C-banding pattern and polymorphism of Aegilops caudata and chromosomal constitutions of the amphiploid T. aestivum - Ae. caudata and six derived chromosome addition lines

Development of Aegilops comosa and Aegilops caudata-specific molecular markers and fluorescence in situ hybridization probes based on specific-locus amplified fragment sequencing

As tertiary gene pools of wheat, Aegilops comosa and Ae. caudata contain many excellent genes/traits and gradually become important and noteworthy wild resources for wheat improvement worldwide. However, the lack of molecular markers and cytological probes with good specificity and high sensitivity limits the development and utilization of Triticum aestivum-Ae. comosa (Ta. Aeco)/Ae. caudata (Ta. Aeca) introgression lines. Using specific-locus amplified fragment sequencing, two Ae. comosa and one Ae. caudata accessions, Chinese Spring, and three Ta. Aeco and Ta. Aeca introgression lines each were sequenced to develop new molecular markers and cytological probes. After strict sequence comparison and verification in different materials, a total of 39 molecular markers specific to three chromosomes in Ae. comosa (nine, seven, and 10 markers for 1M, 2M, and 7M, respectively) and Ae. caudata (two, six, and five markers for 3C, 4C, and 5C, respectively) and 21 fluorescence in situ hybridization (FISH) probes (one centromeric probe with signals specific to the M chromosomes, two centromeric probes with signals in all the tested genomes, and six, eight, and four FISH probes specific to the M, C, and M, C, and U chromosomes, respectively) were successfully exploited. The newly developed molecular markers and cytological probes could be used in karyotype studies, centromere evolutionary analyses of Aegilops, and had the ability to detect the fusion centromeres and small-fragment translocations in introgression lines.

Cytogenetic features of intergeneric amphydiploids and genome-substituted forms of wheat

Synthetic intergeneric amphydiploids and genome-substituted wheat forms are an important source for transferring agronomically valuable genes from wild species into the common wheat (Triticum aestivum L.) genome. They can be used both in academic research and for breeding purposes as an original material for developing wheat-alien addition and substitution lines followed by translocation induction with the aid of irradiation or nonhomologous chromosome pairing. The chromosome sets and genome constitutions of allopolyploids are usually verified in early hybrid generations, whereas the subsequent fate of these hybrids remains unknown in most cases. Here we analyze karyotypes of five hexa- (2n = 6x = 42) and octoploid (2n = 8x = 56) amphydiploids of wheat with several species of the Aegilops, Haynaldia, and Hordeum genera, and six genome-substituted wheat-Aegilops forms, which were developed over 40 years ago and have been maintained in different gene banks. The analyses involve C-banding and fluorescence in situ hybridization (FISH) with pAs1 and pSc119.2 probes. We have found that most accessions are cytologically stable except for Avrodes (genome BBAASS, a hexaploid genome-substituted hybrid of wheat and Aegilops speltoides), which segregated with respect to chromosome composition after numerous reproductions. Chromosome analysis has not confirmed the presence of the N genome from Ae. uniaristata Vis. in the genome-substituted hybrid Avrotata. Instead, Avrotata carries the D genome. Our study shows that octoploid hybrids, namely AD 7, AD 7147 undergo more complex genome reorganizations as compared to hexaploids: the chromosome number of two presumably octoploid wheat-Aegilops hybrids were reduced to the hexaploid level. Genomes of both forms lost seven chromosome pairs, which represented seven homoeologous groups and derived from different parental subgenomes. Thus, each of the resulting hexaploids carries a synthetic/hybrid genome consisting of a unique combination of chromosomes belonging to different parental subgenomes.

Gametocidal genes: from a discovery to the application in wheat breeding

Some species of the genus Aegilops, a wild relative of wheat, carry chromosomes that after introducing to wheat exhibit preferential transmission to progeny. Their selective retention is a result of the abortion of gametes lacking them due to induced chromosomal aberrations. These chromosomes are termed Gametocidal (Gc) and, based on their effects, they are categorized into three types: mild, intense or severe, and very strong. Gc elements within the same homoeologous chromosome groups of Aegilops (II, III, or IV) demonstrate similar Gc action. This review explores the intriguing dynamics of Gc chromosomes and encompasses comprehensive insights into their source species, behavioral aspects, mode of action, interactions, suppressions, and practical applications of the Gc system in wheat breeding. By delving into these areas, this work aims to contribute to the development of novel plant genetic resources for wheat breeding. The insights provided herein shed light on the utilization of Gc chromosomes to produce chromosomal rearrangements in wheat and its wild relatives, thereby facilitating the generation of chromosome deletions, translocations, and telosomic lines. The Gc approach has significantly advanced various aspects of wheat genetics, including the introgression of novel genes and alleles, molecular markers and gene mapping, and the exploration of homoeologous relationships within Triticeae species. The mystery lies in why gametes possessing Gc genes maintain their normality while those lacking Gc genes suffer abnormalities, highlighting an unresolved research gap necessitating deeper investigation.

Pseudorogneria libanotica Intraspecific Genetic Polymorphism Revealed by Fluorescence In Situ Hybridization with Newly Identified Tandem Repeats and Wheat Single-Copy Gene Probes

The genus Pseudoroegneria (Nevski) Löve (Triticeae, Poaceae) with its genome abbreviated 'St' accounts for more than 60% of perennial Triticeae species. The diploid species Psudoroegneria libanotica (2n = 14) contains the most ancient St genome. Therefore, investigating its chromosomes could provide some fundamental information required for subsequent studies of St genome evolution. Here, 24 wheat cDNA probes covering seven chromosome groups were mapped in P. libanotica to distinguish homoelogous chromosomes, and newly identified tandem repeats were performed to differentiate seven chromosome pairs. Using these probes, we investigated intraspecific population chromosomal polymorphism of P. libanotica. We found that (i) a duplicated fragment of the 5St long arm was inserted into the short arm of 2St; (ii) asymmetrical fluorescence in situ hybridization (FISH) hybridization signals among 2St, 5St, and 7St homologous chromosome pairs; and (iii) intraspecific population of polymorphism in P. libanotica. These observations established the integrated molecular karyotype of P. libanotica. Moreover, we suggested heterozygosity due to outcrossing habit and adaptation to the local climate of P. libanotica. Specifically, the generated STlib_96 and STlib_98 repeats showed no cross-hybridization signals with wheat chromosomes, suggesting that they are valuable for identifying alien chromosomes or introgressed fragments of wild relatives in wheat.

Analysis of Structural Genomic Diversity in Aegilops umbellulata, Ae. markgrafii, Ae. comosa, and Ae. uniaristata by Fluorescence In Situ Hybridization Karyotyping

Fluorescence in situ hybridization karyotypes have been widely used for evolutionary analysis on chromosome organization and genetic/genomic diversity in the wheat alliance (tribe Triticeae of Poaceae). The karyotpic diversity of Aegilops umbellulata, Ae. markgrafii, Ae. comosa subsp. comosa and subsp. subventricosa, and Ae. uniaristata was evaluated by the fluorescence in situ hybridization (FISH) probes oligo-pSc119.2 and pTa71 in combination with (AAC)5, (ACT)7, and (CTT)12, respectively. Abundant intra- and interspecific genetic variation was discovered in Ae. umbellulata, Ae. markgrafii, and Ae. comosa, but not Ae. uniaristata. Chromosome 7 of Ae. umbellulata had more variants (six variants) than the other six U chromosomes (2-3 variants) as revealed by probes oligo-pSc119.2 and (AAC)5. Intraspecific variation in Ae. markgrafii and Ae. comosa was revealed by oligo-pSc119.2 in combination with (ACT)7 and (CTT)12, respectively. At least five variants were found in every chromosome of Ae. markgrafii and Ae. comosa, and up to 18, 10, and 15 variants were identified for chromosomes 2 of Ae. markgrafii, 4 of Ae. comosa subsp. comosa, and 6 of Ae. comosa subsp. subventricosa. The six Ae. uniaristata accessions showed identical FISH signal patterns. A large number of intra-specific polymorphic FISH signals were observed between the homologous chromosomes of Ae. markgrafii and Ae. comosa, especially chromosomes 1, 2, 4, and 7 of Ae. markgrafii, chromosome 4 of Ae. comosa subsp. comosa, and chromosome 6 of Ae. comosa subsp. subventricosa. Twelve Ae. comosa and 24 Ae. markgrafii accessions showed heteromorphism between homologous chromosomes. Additionally, a translocation between the short arms of chromosomes 1 and 7 of Ae. comosa PI 551038 was identified. The FISH karyotypes can be used to clearly identify the chromosome variations of each chromosome in these Aegilops species and also provide valuable information for understanding the evolutionary relationships and structural genomic variation among Aegilops species.

Development of Wheat-Aegilops caudata Introgression Lines and Their Characterization Using Genome-Specific KASP Markers

Aegilops caudata L. [syn. Ae. markgrafii (Greuter) Hammer], is a diploid wild relative of wheat (2n = 2x = 14, CC) and a valuable source for new genetic diversity for wheat improvement. It has a variety of disease resistance factors along with tolerance for various abiotic stresses and can be used for wheat improvement through the generation of genome-wide introgressions resulting in different wheat-Ae. caudata recombinant lines. Here, we report the generation of nine such wheat-Ae. caudata recombinant lines which were characterized using wheat genome-specific KASP (Kompetitive Allele Specific PCR) markers and multi-color genomic in situ hybridization (mcGISH). Of these, six lines have stable homozygous introgressions from Ae. caudata and will be used for future trait analysis. Using cytological techniques and molecular marker analysis of the recombinant lines, 182 KASP markers were physically mapped onto the seven Ae. caudata chromosomes, of which 155 were polymorphic specifically with only one wheat subgenome. Comparative analysis of the physical positions of these markers in the Ae. caudata and wheat genomes confirmed that the former had chromosomal rearrangements with respect to wheat, as previously reported. These wheat-Ae. caudata recombinant lines and KASP markers are useful resources that can be used in breeding programs worldwide for wheat improvement. Additionally, the genome-specific KASP markers could prove to be a valuable tool for the rapid detection and marker-assisted selection of other Aegilops species in a wheat background.

Cytological markers used for identification and transfer of Aegilops spp. chromatin carrying valuable genes into cultivated forms of Triticum

There are many reports describing chromosome structure, organization and evolution within goatgrasses (Aegilops spp.). Chromosome banding and fluorescence in situ hybridization techniques are main methods used to identify Aegilops Linnaeus, 1753 chromosomes. These data have essential value considering the close genetic and genomic relationship of goatgrasses with wheat (Triticumaestivum Linnaeus, 1753) and triticale (× Triticosecale Wittmack, 1899). A key question is whether those protocols are useful and effective for tracking Aegilops chromosomes or chromosome segments in genetic background of cultivated cereals. This article is a review of scientific reports describing chromosome identification methods, which were applied for development of prebreeding plant material and for transfer of desirable traits into Triticum Linnaeus, 1753 cultivated species. Moreover, this paper is a resume of the most efficient cytomolecular markers, which can be used to follow the introgression of Aegilops chromatin during the breeding process.

Molecular and Cytogenetic Characterization of Six Wheat-Aegilops markgrafii Disomic Addition Lines and Their Resistance to Rusts and Powdery Mildew

Aegilops markgrafii (Greuter) Hammer is an important source of genes for resistance to abiotic stresses and diseases in wheat (Triticum aestivum L.). A series of six wheat 'Alcedo'-Ae. markgrafii chromosome disomic addition lines, designated as AI(B), AII(C), AIII(D), AV(E), AIV(F), and AVIII(G) carrying the Ae. markgrafii chromosomes B, C, D, E, F, and G, respectively, were tested with SSR markers to establish homoeologous relationships to wheat and identify markers useful in chromosome engineering. The addition lines were evaluated for resistance to rust and powdery mildew diseases. The parents Alcedo and Ae. markgrafii accession 'S740-69' were tested with 1500 SSR primer pairs and 935 polymorphic markers were identified. After selecting for robust markers and confirming the polymorphisms on the addition lines, 132 markers were considered useful for engineering and establishing homoeologous relationships. Based on the marker analysis, we concluded that the chromosomes B, C, D, E, F, and G belong to wheat homoeologous groups 2, 5, 6, 7, 3, and 4, respectively. Also, we observed chromosomal rearrangements in several addition lines. When tested with 20 isolates of powdery mildew pathogen (Blumeria graminis f. sp. tritici) from five geographic regions of the United States, four addition lines [AIII(D), AV(E), AIV(F), and AVIII(G)] showed resistance to some isolates, with addition line AV(E) being resistant to 19 of 20 isolates. The addition lines were tested with two races (TDBJ and TNBJ) of the leaf rust pathogen (Puccinia triticina), and only addition line AI(B) exhibited resistance at a level comparable to the Ae. markgrafii parent. Addition lines AII(C) and AIII(D) had been previously identified as resistant to the Ug99 race group of the stem rust pathogen (Puccinia graminis f. sp. tritici). The addition lines were also tested for resistance to six United States races (PSTv-4, PSTv-14, PSTv-37, PSTv-40, PSTv-51, and PSTv-198) of the stripe rust pathogen (Puccinia striiformis f. sp. tritici); we found no resistance either in Alcedo or any of the addition lines. The homoeologous relationships of the chromosomes in the addition lines, molecular markers located on each chromosome, and disease resistance associated with each chromosome will allow for chromosome engineering of the resistance genes.

Interspecific and intergeneric hybridization as a source of variation for wheat grain quality improvement

The hybridization events with wild relatives and old varieties are an alternative source for enlarging the wheat quality variability. This review describes these process and their effects on the technological and nutritional quality. Wheat quality and its end-uses are mainly based on variation in three traits: grain hardness, gluten quality and starch. In recent times, the importance of nutritional quality and health-related aspects has increased the range of these traits with the inclusion of other grain components such as vitamins, fibre and micronutrients. One option to enlarge the genetic variability in wheat for all these components has been the use of wild relatives, together with underutilised or neglected wheat varieties or species. In the current review, we summarise the role of each grain component in relation to grain quality, their variation in modern wheat and the alternative sources in which wheat breeders have found novel variation.

Genetic classification of Aegilops columnaris Zhuk. (2n=4x=28, UcUcXcXc) chromosomes based on FISH analysis and substitution patterns in common wheat × Ae. columnaris introgressive lines

Aegilops columnaris is a tetraploid species originated from Ae. umbellulata (2n=2x=14, UU) and a yet unknown diploid grass species. Although Ae. columnaris possesses some agronomically valuable traits, such as heat and drought tolerance and resistance to pests, it has never been used in wheat breeding because of difficulties in producing hybrids and a lack of information on the relationships between Ae. columnaris and common wheat chromosomes. In this paper, we report the development of 57 wheat - Ae. columnaris introgressive lines covering 8 of the14 chromosomes of Aegilops. Based on substitution spectra of hybrids and the results of FISH analysis of the parental Ae. columnaris line with seven DNA probes, we have developed the genetic nomenclature of the U^c and X^c chromosomes. Genetic groups and genome affinities were established for 11 of 14 chromosomes; the classification of the remaining three chromosomes remains unsolved. Each Ae. columnaris chromosome was characterized on the basis of C-banding pattern and the distribution of seven DNA sequences. Introgression processes were shown to depend on the parental wheat genotype and the level of divergence of homoeologous chromosomes. We found that lines carrying chromosome 5X^c are resistant to leaf rust; therefore, this chromosome could possess novel resistance genes that have never been utilized in wheat breeding.

Major structural genomic alterations can be associated with hybrid speciation in Aegilops markgrafii (Triticeae)

During evolutionary history many grasses from the tribe Triticeae have undergone interspecific hybridization, resulting in allopolyploidy; whereas homoploid hybrid speciation was found only in rye. Homoeologous chromosomes within the Triticeae preserved cross-species macrocolinearity, except for a few species with rearranged genomes. Aegilops markgrafii, a diploid wild relative of wheat (2n = 2x = 14), has a highly asymmetrical karyotype that is indicative of chromosome rearrangements. Molecular cytogenetics and next-generation sequencing were used to explore the genome organization. Fluorescence in situ hybridization with a set of wheat cDNAs allowed the macrostructure and cross-genome homoeology of the Ae. markgrafii chromosomes to be established. Two chromosomes maintained colinearity, whereas the remaining were highly rearranged as a result of inversions and inter- and intrachromosomal translocations. We used sets of barley and wheat orthologous gene sequences to compare discrete parts of the Ae. markgrafii genome involved in the rearrangements. Analysis of sequence identity profiles and phylogenic relationships grouped chromosome blocks into two distinct clusters. Chromosome painting revealed the distribution of transposable elements and differentiated chromosome blocks into two groups consistent with the sequence analyses. These data suggest that introgressive hybridization accompanied by gross chromosome rearrangements might have had an impact on karyotype evolution and homoploid speciation in Ae. markgrafii.

Dynamic nucleolar activity in wheat × Aegilops hybrids: evidence of C-genome dominance

NOR loci of C-subgenome are dominant in wheat × Aegilops interspecific hybrids, which may have evolutionary implications for wheat group genome dynamics and evolution. After interspecific hybridisation, some genes are often expressed from only one of the progenitor species, shaping subsequent allopolyploid genome evolution processes. A well-known example is nucleolar dominance, i.e. the formation of cell nucleoli from chromosomes of only one parental species. We studied nucleolar organizing regions (NORs) in diploid Aegilops markgrafii (syn: Ae. caudata; CC), Ae. umbellulata (UU), allotetraploids Aegilops cylindrica (C^cC^cD^cD^c) and Ae. triuncialis (C^tC^tU^tU^t), synthetic interspecific F₁ hybrids between these two allotetraploids and bread wheat (Triticum aestivum, AABBDD) and in F₃ generation hybrids with genome composition AABBDDC^tC^tU^tU^t using silver staining and fluorescence in situ hybridization (FISH). In Ae. markgrafii (CC), NORs of both 1C and 5C or only 5C chromosome pairs were active in different individual cells, while only NORs on 1U chromosomes were active in Ae. umbellulata (UU). Although all 35S rDNA loci of the C^t subgenome (located on 1C^t and 5C^t) were active in Ae. triuncialis, only one pair (occupying either 1C^c or 5C^c) was active in Ae. cylindrica, depending on the genotype studied. These C-genome expression patterns were transmitted to the F₁ and F₃ generations. Wheat chromosome NOR activity was variable in Ae. triuncialis × T. aestivum F₁ seeds, but silenced by the F₃ generation. No effect of maternal or paternal cross direction was observed. These results indicate that C-subgenome NOR loci are dominant in wheat × Aegilops interspecific hybrids, which may have evolutionary implications for wheat group genome dynamics and allopolyploid evolution.

Agronomic Traits and Molecular Marker Identification of Wheat-Aegilops caudata Addition Lines

Aegilops caudata is an important gene source for wheat breeding. Intensive evaluation of its utilization value is an essential first step prior to its application in breeding. In this research, the agronomical and quality traits of Triticum aestivum-Ae. caudata additions B-G (homoeologous groups not identified) were analyzed and evaluated. Disease resistance tests showed that chromosome D of Ae. caudata might possess leaf rust resistance, and chromosome E might carry stem rust and powdery mildew resistance genes. Investigations into agronomical traits suggested that the introduction of the Ae. caudata chromosome in addition line F could reduce plant height. Grain quality tests showed that the introduction of chromosomes E or F into wheat could increase its protein and wet gluten content. Therefore, wheat-Ae. caudata additions D-F are all potentially useful candidates for chromosome engineering activities to create useful wheat-alien chromosome introgressions. A total of 55 EST-based molecular markers were developed and then used to identify the chromosome homoeologous group of each of the Ae. caudata B-G chromosomes. Marker analysis indicated that the Ae. caudata chromosomes in addition lines B to G were structurally altered, therefore, a large population combined with intensive screening pressure should be taken into consideration when inducing and screening for wheat-Ae. caudata compensating translocations. Marker data also indicated that the Ae. caudata chromosomes in addition lines C-F were 5C, 6C, 7C, and 3C, respectively, while the homoeologous group of chromosomes B and G of Ae. caudata are as yet undetermined and need further research.

Mapping of novel powdery mildew resistance gene(s) from Agropyron cristatum chromosome 2P

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. 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.

Dissecting the U, M, S and C genomes of wild relatives of bread wheat (Aegilops spp.) into chromosomes and exploring their synteny with wheat

Goat grasses (Aegilops spp.) contributed to the evolution of bread wheat and are important sources of genes and alleles for modern wheat improvement. However, their use in alien introgression breeding is hindered by poor knowledge of their genome structure and a lack of molecular tools. The analysis of large and complex genomes may be simplified by dissecting them into single chromosomes via flow cytometric sorting. In some species this is not possible due to similarities in relative DNA content among chromosomes within a karyotype. This work describes the distribution of GAA and ACG microsatellite repeats on chromosomes of the U, M, S and C genomes of Aegilops, and the use of microsatellite probes to label the chromosomes in suspension by fluorescence in situ hybridization (FISHIS). Bivariate flow cytometric analysis of chromosome DAPI fluorescence and fluorescence of FITC-labelled microsatellites made it possible to discriminate all chromosomes and sort them with negligible contamination by other chromosomes. DNA of purified chromosomes was used as a template for polymerase chain reation (PCR) using Conserved Orthologous Set (COS) markers with known positions on wheat A, B and D genomes. Wheat-Aegilops macrosyntenic comparisons using COS markers revealed significant rearrangements in the U and C genomes, while the M and S genomes exhibited structure similar to wheat. Purified chromosome fractions provided an attractive resource to investigate the structure and evolution of the Aegilops genomes, and the COS markers assigned to Aegilops chromosomes will facilitate alien gene introgression into wheat.

Molecular and Cytogenetic Characterization of a Powdery Mildew-Resistant Wheat-Aegilops mutica Partial Amphiploid and Addition Line

Aegilops mutica Boiss., a diploid species (2n = 2x = 14, TT), has been rarely studied before. In this research, a hexaploid wheat (cv. Chinese Spring)-Ae. mutica partial amphiploid and a wheat-Ae. mutica addition line were characterized by chromosome karyotyping, FISH using oligonucleotides Oligo-pTa535-1, Oligo-pSc119.2-1, and (GAA)8 as probes, and EST-based molecular markers. The results showed that the partial amphiploid strain consisted of 20 pairs of wheat chromosomes and 7 pairs of Ae. mutica chromosomes, with both wheat 7B chromosomes missing. EST-based molecular marker data suggested that the wheat-Ae. mutica addition line carries the 7T chromosome. Resistance tests indicated that both the partial amphiploid and the 7T addition line were highly resistant to powdery mildew, whereas the wheat control line Chinese Spring was highly susceptible, indicating the presence of a potentially new powdery mildew resistance gene on the Ae. mutica 7T chromosome. The karyotype, FISH patterns, and molecular markers can now be used to identify Ae. mutica chromatin in a wheat background, and the 7T addition could be used as a new powdery mildew resistance source for wheat breeding.

Flow sorting of C-genome chromosomes from wild relatives of wheat Aegilops markgrafii, Ae. triuncialis and Ae. cylindrica, and their molecular organization

BACKGROUND AND AIMS

Aegilops markgrafii (CC) and its natural hybrids Ae. triuncialis (U(t)U(t)C(t)C(t)) and Ae. cylindrica (D(c)D(c)C(c)C(c)) represent a rich reservoir of useful genes for improvement of bread wheat (Triticum aestivum), but the limited information available on their genome structure and the shortage of molecular (cyto-) genetic tools hamper the utilization of the extant genetic diversity. This study provides the complete karyotypes in the three species obtained after fluorescent in situ hybridization (FISH) with repetitive DNA probes, and evaluates the potential of flow cytometric chromosome sorting.

METHODS

The flow karyotypes obtained after the analysis of 4',6-diamidino-2-phenylindole (DAPI)-stained chromosomes were characterized and the chromosome content of the peaks on the flow karyotypes was determined by FISH. Twenty-nine conserved orthologous set (COS) markers covering all seven wheat homoeologous chromosome groups were used for PCR with DNA amplified from flow-sorted chromosomes and genomic DNA.

KEY RESULTS

FISH with repetitive DNA probes revealed that chromosomes 4C, 5C, 7C(t), T6U(t)S.6U(t)L-5C(t)L, 1C(c) and 5D(c) could be sorted with purities ranging from 66 to 91 %, while the remaining chromosomes could be sorted in groups of 2-5. This identified a partial wheat-C-genome homology for group 4 and 5 chromosomes. In addition, 1C chromosomes were homologous with group 1 of wheat; a small segment from group 2 indicated 1C-2C rearrangement. An extensively rearranged structure of chromosome 7C relative to wheat was also detected.

CONCLUSIONS

The possibility of purifying Aegilops chromosomes provides an attractive opportunity to investigate the structure and evolution of the Aegilops C genome and to develop molecular tools to facilitate the identification of alien chromatin and support alien introgression breeding in bread wheat.

The effects of chromosome 6P on fertile tiller number of wheat as revealed in wheat-Agropyron cristatum chromosome 5A/6P translocation lines

This study explored the genetic constitutions of several wheat- A. cristatum translocation lines and determined the effects of A. cristatum 6P chromosome segments on fertile tiller number in wheat. Progress in wheat breeding is hampered by a relatively narrow range of genetic variation. To overcome this hurdle, wild relatives of common wheat with superior agronomic traits are often used as donors of desirable genes in wheat-breeding programs. One of the successfully utilized wheat wild relatives is Agropyron cristatum (L.) Gaertn (2n = 4x = 28; genomes PPPP). We previously reported that WAT31-13 was a wheat-A. cristatum 5A-6P reciprocal translocation line with higher fertile tiller number and grain number per spike compared to common wheat. However, WAT31-13 was genetically unstable. In this study, we analyzed the 43 genetically stable progenies from WAT31-13 using genomic in situ hybridization, dual-color fluorescence in situ hybridization, and molecular markers. We classified them into three translocation types (TrS, TrL and TrA) and seven subtypes, and also pinpointed the translocation breakpoint. The genotypic data, combined with the phenotypes of each translocation type, enabled us to physically map agronomic traits to specific A. cristatum 6P chromosome arms or segments. Our results indicated that A. cristatum chromosome 6P played an important role in regulating fertile tiller number, and that positive and negative regulators of fertile tiller number existed on the A. cristatum chromosome arm 6PS and 6PL, respectively. By exploring the relationship between fertile tiller number and A. cristatum chromosome segment, this study presented a number of feasible approaches for creation, analysis, and utilization of wheat-alien chromosome translocation lines in genetic improvement of wheat.

Molecular-cytogenetic analysis of Aegilops triuncialis and identification of its chromosomes in the background of wheat

Background

Species belonging to the genus Aegilops L. are an important source of genetic material for expanding genetic variability of wheat. Ae. triuncialis is an allotetraploid in this genus which was originated from hybridization of Ae. umbellulata and Ae. markgrafii (Greuter) Hammer. Although the Ae. triuncialis karyotype was thoroughly examined by conventional chromosome staining and Giemsa C-banding, it is still poorly characterized using FISH markers. The objective of this study was to test the fluorescence in situ hybridization (FISH) patterns of Ae. triuncialis (2n = 4x = 28, C^tC^tU^tU^t) chromosomes using different repetitive sequences and to compare the produced patterns to the chromosomes of its diploid ancestors, with the aim of establishing a generalized Ae. triuncialis idiogram and detection of Aegilops chromosomes in the background of wheat.

Results

The probes pSc119.2-1, pTa535-1, pAs1-1, (CTT)₁₀ and the 45S rDNA clone from wheat (pTa71) were hybridized to chromosomes of Ae. triuncialis and compared with its diploid progenitors (Ae. umbellulata Zhuk., 2n = 2x = 14, UU and Ae. markgrafii (Greuter) Hammer, 2n = 2x = 14, CC) and Ae. cylindrica Host. (2n = 4x = 28, D^cD^cC^cC^c), another tetraploid species containing the C-genome. Ae. cylindrica was further analyzed by genomic in situ hybridization (GISH) using C genome probe in order to identify any possible translocation.

Conclusions

In general, FISH patterns of the U^t- and C^t-genome chromosomes of Ae. triuncialis were similar to those of U- and C-genome chromosomes of the diploid progenitor species Ae. umbellulata and Ae. markgrafii respectively, although some differences were observed. Two major 45S rDNA loci were revealed in the short arm of chromosomes A and C, of the C^t genome which correspond to homoeologous groups 1 and 5 respectively. Minor 45S rDNA loci were mapped on the short arm of chromosomes 1U^t and 5U^t. GISH analysis revealed three different non-reciprocal homologous or heterologous translocations between C^c and D^c chromosomes in all studied accessions of Ae. cylindrica.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-014-0091-6) contains supplementary material, which is available to authorized users.

Analysis of lignin-carbohydrate and lignin-lignin linkages after hydrolase treatment of xylan-lignin, glucomannan-lignin and glucan-lignin complexes from spruce wood

Xylan-lignin (XL), glucomannan-lignin (GML) and glucan-lignin (GL) complexes were isolated from spruce wood, hydrolyzed with xylanase or endoglucanase/β-glucosidase, and analyzed by analytical pyrolysis and 2D-NMR. The enzymatic hydrolysis removed most of the polysaccharide moieties in the complexes, and the lignin content and relative abundance of lignin-carbohydrate linkages increased. Analytical pyrolysis confirmed the action of the enzymatic hydrolysis, with strong decreases of levoglucosane and other carbohydrate-derived products. Unexpectedly it also revealed that the hydrolase treatment alters the pattern of lignin breakdown products, resulting in higher amounts of coniferyl alcohol. From the anomeric carbohydrate signals in the 2D-NMR spectra, phenyl glycoside linkages (undetectable in the original complexes) could be identified in the hydrolyzed GML complex. Lower amounts of glucuronosyl and benzyl ether linkages were also observed after the hydrolysis. From the 2D-NMR spectra of the hydrolyzed complexes, it was concluded that the lignin in GML is less condensed than in XL due to its higher content in β-O-4' ether substructures (62 % of side chains in GML vs 53 % in XL) accompanied by more coniferyl alcohol end units (16 vs 13 %). In contrast, the XL lignin has more pinoresinols (11 vs 6 %) and dibenzodioxocins (9 vs 2 %) than the GML (and both have ~13 % phenylcoumarans and 1 % spirodienones). Direct 2D-NMR analysis of the hydrolyzed GL complex was not possible due to its low solubility. However, after sample acetylation, an even less condensed lignin than in the GML complex was found (with up to 72 % β-O-4' substructures and only 1 % pinoresinols). The study provides evidence for the existence of structurally different lignins associated to hemicelluloses (xylan and glucomannan) and cellulose in spruce wood and, at the same time, offers information on some of the chemical linkages between the above polymers.

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

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. To transfer agronomically important genes from wild relatives to bread wheat (Triticum aestivum L., 2n = 6 x = 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 1 U-6 U 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#3 L of Thinopyrum intermedium and the long arm of the group-7 wheat chromosomes.

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

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. To transfer agronomically important genes from wild relatives to bread wheat (Triticum aestivum L., 2n = 6 x = 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 1 U-6 U 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#3 L of Thinopyrum intermedium and the long arm of the group-7 wheat chromosomes.

Molecular cytogenetic characterization of the Aegilops biuncialis karyotype

Aegilops biuncialis can be hybridized with wheat (Triticum spp) and has been used for wheat breeding and genetic studies. The A. biuncialis karyotype (U(b) U(b) M(b) M(b)) was investigated based on three A. biuncialis accessions grown in China. Two pairs of SAT chromosomes were identified as 1U(b) and 5U(b), with a karyotype formula of 2n = 4x = 28 = 14m + 10sm + 4st. Fluorescence in situ hybridization (FISH) and C-banding approaches were used to analyze the A. biuncialis accession chromosomes at the mitotic stage. Based on the C-banding and FISH patterns, all U(b) and M(b) chromosomes could be discriminated simultaneously; the three A. biuncialis accessions exhibited similar patterns, suggesting a common origin. The U(b) genome from A. biuncialis resembled the U genome in the diploid species A. umbellulata, and it may be related to the tetraploid species containing the U genome. The M(b) genome had some differences compared to the M genome in the diploid species A. comosa, and it may be related to the tetraploid species possessing the M genome. A generalized ideogram was proposed for the A. biuncialis genome, which could be useful for standardized and accurate identification of the A. biuncialis karyotype and chromosomes.

Introgression of a leaf rust resistance gene from Aegilops caudata to bread wheat

Rusts are the most important biotic constraints limiting wheat productivity worldwide. Deployment of cultivars with broad spectrum rust resistance is the only environmentally viable option to combat these diseases. Identification and introgression of novel sources of resistance is a continuous process to combat the ever evolving pathogens. The germplasm of nonprogenitor Aegilops species with substantial amount of variability has been exploited to a limited extent. In the present investigation introgression, inheritance and molecular mapping of a leaf rust resistance gene of Ae. caudata (CC) acc. pau3556 in cultivated wheat were undertaken. An F(2) population derived from the cross of Triticum aestivum cv. WL711 - Ae. caudata introgression line T291-2 with wheat cultivar PBW343 segregated for a single dominant leaf rust resistance gene at the seedling and adult plant stages. Progeny testing in F(3) confirmed the introgression of a single gene for leaf rust resistance. Bulked segregant analysis using polymorphic D-genome-specific SSR markers and the cosegregation of the 5DS anchored markers (Xcfd18, Xcfd78, Xfd81 and Xcfd189) with the rust resistance in the F(2) population mapped the leaf rust resistance gene (LrAC) on the short arm of wheat chromosome 5D. Genetic complementation and the linked molecular markers revealed that LrAC is a novel homoeoallele of an orthologue Lr57 already introgressed from the 5M chromosome of Ae. geniculata on 5DS of wheat.

Genome differentiation in Aegilops. 1. Distribution of highly repetitive DNA sequences on chromosomes of diploid species

Genome differentiation in 12 diploid Aegilops species was analyzed using in situ hybridization with the highly repetitive DNA sequences pSc119 and pAs1 and C-banding. Chromosomes of all these diploid Aegilops species hybridized with the pSc119 probe; however, the level of hybridization and labeling patterns differed among genomes. Only four species (Ae. squarrosa, Ae. comosa, Ae. heldreichii, and Ae. uniaristata) showed distinct hybridization with pAs1. The labeling patterns were species-specific and chromosome-specific. Differences in in situ hybridization (ISH) patterns, also observed by C-banding, exist between the karyotypes of Ae. comosa and Ae. heldreichii, suggesting that they are separate, although closely related, subspecies. The S genome of Ae. spelioides was most similar to the B and G genomes of polyploid wheats on the basis of both C-banding and ISH patterns, but was different from other species of section Sitopsis. These species had different C-banding patterns but they were similar to each other and to Ae. mutica in the distribution of pSc119 hybridization sites. Two types of labeling were detected in Ae. squarrosa with the pAs1 probe. The first resembled that of the D-genome chromosomes of bread wheat, Triticum aestivum L. em. Thell., while the second was similar to the D genome of some of the polyploid Aegilops species. Relationships among diploid Aegilops species and the possible mechanisms of genome differentiation are discussed. Key words : wheat, Triticum, Aegilops, in situ hybridization, C-banding, evolution.

Genetic diversity of Greek Aegilops species using different types of nuclear genome markers

Random Amplified Polymorphic DNA (RAPD) and Inter-Simple Sequence Repeat (ISSR) analyses were used to evaluate genetic variability and relationships of Greek Aegilops species. Thirty-eight accessions of seven Greek Aegilops species [Ae. triuncialis (genome UC), Ae. neglecta (UM), Ae. biuncialis (UM), Ae. caudata (C), Ae. comosa (M), Ae. geniculata (MU) and Ae. umbellulata (U)] as well as Triticum accessions were studied. Nineteen RAPD and ten ISSR primers yielded 344 and 170 polymorphic bands, respectively, that were used for the construction of dendrograms. Regardless of the similarity coefficient and marker type used, UPGMA placed 38 Aegilops accessions into one branch while the other branch consisted of wheat species. Within the Aegilops cluster, subgroups were identified that included species that shared the same genome or belonged to the same botanical section. Within the Triticum cluster, two robust subgroups were formed, one including diploid wheat and another including polyploid wheat. In conclusion, results showed that there is genetic diversity in the Greek Aegilops species studied, and clustering based on genetic similarities was in agreement with botanical classifications.

Cytogenetic and molecular characterization of a durum alien disomic addition line with enhanced tolerance to Fusarium head blight

Current durum wheat (Triticum turgidum L. subsp. durum (Desf.)) cultivars have little or no resistance to Fusarium head blight (FHB), a ravaging disease of cereal crops. A diploid wheatgrass, Lophopyrum elongatum (Host) A. Löve (2n = 2x = 14, EE genome), is an excellent source of FHB resistance. Through an extensive intergeneric hybridization using durum cultivar Langdon, we have developed a disomic alien addition line, named DGE-1 (2n = 28 + 2), with a wheatgrass chromosome pair. We used a unique method for isolating the addition line taking advantage of unreduced gametes functioning in Langdon x L. elongatum F1 hybrids in their first backcross to the Langdon parent, resulting in 35-chromosome plants from which we derived DGE-1. The addition line DGE-1 has a plant type similar to its Langdon parent, although it is shorter in height with narrower leaves and shorter spikes. It is meiotically and reproductively stable, generally forming 15 bivalents with two chiasmata each. The alien chromosome pair from the grass confers FHB resistance to the addition line, which has less than 21% infection on the visual scale, mean = 6.5%. Using various biochemical and molecular techniques (Giemsa C-banding, fluorescent genomic in situ hybridization (fl-GISH), chromosome-specific simple sequence repeat (SSR) markers, targeted region amplified polymorphism (TRAP) markers, and sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE)), we have shown that the extra chromosome involved is 1E of L. elongatum. This is the first time that FHB resistance has been discovered on chromosome 1E. We have established a chromosome-specific marker for 1E that may be used to screen fertile hybrid derivatives and durum addition lines for this chromosome that confers FHB resistance.

Karyotype and C-banding patterns of mitotic chromosomes in Heteranthelium piliferum

The C-banded karyotype of Heteranthelium piliferum species was studied in a natural population from northwest of Iran using aceto-iron-hematoxilin staining and C-banding technique. Chromosome measurements including long arm, short arm and chromosome lengths, arm ratio index, relative chromosome length, heterochromatin percent per chromosome and per chromosome set were made. It was revealed that the karyotype of this species is symmetric and consists of 7 pairs of metacentric chromosomes. Arm ratio index values ranged from 1.01 in chromosome G to 1.44 in chromosome D. One of the chromosomes had a satellite located on the end of its long arm (chromosome G). The Q genome of this species like A, B, D, S, M and M, genomes in diploid species of Aegilops-Trticum group, H genome in Hordeum, E genome in Agropyron and R genome in Secale has metacentric or sub-metacentric chromosomes.

Cytogenetics in the age of molecular genetics

From the beginning of the 20th Century, we have seen tremendous advances in knowledge and understanding in almost all biological disciplines, including genetics, molecular biology, structural and functional genomics, and biochemistry. Among these advances, cytogenetics has played an important role. This paper details some of the important milestones of modern cytogenetics. Included are the historical role of cytogenetics in genetic studies in general and the genetics stocks produced using cytogenetic techniques. The basic biological questions cytogenetics can address and the important role and practical applications of cytogenetics in applied sciences, such as in agriculture and in breeding for disease resistance in cereals, are also discussed. The goal of this paper is to show that cytogenetics remains important in the age of molecular genetics, because it is inseparable from overall genome analysis. Cytogenetics complements studies in other disciplines within the field of biology and provides the basis for linking genetics, molecular biology and genomics research.

Detection of alien chromatin introgression from Thinopyrum into wheat using S genomic DNA as a probe – A landmark approach for Thinopyrum genome research

The introduction of alien genetic variation from the genus Thinopyrum through chromosome engineering into wheat is a valuable and proven technique for wheat improvement. A number of economically important traits have been transferred into wheat as single genes, chromosome arms or entire chromosomes. Successful transfers can be greatly assisted by the precise identification of alien chromatin in the recipient progenies. Chromosome identification and characterization are useful for genetic manipulation and transfer in wheat breeding following chromosome engineering. Genomic in situ hybridization (GISH) using an S genomic DNA probe from the diploid species Pseudoroegneria has proven to be a powerful diagnostic cytogenetic tool for monitoring the transfer of many promising agronomic traits from Thinopyrum. This specific S genomic probe not only allows the direct determination of the chromosome composition in wheat-Thinopyrum hybrids, but also can separate the Th. intermedium chromosomes into the J, J(S) and S genomes. The J(S) genome, which consists of a modified J genome chromosome distinguished by S genomic sequences of Pseudoroegneria near the centromere and telomere, carries many disease and mite resistance genes. Utilization of this S genomic probe leads to a better understanding of genomic affinities between Thinopyrum and wheat, and provides a molecular cytogenetic marker for monitoring the transfer of alien Thinopyrum agronomic traits into wheat recipient lines.

Analysis of HMW glutenin subunits and their coding sequences in two diploid Aegilops species

Considerable progress has been made in understanding the structure, function and genetic regulation of high-molecular-weight (HMW) glutenin subunits in hexaploid wheat. In contrast, less is known about these types of proteins in wheat related species. In this paper, we report the analysis of HMW glutenin subunits and their coding sequences in two diploid Aegilops species, Aegilops umbellulata (UU) and Aegilops caudata (CC). SDS-PAGE analysis demonstrated that, for each of the four Ae. umbellulata accessions, there were two HMW glutenin subunits (designated here as 1Ux and 1Uy) with electrophoretic mobilities comparable to those of the x- and y-type subunits encoded by the Glu-D1 locus, respectively. In our previous study involving multiple accessions of Ae. caudata, two HMW glutenin subunits (designated as 1Cx and 1Cy) with electrophoretic mobilities similar to those of the subunits controlled by the Glu-D1 locus were also detected. These results indicate that the U genome of Ae. umbellulata and the C genome of Ae. caudata encode HMW glutenin subunits that may be structurally similar to those specified by the D genome. The complete open reading frames (ORFs) coding for x- and y-type HMW glutenin subunits in the two diploid species were cloned and sequenced. Analysis of deduced amino acid sequences revealed that the primary structures of the x- and y-type HMW glutenin subunits of the two Aegilops species were similar to those of previously published HMW glutenin subunits. Bacterial expression of modified ORFs, in which the coding sequence for the signal peptide was removed, gave rise to proteins with electrophoretic mobilities identical to those of HMW glutenin subunits extracted from seeds, indicating that upon seed maturation the signal peptide is removed from the HMW glutenin subunit in the two species. Phylogenetic analysis showed that 1Ux and 1Cx subunits were most closely related to the 1Dx type subunit encoded by the Glu-D1 locus. The 1Uy subunit possessed a higher level of homology to the 1Dy-type subunit compared with the 1Cy subunit. In conclusion, our study suggests that the Glu-U1 locus of Ae. umbellulata and the Glu-C1 locus of Ae. caudata specify the expression of HMW glutenin subunits in a manner similar to the Glu-D1 locus. Consequently, HMW glutenin subunits from the two diploid species may have potential value in improving the processing properties of hexaploid wheat varieties.

Molecular cytogenetic analysis ofAegilops cylindrica Host

The genomic constitution of Aegilops cylindrica Host (2n = 4x = 28, DcDcCcCc) was analyzed by C-banding, genomic in situ hybridization (GISH), and fluorescence in situ hybridization (FISH) using the DNA clones pSc119, pAs1, pTa71, and pTA794. The C-banding patterns of the Dc- and Cc-genome chromosomes of Ae. cylindrica are similar to those of D-and C-genome chromosomes of the diploid progenitor species Ae. tauschii Coss. and Ae. caudata L., respectively. These similarities permitted the genome allocation and identification of the homoeologous relationships of the Ae. cylindrica chromosomes. FISH analysis detected one major 18S-5.8S-25S rDNA locus in the short arm of chromosome 1Cc. Minor 18S-5.8S-25S rDNA loci were mapped in the short arms of 5Dc and 5Cc. 5S rDNA loci were identified in the short arm of chromosomes 1Cc, 5Dc, 5Cc, and 1Dc. GISH analysis detected intergenomic translocation in three of the five Ae. cylindrica accessions. The breakpoints in all translocations were non-centromeric with similar-sized segment exchanges.Key words: Aegilops cylindrica, C-banding, GISH, FISH, genome evolution.

Genetics of resistance to wheat leaf rust

Leaf rust (caused by Puccinia recondita f. sp. tritici) is the most widespread and regularly occurring rust on wheat. Genetic resistance is the most economical method of reducing yield losses due to leaf rust. To date, 46 leaf rust resistance genes have been designated and mapped in wheat. Resistance gene expression is dependent on the genetics of host-parasite interaction, temperature conditions, plant developmental stage, and interaction between resistance genes with suppressors or other resistance genes in the wheat genomes. Genes expressed in seedling plants have not provided long-lasting effective leaf rust resistance. Adult-plant resistance genes Lr13 and Lr34 singly and together have provided the most durable resistance to leaf rust in wheat throughout the world. Continued efforts to isolate, characterize, and map leaf rust resistance genes is essential given the ability of the leaf rust fungus to overcome deployed resistance genes.

Standard karyotype of Triticum searsii and its relationship with other S-genome species and common wheat

C-banding polymorphism was analyzed in 14 accessions of Triticum searsii from Israel, and a generalized idiogram of the species was established. One accession was homozygous for whole arm translocations T1S(s)S·4S(s)S and T1S(s)L·4S(s)L. C-banding analysis was also used to identify 7 T. aestivum cv 'Chinese Spring'-T. searsii disomic chromosome addition lines, 14 ditelosomic chromosome addition lines, 21 disomic whole chromosome, and 31 ditelosomic chromosome substitution lines. The identity of these lines was further confirmed by meiotic pairing analysis. Sporophytic and gametophytic compensation tests were used to determine the homoeologous relationships of the T. searsii chromosomes. The results show that the T. searsii chromosomes do not compensate well for their wheat homoeologues. The C-banding patterns of T. searsii chromosomes are distinct from those of other S-genome species and from the B-genome chromosomes of wheat, indicating that T. searsii is not a direct B-genome donor species of T. turgidum and T. aestivum.

Standard karyotype of Triticum umbellulatum and the characterization of derived chromosome addition and translocation lines in common wheat

A standard karyotype and a generalized idiogram of Triticum umbellulatum (syn. Aegilops umbellulata, 2n = 2x = 14) was established based on C-banding analysis of ten accessions of different geographic origin and individual T. umbellulatum chromosomes in T. aestivum - T. umbellulatum chromosome addition lines. Monosomic (MA) and disomic (DA) T. aestivum - T. umbellulatum chromosome addition lines (DA1U = B, DA2U = D, MA4U = F, DA5U = C, DA6U = A, DA7U = E = G) and telosomic addition lines (DA1US, DA1UL, DA2US, DA2UL, DA4UL, MA5US, (+ iso 5US), DA5UL, DA7US, DA7UL) were analyzed. Line H was established as a disomic addition line for the translocated wheat - T. umbellulatum chromosome T2DS·4US. Radiation-induced wheat - T. umbellulatum translocation lines resistant to leaf rust (Lr9) were identified as T40 = T6BL·6BS-6UL, T41 = T4BL·4BS-6UL, T44 = T2DS·2DL-6UL, T47 = 'Transfer' = T6BS·6BL-6UL and T52 = T7BL·7BS-6UL. Breakpoints and sizes of the transferred T. umbellulatum segments in these translocations were determined by in situ hybridization analysis using total genomic T. umbellulatum DNA as a probe.

Radiation-induced nonhomoeologous wheat-Agropyron intermedium chromosomal translocations conferring resistance to leaf rust

The Agropyron intermedium chromosome 7Ai #2 is the source of the leaf rust resistance gene Lr38 which was transferred to wheat by irradiation. The chromosomal constitutions of eight radiation-induced rust-resistant wheat-Agropyron intermedium derivatives were analyzed by C-banding and genomic in-situ hybridization (GISH). Five lines were identified as wheat Ag. intermedium chromosome translocation lines with the translocation chromosomes T2AS·2AL-7Ai#2L, T5AL · 5AS-7Ai # 2L, T1DS · 1DL-7Ai # 2L, T3DL · 3DS-7Ai#2L, and T6DS · 6DL-7Ai#2L. The sizes of the 7Ai#2L segments in mitotic metaphases of these translocations are 2.42 μm, 4.20 μm, 2.55 μm, 2.78 μm, and 4.19 μm, respectively. One line was identified as a wheat-Ag. intermedium chromosome addition line. The added Ag. intermedium chromosome in this line is different from 7Ai # 2. This line has resistance to leaf rust and stem rust. Based on the rust reactions, and the C-banding and GISH results, the remaining two lines do not contain any Ag. intermedium-derived chromatin.

Molecular detection of Lophopyrum chromatin in wheat-Lophopyrum recombinants and their use in the physical mapping of chromosome 7D

In situ hybridisation and restriction fragment length polymorphism (RFLP) analysis were used to determine the relative location of the translocation breakpoint and the size of the integrated chromatin segment in hexaploid wheat-Lophopyrum translocation stocks. Three 7el2-7D recombinant stocks were Robertsonian translocations, 7DS.7el. The remaining recombinant stock (KS10-2) was 7elS.7el-7DL and contained only the distal one-half of the long arm of 7D. The recombinant stock with 7el1 (K11695) could be designated 7DS.7DL-7el where approximately the distal one-half of 7DL was replaced. RFLP analysis indicated that on the 7DL RFLP map the breakpoints for K11695 and KS10-2 are in different locations and that the two recombinants contain an overlapping region (a common region) of the Lophopyrum chromosome 7 in which Lr19, a leaf-rust resistant gene, is located. RFLP analysis also indicated that RFLP markers which mapped to within 1.5 cm of the centromere of chromosome 7D are located in the distal half of the long arm.