Search

Key message: Two recessive powdery mildew resistance loci pmAeCIae8_2DS and pmAeCIae8_7DS from Aegilops tauschii were mapped and two synthesized hexaploid wheat lines were developed by distant hybridization. Wheat powdery mildew (Pm), one of the worldwide destructive fungal diseases, causes significant yield loss up to 30%. The identification of new Pm resistance genes will enrich the genetic diversity of wheat breeding for Pm resistance. Aegilops tauschii is the ancestor donor of sub-genome D of hexaploid wheat. It provides beneficial genes that can be easily transferred into wheat by producing synthetic hexaploid wheat followed by genetic recombination. We assessed the Pm resistance level of 35 Ae. tauschii accessions from different origins. Accession CIae8 exhibited high Pm resistance. Inheritance analysis and gene mapping were performed using F2 and F2:3 populations derived from the cross between CIae8 and a Pm susceptible accession PI574467. The Pm resistance of CIae8 was controlled by two independent recessive genes. Bulked segregate analysis using a 55 K SNP array revealed the SNPs were mainly enriched into genome regions, i.e. 2DS (13.5–20 Mb) and 7DS (4.0–15.5 Mb). The Pm resistance loci were named as pmAeCIae8_2DS and pmAeCIae8_7DS, respectively. By recombinant screening, we narrowed the pmAeCIae8_2DS into a 370-kb interval flanked by markers CINAU-AE7800 (14.89 Mb) and CINAU-AE20 (15.26 Mb), and narrowed the pmAeCIae8_7DS into a 260-kb interval flanked by markers CINAU-AE58 (4.72 Mb) and CINAU-AE25 (4.98 Mb). The molecular markers closely linked with the resistance loci were developed, and two synthesized hexaploid wheat (SHW) lines were produced. These laid the foundation for cloning of the two resistance loci and for transferring the resistance into common wheat. [ABSTRACT FROM AUTHOR]

Key message: A new FHB resistance locus FhbRc1 was identified from the R. ciliaris chromosome 7Sc and transferred into common wheat by developing alien translocation lines. Fusarium head blight (FHB) caused by multiple Fusarium species is a globally destructive disease of common wheat. Exploring and utilization of resources with FHB resistance are the most effective and environmentally beneficial approach for the disease control. Roegneria ciliaris (Trin.) Nevski (2n = 4x = 28, ScScYcYc), a tetraploid wheat wild relative, possesses high resistance to FHB. In the previous study, a complete set of wheat-R. ciliaris disomic addition (DA) lines were evaluated for FHB resistance. DA7Sc had stable FHB resistance, which was confirmed to be derived from alien chromosome 7Sc. We tentatively designated the resistant locus as FhbRc1. For better utilization of the resistance in wheat breeding, we developed translocations by inducing chromosome structural aberrations using iron irradiation and the homologous pairing gene mutant ph1b. Totally, 26 plants having various 7Sc structural aberrations were identified. By marker analysis, a cytological map of 7Sc was constructed and 7Sc was dissected into 16 cytological bins. Seven alien chromosome aberration lines, which all had the bin 7Sc-1 on the long arm of 7Sc, showed enhanced FHB resistance. Thus, FhbRc1 was mapped to the distal region of 7ScL. A homozygous translocation line T4BS·4BL-7ScL (NAURC001) was developed. It showed improved FHB resistance, while had no obvious genetic linkage drag for the tested agronomic traits compared with the recurrent parent Alondra’s. When transferring the FhbRc1 into three different wheat cultivars, the derived progenies having the translocated chromosome 4BS·4BL-7ScL all showed improved FHB resistance. This revealed the potential value of the translocation line in wheat breeding for FHB resistance. [ABSTRACT FROM AUTHOR]

Key message: The QYm.nau-2D locus conferring wheat yellow mosaic virus resistance is an exotic introgression and we developed 11 diagnostic markers tightly linked to QYm.nau-2D. Wheat yellow mosaic virus (WYMV) is a serious disease of winter wheat in China. Breeding resistant varieties is the most effective strategy for WYMV control. A WYMV resistant locus QYm.nau-2D on the chromosome arm 2DL has been repeatedly reported but the mapped region is large. In the present study, we screened recombinants using a biparental population and mapped QYm.nau-2D into an 18.8 Mb physical interval. By genome-wide association studies of 372 wheat varieties for WYMV resistance in four environments, we narrowed down QYm.nau-2D into a 16.4 Mb interval. Haplotype analysis indicated QYm.nau-2D were present as six different states due to recombination during hybridization breeding. QYm.nau-2D was finally mapped into a linkage block of 11.2 Mb. Chromosome painting using 2D specific probes and collinearity analysis among the published sequences corresponding to QYm.nau-2D region indicated the block was an exotic introgression. The Illumina-sequenced reads of four diploid Aegilops species were mapped to the sequence of Fielder, a variety having the introgression. The mapping reads were significantly increased at the putative introgression regions of Fielder. Ae. uniaristata (NN) had the highest mapping reads, suggesting that QYm.nau-2D was possibly an introgression from genome N. We investigated the agronomic performances of different haplotypes and observed no linkage drag of the alien introgression for the 15 tested traits. For marker-assisted selection of QYm.nau-2D, we developed 11 diagnostic markers tightly linked to the locus. This research provided a case study of an exotic introgression, which has been utilized in wheat improvement for WYMV resistance. [ABSTRACT FROM AUTHOR]

Key message: A cytological map of Haynaldia villosa chromosome arm 4VS was constructed to facilitate the identification and utilization of beneficial genes on 4VS. Induction of wheat-alien chromosomal structure aberrations not only provides new germplasm for wheat improvement, but also allows assignment of favorable genes to define physical regions. Especially, the translocation or introgression lines carrying alien chromosomal fragments with different sizes are useful for breeding and alien gene mapping. Chromosome arm 4VS of Haynaldia villosa (L.) Schur (syn. Dasypyrum villosum (L.) P. Candargy) confers resistances to eyespot and wheat yellow mosaic virus (WYMV). In this research, we used both irradiation and the pairing homoeologous gene (Ph) mutant to induce chromosomal aberrations or translocations. By using the two approaches, a structural aberration library of chromosome arm 4VS was constructed. In this library, there are 57 homozygous structural aberrations, in which, 39 were induced by the Triticum aestivum cv. Chinese Spring (CS) ph1b mutant (CS ph1b) and 18 were induced by irradiation. The aberrations included four types, i.e., terminal translocation, interstitial translocation, deletion and complex structural aberration. The 4VS cytological map was constructed by amplification in the developed homozygous aberrations using 199 4VS-specific markers, which could be allocated into 39 bins on 4VS. These bins were further assigned to their corresponding physical regions of chromosome arm 4DS based on BLASTn search of the marker sequences against the reference sequence of Aegilops tauschii Cosson. The developed genetic stocks and cytological map provide genetic stocks for wheat breeding as well as alien gene tagging. [ABSTRACT FROM AUTHOR]

The domesticated gene Q on wheat chromosome 5A (5AQ) encodes an AP2 transcription factor. The 5AQ was originated from a G to A mutation in exon 8 and/or C to T transition in exon 10 and resulted in free-threshing and subcompact spike characters of bread wheat. The Q homeoalleles on 5B and 5D are either a pseudogene or expressed at a low level. Our previous study identified a mutant, named NAUH164, by EMS treatment of wheat variety Sumai 3. The mutant exhibits compact spike and dwarfness, and the mutated locus Rht23 was mapped to the distal of the long arm of chromosome 5D, where 5Dq was located. To investigate the relationship of Rht23 and 5Dq, sequences and expression patterns of 5Dq from Sumai 3 and NAUH164 were compared. The two genotypes had a G3147A single nucleotide polymorphism (SNP), which was predicted to be located within the miR172 binding site of 5Dq. Based on this SNP, an SNP marker was developed and linkage analysis using a (NAUH164 × Alondra’s) RIL population showed the marker was co-segregated with the Rht23 mutant traits. The qRT-PCR and Northern blot showed that in NAUH164, the expression of 5Dq was significantly up-regulated, and consistently, the expression of Ta-miR172 was down-regulated in leaves, stems and spikes. Our results demonstrated that point mutation in the miR172 binding site of the 5Dq likely increased its transcript level via a reduction in miRNA-dependent degradation, and this resulted in pleiotropic effects on spike compactness and plant dwarfness. [ABSTRACT FROM AUTHOR]

Key message: A complete set wheat-R. ciliaris disomic addition lines (DALs) were characterized and the homoeologous groups and genome affinities of R. ciliaris chromosomes were determined.Abstract: Wild relatives are rich gene resources for cultivated wheat. The development of alien addition chromosome lines not only greatly broadens the genetic diversity, but also provides genetic stocks for comparative genomics studies. Roegneria ciliaris (genome ScScYcYc), a tetraploid wild relative of wheat, is tolerant or resistant to many abiotic and biotic stresses. To develop a complete set of wheat-R. ciliaris disomic addition lines (DALs), we undertook a euplasmic backcrossing program to overcome allocytoplasmic effects and preferential chromosome transmission. To improve the efficiency of identifying chromosomes from Sc and Yc, we established techniques including sequential genomic in situ hybridization/fluorescence in situ hybridization (FISH) and molecular marker analysis. Fourteen DALs of wheat, each containing one pair of R. ciliaris chromosomes pairs, were characterized by FISH using four repetitive sequences [pTa794, pTa71, RcAfa and (GAA)10] as probes. One hundred and sixty-two R. ciliaris-specific markers were developed. FISH and marker analysis enabled us to assign the homoeologous groups and genome affinities of R. ciliaris chromosomes. FHB resistance evaluation in successive five growth seasons showed that the amphiploid, DA2Yc, DA5Yc and DA6Sc had improved FHB resistance, indicating their potential value in wheat improvement. The 14 DALs are likely new gene resources and will be phenotyped for more agronomic performances traits. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Key message: A novel high-tillering dwarf mutant in common wheat Wangshuibai was characterized and mapped to facilitate breeding for plant height and tiller and the future cloning of the causal gene. Abstract: Tiller number and plant height are two major agronomic traits in cereal crops affecting plant architecture and grain yield. NAUH167, a mutant of common wheat landrace Wangshuibai induced by ethylmethyl sulfide (EMS) treatment, exhibits higher tiller number and reduced plant height. Microscope observation showed that the dwarf phenotype was attributed to the decrease in the number of cells and their length. The same as the wild type, the mutant was sensitive to exogenous gibberellins. Genetic analysis showed that the high-tillering number and dwarf phenotype were related and controlled by a partial recessive gene. Using a RIL population derived from the cross NAUH167/Sumai3, a molecular marker-based genetic map was constructed. The map consisted of 283 loci, spanning a total length of 1007.98 cM with an average markers interval of 3.56 cM. By composite interval mapping, a stable major QTL designated QHt.nau- 2D controlling both traits, was mapped to the short arm of chromosome 2D flanked by markers Xcfd11 and Xgpw361. To further map the QHt.nau- 2D loci, another population consisted of 180 F progeny from a cross 2011I-78/NAUH167 was constructed. Finally, QHt.nau- 2D was located within a genetic region of 0.8 cM between markers QHT239 and QHT187 covering a predicted physical distance of 6.77 Mb. This research laid the foundation for map-based cloning of QHt.nau- 2D and would facilitate the characterization of plant height and tiller number in wheat. [ABSTRACT FROM AUTHOR]

The wheat spindle streak mosaic virus (WSSMV) or wheat yellow mosaic virus (WYMV) resistance gene, Wss1, from Haynaldia villosa, was previously mapped to the chromosome arm 4VS by the development of 4V (4D) substitution and T4DL·4VS translocation lines. For better utilization and more accurate mapping of the Wss1, in this research, the CS ph1b mutant was used to induce new translocations with shortened 4VS chromosome fragments. Thirty-five homozygous translocations with different alien fragment sizes and breakpoints of 4VS were identified by GISH and molecular marker analysis. By field test, it was found that all the identified terminal translocations characterized as having smaller 4VS chromosome segments in the chromosome 4DS were highly resistant to WYMV, while all the interstitial translocations with 4VS inserted into the 4DS were WYMV susceptible. Marker analysis using 32 4VS-specific markers showed that both the terminal and interstitial translocations had different alien fragment sizes. Five specific markers could be detected in the WYMV-resistant terminal translocation line NAU421 with the shortest introduced 4VS fragment, indicating they can be used for marker-assisted selection in wheat breeding. Based on the resistance evaluation, GISH and molecular marker analysis of the available translocations, the gene(s) conferring the WYMV resistance on 4VS could be further cytologically mapped to the distal region of 4VS, immersed in the bin of FL 0.78–1.00. The newly developed small fragment translocations with WYMV resistance and 4VS specific markers have laid solid groundwork for the utilization in wheat breeding for WYMV resistance as well as further cloning of Wss1. [ABSTRACT FROM AUTHOR]

The wheat spindle streak mosaic virus (WSSMV) or wheat yellow mosaic virus (WYMV) resistance gene, Wss1, from Haynaldia villosa, was previously mapped to the chromosome arm 4VS by the development of 4V (4D) substitution and T4DL·4VS translocation lines. For better utilization and more accurate mapping of the Wss1, in this research, the CS ph1b mutant was used to induce new translocations with shortened 4VS chromosome fragments. Thirty-five homozygous translocations with different alien fragment sizes and breakpoints of 4VS were identified by GISH and molecular marker analysis. By field test, it was found that all the identified terminal translocations characterized as having smaller 4VS chromosome segments in the chromosome 4DS were highly resistant to WYMV, while all the interstitial translocations with 4VS inserted into the 4DS were WYMV susceptible. Marker analysis using 32 4VS-specific markers showed that both the terminal and interstitial translocations had different alien fragment sizes. Five specific markers could be detected in the WYMV-resistant terminal translocation line NAU421 with the shortest introduced 4VS fragment, indicating they can be used for marker-assisted selection in wheat breeding. Based on the resistance evaluation, GISH and molecular marker analysis of the available translocations, the gene(s) conferring the WYMV resistance on 4VS could be further cytologically mapped to the distal region of 4VS, immersed in the bin of FL 0.78–1.00. The newly developed small fragment translocations with WYMV resistance and 4VS specific markers have laid solid groundwork for the utilization in wheat breeding for WYMV resistance as well as further cloning of Wss1. [ABSTRACT FROM AUTHOR]