Cereal cyst nematode resistance gene <Emphasis Type="Italic">CreV</Emphasis> effective against <Emphasis Type="Italic">Heterodera filipjevi</Emphasis> transferred from chromosome 6VL of <Emphasis Type="Italic">Dasypyrum villosum</Emphasis> to bread wheat

Cereal cyst nematodes (CCN) are a global economic problem for cereal production. Heterodera filipjevi is one of the most commonly identified and widespread CCN species found in many wheat production regions of the world. Transferring novel genes for resistance to H. filipjevi from wild relatives of wheat is a promising strategy for protection of wheat crops. A set of wheat–Dasypyrum villosum chromosome addition lines, T6V#4S·6AL translocation lines and their donor parental lines were tested for their response to the nematode. D. villosum and wheat–D. villosum disomic addition line DA6V#4 were resistant. As T6V#4S·6AL translocation lines were susceptible, resistance was presumed to be located on chromosome 6V#4L. The objective of this study was to produce and characterize wheat–6V#4L translocations and confirm the chromosome location of the resistance. Introgression lines T6V#4L·6AS, T6V#4L-4BL·4BS and DT6V#4L were developed and subjected to molecular cytogenetic analysis. These and four additional wheat–6V#4 introgression lines were tested for response to H. filipjevi in the greenhouse. The results indicated that introgression lines DA6V#4, T6V#4L·6AS, T6V#4L-4BL·4BS, T6V#4L·6V#4S-7BS and DT6VL#4 had higher levels of H. filipjevi resistance than their recurrent parent. However, Del6V#4L-1 and translocation line T6V#4S·6AL were equally susceptible to wheat cv. Chinese Spring. The CCN resistance gene, temporarily named CreV, was therefore physically mapped to chromosome arm 6V#4L FL 0.80–1.00. Translocation chromosomes T6V#4L·6AS transferred to a modern wheat cv. Aikang 58 with its co-dominant molecular markers could be utilized as a novel germplasm for CCN resistance breeding in wheat.     

Molecular cytogenetic identification of a wheat–<Emphasis Type="Italic">Aegilops geniculata</Emphasis> Roth 7M<Superscript>g</Superscript> disomic addition line with powdery mildew resistance

Aegilops geniculata Roth is an important germplasm resource for the transfer of beneficial genes into common wheat (Triticum aestivum L.). A new disomic addition line NA0973-5-4-1-2-9-1 was developed from the BC₁F₆ progeny of the cross wheat cv. Chinese Spring (CS)/Ae. geniculata SY159//CS. We characterized this new line by morphological and cytogenetic identification, analysis of functional molecular markers, genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH), and disease resistance evaluation. Cytological observations suggested that NA0973-5-4-1-2-9-1 contained 44 chromosomes and formed 22 bivalents at meiotic metaphase I. The GISH investigations showed that the line contained 42 wheat chromosomes and a pair of Ae. geniculata chromosomes. EST-STS multiple loci markers and PLUG (PCR-based landmark unique gene) markers confirmed that the introduced Ae. geniculata chromosomes belonged to homoeologous group 7. FISH identification suggested that NA0973-5-4-1-2-9-1 possessed an additional pair of 7M^g chromosomes, and at the same time, there were structural differences in a pair of 6D chromosomes between NA0973-5-4-1-2-9-1 and TA7661 (CS-AEGEN DA 7M^g). After inoculation with powdery mildew (Blumeria graminis f. sp. tritici, Bgt) isolates E09, NA0973-5-4-1-2-9-1 exhibited a powdery mildew resistance infection type different from that of TA7661, and we conclude that the powdery mildew resistance of NA0973-5-4-1-2-9-1 originated from its parent Ae. geniculata SY159. Therefore, NA0973-5-4-1-2-9-1 can be used as a donor source for introducing novel disease resistance genes into wheat during breeding programs with the assistance of molecular and cytogenetic markers.     

Whole genome development of intron targeting (IT) markers specific for <Emphasis Type="Italic">Dasypyrum villosum</Emphasis> chromosomes based on next-generation sequencing technology

Dasypyrum villosum (Dv), a wild relative of wheat, is an important and useful gene resource for wheat improvement. A large number of wheat-Dv aneuploid lines harboring whole or fragments of Dv chromosomes have been developed. However, the lack of sufficient molecular markers hindered accurate identification of Dv chromatin, especially when the introgressed fragments are small. Development of molecular markers covering the whole Dv genome and evenly distributed on different chromosome regions is not only useful for the detection of the introgressed alien chromatin in wheat background, but also provides evidence of the syntenic relationship between homoeologous chromosomes. In the present study, in order to develop high density and evenly distributed molecular markers on individual Dv chromosomes, genomic DNA of Dv leaves was sequenced and assembled. Sequence assemblies of all wheat chromosomes were first used to identify exon–exon junctions and localize introns in Dv. Intron length polymorphisms suitable for designing Dv primers flanking introns were evaluated, and a total of 1624 intron targeting (IT) markers was designed. By using the Chinese Spring, the Triticum durum-Dv amphiploid and the Dv sequenced DNA libraries, 841 IT molecular markers specific for Dv chromosomes were developed, with maximum efficiency up to 51.79%. We assigned the 841 IT markers to seven Dv chromosomes (1V–7V) using seven wheat–Dv chromosome addition and substitution lines: 135 to 1V, 175 to 2V, 120 to 3V, 89 to 4V, 140 to 5V, 71 to 6V, and 111 to 7V, respectively. Using T. aestivum-Dv telosomic and whole arm translocation lines, they were further located on the short or long chromosome arms. These specific markers for individual chromosomes of Dv provided efficient tools for the characterization of structural variation involving the individual chromosome of Dv, as well as for the selection of useful genes located on individual Dv chromosome in breeding programs.     

Molecular mapping of stripe rust resistance gene <Emphasis Type="Italic">YrHu</Emphasis> derived from <Emphasis Type="Italic">Psathyrostachys huashanica</Emphasis>

Wheat stripe rust is a destructive disease that affects most wheat-growing areas worldwide. Resistance genes from related species and genera add to the genetic diversity available to wheat breeding programs. The stripe rust-resistant introgression line H9020-17-25-6-4 was developed from a cross of resistant Psathyrostachys huashanica with the susceptible wheat cultivar 7182. H9020-17-25-6-4 is resistant to all existing Chinese stripe rust races, including the three most widely virulent races, CYR32, CYR33, and V26. We attempted to characterize this new line by genomic in situ hybridization (GISH) and genetic analysis. GISH using P. huashanica genomic DNA as a probe indicated that the translocated segment was too small to be detected. Genetic analysis involving F₁, F₂, and F_2:3 materials derived from a cross of Mingxian 169 and H9020-17-25-6-4 indicated that a single dominant gene from H9020-17-25-6-4, temporarily designated YrHu, conferred resistance to CYR29 and CYR33. A genetic map consisting of four simple sequence repeat, two sequence-tagged site (STS), and two sequence-related amplified polymorphism markers was constructed. YrHu was located on the short arm of chromosome 3A and was about 0.7 and 1.5 cM proximal to EST-STS markers BG604577 and BE489244, respectively. Both the gene and the closely linked markers could be used in marker-assisted selection.     

An intercalary translocation from <Emphasis Type="Italic">Agropyron</Emphasis><Emphasis Type="Italic">cristatum</Emphasis> 6P chromosome into common wheat confers enhanced kernel number per spike

Main conclusion

This study explored 6P chromosomal translocations in wheat, and determined the effects of 6P intercalary chromosome segments on kernel number per wheat spike. Exploiting and utilising gene(s) from wild relative species has become an essential strategy for wheat crop improvement. In the translocation line Pubing2978, the intercalary 6P chromosome segment from Agropyron cristatum (L.) Gaertn. (2n = 4x = 28, PPPP) carried valuable multi-kernel gene(s) and was selected from the offspring of the common wheat plant Fukuho and the irradiated wheat-A. cristatum 6P disomic substitution line 4844-8. Genomic in situ hybridisation (GISH), dual-colour fluorescence in situ hybridisation (FISH), and molecular markers were used to detect the small segmental 6P chromosome in the wheat background and its translocation breakpoint. Cytological studies demonstrated that Pubing2978 was a T1AS-6PL-1AS·1AL intercalary translocation with 42 chromosomes. The breakpoint was located near the centromeric region on the wheat chromosome 1AS and was flanked by the markers SSR12 and SSR283 based on an F₂ linkage map. The genotypic data, combined with the phenotypic information, implied that A. cristatum 6P chromosomal segment plays an important role in regulating the kernel number per spike (KPS). By comparison, the mean value of KPS in plants with translocations was approximately 10 higher than that in plants without translocations in three segregated populations. Moreover, the improvement in KPS was likely achieved by increasing both the spikelet number per spike (SNS) and the kernel number per spikelet. These excellent agronomic traits laid the foundation for further investigation of valuable genes and make the Pubing2978 line a promising germplasm for wheat breeding.

     

Molecular Analysis of the Triticale Lines with Different <Emphasis Type="Italic">Vrn</Emphasis> Gene Systems Using Microsatellite Markers and Hybridization In Situ

Hexaploid triticale (×Triticosecale Wittmack) lines were examined using molecular markers and the hybridization in situ technique. Triticale lines were generated based on wheat varieties differing by the Vrn gene systems and the earing times. Molecular analysis was performed using Xgwm and Xrms microsatellite markers with the known chromosomal localization in the common wheat Triticum aestivum, and rye Secale cereale genomes. Comparative molecular analysis of triticale lines and their parental forms showed that all lines contained A and B genomes of common wheat and also rye homoeologous chromosomes. In the three lines the presence of D genome markers, mapped to the chromosomes 2D and 7D, was demonstrated. This was probably the consequence of the translocations of homoeologous chromosomes from wheat genomes, which took part during the process of triticale formation. The data obtained by use of genomic in situ hybridization supported the data of molecular genetic analysis. In none of the lines wheat-rye translocations or recombinations were observed. These findings suggest that the change of the period between the seedling appearance and earing time in triticale lines compared to the initial wheat lines, resulted from the inhibitory effect of rye genome on wheat vernalization genes.     

The eyespot resistance genes <Emphasis Type="Italic">Pch1</Emphasis> and <Emphasis Type="Italic">Pch2</Emphasis> of wheat are not homoeoloci

Key message

Phenotyping and mapping data reveal that chromosome intervals containing eyespot resistance genes Pch1 and Pch2 on 7D and 7A, respectively, do not overlap, and thus, these genes are not homoeloci.

Abstract

Eyespot is a stem-base fungal disease of cereals growing in temperate regions. Two main resistances are currently available for use in wheat. Pch1 is a potent single major gene transferred to wheat from Aegilops ventricosa and located on the distal end of chromosome 7D. Pch2, a moderate resistance deriving from Cappelle Desprez, is located at the end of 7AL. The relative positions of Pch1 and Pch2 on 7D and 7A, respectively, suggest that they are homoeoloci. A single seed decent recombinant F7 population was used to refine the position of Pch2 on 7A. New markers designed to 7D also allowed the position of Pch1 to be further defined. We exploited the syntenic relationship between Brachypodium distachyon and wheat to develop 7A and 7D specific KASP markers tagging inter-varietal and interspecific SNPs and allow the comparison of the relative positions of Pch1 and Pch2 on 7D and 7A. Together, phenotyping and mapping data reveal that the intervals containing Pch1 and Pch2 do not overlap, and thus, they cannot be considered homoeloci. Using this information, we analysed two durum wheat lines carrying Pch1 on 7A to determine whether the Ae.ventricosa introgression extended into the region associated with Pch2. This identified that the introgression is distal to Pch2 on 7A, providing further evidence that the genes are not homoeoloci. However, it is feasible to use this material to pyramid Pch1 and Pch2 on 7A in a tetraploid background and also to increase the copy number of Pch1 in combination with Pch2 in a hexaploid background.

     

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.     

Production of wheat-rye substitution lines based on winter rye cultivars with karyotype identification by means of C-banding,GISH, and SSR markers

The study presents a continuation of the research aimed at producing of wheat-rye substitution lines (2n = 42) based on the cross (Triticum aestivum L. × Secale sereale L.) × Triticum aestivum L., and using winter rye cultivars Vyatka and Vietnamskaya Mestnaya. In BC 1 F 5 two lines were identified, having karyotypes in which a pair of homologous wheat chromosomes was substituted by a homeologous pair of rye chromosomes. The chromosome composition of these lines was analyzed using C-banding, GISH, and SSR markers. It was demonstrated that karyotype of each line included a single pair of rye chromosomes and lacked wheat-rye translocations. The rye chromosomes were identified, and the chromosomes of wheat, at which the substitutions occurred, were determined. The lines generated by crosses with rye of Vyatka and Vietnamskaya Mestnaya cultivars were designated 1Rv(1A) and 5Rviet(5A), respectively. Chromosome identification and classification of the lines makes it possible to use them in breeding programs and genetic studies.     

Mapping of novel powdery mildew resistance gene(s) from <Emphasis Type="Italic">Agropyron cristatum</Emphasis> chromosome 2P

Key message

A physical map of Agropyron cristatum 2P chromosome was constructed for the first time and the novel powdery mildew resistance gene(s) from chromosome 2P was(were) also mapped.

Abstract

Agropyron cristatum (L.) Gaertn. (2n = 28, PPPP), a wild relative of common wheat, is highly resistant to powdery mildew. Previous studies showed that wheat-A. cristatum 2P disomic addition line II-9-3 displayed high resistance to powdery mildew, and the resistance was attributable to A. cristatum chromosome 2P. To utilize and physically map the powdery mildew resistance gene(s), 15 wheat-A. cristatum 2P translocation lines and three A. cristatum 2P deletion lines with different chromosomal segment sizes, obtained from II-9-3 using ⁶⁰Co-γ ray irradiation, were characterized using cytogenetic and molecular marker analysis. A. cristatum 2P chromosomal segments in the translocations were translocated to different wheat chromosomes, including 1A, 4A, 5A, 6A, 7A, 1B, 2B, 3B, 7B, 3D, 4D, and 6D. A physical map of the 2P chromosome was constructed with 82 STS markers, consisting of nine bins with 34 markers on 2PS and eight bins with 48 markers on 2PL. The BC₁F₂ populations of seven wheat-A. cristatum 2P translocation lines (2PT-3, 2PT-4, 2PT-5, 2PT-6, 2PT-8, 2PT-9, and 2PT-10) were developed by self-pollination, tested with powdery mildew and genotyped with 2P-specific STS markers. From these results, the gene(s) conferring powdery mildew resistance was(were) located on 2PL bin FL 0.66–0.86 and 19 2P-specific markers were identified in this bin. Moreover, two new powdery mildew-resistant translocation lines (2PT-4 and 2PT-5) with small 2PL chromosome segments were obtained. The newly developed wheat lines with powdery mildew resistance and the closely linked molecular markers will be valuable for wheat disease breeding in the future.

     

Genome-wide association mapping of resistance to eyespot disease (<Emphasis Type="Italic">Pseudocercosporella herpotrichoides</Emphasis>) in European winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) and fine-mapping of <Emphasis Type="Italic">Pch1</Emphasis>

Key message

Genotypes with recombination events in the Triticum ventricosum introgression on chromosome 7D allowed to fine-map resistance gene Pch1, the main source of eyespot resistance in European winter wheat cultivars.

Abstract

Eyespot (also called Strawbreaker) is a common and serious fungal disease of winter wheat caused by the necrotrophic fungi Oculimacula yallundae and Oculimacula acuformis (former name Pseudocercosporella herpotrichoides). A genome-wide association study (GWAS) for eyespot was performed with 732 microsatellite markers (SSR) and 7761 mapped SNP markers derived from the 90 K iSELECT wheat array using a panel of 168 European winter wheat varieties as well as three spring wheat varieties and phenotypic evaluation of eyespot in field tests in three environments. Best linear unbiased estimations (BLUEs) were calculated across all trials and ranged from 1.20 (most resistant) to 5.73 (most susceptible) with an average value of 4.24 and a heritability of H ² = 0.91. A total of 108 SSR and 235 SNP marker–trait associations (MTAs) were identified by considering associations with a ?log₁₀ (P value) ≥3.0. Significant MTAs for eyespot-score BLUEs were found on chromosomes 1D, 2A, 2D, 3D, 5A, 5D, 6A, 7A and 7D for the SSR markers and chromosomes 1B, 2A, 2B, 2D, 3B and 7D for the SNP markers. For 18 varieties (10.5%), a highly resistant phenotype was detected that was linked to the presence of the resistance gene Pch1 on chromosome 7D. The identification of genotypes with recombination events in the introgressed genomic segment from Triticum ventricosum harboring the Pch1 resistance gene on chromosome 7DL allowed the fine-mapping of this gene using additional SNP markers and a potential candidate gene Traes_7DL_973A33763 coding for a CC-NBS-LRR class protein was identified.

     

Development of a complete set of wheat–barley group-7 Robertsonian translocation chromosomes conferring an increased content of β-glucan

Key message

A complete set of six compensating Robertsonian translocation chromosomes involving barley chromosome 7H and three chromosomes of hexaploid wheat was produced. Grain β-glucan content increased in lines containing 7HL.

Abstract

Many valuable genes for agronomic performance, disease resistance and increased yield have been transferred from relative species to wheat (Triticum aestivum L.) through whole-arm Robertsonian translocations (RobT). Although of a great value, the sets of available translocations from barley (Hordeum vulgare L.) are limited. Here, we present the production of a complete set of six compensating RobT chromosomes involving barley chromosome 7H and three group-7 chromosomes of wheat. The barley group-7 long-arm RobTs had a higher grain β-glucan content compared to the wheat control. The β-glucan levels varied depending on the temperature and were higher under hot conditions. Implicated in this increase, the barley cellulose synthase-like F6 gene (CslF6) responsible for β-glucan synthesis was physically mapped near the centromere in the long arm of barley chromosome 7H. Likewise, wheat CslF6 homoeologs were mapped near the centromere in the long arms of all group-7 wheat chromosomes. With the set of novel wheat–barley translocations, we demonstrate a valuable increase of β-glucan, along with a resource of genetic stocks that are likely to carry many other important genes from barley into wheat.

     

Induced Homoeologous Pairing for Transfer of Useful Variability for High Grain Fe and Zn from <Emphasis Type="Italic">Aegilops kotschyi</Emphasis> into Wheat

Biofortification of bread wheat by the transfer of useful variability of high grain Fe and Zn from Aegilops kotschyi through induced homoeologous pairing is the most feasible approach to alleviate micronutrient malnutrition worldwide. Deficiency of chromosome 5B in interspecific hybrids allows homoeologous pairing and recombination of chromosomes of wheat with those of the related species. The interspecific hybrid plants without 5B chromosome showed much higher chromosome pairing than did the plants with 5B. The F₁ plants without 5B chromosome were selected and repeatedly backcrossed with wheat cultivar PBW343. The chromosome number of BC₂F₁ plants ranged from 43 to 60 with several univalents and multivalents. Molecular markers and GISH analysis confirmed the introgression of U/S chromosomes of Ae. kotschyi and their fragments in wheat. The BC₂F₂ plants showed up to 125 % increase in Fe and 158 % increase in Zn compared to PBW343 with Lr24 and Yr36. Induced homoeologous pairing in the absence of 5B was found to be an effective approach for transfer of useful variability for enhanced grain Fe and Zn content for biofortification of wheat for high grain micronutrient content.     

The <Emphasis Type="Italic">Agropyron cristatum</Emphasis> karyotype,chromosome structure and cross-genome homoeology as revealed by fluorescence in situ hybridization with tandem repeats and wheat single-gene probes

Key message

Fluorescence in situ hybridization with probes for 45 cDNAs and five tandem repeats revealed homoeologous relationships of Agropyron cristatum with wheat. The results will contribute to alien gene introgression in wheat improvement.

Abstract

Crested wheatgrass (Agropyron cristatum L. Gaertn.) is a wild relative of wheat and a promising source of novel genes for wheat improvement. To date, identification of A. cristatum chromosomes has not been possible, and its molecular karyotype has not been available. Furthermore, homoeologous relationship between the genomes of A. cristatum and wheat has not been determined. To develop chromosome-specific landmarks, A. cristatum genomic DNA was sequenced, and new tandem repeats were discovered. Their distribution on mitotic chromosomes was studied by fluorescence in situ hybridization (FISH), which revealed specific patterns for five repeats in addition to 5S and 45S ribosomal DNA and rye subtelomeric repeats pSc119.2 and pSc200. FISH with one tandem repeat together with 45S rDNA enabled identification of all A. cristatum chromosomes. To analyze the structure and cross-species homoeology of A. cristatum chromosomes with wheat, probes for 45 mapped wheat cDNAs covering all seven chromosome groups were localized by FISH. Thirty-four cDNAs hybridized to homoeologous chromosomes of A. cristatum, nine hybridized to homoeologous and non-homoeologous chromosomes, and two hybridized to unique positions on non-homoeologous chromosomes. FISH using single-gene probes revealed that the wheat-A. cristatum collinearity was distorted, and important structural rearrangements were observed for chromosomes 2P, 4P, 5P, 6P and 7P. Chromosomal inversions were found for pericentric region of 4P and whole chromosome arm 6PL. Furthermore, reciprocal translocations between 2PS and 4PL were detected. These results provide new insights into the genome evolution within Triticeae and will facilitate the use of crested wheatgrass in alien gene introgression into wheat.

     

Precise transfers of genes for high grain iron and zinc from wheat-<Emphasis Type="Italic">Aegilops</Emphasis> substitution lines into wheat through pollen irradiation

Nearly 2 billion people worldwide are suffering from iron (Fe) deficiency anemia and zinc (Zn) deficiency. The available elite bread wheat cultivars have inherently low grain micronutrient content. Biofortification for grain Fe and Zn content is one of the most feasible and cost-effective approach for combating widespread deficiency of the micronutrients. QTL controlling high grain Fe and Zn have been mapped on groups 2 and 7 chromosomes of Triticeae. The present study was initiated for precise transfers of genes for high grain Fe and Zn on group 2 and 7 chromosomes of wheat-Aegilops substitution lines to wheat cultivars using pollen radiation hybridization. The pollen radiation hybrids (PRH₁) derived from 1.75 krad irradiated spikes showed the presence of univalents and multivalents in meiotic metaphase-I indicating the effectiveness of radiation dose. In the advanced generation PRH₅, the plants selected with stable chromosome number and high grain Fe and Zn content were analyzed with wheat groups 2 and 7 chromosome specific intron targeted amplified polymorphism (ITAP) markers of the metal homeostasis genes to monitor the transfers of alien genes from the substituted Aegilops chromosomes. The group 2 chromosome derivatives showed the presence of NAS2, FRO2, VIT1, and ZIP2 Aegilops genes whereas the group 7 derivatives had YSL15, NAM, NRAMP5, IRO3, and IRT2 Aegilops genes. The pollen radiation hybrids of both the groups 2 and 7 chromosomes showed more than 30% increase in grain Fe and Zn content with improved yield than the elite wheat cultivar PBW343 LrP indicating small and compensating transfers of metal homeostasis genes of Aegilops into wheat.     

Exploiting the <Emphasis Type="Italic">ZIP4</Emphasis> homologue within the wheat <Emphasis Type="Italic">Ph1</Emphasis> locus has identified two lines exhibiting homoeologous crossover in wheat-wild relative hybrids

Despite possessing related ancestral genomes, hexaploid wheat behaves as a diploid during meiosis. The wheat Ph1 locus promotes accurate synapsis and crossover of homologous chromosomes. Interspecific hybrids between wheat and wild relatives are exploited by breeders to introgress important traits from wild relatives into wheat, although in hybrids between hexaploid wheat and wild relatives, which possess only homoeologues, crossovers do not take place during meiosis at metaphase I. However, in hybrids between Ph1 deletion mutants and wild relatives, crossovers do take place. A single Ph1 deletion (ph1b) mutant has been exploited for the last 40 years for this activity. We show here that chemically induced mutant lines, selected for a mutation in TaZIP4-B2 within the Ph1 locus, exhibit high levels of homoeologous crossovers when crossed with wild relatives. Tazip4-B2 mutant lines may be more stable over multiple generations, as multivalents causing accumulation of chromosome translocations are less frequent. Exploitation of such Tazip4-B2 mutants, rather than mutants with whole Ph1 locus deletions, may therefore improve introgression of wild relative chromosome segments into wheat.     

Mapping of common bunt resistance gene <Emphasis Type="Italic">Bt9</Emphasis> in wheat

Key message

The Bt9 resistance locus was mapped and shown to be distinct from the Bt10 locus. New markers linked to Bt9 have been identified and may be used to breed for resistance towards the seed-borne disease.

Abstract

Increasing organic wheat production in Denmark, and in other wheat-producing areas, in conjunction with legal requirements for organic seed production, may potentially lead to a rise in common bunt occurrence. As systemic pesticides are not used in organic farming, organic wheat production systems may benefit from genetic resistances. However, little is known about the underlying genetic mechanisms and locations of the resistance factors for common bunt resistance in wheat. A double haploid (DH) population segregating for common bunt resistance was used to identify the chromosomal location of common bunt resistance gene Bt9. DH lines were phenotyped in three environments and genotyped with DArTseq and SSR markers. The total length of the resulting linkage map was 2882 cM distributed across all 21 wheat chromosomes. Bt9 was mapped to the distal end of chromosome 6DL. Since wheat common bunt resistance gene Bt10 is also located on chromosome 6D, the possibility of their co-location was investigated. A comparison of marker sequences linked to Bt9 and Bt10 on physical maps of chromosome 6D confirmed that Bt9 and Bt10 are two distinct resistance factors located at the distal (6DL) and proximal (6DS) end, respectively, of chromosome 6D. Five new SSR markers Xgpw4005-1, Xgpw7433, Xwmc773, Xgpw7303 and Xgpw362 and many SNP and PAV markers flanking the Bt9 resistance locus were identified and they may be used in the future for marker-assisted selection.

     

Characterisation of <Emphasis Type="Italic">Thinopyrum bessarabicum</Emphasis> chromosomes through genome-wide introgressions into wheat

Key message

Genome-wide introgressions of Thinopyrum bessarabicum into wheat resulted in 12 recombinant lines. Cytological and molecular techniques allowed mapping of 1150 SNP markers across all seven chromosomes of the J genome.

Abstract

Thinopyrum bessarabicum (2n = 2x = 14, JJ) is an important source for new genetic variation for wheat improvement due to its salinity tolerance and disease resistance. Its practical utilisation in wheat improvement can be facilitated through development of genome-wide introgressions leading to a variety of different wheat–Th . bessarabicum translocation lines. In this study, we report the generation of 12 such wheat–Th . bessarabicum recombinant lines, through two different crossing strategies, which were characterized using sequential single colour and multi-colour genomic in situ hybridization (sc-GISH and mc-GISH), multi-colour fluorescent in situ hybridization (mc-FISH) and single nucleotide polymorphic (SNP) DNA markers. We also detected 13 lines containing different Th. bessarabicum chromosome aberrations through sc-GISH. Through a combination of molecular and cytological analysis of all the 25 lines containing Th. bessarabicum recombinants and chromosome aberrations we were able to physically map 1150 SNP markers onto seven Th. bessarabicum J chromosomes which were divided into 36 segmental blocks. Comparative analysis of the physical map of Th. bessarabicum and the wheat genome showed that synteny between the two species is highly conserved at the macro-level and confirmed that Th. bessarabicum contains the 4/5 translocation also present in the A genome of wheat. These wheat–Th . bessarabicum recombinant lines and SNP markers provide a useful genetic resource for wheat improvement with the latter having a wider impact as a tool for detection of introgressions from other Thinopyrum species containing the J or a closely-related genome such as Thinopyrum intermedium (J^rJ^rJ^vsJ^vsStSt) and Thinopyrum elongatum (E^eE^e), respectively.

     

<Emphasis Type="Italic">Pm62</Emphasis>, an adult-plant powdery mildew resistance gene introgressed from <Emphasis Type="Italic">Dasypyrum villosum</Emphasis> chromosome arm 2VL into wheat

Key message

Pm62, a novel adult-plant resistance (APR) gene against powdery mildew, was transferred from D. villosum into common wheat in the form of Robertsonian translocation T2BS.2VL#5.

Abstract

Powdery mildew, which is caused by the fungus Blumeria graminis f. sp. tritici, is a major disease of wheat resulting in substantial yield and quality losses in many wheat production regions of the world. Introgression of resistance from wild species into common wheat has application for controlling this disease. A Triticum durum-Dasypyrum villosum chromosome 2V#5 disomic addition line, N59B-1 (2n?=?30), improved resistance to powdery mildew at the adult-plant stage, which was attributable to chromosome 2V#5. To transfer this resistance into bread wheat, a total of 298 BC₁F₁ plants derived from the crossing between N59B-1 and Chinese Spring were screened by combined genomic in situ hybridization and fluorescent in situ hybridization, 2V-specific marker analysis, and reaction to powdery mildew to confirm that a dominant adult-plant resistance gene, designated as Pm62, was located on chromosome 2VL#5. Subsequently, the 2VL#5 (2D) disomic substitution line (NAU1825) and the homozygous T2BS.2VL#5 Robertsonian translocation line (NAU1823), with normal plant vigor and full fertility, were identified by molecular and cytogenetic analyses of the BC₁F₂ generation. The effects of the T2BS.2VL#5 recombinant chromosome on agronomic traits were also evaluated in the F₂ segregation population. The results suggest that the translocated chromosome may have no distinct effect on plant height, 1000-kernel weight or flowering period, but a slight effect on spike length and seeds per spike. The translocation line NAU1823 has being utilized as a novel germplasm in breeding for powdery mildew resistance, and the effects of the T2BS.2VL#5 recombinant chromosome on yield-related and flour quality characters will be further assessed.