H9, H10, and H11 compose a cluster of Hessian fly-resistance genes in the distal gene-rich region of wheat chromosome 1AS

H9, H10, and H11 are major dominant resistance genes in wheat, expressing antibiosis against Hessian fly [(Hf) Mayetiola destructor (Say)] larvae. Previously, H9 and H10 were assigned to chromosome 5A and H11 to 1A. The objectives of this study were to identify simple-sequence-repeat (SSR) markers for fine mapping of these genes and for marker-assisted selection in wheat breeding. Contrary to previous results, H9 and H10 did not show linkage with SSR markers on chromosome 5A. Instead, H9, H10, and H11 are linked with SSR markers on the short arm of chromosome 1A. Both H9 and H10 are tightly linked to flanking markers Xbarc263 and Xcfa2153 within a genetic distance of 0.3–0.5 cM. H11 is tightly linked to flanking markers Xcfa2153 and Xbarc263 at genetic distances of 0.3 cM and 1.7 cM. Deletion bin mapping assigned these markers and genes to the distal 14% of chromosome arm 1AS, where another Hf-resistance gene, Hdic (derived from emmer wheat), was also mapped previously. Marker polymorphism results indicated that a small terminal segment of chromosome 1AS containing H9 or H10 was transferred from the donor parent to the wheat lines Iris or Joy, and a small intercalary fragment carrying H11 was transferred from the resistant donor to the wheat line Karen. Our results suggest that H9, H10, H11, Hdic, and the previously identified H9- or H11-linked genes (H3, H5, H6, H12, H14, H15, H16, H17, H19, H28, and H29) may compose a cluster (or family) of Hf-resistance genes in the distal gene-rich region of wheat chromosome 1AS; and H10 most likely is the same gene as H9.Mention of commercial or proprietary product does not constitute an endorsement by the USDA.     

Hessian fly resistance genes <Emphasis Type="Italic">H16</Emphasis> and <Emphasis Type="Italic">H17</Emphasis> are mapped to a resistance gene cluster in the distal region of chromosome 1AS in wheat

Hessian fly [Mayetiola destructor (Say)] is one of the major insect pests of wheat (Triticum aestivum L.) worldwide. Hessian fly (Hf)-resistance genes H16 and H17 were reported to condition resistance to Hf biotype L that is prevalent in many wheat-growing areas of eastern USA, and both of them were previously assigned to wheat chromosome 5A by their linkage to H9. The objectives in this study were to (1) map H16 and H17 independent of their linkage with H9 and (2) identify DNA markers that co-segregate with H16 or H17, and that are useful for selection of these genes in segregating populations and to combine these genes with other Hf-resistance genes in wheat cultivars. Contrary to previously reported locations, H16 and H17 did not show linkage with the molecular markers on chromosome 5A. Instead, both of them are linked with the molecular markers on the short arm of chromosome 1A (1AS). The simple sequence repeat (SSR) marker Xpsp2999 and EST-derived SSR (eSSR) marker Xwem6b are two flanking markers that are linked to H16 at genetic distances of 3.7 and 5.5 cM, respectively. Similarly, H17 is located between markers Xpsp2999 and Xwem6b at genetic distances of 6.2 and 5.1 cM, respectively. Five other SSR and eSSR markers including Xcfa2153, Xbarc263, Xwem3a, Xwmc329, and Xwmc24 were also linked to H16 and H17 at close genetic distances. These closely linked molecular markers should be useful for pyramiding H16 and H17 with other Hessian fly resistance genes in a single wheat genotype. In addition, using Chinese Spring deletion line bin mapping we positioned all of the linked markers and the Hf-resistance genes (H16 and H17) to the distal 14% of chromosome 1AS, where Hf-resistance genes H9, H10, and H11 are located. Our results together with previous studies suggest that Hf-resistance genes H9, H10, H11, H16, and H17 along with the pathogen resistance genes Pm3 and Lr10 appear to occupy a resistance gene cluster in the distal region of chromosome 1AS in wheat. Contribution from Purdue Univ. Agric. Res. Programs Journal Article No. 2007-18105.     

<Emphasis Type="Italic">Lr41, Lr39,</Emphasis> and a leaf rust resistance gene from<Emphasis Type="Italic"> Aegilops cylindrica</Emphasis> may be allelic and are located on wheat chromosome 2DS

The leaf rust resistance gene Lr41 in wheat germplasm KS90WGRC10 and a resistance gene in wheat breeding line WX93D246-R-1 were transferred to Triticum aestivum from Aegilops tauschii and Ae. cylindrica, respectively. The leaf rust resistance gene in WX93D246-R-1 was located on wheat chromosome 2D by monosomic analysis. Molecular marker analysis of F₂ plants from non-critical crosses determined that this gene is 11.2 cM distal to marker Xgwm210 on the short arm of 2D. No susceptible plants were detected in a population of 300 F₂ plants from a cross between WX93D246-R-1 and TA 4186 (Lr39), suggesting that the gene in WX93D246-R-1 is the same as, or closely linked to, Lr39. In addition, no susceptible plants were detected in a population of 180 F₂ plants from the cross between KS90WGRC10 and WX93D246-R-1. The resistance gene in KS90WGRC10, Lr41, was previously reported to be located on wheat chromosome 1D. In this study, no genetic association was found between Lr41 and 51 markers located on chromosome 1D. A population of 110 F₃ lines from a cross between KS90WGRC10 and TAM 107 was evaluated with polymorphic SSR markers from chromosome 2D and marker Xgdm35 was found to be 1.9 cM proximal to Lr41. When evaluated with diverse isolates of Puccinia triticina, similar reactions were observed on WX93D246-R-1, KS90WGRC10, and TA 4186. The results of mapping, allelism, and race specificity test indicate that these germplasms likely have the same gene for resistance to leaf rust.Contribution number 03-348-J from the Kansas Agricultural Experimental Station, Manhattan, KansasCommunicated by J. Dvorak     

Hessian fly resistance gene H13 is mapped to a distal cluster of resistance genes in chromosome 6DS of wheat

H13 is inherited as a major dominant resistance gene in wheat. It was previously mapped to chromosome 6DL and expresses a high level of antibiosis against Hessian fly (Hf) [Mayetiola destructor (Say)] larvae. The objective of this study was to identify tightly linked molecular markers for marker-assisted selection in wheat breeding and as a starting point toward the map-based cloning of H13. Fifty-two chromosome 6D-specific microsatellite (simple sequence repeat) markers were tested for linkage to H13 using near-isogenic lines Molly (PI 562619) and Newton-207, and a segregating population consisting of 192 F_2:3 families derived from the cross PI 372129 (Dn4) × Molly (H13). Marker Xcfd132 co-segregated with H13, and several other markers were tightly linked to H13 in the distal region of wheat chromosome 6DS. Deletion analysis assigned H13 to a small region closely proximal to the breakpoint of del6DS-6 (FL 0.99). Further evaluation and comparison of the H13-linked markers revealed that the same chromosome region may also contain H23 in KS89WGRC03, an unnamed H gene (H_WGRC4) in KS89WGRC04, the wheat curl mite resistance gene Cmc4, and a defense response gene Ppo for polyphenol oxidase. Thus, these genes comprise a cluster of arthropod resistance genes. Marker analysis also revealed that a very small intercalary chromosomal segment carrying H13 was transferred from the H13 donor parent to the wheat line Molly.Mention of commercial or proprietary product does not constitute an endorsement by the USDA.     

RELP markers linked to two Hessian fly-resistance genes in wheat (Triticum aestivum L.) from Triticum tauschii (coss.) Schmal

Summary Restriction fragment length polymorphism (RFLP) markers linked to genes controlling Hessian fly resistance from Triticum tauschii (Coss.) Schmal. were identified for two wheat (Triticum aestivum L.) germ plasm lines KS89WGRC3 (C3) and KS89WGRC6 (C6). Forty-six clones with loci on chromosomes of homoeologous group 3 and 28 clones on those of group 6 were surveyed for polymorphisms. Eleven and 12 clones detected T. tauschii loci in the two lines, respectively. Analysis of F₂ progenies indicated that the Hessian fly resistance gene H23 identified in C3 is linked to XksuH4 (6.9 cM) and XksuG48 (A) (15.6 cM), located on 6D. The resistance gene H24 in C6 is linked to XcnlBCD451 (5.9 cM), XcnlCD0482 (5.9 cM) and XksuG48 (B) (12.9 cM), located on 3DL.Paper No. 810 of the Cornell Plant Breeding Series     

H22, a major resistance gene to the Hessian fly (Mayetiola destructor), is mapped to the distal region of wheat chromosome 1DS

H22 is a major resistance gene conferring high-level of antibiosis to Hessian fly [Mayetiola destructor (Say)] larvae. It was previously assigned to wheat chromosome 1D through monosomic analysis (Raupp et al. in J Hered 84:142–145, 1993). The objective of this study was to identify molecular markers that can be used for marker-assisted selection for wheat breeding, and to further map this gene toward map-based cloning. Forty-five simple sequence repeat (SSR) and sequence-tagged site (STS) markers specific to chromosome 1D were evaluated for linkage to H22 using a segregating population consisting of 192 F_2:3 families, which were derived from the cross Tugela-Dn1 × KS85WGRC01(H22). The STS Xhor2kv and SSR Xgdm33 are two flanking markers that are tightly linked to H22 at genetic distances of 0.3 and 1.0 cM, respectively. Five other SSR markers including Xgpw7082, Xwmc147, Xcfd15, Xwmc432 and Xwmc336 were also linked to H22 at the distance from 0.8 to 20.8 cM. Analysis of Chinese Spring (CS) deletion lines revealed that all the H22-linked markers are located distal to the breakpoint of del 1DS-5, indicating that the H22 gene is located at the distal 30% region on the short arm of wheat chromosome 1D. Genomic comparison suggested that the H22 gene is located in the same or similar chromosomal region as the leaf rust resistance genes Lr21 and Lr40 on 1DS, and orthologous to the H9 gene cluster of 1AS.     

小麦农家品种赤壳中一个主效抗条锈病基因的微卫星标记和定位

小麦农家品种赤壳(苏1900)对当前我国小麦条锈菌(Puccinia striiformis Westend.f.sp.tritici)多个流行小种均有较好抗性。遗传分析表明,该品种对条中32号小种的抗性是由一对显性基因控制。本文采用分离群体分析法(bulked segregant analysis,BSA)和微卫星多态性分析方法,对该基因进行了分子标记和定位研究。用Taichung29×赤壳的F2代分离群体建立抗、感DNA池,共筛选了400多对SSR引物,发现5个标记Xwmc44、Xgwm259、Xwmc367、Xcfa2292、Xbarc80在抗、感DNA池间与在抗、感亲本间同样具有多态性,它们均位于1BL染色体臂上。经用具有140株抗病株、60株感病株共200株植株的F2代分离群体进行的遗传连锁性检测,上述5个标记均与目的基因相连锁,遗传距离分别为8.3cM、9.1cM、17.2cM、20.6cM和31.6cM。用全套21个中国春缺-四体材料进行的检测进一步证实了这5个SSR标记均位于小麦1B染色体上。综合上述结果,将赤壳中的主效抗条锈病基因YrChk定位在1BL染色体臂上。与以前已定位于1B染色体上的抗条锈病基因的比较研究表明,YrChk基因可能是一个新的抗条锈病基因。小麦农家品种中抗病基因资源的发掘和利用将有助于提高我国小麦生产品种中的抗病基因丰富度,有助于改善长期以来小麦生产品种中抗病基因单一化的局面。     

Precisely mapping a major gene conferring resistance to Hessian fly in bread wheat using genotyping-by-sequencing

Background

One of the reasons hard red winter wheat cultivar ‘Duster’ (PI 644016) is widely grown in the southern Great Plains is that it confers a consistently high level of resistance to biotype GP of Hessian fly (Hf). However, little is known about the genetic mechanism underlying Hf resistance in Duster. This study aimed to unravel complex structures of the Hf region on chromosome 1AS in wheat by using genotyping-by-sequencing (GBS) markers and single nucleotide polymorphism (SNP) markers.

Results

Doubled haploid (DH) lines generated from a cross between two winter wheat cultivars, ‘Duster’ and ‘Billings’ , were used to identify genes in Duster responsible for effective and consistent resistance to Hf. Segregation in reaction of the 282 DH lines to Hf biotype GP fit a one-gene model. The DH population was genotyped using 2,358 markers developed using the GBS approach. A major QTL, explaining 88% of the total phenotypic variation, was mapped to a chromosome region that spanned 178 cM and contained 205 GBS markers plus 1 SSR marker and 1 gene marker, with 0.86 cM per marker in genetic distance. The analyses of GBS marker sequences and further mapping of SSR and gene markers enabled location of the QTL-containing linkage group on the short arm of chromosome 1A. Comparative mapping of the common markers for the gene for QHf.osu-1A^d in Duster and the Hf-resistance gene for QHf.osu-1A⁷⁴ in cultivar ‘2174’ showed that the two Hf resistance genes are located on the same chromosome arm 1AS, only 11.2 cM apart in genetic distance. The gene at QHf.osu-1A^d in Duster has been delimited within a 2.7 cM region.

Conclusion

Two distinct resistance genes exist on the short arm of chromosome 1A as found in the two hard red winter cultivars, 2174 and Duster. Whereas the Hf resistance gene in 2174 is likely allelic to one or more of the previously mapped resistance genes (H9, H10, H11, H16, or H17) in wheat, the gene in Duster is novel and confers a more consistent phenotype than 2174 in response to biotype GP infestation in controlled-environment assays.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1297-7) contains supplementary material, which is available to authorized users.     

Mapping QTLs for pre-harvest sprouting tolerance on chromosome 2D in a synthetic hexaploid wheat×common wheat cross

Based on segregation distortion of simple sequence repeat (SSR) molecular markers, we detected a significant quantitative trait loci (QTL) for pre-harvest sprouting (PHS) tolerance on the short arm of chromosome 2D (2DS) in the extremely susceptible population of F₂ progeny generated from the cross of PHS tolerant synthetic hexaploid wheat cultivar ‘RSP’ and PHS susceptible bread wheat cultivar ‘88–1643’. To identify the QTL of PHS tolerance, we constructed two SSR-based genetic maps of 2DS in 2004 and 2005. One putative QTL associated with PHS tolerance, designatedQphs.sau-2D, was identified within the marker intervalsXgwm261-Xgwm484 in 2004 and in the next year, nearly in the same position, between markerswmc112 andXgwm484. Confidence intervals based on the LOD-drop-off method ranged from 9 cM to 15.4 cM and almost completely overlapped with marker intervalXgwm261-Xgwm484. Flanking markers near this QTL could be assigned to the C-2DS1-0.33 chromosome bin, suggesting that the gene(s) controlling PHS tolerance is located in that chromosome region. The phenotypic variation explained by this QTL was about 25.73–27.50%. Genotyping of 48 F₆ PHS tolerant plants derived from the cross between PHS tolerant wheat cultivar ‘RSP’ and PHS susceptible bread wheat cultivar ‘MY11’ showed that the allele ofQphs.sau-2D found in the ‘RSP’ genome may prove useful for the improvement of PHS tolerance.     

Identification and genetic mapping of <Emphasis Type="Italic">pm42</Emphasis>, a new recessive wheat powdery mildew resistance gene derived from wild emmer (<Emphasis Type="Italic">Triticum turgidum var. dicoccoides</Emphasis>)

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most important wheat diseases worldwide in areas with cool or maritime climates. Wild emmer (Triticum turgidum var. dicoccoides) is an important potential donor of disease resistances and other traits for common wheat improvement. A powdery mildew resistance gene was transferred from wild emmer accession G-303-1M to susceptible common wheat by crossing and backcrossing, resulting in inbred line P63 (Yanda1817/G-303-1 M//3*Jing411, BC₂F₆). Genetic analysis of an F₂ population and the F_2:3 families developed from a cross of P63 and a susceptible common wheat line Xuezao showed that the powdery mildew resistance in P63 was controlled by a single recessive gene. Molecular markers and bulked segregant analysis were used to characterize and map the powdery mildew resistance gene. Nine genomic SSR markers (Xbarc7, Xbarc55, Xgwm148, Xgwm257, Xwmc35, Xwmc154, Xwmc257, Xwmc382, Xwmc477), five AFLP-derived SCAR markers (XcauG3, XcauG6, XcauG10, XcauG20, XcauG22), three EST–STS markers (BQ160080, BQ160588, BF146221) and one RFLP-derived STS marker (Xcau516) were linked to the resistance gene, designated pm42, in P63. pm42 was physically mapped on chromosome 2BS bin 0.75–0.84 using Chinese Spring nullisomic-tetrasomic, ditelosomic and deletion lines, and was estimated to be more than 30 cM proximal to Xcau516, a RFLP-derived STS marker that co-segregated with the wild emmer-derived Pm26 which should be physically located in 2BS distal bin 0.84–1.00. pm42 was highly effective against 18 of 21 differential Chinese isolates of B. graminis f. sp. tritici. The closely linked molecular markers will enable the rapid transfer of pm42 to wheat breeding populations thus adding to their genetic diversity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. W. Hua, Z. Liu, and J. Zhu contributed equally to this work.     

Microsatellite markers linked to 2 powdery mildew resistance genes introgressed from Triticum carthlicum accession PS5 into common wheat.

Two dominant powdery mildew resistance genes introduced from Triticum carthlicum accession PS5 to common wheat were identified and tagged using microsatellite markers. The gene designated PmPS5A was placed on wheat chromosome 2AL and linked to the microsatellite marker Xgwm356 at a genetic distance of 10.2 cM. Based on the information of its origin, chromosome location, and reactions to 5 powdery mildew isolates, this gene could be a member of the complex Pm4 locus. The 2nd gene designated PmPS5B was located on wheat chromosome 2BL with 3 microsatellite markers mapping proximally to the gene: Xwmc317 at 1.1 cM; Xgwm111 at 2.2 cM; and Xgwm382 at 4.0 cM; and 1 marker, Xgwm526, mapping distally to the gene at a distance of 18.1 cM. Since this gene showed no linkage to the other 2 known powdery mildew resistance genes on wheat chromosome 2B, Pm6 and Pm26, we believe it is a novel powdery mildew resistance gene and propose to designate this gene as Pm33.     

Genetic dissection of seminal root architecture in elite durum wheat germplasm

Although root architecture has been shown to play an important role in crop performance, particularly under drought conditions, no information is available on the genetic control of root traits in durum wheat, a crop largely grown in rainfed areas with low rainfall. In our study, a panel of 57 elite durum wheat accessions were evaluated under controlled conditions for root and shoot traits at the seedling stage. Significant genetic variability was detected for all the root and shoot traits that were investigated. Correlation analysis suggested that root and shoot features were only partially controlled by common sets of genes. The high linkage disequilibrium (up to 5 cM) present in the germplasm collection herein considered allowed us to use simple sequence repeat‐based association mapping to identify chromosome regions with significant effects on the investigated traits. In total, 15 chromosome regions showed significant effects on one or more root architectural features. A number of these regions also influenced shoot traits and, in some cases, plant height measured in field conditions. Major effects were detected on chromosome arms 2AL (at Xgwm294), 7AL (at Xcfa2257 and Xgwm332) and 7BL (at Xgwm577 and Xcfa2040). The accessions with the most remarkable differences in root features will provide a valuable opportunity to assemble durum wheat mapping populations well suited for ascertaining the effects of root architecture on water use efficiency and grain yield.     

Pm34: a new powdery mildew resistance gene transferred from Aegilops tauschii Coss. to common wheat (Triticum aestivum L.)

Powdery mildew is a major fungal disease in wheat growing areas worldwide. A novel source of resistance to wheat powdery mildew present in the germplasm line NC97BGTD7 was genetically characterized as a monogenic trait in greenhouse and field trials using F₂ derived lines from a NC97BGTD7 X Saluda cross. Microsatellite markers were used to map and tag this resistance gene, now designated Pm34. Three co-dominant microsatellite markers linked to Pm34 were identified and their most likely order was established as: Xbarc177-5D, 5.4cM, Pm34, 2.6cM, Xbarc144-5D, 14cM, Xgwm272-5D. These microsatellite markers were previously mapped to the long arm of the 5D chromosome and their positions were confirmed using Chinese Spring nullitetrasomic Nulli5D-tetra5A and ditelosomic Dt5DL lines. Pm2, the only other known Pm gene on chromosome 5D, has been mapped to the short arm and its specificity is different from that of Pm34.     

Genetic mapping of Dn7, a rye gene conferring resistance to the Russian wheat aphid in wheat

The Russian wheat aphid is a significant pest problem in wheat and barley in North America. Genetic resistance in wheat is the most effective and economical means to control the damage caused by the aphid. Dn7 is a rye gene located on chromosome 1RS that confers resistance to the Russian wheat aphid. The gene was previously transferred from rye into a wheat background via a 1RS/1BL translocation. This study was conducted to genetically map Dn7 and to characterize the type of resistance the gene confers. The resistant line '94M370' was crossed with a susceptible wheat cultivar that also contains a pair of 1RS/1BL translocation chromosomes. The F₂ progeny from this cross segregated for resistance in a ratio of 3 resistant: 1 susceptible, indicating a single dominant gene. One-hundred and eleven RFLP markers previously mapped on wheat chromosomes 1A, 1B and 1D, barley chromosome 1H and rye chromosome 1R, were used to screen the parents for polymorphism. A genetic map containing six markers linked to Dn7, encompassing 28.2 cM, was constructed. The markers flanking Dn7 were Xbcd1434 and XksuD14, which mapped 1.4 cM and 7.4 cM from Dn7, respectively. Dn7 confers antixenosis, and provides a higher level of resistance than that provided by Dn4. The applications of Dn7 and the linked markers in wheat breeding are discussed.Communicated by J. Dvorak     

Categories of resistance to greenbug (Homoptera: Aphididae) biotype K in wheat lines containing Aegilops tauschii genes

The wheat lines (cultivars) 'Largo', 'TAM110', 'KS89WGRC4', and 'KSU97-85-3' conferring resistance to greenbug, Schizaphis graminum (Rondani), biotypes E, I, and K were evaluated to determine the categories of resistance in each line to greenbug biotype K. Our results indicated that Largo, TAM110, KS89WGRC4, and KSU97-85-3 expressed both antibiosis and tolerance to biotype K. Largo, KS89WGRC4, and KSU97-85-3, which express antixenosis to biotype I, did not demonstrate antixenosis to biotype K. The results indicate that the same wheat lines may possess different categories of resistance to different greenbug biotypes. A new cage procedure for measuring greenbug intrinsic rate of increase (r(m)) was developed, by using both drinking straw and petri dish cages, to improve the efficiency and accuracy of r(m)-based antibiosis measurements.     

Map-based analysis of genes affecting the brittle rachis character in tetraploid wheat (Triticum turgidum L.)

The mature spike rachis of wild emmer [Triticum turgidum L. ssp. dicoccoides (Körn. ex Asch. and Graebner) Thell.] disarticulates spontaneously between each spikelet leading to the dispersion of wedge-type diaspores. By contrast, the spike rachis of domesticated emmer (Triticum turgidum L. ssp. turgidum) fails to disarticulate and remains intact until it is harvested. This major distinguishing feature between wild and domesticated emmer is controlled by two major genes, brittle rachis 2 (Br-A2) and brittle rachis 3 (Br-A3) on the short arms of chromosomes 3A and 3B, respectively. Because of their biological and agricultural importance, a map-based analysis of these genes was undertaken. Using two recombinant inbred chromosome line (RICL) populations, Br-A2, on chromosome 3A, was localized to a ~11-cM region between Xgwm2 and a cluster of linked loci (Xgwm666.1, Xbarc19, Xcfa2164, Xbarc356, and Xgwm674), whereas Br-A3, on chromosome 3B, was localized to a ~24-cM interval between Xbarc218 and Xwmc777. Comparative mapping analyses suggested that both Br-A2 and Br-A3 were present in homoeologous regions on chromosomes 3A and 3B, respectively. Furthermore, Br-A2 and Br-A3 from wheat and Btr1/Btr2 on chromosome 3H of barley (Hordeum vulgare L.) also were homoeologous suggesting that the location of major determinants of the brittle rachis trait in these species has been conserved. On the other hand, brittle rachis loci of wheat and barley, and a shattering locus on rice chromosome 1 did not appear to be orthologous. Linkage and deletion-based bin mapping comparisons suggested that Br-A2 and Br-A3 may reside in chromosomal areas where the estimated frequency of recombination was ~ 4.3 Mb/cM. These estimates indicated that the cloning of Br-A2 and Br-A3 using map-based methods would be extremely challenging.     

Molecular mapping of leaf rust resistance gene <Emphasis Type="Italic">LrBi16</Emphasis> in Chinese wheat cultivar Bimai 16

Leaf rust, caused by Puccinia triticina, is one of the most widespread diseases in common wheat (Triticum aestivum L.) globally. With the objective of identifying and mapping new genes for resistance to leaf rust, F₁, F₂ plants and F₃ lines from a cross between resistant cultivar Bimai 16 and susceptible cultivar Thatcher were inoculated with Chinese Puccinia triticina pathotypes FHTT and PHTS in the greenhouse. In the first seedling test, Bimai 16, Thatcher, 20 F₁ plants, 359 F₂ plants and 298 F₃ lines were inoculated with pathotype FHTT. A set of 1,255 simple sequence repeat (SSR) primer pairs were used to test the parents, and resistant and susceptible bulks. Seven polymorphic markers on chromosome 7BL were used for genotyping the F₂ and F₃ populations. The results indicated that Bimai 16 carried a single dominant resistance gene, temporarily designated LrBi16, closely linked to SSR markers Xcfa2257 and Xgwm344, with genetic distances of 2.8 and 2.9 cM, respectively. In the second seedling test, two dominant resistance genes were identified in Bimai 16 based on seedling reactions of 254 F₂ plants inoculated with pathotype PHTS. One of the genes was LrBi16, and the other was likely to be LrZH84, which is located in chromosome 1BL. The seedling reaction pattern of plants with LrBi16 was different from that of the Thatcher lines, with Lr14a and Lr14b located on chromosome 7BL. It was concluded that LrBi16 is likely to be a new leaf rust resistance gene.     

Microsatellite tagging of the stripe-rust resistance gene YrH52 derived from wild emmer wheat, Triticum dicoccoides, and suggestive negative crossover interference on chromosome 1B

 Stripe rust caused by Puccinia striifomis West. is one of the most devastating diseases relating to wheat production. Wild emmer wheat, Triticum dicoccoides, the tetraploid progenitor of cultivated wheat, has proven to be a valuable source of novel stripe-rust resistance genes for wheat breeding. For example, T. dicoccoides accessions from Mt. Hermon, Israel, are uniformly and highly resistant to stripe-rust. The main objective of the present study is to map a stripe-rust resistance gene, derived from the unique Mt. Hermon population of wild emmer, using microsatellite markers. An F₂ mapping population was established by crossing stripe-rust resistant T. dicoccoides accession H52 from Mt. Hermon with the Triticum durum cultivar Langdon. The stripe-rust resistance derived from accession H52 was found to be controlled by a single dominant gene which was temporarily designated as YrH52. Out of 120 microsatellite markers tested, 109 (91%) showed polymorphism between the parental lines. Among 79 segregating microsatellite loci generated from 56 microsatellite primer pairs, nine were linked to YrH52 with recombination frequencies of 0.02–0.35, and LOD scores of 3.56–54.22. A genetic map of chromosome 1B, consisting of ten microsatellite loci and the stripe-rust resistance gene YrH52, was constructed with a total map length of 101.5 cM. YrH52 is also closely linked to RFLP marker Nor1 with a map distance of 1.4 cM and a LOD value of 29.62. Apparent negative crossover interference was observed in chromosome 1B, especially in the region spanning the centromere. Negative crossover interference may be a common characteristic of gene-rich regions or gene clusters in specific chromosomes. Received: 30 October 1998 / Accepted: 2 November 1998     

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.     

Characterization and chromosomal location of Pm40 in common wheat: a new gene for resistance to powdery mildew derived from Elytrigia intermedium

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a very destructive wheat (Triticum aestivum) disease. Resistance was transferred from Elytrigia intermedium to common wheat by crossing and backcrossing, and line GRY19, that was subsequently selected, possessed a single dominant gene for seedling resistance. Five polymorphic microsatellite markers, Xgwm297, Xwmc335, Xwmc364, Xwmc426 and Xwmc476, on chromosome arm 7BS, were mapped relative to the powdery mildew resistance locus in an F₂ population of Mianyang 11/GRY19. The loci order Xwmc426–Xwmc335–Pm40–Xgwm297–Xwmc364–Xwmc476, with 5.9, 0.2, 0.7, 1.2 and 2.9 cM genetic distances, was consistent with published maps. The resistance gene transferred from Elytrigia intermedium into wheat line GRY19 was novel, and was designated Pm40. The close flanking markers will enable marker assisted transfer of this gene into wheat breeding populations. P.G. Luo and H.Y. Luo contributed equally to the work.