Radiation-induced translocations with reduced Haynaldia villosa chromatin at the Pm21 locus for powdery mildew resistance in wheat

Haynaldia villosa Schur. (syn. Dasypyrum villosum Candargy, 2n = 2x = 14, genome VV), a species related to wheat, is highly resistant to powdery mildew. The powdery mildew resistance gene Pm21 from H. villosa was introduced into common wheat by means of a translocation line T6VS·6AL, where the 6VS chromosome arm of H. villosa was joined at the centromere with wheat chromosome arm 6AL. To develop small alien translocations, especially interstitial translocations of small alien chromosome segments, we irradiated mature female gametes of a T6VS·6AL translocation line with gamma rays. More than 20 new translocations and deletions of 6V chromatin were obtained and subsequently used to map Pm21. Pm21 was located in a small region (FL 0.45–0.58) by genomic in situ hybridization, molecular marker analysis, and powdery mildew response. Two homozygous translocation lines with small H. villosa chromosome fragments carrying Pm21 were identified by fluorescence in situ hybridization and molecular marker analysis: an interstitial translocation in which a small fragment of 6VS is inserted into chromosome 4B and a terminal translocation with a small fragment of 6VS inserted into 1A. These small alien translocations are being transferred into an adapted elite wheat background by backcrossing to allow their easy use in breeding programs.     

Chromosomal location of a Triticum timopheevii--derived powdery mildew resistance gene transferred to common wheat.

A dominant powdery mildew resistance gene introduced from Triticum timopheevii in line 146-155-T of common wheat, Triticum aestivum, was located on chromosome 6B by monosomic analysis. Restriction fragment length polymorphism (RFLP) and microsatellite analyses detected the presence of a T. timopheevii segment, translocated to chromosome 6B, with breakpoints between the loci Xpsr8/Xpsr964 on 6BS and Xpsr154/Xpsr546 on 6BL. The novel powdery mildew resistance gene, which has been designated Pm27, was shown to cosegregate with the microsatellite locus Xpsp3131, which is located on the introgressed T. timopheevii segment. The molecular data confirm the location of Pm27 on the translocated 6B chromosome.     

Genetics and molecular mapping of a male fertility restoration locus (Rfg1) in rye (Secale cereale L.)

 A gene determining the restoration of cytoplasmic genic male sterility (CMS) caused by the Gülzow (G)-type cytoplasm was mapped by analyzing an F₂ and F₃ population comprising 140 and 133 individual plants, respectively. The target gene, designated Rfg1, was mapped on chromosome 4RL distally to three RFLP (Xpsr119, Xpsr167, Xpsr899) and four RAPD (XP01, XAP05, XR11, XS10) loci. Xpsr167 and Xpsr899 are known to be located on the segment of chromosome 4RL which was ancestrally translocated and is homoeologous to the distal end of other Triticeae 6S chromosomes. It is suggested that Rfg1 may be allelic to the gene determining the restoration of rye CMS caused by the Pampa (P) cytoplasm (chromosome 4RL) and to Rfc4 that on rye addition lines of chromosome 4RL restores male fertility of hexaploid wheat with T. timopheevi cytoplasm. Homoeoallelism to two loci for cytoplasmic-male-sterility restoration on chromosomes 6AS and 6BS in hexaploid wheat is also suggested. Received: 1 December 1997 / Accepted: 10 February 1998     

Structural rearrangement in chromosome 2M of Aegilops comosa has prevented the utilization of the Compair and related wheat-Ae. comosa translocations in wheat improvement

The genetic constitutions of chromosome 2M of Aegilops comosa and the derived wheat-Ae. comosa translocations were analyzed by molecular cytogenetic techniques. Hybridization of 15 RFLP markers covering the entire length of the group-2 chromosomes revealed that chromosome 2M was structurally rearranged compared to the homoeologous chromosomes of wheat by either a pericentric inversion or a terminal intrachromosomal translocation. The breakpoint of the rearrangement was located in a region between the loci Xpsr131 and Xcdo405, resulting in the translocation of 47% of 2MS to 2ML. This aberrant structure of 2M allowed homoeologous recombination between 2M and its wheat counterpart only in the translocated segment on 2ML. C-banding and genomic in situ hybridization analyses confirmed that all translocation chromosomes consisted of the complete 2MS arm, a large part of 2ML, and very small distal segments derived from 2AS or 2DS, as expected from the aberrant structure of chromosome 2M. Thus, the translocation in the line 2A-2M?4/2 can be described as T2AS-2M?1L???2M?1S and the translocations in the lines Compair and 2D-2M?3/8 as T2DS-2M?1L???2M?1S. RFLP analysis determined the breakpoints in these translocation chromosomes to be within the telomeric 16% of the wheat chromosome arms. The breakpoint of the 2A/2M translocation was between Xbcd348 and Xcdo783, and that of the 2D/2M translocation was between Xcdo783 and Xpsr666. Because the translocation chromosomes retain the structural aberration found in chromosome 2M, further exploitation of the wheat-Ae. comosa translocations for cultivar improvement is questionable.     

Mapping of esterase loci in <Emphasis Type="Italic">Aegilops uniaristata</Emphasis> and homoeologous group 3 chromosomes of wheat

This study was planned to identify the chromosomal location of esterase loci in wheat (Triticum aestivum), in comparison to Aegilops uniaristata, using wheat Ae. uniaristata disomic addition and translocation lines. Two loci (Est-N1 and Est-N8) were identified on 3N chromosome of Ae. uniaristata and their probable homoeoloci were, for the first time, mapped close to three RFLP probes (Xpsr56, Xpsr394, and Xpsr1196) on homoeologous group 3 wheat chromosomes.     

RFLP mapping of the vernalization (Vrn1) and frost resistance (Fr1) genes on chromosome 5A of wheat

A population of single chromosome recombinant lines was developed from the cross between a frost-sensitive, vernalization-insensitive substitution line, ‘Chinese Spring’ (Triticum spelta 5A) and a frost-tolerant, vernalization-sensitive line, ‘Chinese Spring’ (‘Cheyenne’ 5A), and used to map the genes Vrn1 and Fr1 controlling vernalization requirement and frost tolerance, respectively, relative to RFLP markers located on this chromosome. The Vrn1 and Fr1 loci were located closely linked on the distal portion of the long arm of 5AL, but contrary to previous observations, recombination between them was found. Three RFLP markers, Xpsr426, Xcdo504 and Xwg644 were tightly linked to both. The location of Vrn1 suggests that it is homoeologous to other spring habit genes in related species, particularly the Sh2 locus on chromosome 7 (5H) of barley and the Sp1 locus on chromosome 5R of rye.     

小麦—簇毛麦染色体代换系、易位系特异蛋白组分的双向电泳比较分析

利用双向电泳技术,对栽培小麦(AABBDD)、染色体代换系(6V/6A)、易位系(6VS/6AL)、(6VS/6DL)和簇毛麦(VV)的叶片全蛋白进行了比较研究。在栽培小麦、代换系和两个易位系中检测到超过350个蛋白组分,它们的分子量范围是10~110 KD,等电点在4.5～8.6之间。栽培小麦、6V/6A、6VS/6AL、与6VS/6DL之间的双向电泳谱型极为相似,但与簇毛麦不同。在代换系、两个易位系和簇毛麦中检测到了特异蛋白组分16 KD/pI5.0,而在栽培小麦中未检测到该组分,这些结果表明16 KD/pI5.0蛋白可能定位于簇毛麦V染色体短臂上。     

Comparative molecular mapping of GA insensitive Rht loci on chromosomes 4B and 4D of common wheat (Triticum aestivum L.)

 The two GA-insensitive dwarfing gene loci Rht-B1 and Rht-D1 were mapped using three F₂ populations, segregating for Rht-B1c (Rht3), Rht-D1b (Rht2) or Rht-D1c (Rht10). Rht-B1c was mapped on chromosome 4BS in the centromere region, distal and closely linked to the RFLP markers Xpsr144 (11.9 cM) and Xpsr584 (17.8 cM), but proximal to Xmwg634 (30 cM). Rht-D1c, however, was found to be closely linked to the distally located markers Xpsr921 (0.8 cM) and Xmwg634 (1.5 cM). The homoeologous relationships between the GA-insensitive dwarfing genes within the Triticeae are discussed. Received: 2 May 1997 / Accepted: 9 June 1997     

Suppressed recombination rate in 6VS/6AL translocation region carrying the Pm21 locus introgressed from Haynaldia villosa into hexaploid wheat

Pm21 is an effective gene for powdery mildew resistance transferred from Haynaldia villosa into common wheat cultivars. No virulence against this gene has been detected so far. A set of 42 powdery mildew isolates collected in Israel and tested in the current study also revealed no virulence against this gene. Pm21 was previously reported to be located on the short arm of 6VS/6AL translocation chromosome. We constructed a high-density genetic map of chromosome 6A, consisting of 28 PCR markers and the Pm21 gene. A comparison with previously published genetic maps of wheat chromosome 6A revealed that the recombination rate in the 6VS/6AL translocation region was poor. We assume that suppressed recombination caused by the alien H. villosa genetic material is the most reasonable explanation for the tight genetic linkage and the inadequacy between the Pm21 genetic map and the Pm21 physical map of 6A. A large number of sequence-tag sites (STS) and simple sequence repeat markers, which co-segregate with or are closely linked to the Pm21 gene, and the conversion of three resistance gene analog markers into new STS markers, provide a reliable and easy-to-use molecular tool for marker-assisted selection of Pm21 in wheat breeding programs. An additional gene, Pm31, previously reported to be derived from Triticum dicoccoides, was mapped into a similar genomic location to Pm21. Screening of the parental lines and the mapping population with Pm21 diagnostic markers clearly confirmed that the donor line of Pm31 is H. villosa and not T. dicoccoides. Therefore, we conclude that Pm21 and Pm31 refer to the same gene, derived from H. villosa, and that the designation of Pm31 as a new Pm gene was erroneous.     

Physical mapping of restriction fragment length polymorphism (RFLP) markers in homoeologous groups 1 and 3 chromosomes of wheat by in situ hybridization.

Using wheat ditelosomic lines and in situ hybridization of biotin-labelled DNA probes, 18 restriction fragment length polymorphism (RFLP) markers were physically located on homoeologous groups 1 and 3 chromosomes of wheat. Most of the markers hybridized to chromosome arms in a physical order concordant with the genetic maps. A majority of the markers studied were clustered in non-C-banded, distal euchromatic areas, indicating the presence of recombination hot spots and cold spots in those regions. However, on IBS the markers were well dispersed, which could be due to the abundance of heterochromatin throughout the arm. An inversion between Xpsr653 and Xpsr953 was observed on 1AL. One new Xpsr688 locus, approximately 20-26% from the centromere, was found on 1AS and 1BS. The physical location of Xpsr170 on group 3 chromosomes probably represents an alternative to the loci on the genetic map. Finally, Xpsr313 was mapped to two physical loci on IDL. Five markers were located to bins consistent with the deletion-based physical maps.     

The distribution of RFLP markers on chromosome 2(2H) of barley in relation to the physical and genetic location of 5S rDNA

The 5S rDNA locus on the long arm of barley chromosome 2(2H) was genetically mapped in two crosses in relation to 30 other RFLP loci. Comparison of the genetic maps with the previously published physical position of the 5S rDNA, determined by in-situ hybridization, showed that there was a marked discrepancy between physical and genetic distance in both crosses, with recombination being less frequent in the proximal part of the arm. Pooled information from the present study and other published genetic maps showed that at least 26 of the 44 (59%) RFLPs that have been mapped on 2(2H)L lie distal to the 5S rDNA locus even though this region is only 27% of the physical length of the arm. The distribution of RFLP markers is significantly different from expected (P < 0.01), implying that the low-copy sequences used for RFLP analysis occur more frequently in distal regions of the arm and, or, that sequences in distal regions are more polymorphic.     

Multiple genetic pathways for seed shattering in the grasses

Shattering is an essential seed dispersal mechanism in wild species. It is believed that independent mutations at orthologous loci led to convergent domestication of cereal crops. To investigate genetic relationships of Triticeae shattering genes with those of other grasses, we mapped spike-, barrel- (B-type), and wedge-type (W-type) spikelet disarticulation genes in wheat and its wild relatives. The Br1 gene for W-type disarticulation was mapped to a region delimited by Xpsr598 and Xpsr1196 on the short arm of chromosomes 3A in Triticum timopheevii and 3S in Aegilops speltoides. The spike- and W-type disarticulation genes are allelic at Br1 in Ae. speltoides. The B-type disarticulation gene, designated as Br2, was mapped to an interval of 4.4 cM between Xmwg2013 and Xpsr170 on the long arm of chromosome 3D in Aegilops tauschii, the D-genome donor of common wheat. Therefore, B- and W-type disarticulations are governed by two different orthologous loci on group-3 chromosomes. Based on map position, orthologs of Br1 and Br2 were not detected in barley, maize, rice, and sorghum, indicating multiple genetic pathways for shattering in grasses. The implications of the mapping results are discussed with regard to the evolution of polyploid wheat and domestication of cereals.Supplementary material is available in the online version of this article at     

Molecular genetic mapping of <Emphasis Type="Italic">Gby</Emphasis>, a new greenbug resistance gene in bread wheat

The greenbug, Schizaphis graminum (Rhodani), is one of the major insect pests of wheat worldwide and it is important to develop a basic understanding of the chromosomal locations of known and new greenbug resistance genes. Gby is a new greenbug resistance gene in the wheat line Sandos selection 4040. A mapping population used in this study was derived from a cross of Sandos 4040 and PI220127, a greenbug susceptible wheat land race from Afghanistan. A progeny test indicated that Gby is inherited as a single semi-dominant gene. A genetic linkage map consisting of Gby, Xgwm322 (a wheat microsatellite marker), XksuD2 (an STS marker) and 18 restriction fragment length polymorphism (RFLP) loci was constructed. We used DNA from Chinese Spring 7A deletion lines to show that the gwm332 and ksuD2 amplified fragments mapped in this study are located on a long arm of chromosome 7A. This suggests that Gby is located on wheat chromosome 7A. Gby was mapped to the area in the middle of the island of putative defense response genes that are represented by RFLP markers (Xpsr119, XZnfp, Xbcd98 and Pr1b) previously mapped to the distal part of the short arm of wheat chromosome group 7. This region of chromosome 7A is characterized by a high recombination rate and a high physical density of markers which makes Gby a very good candidate for map-based cloning. The selection accuracy when the RFLP markers Xbcd98, Xpsr119 or XZnfp and Pr1b flanking Gby are used together to tag Gby is 99.78%, suggesting that they can be successfully used in marker assisted selection.     

High-density genetic and physical bin mapping of wheat chromosome 1D reveals that the powdery mildew resistance gene <Emphasis Type="Italic">Pm24</Emphasis> is located in a highly recombinogenic region

Genetic maps of wheat chromosome 1D consisting of 57 microsatellite marker loci were constructed using Chinese Spring (CS) × Chiyacao F₂ and the International Triticeae Mapping Initiative (ITMI) recombinant inbred lines (RILs) mapping populations. Marker order was consistent, but genetic distances of neighboring markers were different in two populations. Physical bin map of 57 microsatellite marker loci was generated by means of 10 CS 1D deletion lines. The physical bin mapping indicated that microsatellite marker loci were not randomly distributed on chromosome 1D. Nineteen of the 24 (79.2%) microsatellite markers were mapped in the distal 30% genomic region of 1DS, whereas 25 of the 33 (75.8%) markers were assigned to the distal 59% region of 1DL. The powdery mildew resistance gene Pm24, originating from the Chinese wheat landrace Chiyacao, was previously mapped in the vicinity of the centromere on the short arm of chromosome 1D. A high density genetic map of chromosome 1D was constructed, consisting of 36 markers and Pm24, with a total map length of 292.7 cM. Twelve marker loci were found to be closely linked to Pm24. Pm24 was flanked by Xgwm789 (Xgwm603) and Xbarc229 with genetic distances of 2.4 and 3.6 cM, respectively, whereas a microsatellite marker Xgwm1291 co-segregated with Pm24. The microsatellite marker Xgwm1291 was assigned to the bin 1DS5-0.70-1.00 of the chromosome arm 1DS. It could be concluded that Pm24 is located in the ‘1S0.8 gene-rich region’, a highly recombinogenic region of wheat. The results presented here would provide a start point for the map-based cloning of Pm24.     

RFLP-based maps of the homoeologous group-6 chromosomes of wheat and their application in the tagging of Pm12, a powdery mildew resistance gene transferred from Aegilops speltoides to wheat

Genetic maps of the homoeologous group-6 chromosomes of bread wheat, Triticum aestivum, have been constructed spanning 103 cM on 6A, 90 cM on 6B and 124 cM on 6D. These maps were transferred to a Chinese Spring (CS) x line #31 cross to locate a dominant powdery mildew resistance gene, Pm12, introgressed into line #31 from Aegilops speltoides. Pm12 was shown to lie on the short arm of translocation chromosome 6BS-6SS.6SL in line #31, but could not be mapped more precisely due to the lack of recombination between the 6S Ae. speltoides segment and chromosome 6B. Possible strategies to reduce the size of the alien segment, which probably encompasses the complete long arm and more than 82% of the short arm of chromosome 6B, are discussed.     

A physical map of the Thinopyrum-derived Lr19 translocation.

Twenty-nine lines with deletions in the Lr19 ('Indis') translocated chromosome segment were used to physically map three Thinopyrum RFLP loci as well as the Sr25 and Sd1 loci. From the data, the relative locations of marker loci on the translocation were determined as: Sd1, Xpsr165, Xpsr105, Xps129, Lr19, Wsp-D1, Sr25/Y. The data confirmed the reported homoeology between the Lr19 segment and chromosome arm 7DL of wheat. Also, it seems that the Lr19 translocation in 'Indis' is very similar to the Lr19 segment in the T4 source and that the former may not derive from Thinopyrum distichum. Key words : deletion mapping, leaf rust resistance.     

Genetic mapping of the powdery mildew resistance gene Pm6 in wheat by RFLP analysis

Pm6 in bread wheat (Triticum aestivum L.), which was transferred from Triticum. timopheevii L., is a gene conferring resistance to the powdery mildew disease caused by Erysiphe graminis f. sp. tritici. Six near-isogenic lines ( NILs ) of Pm6 in a cultivar ’Prins’ background were analyzed to map this gene using restriction fragment length polymorphism (RFLP). Each of the six NILs possessed a T. timopheevii-derived segment, varying in length, and associated with powdery mildew resistance. Lines IGV1–465 (FAO163b/ 7*Prins) and IGV1–467 (Idaed 59B/7*Prins) had the shortest introgressed segments, which were detected only by DNA probes BCD135 and PSR934, respectively. The polymorphic loci detected by both probes were mapped to the long arm of chromosome 2B. Lines IGV1–458 (CI13250/7*Prins) and IGV1–456 (CI12559/8*Prins) contained the longest T. timopheevii segments involving both arms of donor chromosome 2G across the centromere. All these introgressed segments had an overlapping region flanked by the loci xpsr934 and xbcd135 on 2BL. Thus, Pm6 was located in this region since the powdery mildew resistance in all the NILs resulted from the introgressed fragments. Using the F₂ mapping population from a cross of IGV1–463 (PI170914/7*Prins)×Prins, Pm6 was shown to be closely linked to the loci xbcd135 and xbcd266 at a genetic distance of 1.6 cM and 4.8 cM, respectively. BCD135 was successfully used in detecting the presence of Pm6 in different genetic backgrounds. Received: 29 June 1999 / Accepted: 6 July 1999     

The development of PCR-based markers for the selection of eyespot resistance genes Pch1 and Pch2

Two eyespot resistance genes (Pch1 and Pch2) have been characterised in wheat. The potent resistance gene Pch1, transferred from Aegilops ventricosa, is located on the distal end of the long arm of chromosome 7D (7DL). Pch2 derives from the variety Cappelle Desprez and is located at the distal end of chromosome 7AL. The RFLP marker Xpsr121 and the endopeptidase isozyme allele Ep-D1b, are very closely linked to Pch1, probably due to reduced recombination in the region of the introgressed A. ventricosa segment. Pch2 is less closely linked to these markers but is thought to be closer to Xpsr121 than to Ep-A1b. In the present study simple sequence repeat (SSR) markers were integrated into the genetic map of a single chromosome (7D) recombinant (RVPM) population segregating for Pch1. Sequence-tagged-site (STS)-based assays were developed for Xpsp121 and a 7DL wheat EST containing a SSR. SSR markers Xwmc14 and Xbarc97 and the Xpsr121-derived marker co-segregated with Pch1 in the RVPM population. A single chromosome (7A) recombinant population segregating for Pch2 was screened for eyespot resistance and mapped using SSRs. QTL interval mapping closely associated Pch2 with the SSR marker Xwmc525.     

Homoeologous recombination-based transfer and molecular cytogenetic mapping of powdery mildew-resistant gene <Emphasis Type="Italic">Pm57</Emphasis> from <Emphasis Type="Italic">Aegilops searsii</Emphasis> into wheat

Key message

Pm57, a novel resistant gene against powdery mildew, was transferred into common wheat from Ae. searsi and further mapped to 2S ^s #1L at an interval of FL0.75 to FL0.87.

Abstract

Powdery mildew, caused by the fungus Blumeria graminis f. sp. tritici, is one of the most severe foliar diseases of wheat causing reduction in grain yield and quality. Host plant resistance is the most effective and environmentally safe approach to control this disease. Tests of a set of Chinese Spring–Ae. searsii (S^sS^s, 2n?=?2x?=?14) Feldman & Kislev ex K. Hammer disomic addition lines with a mixed isolate of the powdery mildew fungus identified a novel resistance gene(s), designed as Pm57, which was located on chromosome 2S^s#1. Here, we report the development of ten wheat–Ae. searsii recombinants. The wheat chromosomes involved in five of these recombinants were identified by FISH and SSR marker analysis and three of them were resistant to powdery mildew. Pm57 was further mapped to the long arm of chromosome 2S^s#1 at a fraction length interval of FL 0.75 to FL 0.87. The recombinant stocks T2BS.2BL-2S^s#1L 89-346 (TA5108) with distal 2S^s#1L segments of 28% and 89(5)69 (TA5109) with 33% may be useful in wheat improvement. The PCR marker X2L4g9p4/HaeIII was validated to specifically identify the Ae. searsii 2S^s#1L segment harboring Pm57 in T2BS.2BL-2S^s#1L against 16 wheat varieties and advanced breeding lines, and the development of more user-friendly KASP markers is underway.

     

Identification and mapping of a gene conferring resistance to the spot form of net blotch (Pyrenophora teres f maculata) in barley

 Spot form of net blotch (SFNB) (Pyrenophora teres f maculata) is an economically damaging foliar disease of barley in many of the world’s cereal growing areas. The development of SFNB-resistant cultivars may be accelerated through the use of molecular markers. A screen for SFNB resistance in 96 lines identified four new sources of resistance, including a feed variety, ‘Galleon’, for which a fully mapped doubled haploid population was available. Segregation data indicated SFNB resistance was conferred by a single gene in the ‘Galleon’בHaruna Nijo’ cross, positioned on the long arm of chromosome 7H. This gene is designated Rpt4 and is flanked by the RFLP loci Xpsr117(D) and Xcdo673 at distances of 6.9 cM and 25.9 cM, respectively. The marker Xpsr117(D) was validated using another population segregating for Rpt4, correctly predicting SFNB resistance with more than 90% accuracy. Received: 24 September 1998 / Accepted: 19 December 1998