of the D genome. Distorted markers were mapped using Bailey’s 2-point method and revealed skewed regions on 1A, 1DS, 2A, 2B, 4AS and 6B. Comparison with a wide cross [‘Opata’×Synthetic hexaploid (T. tauschii/‘Altar 84’)] showed colinearity for markers on homologous chromosomes, but revealed a large proportion (25%) of markers mapped on non-homoeologous chromosomes, i. e. heterologous markers. The origin of the material and distortion segregation are discussed with particular emphasis on investigations of D-genome markers. Received: 2 May 1996 / Accepted: 2 August 1996