Cytomolecular discrimination of the A<Superscript>m</Superscript> chromosomes of <Emphasis Type="Italic">Triticum monococcum</Emphasis> and the A chromosomes of <Emphasis Type="Italic">Triticum aestivum</Emphasis> using microsatellite DNA repeats

The cytomolecular discrimination of the A^m- and A-genome chromosomes facilitates the selection of wheat-Triticum monococcum introgression lines. Fluorescence in situ hybridisation (FISH) with the commonly used DNA probes Afa family, 18S rDNA and pSc119.2 showed that the more complex hybridisation pattern obtained in T. monococcum relative to bread wheat made it possible to differentiate the A^m and A chromosomes within homoeologous groups 1, 4 and 5. In order to provide additional chromosomal landmarks to discriminate the A^m and A chromosomes, the microsatellite repeats (GAA)_n, (CAG)_n, (CAC)_n, (AAC)_n, (AGG)_n and (ACT)_n were tested as FISH probes. These showed that T. monococcum chromosomes have fewer, generally weaker, simple sequence repeat (SSR) signals than the A-genome chromosomes of hexaploid wheat. A differential hybridisation pattern was observed on 6A^m and 6A chromosomes with all the SSR probes tested except for the (ACT)_n probe. The 2A^m and 2A chromosomes were differentiated by the signals given by the (GAA)_n, (CAG)_n and (AAC)_n repeats, while only (GAA)_n discriminated the chromosomes 3A^m and 3A. Chromosomes 7A^m and 7A could be differentiated by the lack of (GAA)_n and (AGG)_n signals on 7A. As potential landmarks for identifying the A^m chromosomes, SSR repeats will facilitate the introgression of T. monococcum chromatin into wheat.     

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.

     

Development of V chromosome alterations and physical mapping of molecular markers specific to <Emphasis Type="Italic">Dasypyrum villosum</Emphasis>

Wheat-Dasypyrum villosum translocations were induced in the progeny of the amphiploid Triticum durum-D. villosum (AABBVV) by pollen irradiation. The rearranged V genome chromosomes were characterized by genomic/fluorescence in situ hybridization (GISH/FISH) and molecular markers. Twenty wheat-D. villosum translocation chromosomes were selected, including four centric, seven large segments, and nine small segments in a Chinese Spring (CS) background. The four centric translocations were subsequently identified by GISH/FISH and by molecular markers specific to chromosome arms of the Triticeae linkage groups. They were T5DL.4VL, T4BL.7VS, and T4BS.7VL as well as the compensating translocation T7AL.7VS. Using a combination of previously developed V chromosome alterations, 52 translocations or deletions that divided V chromosomes into 42 bins were employed for deletion mapping of molecular markers specific to D. villosum in a wheat background. Ninety-five expressed sequence tag (EST)-sequence-tagged site (STS) and seven SSR markers that were previously reported, as well as 72 STS markers screened in the present study, were physically allocated into 37 of 42 chromosome bins of D. villosum. Multiple loci of EST-STS markers were also mapped using CS nullisomic tetrasomic (NT) and ditelosomic (DT) genetic stocks. Most EST-STS homoeoloci were located on homoeologous chromosomes, suggesting a high degree of homology between the genomes of D. villosum and wheat. Four 4VL-specific markers detected homoeoloci on group 7 chromosomes of wheat, indicating that chromosome 4V of D. villosum shows some affinity to both wheat homoeologous groups 4 and 7. This is the first physical map of D. villosum, which will provide insight into the V genome for molecular breeding.     

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.

     

Development and characterization of a complete set of <Emphasis Type="Italic">Triticum aestivum</Emphasis>–<Emphasis Type="Italic">Roegneria ciliari</Emphasis>s disomic addition lines

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 S^cS^cY^cY^c), 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 S^c and Y^c, 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, DA2Y^c, DA5Y^c and DA6S^c 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.

     

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.     

Comparative analysis of <Emphasis Type="Italic">Agropyron intermedium</Emphasis> (Host) Beauv 6Ag<Superscript>i</Superscript> and 6Ag<Superscript>i</Superscript>2 chromosomes in bread wheat cultivars and lines with wheat–wheatgrass substitutions

A comparative study of wheat–wheatgrass substituted cultivars and lines resistant to leaf rust developed by the Agricultural Research Institute for Southeast Regions (Multi 6R, Belyanka, Favorit, Voevoda, Lebedushka) and Samara Agricultural Research Institute (Tulaikovskaya 5, Tulaikovskaya 10, Tulaikovskaya 100, Tulaikovskaya Zolotistaya) breeding was conducted. A complex analysis using molecular cytogenetic (C-differential banding, fluorescent (FISH) and genomic (GISH) in situ hybridization), molecular (PLUG markers), and biochemical (electrophoretic analysis of gliadins) markers demonstrated that they have a substitition of wheat chromosome 6D by the chromosomes 6Agⁱ and 6Agⁱ2 belonging to the J(=E) Agropyron intermedium (Host) Beauv (=Thinopyrum intermedium (Host) Barkworth & D.R. Dewey) subgenome. In spite of the fact that the chromosomes 6Agⁱ and 6Agⁱ2 differ in the C-banding pattern and demonstrated minor differences in the blocks of gliadin components, they had the identical pattern of pSc119.2 and pAs1 probe distribution and conjugated between themselves with insignificant disturbance. Thus, it was demonstrated that 6Agi and 6Agⁱ2 are homologous chromosomes; however, the question about allelism of their leaf rust resistance genes between themselves requires special studies. Nevertheless, using STS and SCAR markers and taking into account the type of reaction to Puccinia triticina, their non-allelism to the Lr9, Lr19, Lr24, Lr29, Lr38, and Lr47 genes was established. It was revealed that the 6Agⁱ and 6Agⁱ2 chromosomes have a different level of transmission in hybrid F₂ populations depending on the hybrid combination gene background.     

Diversity array technology (DArT) 56K analysis,confirmed by SNP markers,distinguishes one сrested wheatgrass <Emphasis Type="Italic">Agropyron</Emphasis> species from two others found in Kazakhstan

Molecular genetic polymorphism in three species and four subspecies of crested wheatgrass, Agropyron, was studied using 56K diversity array technology (DArT), and the results confirmed with four selected SNP Amplifluor markers. In total, 82 accessions from three species—A. desertorum, A. fragile, and two subspecies of A. cristatum (ssp. cristatum and ssp. pectinatum)—were collected from various regions of Kazakhstan or ordered from Genebank in Russia, for morphological taxonomy and molecular phylogenetic analyses. In the DArT clone analysis, two Agropyron species with narrow linear spikes, A. fragile and A. desertorum, were found to be genetically similar and fell within a single clade (A). Both species share similar eco-geographical origins. All samples of A. cristatum including the two subspecies, ssp. pectinatum and ssp. cristatum, which have short broad spikes, were interspersed within two other clades, B and C, more genetically distanced from the other species. Four SNP Amplifluor markers developed for genetic fragments on different chromosomes confirmed the distinction between the studied species. These results, derived from multiple molecular markers, suggest that the morphological taxonomy of these Agropyron species should be re-considered carefully in the future.     

Molecular cytogenetic characterization of <Emphasis Type="Italic">Triticum timopheevii</Emphasis> chromosomes provides new insight on genome evolution of <Emphasis Type="Italic">T. zhukovskyi</Emphasis>

Triticum timopheevii (2n = 4x = 28, GGA^tA^t) is a tetraploid wheat formerly cultivated in western Georgia. The natural allopolyploid Triticum zhukovskyi is a hexaploid taxon originated from hybridization of T. timopheevii with cultivated einkorn T. monococcum (2n = 2x = 14, A^mA^m). Karyotypically T. timopheevii and T. zhukovskyi differ from other tetraploid and hexaploid wheats and were assigned to the section Timopheevii of the genus Triticum L. Triticum timopheevii and T. zhukovskyi are resistant to many fungal diseases and therefore could potentially be utilized for wheat improvement. We were aiming to precisely identify all T. timopheevii chromosomes and to trace the evolution of T. zhukovskyi. For this, we developed a set of molecular cytogenetic landmarks based on eleven DNA probes. Each chromosome can now be characterized by two to eight probes. The pTa-535 sequence allows the identification of all A^t-genome chromosomes, whereas G-genome and some A^t-genome chromosomes can be identified using (GAA/CTT) _n and pSc119.2 probes. The probes pAesp_SAT86, pAs1, Spelt-1, Spelt-52 and 5S and 45S rDNA can be applied as additional markers to discriminate particular chromosomes or chromosomal regions. The distribution of (GAA/CTT) _n , pTa-535 and pSc119.2 DNA probes on T. timopheevii chromosomes is distinct from other tetraploid wheats and can therefore be used to track individual chromosomes in introgression programs. Our study confirms the origin of T. zhukovskyi from hybridization of T. timopheevii with T. monococcum; however, we show that the emergence was accompanied by changes involving mostly A^t-genome chromosomes. This may be due to the presence of two closely related A-genomes in the T. zhukovskyi karyotype.     

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.

     

Genetic Regulation of Meiotic Chromosome Pairing by Chromosome 3<Emphasis Type="Italic">D</Emphasis> of <Emphasis Type="Italic">Triticum aestivum</Emphasis>

IN hexaploid wheat (Triticum aestivum, 2n = 6x = 42) the constituent genomes A, B and D derive from closely related diploid species (2n = 2x = 14) within the sub-tribe Triticinae^1–4. The seven different chromosomes of each genome have genetically equivalent (homoeologous) chromosomes in the other two genomes⁵. Homoeologous chromosomes generally compensate each other in nullisomic-tetrasomic combinations⁵.     

Development of the first consensus genetic map of intermediate wheatgrass (<Emphasis Type="Italic">Thinopyrum intermedium</Emphasis>) using genotyping-by-sequencing

Key message

Development of the first consensus genetic map of intermediate wheatgrass gives insight into the genome and tools for molecular breeding.

Abstract

Intermediate wheatgrass (Thinopyrum intermedium) has been identified as a candidate for domestication and improvement as a perennial grain, forage, and biofuel crop and is actively being improved by several breeding programs. To accelerate this process using genomics-assisted breeding, efficient genotyping methods and genetic marker reference maps are needed. We present here the first consensus genetic map for intermediate wheatgrass (IWG), which confirms the species’ allohexaploid nature (2n = 6x = 42) and homology to Triticeae genomes. Genotyping-by-sequencing was used to identify markers that fit expected segregation ratios and construct genetic maps for 13 heterogeneous parents of seven full-sib families. These maps were then integrated using a linear programming method to produce a consensus map with 21 linkage groups containing 10,029 markers, 3601 of which were present in at least two populations. Each of the 21 linkage groups contained between 237 and 683 markers, cumulatively covering 5061 cM (2891 cM––Kosambi) with an average distance of 0.5 cM between each pair of markers. Through mapping the sequence tags to the diploid (2n = 2x = 14) barley reference genome, we observed high colinearity and synteny between these genomes, with three homoeologous IWG chromosomes corresponding to each of the seven barley chromosomes, and mapped translocations that are known in the Triticeae. The consensus map is a valuable tool for wheat breeders to map important disease-resistance genes within intermediate wheatgrass. These genomic tools can help lead to rapid improvement of IWG and development of high-yielding cultivars of this perennial grain that would facilitate the sustainable intensification of agricultural systems.

     

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.     

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.     

Development of a wheat single gene FISH map for analyzing homoeologous relationship and chromosomal rearrangements within the Triticeae

Key message

A cytogenetic map of wheat was constructed using FISH with cDNA probes. FISH markers detected homoeology and chromosomal rearrangements of wild relatives, an important source of genes for wheat improvement.

Abstract

To transfer agronomically important genes from wild relatives to bread wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD) by induced homoeologous recombination, it is important to know the chromosomal relationships of the species involved. Fluorescence in situ hybridization (FISH) can be used to study chromosome structure. The genomes of allohexaploid bread wheat and other species from the Triticeae tribe are colinear to some extent, i.e., composed of homoeoloci at similar positions along the chromosomes, and with genic regions being highly conserved. To develop cytogenetic markers specific for genic regions of wheat homoeologs, we selected more than 60 full-length wheat cDNAs using BLAST against mapped expressed sequence tags and used them as FISH probes. Most probes produced signals on all three homoeologous chromosomes at the expected positions. We developed a wheat physical map with several cDNA markers located on each of the 14 homoeologous chromosome arms. The FISH markers confirmed chromosome rearrangements within wheat genomes and were successfully used to study chromosome structure and homoeology in wild Triticeae species. FISH analysis detected 1U-6U chromosome translocation in the genome of Aegilops umbellulata, showed colinearity between chromosome A of Ae. caudata and group-1 wheat chromosomes, and between chromosome arm 7S#3L of Thinopyrum intermedium and the long arm of the group-7 wheat chromosomes.     

Intraspecific divergence in wheats of the Timopheevi group as revealed by in situ hybridization with tandem repeats of the Spelt1 and Spelt52 families

Fluorescent in situ hybridization (FISH) was used to study the distribution of the Spelt1 and Spelt52 repetitive DNA sequences on chromosomes of ten accessions representing three polyploid wheat species of the Timopheevi group: Triticum araraticum (7), T. timopheevii (2), and T. kiharae (1). Sequences of both families were found mostly in the subtelomeric chromosome regions of the G genome. The total number of Spelt1 sites varied from 8 to 14 in the karyotypes of the species under study; their number, location, and size differed among the seven T. araraticum accessions and were the same in the two T. timopheevii accessions and T. kiharae, an amphidiploid T. timopheevii-Aegilops tauschii hybrid. The Spelt52 tandem repeat was detected in the subtelomeric regions of chromosomes 1-4; its sites did not coincide with the Spelt1 sites. The chromosome distribution and signal intensity of the Spelt52 repeats varied in T. araraticum and were the same in T. timopheevii and T. kiharae. The chromosome distributions of the Spelt1 and Spelt52 repeats were compared for the polyploid wheats of the Timopheevi group and diploid Ae. speltoides, a putative donor of the G genome. The comparison revealed a decrease in hybridization level: both the number of sites per genome and the size of sites were lower. The decrease was assumed to result from repeat elimination during polyploidization and subsequent evolution of wheat and from the founder effect, since the origin of Timopheevi wheats might involve the genotype of Ae. speltoides, which is highly polymorphic for the distribution of Spelt1 and Spelt52 sequences and is similar in the chromosome location of the repeats to modern 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.     

FISH-aimed karyotype analysis in <Emphasis Type="Italic">Aconitum</Emphasis> subgen. <Emphasis Type="Italic">Aconitum</Emphasis> reveals excessive rDNA sites in tetraploid taxa

The location of 5S and 35S rDNA sequences in chromosomes of four Aconitum subsp. Aconitum species was analyzed after fluorescence in situ hybridization (FISH). Both in diploids (2n?=?2x?=?16; Aconitum variegatum, A. degenii) and tetraploids (2n?=?4×?=?32; A. firmum, A. plicatum), rDNA repeats were localized exclusively on the shorter arms of chromosomes, in subterminal or pericentromeric sites. All analyzed species showed similar basal genome size (Cx?=?5.31–5.71 pg). The most striking features of tetraploid karyotypes were the conservation of diploid rDNA loci and emergence of many additional 5S rDNA clusters. Chromosomal distribution of excessive ribosomal sites suggests their role in the secondary diploidization of tetraploid karyotypes.     

Wheat chromosome instability in the selfed progeny of the double monosomics 1Rv-1A

Structural alterations of chromosomes are often found in wheat-rye hybrids. In the majority of cases modifications are observed for rye chromosomes, yet chromosome aberration cases are described for wheat, including the progeny of Triticum aestivum disomic and monosomic addition lines. Since wheat-rye substitution and translocation lines are the source of rye chromatin in wheat breeding programs, the information on possible chromosome changes in the genomes of introgressive forms is important. Chromosome behavior in F₁ meiosis and chromosomal composition of F₂ karyotypes for double monosomics 1Rv-1A were studied by applying C-banding, genomic in situ hybridisation (GISH) using rye genomic DNA, and sequential in situ hybridization using repetitive sequences pAs1, pSc119.2 and centromere specific pAet-06 as probes. The double monosomics 1Rv-1A were obtained by crossing of disomic substitution line with chromosome 1A replaced by Secale cereale 1Rv in the bread wheat Saratovskaya 29 (S29) background with S29. The results indicated a high frequency of bipolar chromosome 1Rv orientation, as compared to 1A, at metaphase I (MI) (58.6 and 34.7 % of meiocytes, respectively), and, at anaphase I (AI), chromatid segregation of 1Rv compared to 1A (70.53 and 32.14 % of meiocytes, respectively). In few cases desynapsis of wheat homologues was observed, at AI, the chromosomes randomly distributed between the poles or underwent chromatid segregation. At AI, the two wheat homologues separated onto sister chromatids in 10.89 % of cells.The plants F2 karyotypes were marked with aneuploidy not only of chromosomes 1A and 1Rv, but also of 1D, 2D, 3D, 3B, 3A, 4A, 6D, 6B, 6A, and 7D. Structural changes were observed for the chromosomes of the first homoeologous group (1Rv, 1A, 1D, 1B), as well as for 2B, 5D, 6B, and 7B. The chromosomes 1Rv and 6B often demonstrated aberrations. The types of aberrations were centromeric break, deletions of various sizes, and a changed repeat pSc119.2 localization pattern.     

Genealogical analysis of the use of two wheatgrass (<Emphasis Type="Italic">Agropyron</Emphasis>) species in common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) breeding for disease resistance

During the last 80 years, in order to increase the genetic variability of wheat, translocations containing nine elongated wheatgrass (Agropyron elongatum) and eight intermediate wheatgrass (Agropyron intermedium) genes, which control resistance to pathogens, were transferred to this crop culture. Genealogical and statistical analysis of 1500 varieties developed using the wheatgrass gave evidence of the continuing increase in the proportion of such varieties in the total number of wheat varieties over the last half-century. Translocations from Ag. elongatum most commonly occur in the pedigrees of the varieties from the United States, less frequently they can be found in Australian and Chinese varieties, and they are extremely rare—in European and African ones. Ag. intermedium most frequently occurs in the pedigrees of the Eastern European varieties, mainly in those from Russia, as well as in the varieties from China. The observed uneven distribution of such varieties may be associated with either the effectiveness of the translocation in the development of resistance to the local populations of pathogens or with the effect of the translocation on the adaptive traits of plants. By computer tracking of pedigrees, we performed an inventory of the translocation donors from Ag. elongatum and Ag. intermedium used in the breeding programs in the United States, Russia, Australia, India, and China. The most widely occurring combinations of the gene complex Lr24/Sr24 of Ag. elongatum with other resistance genes were revealed. In Russia, there were developed varieties in which the 6D chromosome was substituted by the 6Ai chromosome of Ag. intermedium, which controls disease resistance and the adaptivity of plants. The identification and introgression of new translocations indicates that the possibilities of using wheatgrass species for broadening of genetic variability of wheat are far from being exhausted.