Molecular mapping of <Emphasis Type="Italic">Thinopyrum</Emphasis>-derived Fusarium head blight resistance in common wheat

Resistance to Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe in wheat (Triticum aestivum L.) was identified in disomic chromosome substitution and translocation lines, into which chromosome 7el₂ had been introgressed from wheatgrass, Thinopyrum ponticum. In this study, two chromosome substitution lines with different origins (designated as el₁ and el₂) and with different reactions to infection by F. graminearum were crossed to develop a segregating mapping population. The objectives of this study were to determine the effectiveness of this type II resistance and map it on chromosome 7el₂. Type II resistance to FHB was characterized in the F₂, F_2:3 families, F_4:5 plants and F_5:6 recombinant inbred lines developed by single-seed descent; and the population was characterized in the F₂ and F₅ with DNA markers along the long arm of 7el. Composite interval mapping revealed a FHB resistance QTL, designated Qfhs.pur-7EL, located in the distal region of the long arm of 7el₂ and delimited with flanking markers XBE445653 and Xcfa2240. Additive effects of Qfhs.pur-7EL reduced the number of diseased spikelets per spike following inoculation of one floret in four experiments by 1.5–2.6 and explained 15.1–32.5% of the phenotypic variation in the populations. Several STS-derived and EST-derived PCR or CAPS markers were developed in this chromosomal region, and showed the specificity of 7el₂ compared to an array of wheat lines possessing other sources of FHB resistance. These markers are useful in an effort to shorten the chromosome segment of 7el₂ and to use for marker-assisted introgression of this resistance into wheat.     

A genetic map of <Emphasis Type="Italic">Lophopyrum ponticum</Emphasis> chromosome 7E,harboring resistance genes to Fusarium head blight and leaf rust

The leaf rust resistance gene Lr19 and Fusarium head blight (FHB) resistance quantitative trait loci (QTL) derived from the wild wheatgrass Lophopyrum ponticum have been located on chromosome 7E. The main objectives of the present study were to develop a genetic map of chromosome 7E and map the two resistance loci using a population of 237 F_7:8 recombinant inbred lines (RILs) derived from a cross between two Thatcher-L. ponticum substitution lines, K11463 (7el₁(7D)) and K2620 (7el₂(7D)). 532 G-SSR, E-SSR and STS markers from wheat chromosome group 7 were screened in the parent lines. Of these, 118 markers were polymorphic, with a polymorphism frequency of 22.2%. A genetic map of L. ponticum chromosome 7E was constructed with 64 markers, covering 95.76 cM, with an average genetic distance of 1.47 cM between markers. The major FHB resistance locus, temporarily assigned as FhbLoP, was mapped to the very distal region of the long arm of chromosome 7E within a 3.71 cM interval flanked by Xcfa2240 and Xswes19, which accounts for 30.46% of the phenotypic variance. Lr19 was bracketed by Xwmc273 and XBE404744, with a map distance of 1.54 and 1.43 cM from either side, respectively. The closely linked markers identified in this study will be helpful for marker-assisted introgression of the L. ponticum-derived FhbLoP and Lr19 genes into elite cultivars of wheat, and the development of a genetic map will accelerate the map-based cloning of these two genes.     

Cytogenetic mapping of a major locus for resistance to Fusarium head blight and crown rot of wheat on <Emphasis Type="Italic">Thinopyrum elongatum</Emphasis> 7EL and its pyramiding with valuable genes from a <Emphasis Type="Italic">Th. ponticum</Emphasis> homoeologous arm onto bread wheat 7DL

Key message

A major locus for resistance to different Fusarium diseases was mapped to the most distal end of Th. elongatum 7EL and pyramided with Th. ponticum beneficial genes onto wheat 7DL.

Abstract

Perennial Triticeae species of the Thinopyrum genus are among the richest sources of valuable genes/QTL for wheat improvement. One notable and yet unexploited attribute is the exceptionally effective resistance to a major wheat disease worldwide, Fusarium head blight, associated with the long arm of Thinopyrum elongatum chromosome 7E (7EL). We targeted the transfer of the temporarily designated Fhb-7EL locus into bread wheat, pyramiding it with a Th. ponticum 7el₁L segment stably inserted into the 7DL arm of wheat line T4. Desirable genes/QTL mapped along the T4 7el₁L segment determine resistance to wheat rusts (Lr19, Sr25) and enhancement of yield-related traits. Mapping of the Fhb-7EL QTL, prerequisite for successful pyramiding, was established here on the basis of a bioassay with Fusarium graminearum of different 7EL-7el₁L bread wheat recombinant lines. These were obtained without resorting to any genetic pairing promotion, but relying on the close 7EL-7el₁L homoeology, resulting in 20% pairing frequency between the two arms. Fhb-7EL resided in the telomeric portion and resistant recombinants could be isolated with useful combinations of more proximally located 7el₁L genes/QTL. The transferred Fhb-7EL locus was shown to reduce disease severity and fungal biomass in grains of infected recombinants by over 95%. The same Fhb-7EL was, for the first time, proved to be effective also against F. culmorum and F. pseudograminearum, predominant agents of crown rot. Prebreeding lines possessing a suitable 7EL-7el₁L gene/QTL assembly showed very promising yield performance in preliminary field tests.

     

Molecular characterization of Fusarium resistance from <Emphasis Type="Italic">Elymus repens</Emphasis> introgressed into bread wheat

A cross was made of Elymus repens onto the wheat cultivar Crocus and BC₁ progeny advanced to BC₁F₇ by single seed descent. Sixteen lines were selected based on agronomic performance and evaluated in an FHB epiphytotic nursery. Eight lines with FHB resistance were selected. Based on GISH analysis, line PI 142-3-1-5 had 42 chromosomes with one pair of chromosomes showing telomeric translocations on both arms. This chromosome was identified as 3D by using SSR markers. An evaluation of lines with single translocations revealed that FHB resistance was contributed by the translocation on the long arm of chromosome 3D. That line has minimal linkage drag and should be amenable to applications inbreeding for disease resistance.     

Trigenomic chromosomes by recombination of <Emphasis Type="Italic">Thinopyrum intermedium </Emphasis>and <Emphasis Type="Italic">Th. ponticum </Emphasis>translocations in wheat

Rusts and barley yellow dwarf virus (BYDV) are among the main diseases affecting wheat production world wide for which wild relatives have been the source of a number of translocations carrying resistance genes. Nevertheless, along with desirable traits, alien translocations often carry deleterious genes. We have generated recombinants in a bread wheat background between two alien translocations: TC5, ex-Thinopyrum (Th) intermedium, carrying BYDV resistance gene Bdv2; and T4m, ex-Th. ponticum, carrying rust resistance genes Lr19 and Sr25. Because both these translocations are on the wheat chromosome arm 7DL, homoeologous recombination was attempted in the double hemizygote (TC5/T4m) in a background homozygous for the ph1b mutation. The identification of recombinants was facilitated by the use of newly developed molecular markers for each of the alien genomes represented in the two translocations and by studying derived F₂, F₃ and doubled haploid populations. The occurrence of recombination was confirmed with molecular markers and bioassays on families of testcrosses between putative recombinants and bread wheat, and in F₂ populations derived from the testcrosses. As a consequence it has been possible to derive a genetic map of markers and resistance genes on these previously fixed alien linkage blocks. We have obtained fertile progeny carrying new tri-genomic recombinant chromosomes. Furthermore we have demonstrated that some of the recombinants carried resistance genes Lr19 and Bdv2 yet lacked the self-elimination trait associated with shortened T4 segments. We have also shown that the recombinant translocations are fixed and stable once removed from the influence of the ph1b. The molecular markers developed in this study will facilitate selection of individuals carrying recombinant Th. intermedium–Th. ponticum translocations (Pontin series) in breeding programs. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

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.     

Meiotic homoeologous recombination-based mapping of wheat chromosome 2B and its homoeologues in <Emphasis Type="Italic">Aegilops speltoides</Emphasis> and <Emphasis Type="Italic">Thinopyrum elongatum</Emphasis>

Key message

We physically dissected and mapped wheat chromosome 2B and its homoeologues in Aegilops speltoides and Thinopyrum elongatum based on meiotic homoeologous recombination, providing a unique physical framework for genome studies.

Abstract

Common wheat has a large and complex genome with narrow genetic diversity and various degrees of recombination between the A, B, and D subgenomes. This has limited the homologous recombination-based genome studies in wheat. Here, we exploited meiotic homoeologous recombination for molecular mapping of wheat chromosome 2B and its homoeologue 2S from Aegilops speltoides and 2E from Thinopyrum elongatum. The 2B–2S and 2B–2E recombination was induced by the ph1b mutant, and recovered using molecular markers and fluorescent genomic in situ hybridization (FGISH). A total of 112 2B–2S and 87 2B–2E recombinants involving different chromosome regions were developed and physically delineated by FGISH. The 2B–2S and 2B–2E recombination hotspots mapped to the subterminal regions on both arms. Recombination hotspots with the highest recombination rates mapped to the short arms. Eighty-three 2B–2S and 67 2B–2E recombinants were genotyped using the wheat 90 K SNP arrays. Based on the genotyping results and FGISH patterns of the recombinants, chromosomes 2B, 2S, and 2E were partitioned into 93, 66, and 46 bins, respectively. In total, 1037 SNPs physically mapped onto distinct bins of these three homoeologous chromosomes. A homoeologous recombination-based bin map was constructed for chromosome 2B, providing a unique physical framework for genome studies in wheat and its relatives. Meiotic homoeologous recombination also facilitates gene introgression to diversify the wheat genome for germplasm development. Therefore, homoeologous recombination-based studies enhance understanding of the wheat genome and its homoeologous counterparts from wild grasses, and expand the genetic variability of the wheat genome.

     

<Emphasis Type="Italic">Pm37</Emphasis>, a new broadly effective powdery mildew resistance gene from <Emphasis Type="Italic">Triticum </Emphasis><Emphasis Type="Italic">timopheevii</Emphasis>

Powdery mildew is an important foliar disease in wheat, especially in areas with a cool or maritime climate. A dominant powdery mildew resistance gene transferred to the hexaploid germplasm line NC99BGTAG11 from T. timopheevii subsp. armeniacum was mapped distally on the long arm of chromosome 7A. Differential reactions were observed between the resistance gene in NC99BGTAG11 and the alleles of the Pm1 locus that is also located on chromosome arm 7AL. Observed segregation in F_2:3 lines from the cross NC99BGTAG11 × Axminster (Pm1a) demonstrate that germplasm line NC99BGTAG11 carries a novel powdery mildew resistance gene, which is now designated as Pm37. This new gene is highly effective against all powdery mildew isolates tested so far. Analyses of the population with molecular markers indicate that Pm37 is located 16 cM proximal to the Pm1 complex. Simple sequence repeat (SSR) markers Xgwm332 and Xwmc790 were located 0.5 cM proximal and distal, respectively, to Pm37. In order to identify new markers in the region, wheat expressed sequence tags (ESTs) located in the distal 10% of 7AL that were orthologous to sequences from chromosome 6 of rice were targeted. The two new EST-derived STS markers were located distal to Pm37 and one marker was closely linked to the Pm1a region. These new markers can be used in marker-assisted selection schemes to develop wheat cultivars with pyramids of powdery mildew resistance genes, including combinations of Pm37 in coupling linkage with alleles of the Pm1 locus.     

<Emphasis Type="Italic">Agropyron elongatum</Emphasis> chromatin localization on the wheat chromosomes in an introgression line

The introgressed small-chromosome segment of Agropyron elongatum (Host.) Neviski (Thinopyrum ponticum Podp.) in F₅ line II-1-3 of somatic hybrid between common wheat (Triticum aestivum L.) and A. elongatum was localized by sequential fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH) and karyotype data. Karyotype analysis offered basic data of arm ratios and relative lengths of 21 pairs of chromosomes in parent wheat Jinan177 and hybrid II-1–3. Using special high repetitive sequences pSc119.2 and pAs1 for FISH, the entire B- and D-genome chromosomes were detected. The FISH pattern of hybrid II-1-3 was the same as that of parent wheat. GISH using whole genomic DNA from A. elongatum as probe determined the alien chromatin. Sequential GISH and FISH, in combination with some of the karyotype data, localized the small chromosome segments of A. elongatum on the specific sites of wheat chromosomes 2AL, 1BL, 5BS, 1DL, 2DL and 6DS. FISH with probe OPF-03₁₂₉₆ from randomly amplified polymorphic DNA (RAPD) detected E-genome chromatin of A. elongatum, which existed in all of the small chromosome segments introgressed. Microsatellite primers characteristic for the chromosome arms above were used to check the localization and reveal the genetic identity. These methods are complementary and provide comprehensive information about the genomic constitution of the hybrid. The relationship between hybrid traits and alien chromatin was discussed.     

Inheritance and mapping of powdery mildew resistance gene <Emphasis Type="Italic">Pm43</Emphasis> introgressed from <Emphasis Type="Italic">Thinopyrum</Emphasis><Emphasis Type="Italic">intermedium</Emphasis> into wheat

Powdery mildew resistance from Thinopyrum intermedium was introgressed into common wheat (Triticum aestivum L.). Genetic analysis of the F₁, F₂, F₃ and BC₁ populations from powdery mildew resistant line CH5025 revealed that resistance was controlled by a single dominant allele. The gene responsible for powdery mildew resistance was mapped by the linkage analysis of a segregating F₂ population. The resistance gene was linked to five co-dominant genomic SSR markers (Xcfd233, Xwmc41, Xbarc11, Xgwm539 and Xwmc175) and their most likely order was Xcfd233–Xwmc41–Pm43–Xbarc11–Xgwm539–Xwmc175 at 2.6, 2.3, 4.2, 3.5 and 7.0 cM, respectively. Using the Chinese Spring nullisomic-tetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome 2DL. As no powdery mildew resistance gene was previously assigned to chromosome 2DL, this new resistance gene was designated Pm43. Pm43, together with the identified closely linked markers, could be useful in marker-assisted selection for pyramiding powdery mildew resistance genes. Runli He and Zhijian Chang contributed equally to this work.     

High-resolution mapping and gene prediction of <Emphasis Type="Italic">Xanthomonas Oryzae</Emphasis> pv. <Emphasis Type="Italic">Oryzae</Emphasis> resistance gene <Emphasis Type="Italic">Xa7</Emphasis>

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a devastating disease in rice worldwide. The resistance gene Xa7, which provides dominant resistance against the pathogen with avirulence (Avr) gene AvrXa7, has proved to be durably resistant to BB. A set of SSR markers were selected from the “gramene” database based on the Xa7 gene initial mapping region on chromosome 6. These markers were used to construct a high-resolution genetic map of the chromosomal region surrounding the Xa7 gene. An F₂ mapping population with 721 highly susceptible individuals derived from a cross between the near isogenic lines (NILs) IRBB7 and IR24 were constructed to localize the Xa7 gene. In a primary analysis with eleven polymorphic SSR markers, Xa7 was located in approximately the 0.28-cM region. To walk closer to the target gene, recombinant F₂ individuals were tested using newly developed STMS (sequence tagged microsatellite) markers. Finally, the Xa7 gene was mapped to a 0.21-cM interval between the markers GDSSR02 and RM20593. The Xa7-linked markers were landed on the reference sequence of cv. Nipponbare through bioinformatics analysis. A contig map corresponding to the Xa7 gene was constructed. The target gene was assumed to span an interval of approximately 118.5-kb which contained a total of fourteen genes released by the TIGR Genome Annotation Version 5.0. Candidate-gene analysis of Xa7 revealed that the fourteen genes encode novel domains that have no amino acid sequence similar to other cloned Xa(xa) genes. Shen Chen and Zhanghui Huang are contributed equally to this work.     

Susceptibility to <Emphasis Type="Italic">Fusarium </Emphasis>head blight is associated with the <Emphasis Type="Italic">Rht-D1b</Emphasis> semi-dwarfing allele in wheat

Fusarium head blight (FHB) is an important disease of wheat worldwide. The cultivar Spark is more resistant than most other UK winter wheat varieties but the genetic basis for this is not known. A mapping population from a cross between Spark and the FHB susceptible variety Rialto was used to identify quantitative trait loci (QTL) associated with resistance. QTL analysis across environments revealed nine QTL for FHB resistance and four QTL for plant height (PH). One FHB QTL was coincident with the Rht-1D locus and accounted for up to 51% of the phenotypic variance. The enhanced FHB susceptibility associated with Rht-D1b is not an effect of PH per se as other QTL for height segregating in this population have no influence on susceptibility. Experiments with near-isogenic lines supported the association between susceptibility and the Rht-D1b allele conferring the semi-dwarf habit. Our results demonstrate that lines carrying the Rht-1Db semi-dwarfing allele are compromised in resistance to initial infection (type I resistance) while being unaffected in resistance to spread within the spike (type II resistance).     

Molecular mapping of powdery mildew resistance gene <Emphasis Type="Italic">PmHNK</Emphasis> in winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivar Zhoumai 22

The Chinese winter wheat cultivar Zhoumai 22 is highly resistant to powdery mildew. The objectives of this study were to map a powdery mildew resistance gene in Zhoumai 22 using molecular markers and investigate its allelism with Pm13. A total of 278 F₂ and 30 BC₁ plants, and 143 F₃ lines derived from the cross between resistant cultivar Zhoumai 22 and susceptible cultivar Chinese Spring were used for resistance gene tagging. The 137 F₂ plants from the cross Zhoumai 22/2761-5 (Pm13) were employed for the allelic test of the resistance genes. Two hundred and ten simple sequence repeat (SSR) markers were used to test the two parents, and resistant and susceptible bulks. Subsequently, seven polymorphic markers were used for genotyping the F₂ and F₃ populations. The results indicated that the powdery mildew resistance in Zhoumai 22 was conferred by a single dominant gene, designated PmHNK tentatively, flanked by seven SSR markers Xgwm299, Xgwm108, Xbarc77, Xbarc84, Xwmc326, Xwmc291 and Xwmc687 on chromosome 3BL. The resistance gene was closely linked to Xwmc291 and Xgwm108, with genetic distances of 3.8 and 10.3 cM, respectively, and located on the chromosome bin 3BL-7-0.63-1.0 in the test with a set of deletion lines. Seedling tests with seven isolates of Blumeria graminis f. sp. tritici (Bgt) and allellic test indicated that PmHNK is different from Pm13, and Pm41 seems also to be different from PmHNK due to its origin from T. dicoccoides and molecular evidence. These results indicate that PmHNK is likely to be a novel powdery mildew resistance gene in wheat.     

Exploiting co-linearity among grass species to map the <Emphasis Type="Italic">Aegilops ventricosa-</Emphasis>derived <Emphasis Type="Italic">Pch1</Emphasis> eyespot resistance in wheat and establish its relationship to <Emphasis Type="Italic">Pch2</Emphasis>

Introgressions into wheat from related species have been widely used as a source of agronomically beneficial traits. One such example is the introduction of the potent eyespot resistance gene Pch1 from the wild relative Aegilops ventricosa onto chromosome 7DL of wheat. In common with genes carried on many other such introgressions, the use of Pch1 in commercial wheat varieties has been hindered by linkage drag with yield-limiting traits. Attempts to break this linkage have been frustrated by a lack of co-dominant PCR markers suitable for identifying heterozygotes in F₂ populations. We developed conserved orthologous sequence (COS) markers, utilising the Brachypodium distachyon (Brachypodium) genome sequence, to provide co-dominant markers in the Pch1 region. These were supplemented with previously developed sequence-tagged site (STS) markers and simple sequence repeat (SSR) markers. Markers were applied to a panel of varieties and to a BC₆ F₂ population, segregating between wheat and Ae. ventricosa over the distal portion of 7DL, to identify recombinants in the region of Pch1. By exploiting co-linearity between wheat chromosome 7D, Brachypodium chromosome 1, rice chromosome 6 and sorghum chromosome 10, Pch1 was located to an interval between the flanking markers Xwg7S and Xcos7-9. Furthermore candidate gene regions were identified in Brachypodium (364 Kb), rice (178 Kb) and sorghum (315 Kb) as a prelude to the map-based cloning of the gene. In addition, using homoeologue transferable markers, we obtained evidence that the eyespot resistances Pch1 and Pch2 on chromosomes 7D and 7A, respectively, are potentially homoeoloci. It is anticipated that the COS marker methodology could be used for the identification of recombinants in other introgressions into wheat from wild relatives. This would assist the mapping of genes of interest and the breaking of deleterious linkages to enable greater use of these introgressions in commercial varieties.     

Molecular mapping of resistance gene to English grain aphid (<Emphasis Type="Italic">Sitobion avenae</Emphasis> F.) in <Emphasis Type="Italic">Triticum durum</Emphasis> wheat line C273

The English grain aphid, Sitobion avenae (Fabricius), is one of the most important insect pests causing substantial yield losses in wheat production in China and other grain-growing areas in the world. The efficient utilization of wheat genes for resistance to English grain aphid (EGA) provides an efficient, economic and environmentally sound approach to reduce the yield losses. In the present study, the wheat line C273 (Triticum durum AABB, 2n = 4x = 28), is resistant to EGA in greenhouse and field tests. To identify the resistance gene, designated RA-1 temporarily, C273 was crossed with susceptible genotype Poland 305 (T. polonicum, AABB, 2n = 4x = 28). The F₁, F₂ and F_2:3 lines were tested with EGA in the field and greenhouse. The results indicated that RA-1 is a single dominant gene, closely linked to the microsatellite markers (SSR) Xwmc179, Xwmc553 and Xwmc201 on chromosome 6AL at genetic distances of 3.47, 4.73 and 7.57 cM, respectively. The three SSR markers will be valuable in marker-assisted selection for resistance to EGA as well as for cloning this gene in the future.     

Molecular identification of a new powdery mildew resistance gene <Emphasis Type="Italic">Pm41</Emphasis> on chromosome 3BL derived from wild emmer (<Emphasis Type="Italic">Triticum turgidum</Emphasis> var. <Emphasis Type="Italic">dicoccoides</Emphasis>)

Powdery mildew caused by Blumeria graminis f. sp. tritici is an important wheat disease in China and other parts of the world. Wild emmer (Triticum turgidum var. dicoccoides) is the immediate progenitor of cultivated tetraploid and hexaploid wheats and thus an important resource for wheat improvement. Wild emmer accession IW2 collected from Mount Hermon, Israel, is highly resistant to powdery mildew at the seedling and adult plant stages. Genetic analysis using an F₂ segregating population and F_2:3 families, derived from a cross between susceptible durum cultivar Langdon and wild emmer accession IW2, indicated that a single dominant gene was responsible for the resistance of IW2. Bulked segregant and molecular marker analyses detected that six polymorphic SSR, one ISBP, and three EST-STS markers on chromosome 3BL bin 0.63–1.00 were linked to the resistance gene. Allelic variations of resistance-linked EST-STS marker BE489472 revealed that the allele was present only in wild emmer but absent in common wheat. Segregation distortion was observed for the powdery mildew resistance allele and its linked SSR markers with preferential transmission of Langdon alleles over IW2 alleles. The resistance gene was introgressed into common wheat by backcrossing and marker-assisted selection. Since no designated powdery mildew resistance gene has been found on chromosome 3BL, the resistance gene derived from wild emmer accession IW2 appears to be new one and was consequently designated Pm41. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Genetic characterization and mapping of major gene resistance to potato leafroll virus in <Emphasis Type="Italic">Solanum</Emphasis><Emphasis Type="Italic">tuberosum</Emphasis> ssp. <Emphasis Type="Italic">andigena</Emphasis>

Major gene inheritance of resistance to Potato leafroll virus (PLRV) was demonstrated in a parthenogenic population derived from the highly resistant tetraploid andigena landrace, LOP-868. This major gene or chromosome region seems to control a single mechanism for resistance to infection and virus accumulation in this source. About 149 dihaploid lines segregated in a ratio of 107 resistant to 32 susceptible, fitting the expected ratio for inheritance of a duplex gene under random chromatid segregation. A tetraploid AFLP map was constructed using as reference the ultra high density (UHD) map. All AFLP markers associated with PLRV resistance mapped to the same linkage group. Map position was confirmed by analysis of previously-mapped SSR markers. Rl _adg is located on the upper arm of chromosome V, at 1 cM from its most closely linked AFLP marker, E35M48.192. This marker will be used to develop allele-specific primers or a pair of flanking PCR-based markers for their use in marker assisted selection.     

Features of alloplasmic wheat-barley substitution and addition lines (<Emphasis Type="Italic">Hordeum marinum</Emphasis> subsp. <Emphasis Type="Italic">gussoneanum</Emphasis>)-<Emphasis Type="Italic">Triticum aestivum</Emphasis>

Two alloplasmic wheat-barley substitution lines were studied: a line replaced at three pairs of chromosomes 1H ^mar (1B), 5H ^mar (5D), and 7H ^mar (7D), and the disomic-substituted line 7H ^mar (7D). The lines were constructed on the basis of individual plants from BC₁F₈ and BC₂F₆ progeny of barley-wheat hybrids (H. marinum subsp. gussoneanum Hudson (= H. geniculatum All.) (2n = 28) × T. aestivum L.) (2n = 42) (Pyrotrix 28), respectively. Moreover, the alloplasmic wheat-barley ditelosomic addition line 7HL ^mar isolated among plants from the BC₁F₆ progeny of a barley-wheat amphiploid was studied, which in this work corresponds to BC₂F₁₀ and BC₂F₁₁ progeny. It was ascertained that when grown in the field, these alloplasmic lines manifest stable self-fertility. Plants of the given lines are characterized by low height, shortened ears, the fewer number of stems and ears, and of spikelets in the ear, by decreased grain productivity and weight of 1000 grains, in comparison with the common wheat cultivar Pyrotrix 28. The inhibition of trait expression in alloplasmic wheat-barley substitution and addition lines may be connected not only with the influence of wild barley chromosomes functioning in the genotypic environment of common wheat, but also with the effect of the barley cytoplasm. The alloplasmic line with substitution of chromosomes 1H ^mar (1B), 5H ^mar (5D), and 7H ^mar (7D) or the alloplasmic line 5HL ^mar with ditelosomic addition have, in comparison with the common wheat cultivar Pyrotrix 28, an increased grain protein content, which is explained by the effect of wild barley H. marinum subsp. gussoneanum chromosomes.     

Molecular characterization of a wheat -<Emphasis Type="Italic">Thinopyrum ponticum</Emphasis> partial amphiploid and its derived substitution line for resistance to stripe rust

Stripe rust (caused by Puccinia striiformis) occurs annually in most wheat-growing areas of the world. Thinopyrum ponticum has provided novel rust resistance genes to protect wheat from this fungal disease. Wheat – Th. ponticum partial amphiploid line 7430 and a substitution line X005 developed from crosses between wheat and 7430 were resistant to stripe rust isolates from China. Genomic in situ hybridization (GISH) analysis using Pseudoroegneria spicata genomic DNA as a probe demonstrated that the partial amphiploid line 7430 contained ten J^s and six J genome chromosomes, and line X005 had a pair of J^s-chromosomes. Giemsa-C banding further revealed that both lines 7430 and X005 were absent of wheat chromosomes 6B. The EST based PCR confirmed that the introduced J^s chromosomes belonging to linkage group 6, indicating that line X005 was a 6J^s/6B substitution line. Both resistance observation and sequence characterized amplified region (SCAR) markers displayed that the introduced chromosomes 6J^s were responsible for the stripe rust resistances. Therefore, lines 7430 and X005 can be used as a donor in wheat breeding for stripe rust resistance.     

Molecular cytogenetic identification of a novel dwarf wheat line with introgressed <Emphasis Type="Italic">Thinopyrum ponticum</Emphasis> chromatin

Novel dwarfing germplasms and dwarfing genes are valuable for the wheat breeding. A novel semi-dwarf line, 31505-1, with reduced height compared with its common wheat parent, was derived from a cross between common wheat and Thinopyrum ponticum. Cytological studies demonstrated that 31505-1 contained 42 chromosomes and formed 21 bivalents at meiotic metaphase I. Genomic in situ hybridization (GISH) analysis showed that 31505-1 had no large Th. ponticum chromosome fragments. Fluorescence in situ hybridization (FISH) results revealed the absence of a pAs1 hybridization band on 2DL chromosome of 31505-1. Two SSR markers (Xwmc41 and Xcfd168) and two STS markers (Xmag4059 and Xmag3596), which were located on 2D chromosome, amplified unique bands of Th. Ponticum in 31505-1. These revealed presence of an introgressed Th. ponticum segment in 2DL chromosome of dwarf line 31505-1, although the alien segment could not be detected by GISH.