Fixation of translocation 2A·4B infers the monophyletic origin of Ethiopian tetraploid wheat

Analysis of structural chromosomal polymorphism revealed the presence of a previously reported 2A·4B translocation common to all 15 strains of Ethiopian tetraploid wheat examined. Using the C-banding technique, we found two new translocations,T1B·6B and T5B·6B, and a pericentric inversion of chromosome 5A. The C-banding pattern indicated that in all three translocations the breakpoint was located in the centromeric region. Sequential N-banding and genomic in situ hybridization (GISH) confirmed the location of the breakpoint of translocation 2A·4B, and revealed that the breakpoint of another known translocation, 2A-2B, was in the proximal region of 2BL. The fixation of the 2A·4B translocation indicates the monophyletic origin of Ethiopian tetraploid wheat and the presence of a very severe bottleneck effect during its dispersal. Received: 29 June 1999 / Accepted: 18 February 2000     

Visualization of A- and B-genome chromosomes in wheat (Triticum aestivum L.) x jointed goatgrass (Aegilops cylindrica Host) backcross progenies.

Wheat (Triticum aestivum) and jointed goatgrass (Aegilops cylindrica) can cross with each other, and their self-fertile backcross progenies frequently have extra chromosomes and chromosome segments, presumably retained from wheat, raising the possibility that a herbicide resistance gene might transfer from wheat to jointed goatgrass. Genomic in situ hybridization (GISH) was used to clarify the origin of these extra chromosomes. By using T. durum DNA (AABB genome) as a probe and jointed goatgrass DNA (CCDD genome) as blocking DNA, one, two, and three A- or B-genome chromosomes were identified in three BC2S2 individuals where 2n = 29, 30, and 31 chromosomes, respectively. A translocation between wheat and jointed goatgrass chromosomes was also detected in an individual with 30 chromosomes. In pollen mother cells with meiotic configuration of 14 II + 2 I, the two univalents were identified as being retained from the A or B genome of wheat. By using Ae. markgrafii DNA (CC genome) as a probe and wheat DNA (AABBDD genome) as blocking DNA. 14 C-genome chromosomes were visualized in all BC2S2 individuals. The GISH procedure provides a powerful tool to detect the A or B-genome chromatin in a jointed goatgrass background, making it possible to assess the risk of transfer of herbicide resistance genes located on the A or B genome of wheat to jointed goatgrass.     

Transfer of small chromosome fragments of<Emphasis Type="Italic">Agropyron elongatum</Emphasis> to wheat chromosome via asymmetric somatic hybridization

The chromosome constitution of hybrids and chromatin patterns of Agropyron elongatum (Host)Neviski in F₅ somatic hybrid lines -1–3 and I-1-9 between Triticum aestivum L. and A. elongatum were analyzed. Based on the statistic data of pollen mother cells, F₅ I-1-9 and-1-3 had 20–21 bivalents with a frequency of 84.66% and 85.28%, of which, 89.83% and 89.57% were ring bivalents. The result indicated that both hybrid lines were basically stable in the chromosome constitution and behavior. RAPD analysis showed that the two hybrids contained biparental and integrated DNA. GISH (Genome in situ hybridization) revealed that in the form of small chromosome segments, A. elongatum chromatin was scattered on 4–6 wheat chromosomes near by the region of centromere and telomere in the two hybrid lines. SSR analysis indicated that A. elongatum DNA segments were distributed on the 2A, 5B, 6B and 2D wheat chromosomes in the hybrids, which was in accordance with the GISH results that small-segments intercalated poly-site.     

A cytogenetic study of the blue-grain line of the common wheat cultivar Saratovskaya 29

The chromosome composition of the blue-grain line i:S29Ba of the cultivar Saratovskaya 29 was identified by cytological, GISH, and microsatellite analyses and C-banding. It was found that common wheat chromosome 4B of the cultivar Saratovskaya 29 was substituted with the Agropyron elongatum Host. chromosome carrying the gene for blue grain (s:S294Ag(4B)) during the construction of this nearly isogenic line. The blue-grain line was tested for productivity. The substitution of total chromosome 4B of the cultivar Saratovskaya 29 by Ag. elongatum chromosome 4 did not significantly affect the spike productivity parameters and grain quality with the exception of spike length (plus effect), spike density, and vitreousness (minus effects). The blue-grain line with s:S294Ag(4B) can be used in further studies associated with chromosome engineering in cereals and wheat breeding.     

Transfer of small chromosome fragments of Agropyron elongatum to wheat chromosome via asymmetric somatic hybridization

~~Transfer of small chromosome fragments of Agropyron elongatum to wheat chromosome via asymmetric somatic hybridization1 .Dong,Y.C,GenePools of common wheat,Journal of Triticeae CroPs(in Chinese),2000,20(3):78-81. 2 .Wei,Y.M.,Zheng,YL.Zhou,R.H., Detectlon of the rye chro- matin in multisPikelet wheat germplasm 10-A background using fluorescence in situ hybridization(FISH)and RFLP markers,Acta Bot.Sinica(in Chinese),1999,41(7):722-725. 3 .Xiang,E N.,Xia,G M.…     

Nuclear and cytoplasmic genome composition of Solanum bulbocastanum (+) S. tuberosum somatic hybrids.

Somatic hybrids between the wild incongruent species Solanum bulbocastanum (2n = 2x = 24) and S. tuberosum haploids (2n = 2x = 24) have been characterized for their nuclear and cytoplasmic genome composition. Cytologic observations revealed the recovery of 8 (near-)tetraploid and 3 hexaploid somatic hybrids. Multicolor genomic in situ hybridization (GISH) analysis was carried out to study the genomic dosage of the parental species in 5 somatic hybrids with different ploidy. The GISH procedure used was effective in discriminating parental genomes in the hybrids; most chromosomes were unambiguously colored. Two (near-)tetraploid somatic hybrids showed the expected 2:2 cultivated-to-wild genomic dosage; 2 hexaploids revealed a 4:2 cultivated-to-wild genomic dosage, and 1 hexaploid had a 2:4 cultivated-to-wild genomic dosage. Characterization of hybrid cytoplasmic genomes was performed using gene-specific primers that detected polymorphisms between the fusion parents in the intergenic regions. The analysis showed that most of the somatic hybrids inherited the plastidial and mitochondrial DNA of the cultivated parent. A few hybrids, with a rearranged mitochondrial genome (showing fragments derived from both parents), were also identified. These results confirmed the potential of somatic hybridization in producing new variability for genetic studies and breeding.     

应用基因组原位杂交及RFLP标记鉴定小麦中的大麦染色体

用生物素（Biotin-6-dUTP)标记的大麦Betzes基因组DNA作探针,以普通小麦中国春总DNA作封阻进行基因组原位杂交（Genomeinsituhybridization,简称GISH）,从13株小麦-大麦杂交后代中鉴定出2个含有3条大麦Betzes2H染色体的材料（2n＝43）;2个2H单体异代换系（2n＝42）;7个2H二体异代换系（2n＝42）。用已定位在小麦第2部分同源群短臂上的探针psr131进行RFLP分析,结果表明大麦Betzes、代换系A5有1条区别于小麦中国春的特异带,A     

New Types of Wheat Chromosomal Structural Variations in Derivatives of Wheat-Rye Hybrids

Background

Chromosomal rearrangements induced by wheat-rye hybridization is a very well investigated research topic. However, the structural alterations of wheat chromosomes in wheat-rye hybrids are seldom reported.

Methodology/Principal Findings

Octoploid triticale lines were derived from common wheat Triticum. aestivum L. ‘Mianyang11’×rye Secale cereale L. ‘Kustro’. Some progeny were obtained by the controlled backcrossing of triticale with ‘Mianyang11’ and common wheat T. aestivum L. ‘Chuannong27’ followed by self-fertilization. Fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH) using Oligo-pSc119.2-1, Oligo-pTa535-1 and rye genomic DNA as probes were used to analyze the mitotic chromosomes of these progeny. Alterations of wheat chromosomes including 5A, 6A, 1B, 2B, 6B, 7B, 1D, 3D and 7D were observed. 5AL arm carrying intercalary Oligo-pSc119.2-1, Oligo-pTa535-1 or both Oligo-pSc119.2-1 and Oligo-pTa535-1 signals, 6AS, 1BS and 1DL arms containing terminal Oligo-pSc119.2-1 signal, 6BS and 3DS arms without terminal Oligo-pSc119.2-1 signal, 7BS without subtelomeric Oligo-pSc119.2-1 signal and 7DL with intercalary Oligo-pSc119.2-1 signal have been observed. However, these changed wheat chromosomes have not been detected in ‘Mianyang11’ and Chuannong 27. The altered 5A, 6A, 7B and 7D chromosomes in this study have not been reported and represent several new karyotype structures of common wheat chromosomes.

Conclusions/Significance

These rearranged wheat chromosomes in the present study afford some new genetic variations for wheat breeding program and are valuable materials for studying the biological function of tandem repetitive DNA sequences.     

Mapping of QTL for Fusarium head blight resistance and morphological and developmental traits in three backcross populations derived from Triticum dicoccum?×?Triticum durum

Breeding for resistance to Fusarium head blight (FHB) in durum wheat continues to be hindered by the lack of effective resistance sources. Only limited information is available on resistance QTL for FHB in tetraploid wheat. In this study, resistance to FHB of a Triticum dicoccum line in the background of three Austrian T. durum cultivars was genetically characterized. Three populations of BC₁F₄-derived RILs were developed from crosses between the resistant donor line T. dicoccum-161 and the Austrian T. durum recipient varieties DS-131621, Floradur and Helidur. About 130 BC₁F₄-derived lines per population were evaluated for FHB response using artificial spray inoculation in four field experiments during two seasons. Lines were genetically fingerprinted using SSR and AFLP markers. Genomic regions on chromosomes 3B, 4B, 6A, 6B and 7B were significantly associated with FHB severity. FHB resistance QTL on 6B and 7B were identified in two populations and a resistance QTL on 4B appeared in three populations. The alleles that enhanced FHB resistance were derived from the T. dicoccum parent, except for the QTL on chromosome 3B. All QTL except the QTL on 6A mapped to genomic regions where QTL for FHB have previously been reported in hexaploid wheat. QTL on 3B and 6B coincided with Fhb1 and Fhb2, respectively. This implies that tetraploid and hexaploid wheat share common genomic regions associated with FHB resistance. QTL for FHB resistance on 4B co-located with a major QTL for plant height and mapped at the position of the Rht-B1 gene, while QTL on 7B overlapped with QTL for flowering time.     

Use of RFLPs to determine the chromosome composition of tetraploid triticale (A/B)(A/B)RR.

Tetraploid triticale, (A/B)(A/B)RR (2n = 28), is a botanical novelty, an amphiploid composed of a diploid rye and a 14 chromosome wheat genome made up of chromosomes of the A and B genomes of tetraploid wheat. Restriction fragment length polymorphism (RFLP) markers were used to elucidate the chromosome composition of the mixed wheat genome of 35 different tetraploid triticale lines. Of 128 possible A/B chromosome pair combinations, only 6 were found among these lines, with a prevalence of the 1A, 2A, 3B, 4B, 5B, 6B, and 7B karyotype. In most triticale lines stable wheat genomes made up of only homologous A or B genome chromosome pairs were identified, however, in some lines homoeologous chromosome pairs were found. In this paper we demonstrate that RFLPs can be used successfully as an alternative to C-banding for the identification of the chromosome composition of tetraploid triticale and discuss the possible selective advantage of specific chromosome composition.     

Genome inheritance in populations derived from hexaploid/tetraploid and tetraploid/hexaploid wheat crosses

Hexaploid/tetraploid and tetraploid/hexaploid wheat hybrids were established using the hexaploid (Triticum aestivum L.) bread wheat LRC2010-150 and the tetraploid durum wheat (T. turgidum spp. durum) WID802. Thirty F₂ progeny from each cross were characterised using Diversity Arrays Technology (DArTseq?) markers to determine whether there are differences between the crosses in the proportion of A, B and D genomic material inherited from each parent. Inheritance of the A and B genome from the tetraploid durum parent varied from 32 to 63% among the 60 lines assessed, and results indicated significant differences between the two F₂ populations in the mean overall proportion of chromosomes A and B inherited from each parent. Significant differences were also observed between the crosses in the proportion of chromosomal segments on 2B, 3A, 3B and 4A inherited from the tetraploid parent. The F₂ populations also showed significant differences in the average retention of D chromosomes per line with the tetraploid/hexaploid cross retaining a mean of 2.83 chromosomes while the reciprocal cross retained a mean of 1.8 chromosomes per line. A strong negative correlation was observed in individual lines from both populations between the proportion of the A and B genome inherited from the tetraploid durum parent and the retention of the D genome. The implication of these results for the design of efficient crossing strategies between hexaploid and tetraploid wheats is discussed.     

Phylogenetic analysis of tetraploid wheat based on nuclear DMC1 gene

Tetraploid wheat (AABB or AAGG, 2n = 4x = 28) holds an important place in Triticum. It includes two allopolyploid species, Triticum turgidum and Triticum timopheevii. Many problems concerning the phylogenetic relationships among tetraploid wheat species remain unresolved. In this study, sequences data for the nuclear DMC1 gene from 61 accessions of Triticum and Aegilops species, representing diploid and tetraploid species, were used to examine the phylogenetic relationships among tetraploid wheat. Phylogenetic trees were constructed using maximum-likelihood and neighbor-joining approaches, and gene flow and genetic differentiation values were computed. The results indicated that the A genome of tetraploid wheat originated from T. urartu rather than T. monococcum, and Aegilops speltoides was the donor of the B and G genomes. Hulled tetraploid wheat accessions formed a subclade, and naked tetraploid wheat got other subclade, indicating that at least two intermediary subspecies were involved in the evolution of T. turgidum. Triticum turgidum and T. timopheevii might have simultaneously originated from a hybridization events. These results indicated that the DMC1 gene sequences are useful for resolution of the molecular phylogenetic relationships of tetraploid wheat.     

Spontaneous and Divergent Hexaploid Triticales Derived from Common Wheat × Rye by Complete Elimination of D-Genome Chromosomes

Background

Hexaploid triticale could be either synthesized by crossing tetraploid wheat with rye, or developed by crossing hexaploid wheat with a hexaploid triticale or an octoploid triticale.

Methodology/Principal Findings

Here two hexaploid triticales with great morphologic divergence derived from common wheat cultivar M8003 (Triticum aestivum L.) × Austrian rye (Secale cereale L.) were reported, exhibiting high resistance for powdery mildew and stripe rust and potential for wheat improvement. Sequential fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH) karyotyping revealed that D-genome chromosomes were completely eliminated and the whole A-genome, B-genome and R-genome chromosomes were retained in both lines. Furthermore, plentiful alterations of wheat chromosomes including 5A and 7B were detected in both triticales and additionally altered 5B, 7A chromosome and restructured chromosome 2A was assayed in N9116H and N9116M, respectively, even after selfing for several decades. Besides, meiotic asynchrony was displayed and a variety of storage protein variations were assayed, especially in the HMW/LMW-GS region and secalins region in both triticales.

Conclusion

This study confirms that whole D-genome chromosomes could be preferentially eliminated in the hybrid of common wheat × rye, “genome shock” was accompanying the allopolyploidization of nascent triticales, and great morphologic divergence might result from the genetic variations. Moreover, new hexaploid triticale lines contributing potential resistance resources for wheat improvement were produced.     

用顺序GISH-FISH 技术鉴定小麦-中间偃麦草小片段易位系

利用顺序基因组-重复序列原位杂交技术对1个来自中3不育系和普通小麦恢75杂种后代稳定株系H96276-2的染色体组成进行了分析。以中间偃麦草（Agropyronintermedium）基因组DNA为探针的荧光原位杂交结果表明,H96276-2的体细胞中有42条染色体,包括20对小麦染色体和1对小麦-中间偃麦草易位染色体,中间偃麦草染色体的易位片段位于1对小麦染色体的端部。进而用重复序列探针pSc119进行第2次荧光原位杂交,证明H96276-2中的中间偃麦草染色体易位片段位于小麦2B染色体的短臂上。     

Map-based analysis of the tenacious glume gene Tg-B1 of wild emmer and its role in wheat domestication

The domestication of wheat was instrumental in spawning the civilization of humankind, and it occurred through genetic mutations that gave rise to types with non-fragile rachises, soft glumes, and free-threshing seed. Wild emmer (Triticum turgidum ssp. dicoccoides), the tetraploid AB-genome progenitor of domesticated wheat has genes that confer tenacious glumes (Tg) that underwent genetic mutations to give rise to free-threshing wheat. Here, we evaluated disomic substitution lines involving chromosomes 2A and 2B of wild emmer accessions substituted for homologous chromosomes in tetraploid and hexaploid backgrounds. The results suggested that both chromosomes 2A and 2B of wild emmer possess genes that inhibit threshability. A population of recombinant inbred lines derived from the tetraploid durum wheat variety Langdon crossed with a Langdon — T. turgidum ssp. dicoccoides accession PI 481521 chromosome 2B disomic substitution line was used to develop a genetic linkage map of 2B, evaluate the genetics of threshability, and map the gene derived from PI 481521 that inhibited threshability. A 2BS linkage map comprised of 58 markers was developed, and markers delineated the gene to a 2.3 cM interval. Comparative analysis with maps containing the tenacious glume gene Tg-D1 on chromosome arm 2DS from Aegilops tauschii, the D genome progenitor of hexaploid wheat, revealed that the gene inhibiting threshability in wild emmer was homoeologous to Tg-D1 and therefore designated Tg-B1. Comparative analysis with rice and Brachypodium distachyon indicated a high level of divergence and poorly conserved colinearity, particularly near the Tg-B1 locus. These results provide a foundation for further studies involving Tg-B1, which, together with Tg-D1, had profound influences on wheat domestication.     

Variability of microsatellites BM224 and Bcal7 in populations of green toads (Bufo viridis complex) differing by nuclear DNA content and ploidy

The variability of microsatellites BM224 and Bcal7 was studied for the first time in three species of the diploid-polyploid complex of Bufo viridis (B. viridis, B. oblongus, and B. pewzowi). The locus Bcal7 was established to be monomorphic in all samples studied. In microsatellite BM224, three allele variants were found. Among tetraploid toads, the western Asiatic species B. oblongus was characterized by one allele only, the eastern B. pewzowi, by the two other alleles. A similar distribution was also revealed in triploid individuals on the borders of range between tetraploid and diploid species. Among the diploid species B. viridis samples, all three allele variants of microsatellite BM224 were observed. Their distribution in the area proved to be geographically determined. In diploid toads, a similarity was revealed between the distribution of microsatellite BM224 alleles and variability of the nuclear DNA content.     

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.     

Genome composition, stability and fertility of hexaploid alloploids between Triticum turgidum var. carthlicum and Leymus racemosus

Hexaploid alloploids between the tetraploid wheat Triticum carthlicum and the perennial tetraploid Leymus racemosus were analysed for chromosome composition and cytogenetic stability. GISH analysis showed different lines to have from 11 to 16 Leymus chromosomes. The alloploids showed a relatively high frequency of univalents in meiotic metaphase and of aneuploid plants and hence they are not stable. The seedset is lower than in wheat, but high enough to secure a safe propagation and preservation. The alloploids are discussed in relation to widening the genetic variation of breadwheat and wheat breeding.     

Allopolyploid speciation of the Mexican tetraploid potato species Solanum stoloniferum and S. hjertingii revealed by genomic in situ hybridization

Thirty-six percent of the wild potato (Solanum L. section Petota Dumort.) species are polyploid, and about half of the polyploids are tetraploid species (2n = 4x = 48). Determination of the type of polyploidy and development of the genome concept for members of section Petota traditionally has been based on the analysis of chromosome pairing in species and their hybrids and, most recently, DNA sequence phylogenetics. Based on these data, the genome designation AABB was proposed for Mexican tetraploid species of series Longipedicellata Buk. We investigated this hypothesis with genomic in situ hybridization (GISH) for both representatives of the series, S. stoloniferum Schltdl. and S. hjertingii Hawkes. GISH analysis supports an AABB genome constitution for these species, with S. verrucosum Schltdl. (or its progenitor) supported as the A genome donor and another North or Central American diploid species (S. cardiophyllum Lindl., S. ehrenbergii (Bitter) Rydb., or S. jamesii Torrey) as the B genome donor. GISH analysis of chromosome pairing of S. stoloniferum also confirms the strict allopolyploid nature of this species. In addition, fluorescence in situ hybridization data suggest that 45S rDNA regions of the two genomes of S. stoloniferum were changed during coevolution of A and B genomes of this allotetraploid species.     

Introgression of A- and B-genome of tetraploid triticale chromatin into tetraploid rye

An improvement of rye is one of the mainstream goals of current breeding. Our study is concerned with the introduction of the tetraploid triticale (ABRR) into the 4x rye (RRRR) using classical methods of distant crossing. One hundred fifty BC₁F₉ hybrid plants [(4x rye?×?4x triticales)?×?4x rye] obtained from a backcrossing program were studied. The major aim of this work was to verify the presence of an introgressed A- and B- genome chromatin of triticale in a collection of the 4x rye-tiritcale hybrids and to determine their chromosome compositions. In the present study, karyotypes of the previously reported BC₁F₂s and BC₁F₃s were compared with that of the BC₁F₉ generation as obtained after several subsequent open pollinations. The genomic in situ hybridisation (GISH) allowed us to identify 133 introgression forms in which chromosome numbers ranged between 26 and 32. Using four DNA probes (5S rDNA, 25S rDNA, pSc119.2 and pAs1), the fluorescence in situ hybridisation (FISH) was carried out to facilitate an exact chromosome identification in the hybrid plants. The combination of the multi-colour GISH with the repetitive DNA FISH singled out five types of translocated chromosomes: 2A.2R, 4A.4R, 5A.5R, 5B.5R and 7A.7R among the examined BC₁F₉s. The reported translocation lines could serve as valuable sources of wheat chromatin suitable for further improvements of rye.