Chromosome Translocation Lines Research Articles

Identification of allelic relationship and translocation region among chromosomal translocation lines that leads to less-seed watermelon.

Less-seed and seedless traits are desirable characteristics in watermelon (Citrullus lanatus). Hybridization between watermelon chromosomal translocated lines and wild lines significantly reduced seed counts in the hybrid fruits, approaching even seedless. However, the allelic relationships and the chromosomal translocation breakpoints from different sources are unclear, which limits their utility in breeding practices. This study focused on three groups of chromosomal translocation materials from different sources and conducted inheritance and allelic relationship analysis of translocation points. The results from third-generation genome sequencing and fluorescence in situ hybridization (FISH) revealed that the specific translocations in the naturally mutated material MT-a involved reciprocal translocations between Chr6 and Chr10. The Co60γ radiation-induced mutant material MT-b involved reciprocal translocations between Chr1 and Chr5, Chr4 and Chr8. The Co60γ radiation-induced mutant material MT-c involved complex translocations among Chr1, Chr5, and Chr11. Cytological observation showed that heterozygous translocation hybrids showed chromosomal synapsis abnormalities during meiotic diakinesis. Further, dominant and codominant molecular markers were developed on both sides of the translocation breakpoints, which could facilitate rapid and efficient identification of chromosome translocation lines. This study provides technical guidance for utilizing chromosomal translocation materials in the development of less-seed watermelon varieties.

Rapid and cost-effective molecular karyotyping in wheat, barley, and their cross-progeny by chromosome-specific multiplex PCR

BackgroundInterspecific hybridisation is a powerful tool for increasing genetic diversity in plant breeding programmes. Hexaploid wheat (Triticum aestivum, 2n = 42) × barley (Hordeum vulgare, 2n = 14) intergeneric hybrids can contribute to the transfer of agronomically useful traits by creating chromosome addition or translocation lines as well as full hybrids. Information on the karyotype of hybrid progenies possessing various combinations of wheat and barley chromosomes is thus essential for the subsequent breeding steps. Since the standard technique of chromosome in situ hybridisation is labour-intensive and requires specific skills. a routine, cost-efficient, and technically less demanding approach is beneficial both for research and breeding.ResultsWe developed a Multiplex Polymerase Chain Reaction (MPCR) method to identify individual wheat and barley chromosomes. Chromosome-specific primer pairs were designed based on the whole genome sequences of ‘Chinese Spring’ wheat and ‘Golden Promise’ barley as reference cultivars. A pool of potential primers was generated by applying a 20-nucleotide sliding window with consecutive one-nucleotide shifts on the reference genomes. After filtering for optimal primer properties and defined amplicon sizes to produce an ordered ladder-like pattern, the primer pool was manually curated and sorted into four MPCR primer sets for the wheat A, B, and D sub-genomes, and for the barley genome. The designed MPCR primer sets showed high chromosome specificity in silico for the genome sequences of all 18 wheat and barley cultivars tested. The MPCR primers proved experimentally also chromosome-specific for the reference cultivars as well as for 13 additional wheat and four barley genotypes. Analyses of 16 wheat × barley F1 hybrid plants demonstrated that the MPCR primer sets enable the fast and one-step detection of all wheat and barley chromosomes. Finally, the established genotyping system was fully corroborated with the standard genomic in situ hybridisation (GISH) technique.ConclusionsWheat and barley chromosome-specific MPCR offers a fast, labour-friendly, and versatile alternative to molecular cytogenetic detection of individual chromosomes. This method is also suitable for the high-throughput analysis of distinct (sub)genomes, and, in contrast to GISH, can be performed with any tissue type. The designed primer sets proved to be highly chromosome-specific over a wide range of wheat and barley genotypes as well as in wheat × barley hybrids. The described primer design strategy can be extended to many species with precise genome sequence information.

Molecular Cytogenetic Characterization of Novel 1RS.1BL Translocation and Complex Chromosome Translocation Lines with Stripe Rust Resistance.

Rye is the most important source for the genetic improvement of wheat. In this study, two stable wheat-rye primary 1RS.1BL translocation lines, RT855-13 and RT855-14, were selected and identified by acid polyacrylamide gel electrophoresis (A-PAGE), co-dominant PCR, and multi-color fluorescence in situ hybridization (MC-FISH) from the progeny of the crossing of the wheat cultivar Mianyang11 and a Chinese rye Weining. When more than two independent, simple reciprocal translocations are involved in a carrier, they are defined as complex chromosome translocations (CCT). The MC-FISH results also indicated that CCT occurred in RT855-13; namely that, besides 1RS.1BL translocation chromosomes, there are other two pairs of balanced reciprocal translocations. It was demonstrated that the interchange between a distal segment of 4B and long arm of 3D occurred in the RT855-13. The novel translocation chromosomes in wheat were recorded as 3DS.4BSDS and 3DL-4BSPS.4BL. Reports about CCT as a genetic resource in plant breeding programs are scarce. Both lines expressed high resistance to Puccinia striiformis f. sp. tritici, which are prevalent in China and are virulent on Yr9, and the CCT line RT855-13 retained better resistance as adult plants compared with RT855-14 in the field. Both lines, especially the CCT line RT855-13, exhibited better agronomic traits than their wheat parent, Mianyang11, indicating that both translocation lines could potentially be used for wheat improvement. The results also indicated that the position effects of CCT can lead to beneficial variations in agronomic and resistant traits, making them a valuable genetic resource to wheat breeding programs.

Assessment of Resistance to Cereal Cyst Nematode, Stripe Rust, and Powdery Mildew in Wheat-Thinopyrum intermedium Derivatives and Their Chromosome Composition.

Wide hybridization between wheat and wild relatives such as Thinopyrum intermedium is important for broadening genetic diversity and improving disease resistance in wheat. We developed 30 wheat-Th. intermedium derivatives. Here, we report assessments of their resistance to different pathogens including cereal cyst nematode (CCN; Heterodera spp.), Puccinia striiformis f. tritici Erikss. causing stripe rust, and Blumeria graminis f. tritici (DC.) Speer inciting powdery mildew. Under natural field infection, all the wheat-Th. intermedium lines were resistant to at least one of the pathogens, and four lines were resistant to multiple pathogens. Twenty-nine of 30 tested lines exhibited resistance to H. avenae, a dominant CCN species in wheat fields. Twenty-four lines were resistant to H. filipjevi, an emerging threat to wheat production. Tests of phenotypic responses in the naturally infected field nurseries identified six stripe rust-resistant lines and 13 powdery mildew-resistant lines. Mitotic observation demonstrated that these newly developed wheat-Th. intermedium derivatives included not only octoploid but also chromosome addition, substitution, and translocation lines. Chromosome compositions of the four lines resistant to multiple pathogens were analyzed by genomic in situ hybridization and fluorescence in situ hybridization. The octoploid lines Zhong 10-68 and Zhong 10-117 carried both intact Th. intermedium chromosomes and translocated chromosomes. Line Zhong 10-149 had 42 wheat chromosomes and two wheat ditelosomes plus a pair of T3BS·J translocated chromosomes. Line Zhong 10-160 carried 41 wheat chromosomes plus one pair of the J genome chromosomes of Th. intermedium. The multiple disease-resistant wheat-Th. intermedium derivatives, especially lines with chromosome counts close to that of common wheat, provide valuable materials for wheat resistance breeding programs.

Molecular dissection of Secale africanum chromosome 6Rafr in wheat enabled localization of genes for resistance to powdery mildew and stripe rust

BackgroundIntrogression of chromatin from Secale species into common wheat has for decades been a successful strategy for controlling the wheat diseases. The wild Secale species, Secale africanum Stapf., is a valuable source for resistance to foliar disease of wheat. A wheat-S. africanum chromosome 6Rafr substitution line displayed resistance to both powdery mildew and stripe rust at the adult-plant stage.ResultsWheat-S. africanum chromosome 6Rafr deletion and translocation lines were produced and identified by sequential non-denaturing fluorescence in situ hybridization (ND-FISH) using multiple Oligo-based probes. Different ND-FISH patterns were observed between S. cereale 6R and S. africanum 6Rafr. With reference to the physical map of the draft genome sequence of rye inbred line Lo7, a comprehensive PCR marker analysis indicated that insertions and deletions had occurred by random exchange between chromosomes 6R and 6Rafr. A survey of the wheat- S. africanum 6Rafr lines for disease resistance indicated that a powdery mildew resistance gene(s) was present on the long arm of 6Rafr at FL0.85–1.00, and that a stripe rust resistance gene(s) was located in the terminal region of 6RafrS at FL0.95–1.00. The wheat-S. africanum 6Rafr introgression lines also displayed superior agronomic traits, indicating that the chromosome 6Rafr may have little linkage drag in the wheat background.ConclusionsThe combination of molecular and cytogenetic methods allowed to precisely identify the chromosome rearrangements in wheat- S. africanum 6Rafr substitution, deletion and translocation lines, and compare the structural difference between chromosomes 6R and 6Rafr. The wheat- S. africanum 6Rafr lines containing gene(s) for powdery mildew and stripe rust resistance could be used as novel germplasm for wheat breeding by chromosome engineering.

Identification, Characterization, and Evaluation of Novel Stripe Rust-Resistant Wheat-Thinopyrum intermedium Chromosome Translocation Lines.

Stripe rust is an important disease in wheat, and development of genetic resistance in cultivars is an effective approach to control the disease. Wild species of wheat, such as Thinopyrum intermedium, are an excellent gene source for wheat improvement. In this study, two stripe rust-resistant wheat-Th. intermedium chromosome translocation lines, CH4131 and CH4132, were characterized by cytogenetic and pathological methods. The introgressed chromosome fragment was tagged using amplified fragment-length polymorphism-derived sequence-characterized amplified region (SCAR) markers and intron targeting markers, indicating that CH4131 and CH4132 both possess a homologous group 3 chromatin of Th. intermedium. Genomic in situ hybridization results suggested that a very small Th. intermedium chromosome segment was translocated to the terminal region of wheat 1BS for both lines, forming a configuration of T3Ai-1BS.1BL. The two translocation lines were resistant to stripe rust, and the resistance gene, temporarily designated YrCH-1BS, was likely derived from Th. intermedium. The translocated chromosome fragments have no genetic linkage drag to agronomic performance. The grain quality indexes of these two translocations were higher than local wheat varieties. Therefore, CH4131 and CH4132 could be used as potential gene sources in wheat improvement programs. The SCAR markers are useful to select stripe rust resistance from Th. intermedium.

Physical Mapping of a Novel Locus Conferring Leaf Rust Resistance on the Long Arm of Agropyron cristatum Chromosome 2P.

Wheat leaf rust is one of the most common wheat diseases worldwide and can cause up to 40% wheat yield loss. To combat the growth and spread of leaf rust disease, continual exploration and identification of new and effective resistance genes are needed. Here, we report for the first time a locus conferring leaf rust resistance located on the long arm of Agropyron cristatum chromosome 2P in Triticum aestivum–A. cristatum 2P translocation lines. This study used 50 leaf rust races, including two Chinese major dominant leaf rust races, named by THT and PHT, and other 48 different leaf rust races collected from 11 provinces, 1autonomous region and 1 municipality of China to test the resistance to T. aestivum–A. cristatum 2P chromosome translocation lines and their backcross populations, the results indicated that the novel leaf rust resistance locus was immune or nearly immune to all tested leaf rust races. Four long arm translocation lines with different breakpoints of A. cristatum chromosome 2PL and their backcross populations were tested with leaf rust race THT at the seedling and adult stages and genotyped with 2P-specific STS markers. The results showed that the novel leaf rust resistance locus of the T. aestivum–A. cristatum 2P translocation lines was located in the chromosomal bin FL 0.66–0.86 of 2PL. Therefore, T. aestivum–A. cristatum 2P chromosome translocation lines conferring leaf rust resistance locus could provide a novel disease-resistance resource for future wheat breeding programs.

Molecular cytogenetic identification of a novel wheat-Agropyron elongatum chromosome translocation line with powdery mildew resistance.

Agropyron elongatum (Host.) Neviski (synonym, Thinopyrum ponticum Podp., 2n = 70) has been used extensively as a valuable source for wheat breeding. Numerous chromosome fragments containing valuable genes have been successfully translocated into wheat from A. elongatum. However, reports on the transfer of powdery mildew resistance from A. elongatum to wheat are rare. In this study, a novel wheat-A. elongatum translocation line, 11-20-1, developed and selected from the progenies of a sequential cross between wheat varieties (Lankaoaizaoba, Keyu 818 and BainongAK 58) and A. elongatum, was evaluated for disease resistance and characterized using molecular cytogenetic methods. Cytological observations indicated that 11-20-1 had 42 chromosomes and formed 21 bivalents at meiotic metaphase I. Genomic in situ hybridization analysis using whole genomic DNA from A. elongatum as a probe showed that the short arms of a pair of wheat chromosomes were replaced by a pair of A. elongatum chromosome arms. Fluorescence in situ hybridization, using wheat D chromosome specific sequence pAs1 as a probe, suggested that the replaced chromosome arms of 11-20-1 were 5DS. This was further confirmed by wheat SSR markers specific for 5DS. EST-SSR and EST-STS multiple loci markers confirmed that the introduced A. elongatum chromosome arms belonged to homoeologous group 5. Therefore, it was deduced that 11-20-1 was a wheat-A. elongatum T5DL∙5AgS translocation line. Both resistance observation and molecular marker analyses using two specific markers (BE443538 and CD452608) of A. elongatum in a F2 population from a cross between line 11-20-1 and a susceptible cultivar Yannong 19 verified that the A. elongatum chromosomes were responsible for the powdery mildew resistance. This work suggests that 11-20-1 likely contains a novel resistance gene against powdery mildew. We expect this line to be useful for the genetic improvement of wheat.

Introduction of Thinopyrum intermedium ssp. trichophorum chromosomes to wheat by trigeneric hybridization involving Triticum, Secale and Thinopyrum genera.

Fluorescence in situ hybridization and molecular markers have confirmed that several chromosomes from Thinopyrum intermedium ssp. trichophorum have been added to a wheat background, which originated from a cross between a wheat- Thinopyrum partial amphiploid and triticale. The lines displayed blue grains and resistance to wheat stripe rust. Thinopyrum intermedium has been used as a valuable resource for improving the disease resistance and yield potential of wheat. With the aim to transfer novel genetic variation from Th. intermedium species for sustainable wheat breeding, a new trigeneric hybrid was produced by crossing an octoploid wheat-Th. intermedium ssp. trichophorum partial amphiploid with hexaploid triticale. Fluorescence in situ hybridization (FISH) revealed that Thinopyrum chromosomes were transmitted preferably and the number of rye chromosomes tended to decrease gradually in the selfed derivatives of the trigeneric hybrids. Four stable wheat-Th. intermedium chromosome substitution, addition and translocation lines were selected, and a 2JS addition line, two substitution lines of 4JS(4B) and 4J(4B), and a small 4J.4B translocation line were identified by FISH and molecular markers. It was revealed that the gene(s) responsible for blue grains may located on the FL0.60-1.00 of long arm of Th. intermedium-derived 4J chromosome. Disease resistance screenings indicated that chromosomes 4JS and 2JS appear to enhance the resistance to stripe rust in the adult plant stage. The new germplasm with Th. intermedium introgression shows promise for utilization of Thinopyrum chromosome segments in future wheat improvement.

Characterization of wheat-Secale africanum chromosome 5R(a) derivatives carrying Secale specific genes for grain hardness.

New wheat- Secale africanum chromosome 5R (a) substitution and translocation lines were developed and identified by fluorescence in situ hybridization and molecular markers, and chromosome 5R (a) specific genes responsible for grain hardness were isolated. The wild species, Secale africanum Stapf. (genome R(a)R(a)), serves as a valuable germplasm resource for increasing the diversity of cultivated rye (S. cereale L., genome RR) and providing novel genes for wheat improvement. In the current study, fluorescence in situ hybridization (FISH) and molecular markers were applied to characterize new wheat-S. africanum chromosome 5R(a) derivatives. Labeled rye genomic DNA (GISH) and the Oligo-probes pSc119.2 and pTa535 (FISH) were used to study a wheat-S. africanum amphiploid and a disomic 5R(a) (5D) substitution, and to identify a T5DL.5R(a)S translocation line and 5R(a)S and 5R(a)L isotelosome lines. Twenty-one molecular markers were mapped to chromosome 5R(a) arms which will facilitate future rapid identification of 5R(a) introgressions in wheat backgrounds. Comparative analysis of the molecular markers mapped on 5R(a) with homoeologous regions in wheat confirmed a deletion on the chromosome T5DL.5R(a)S, which suggests that the wheat-S. africanum Robertsonian translocation involving homologous group 5 may not be fully compensating. Complete coding sequences at the paralogous puroindoline-a (Pina) and grain softness protein gene (Gsp-1) loci from S. africanum were cloned and localized onto the short arm of chromosome 5R(a). The S. africanum chromosome 5R(a) substitution and translocation lines showed a reduction in the hardness index, which may be associated with the S. africanum- specific Pina and Gsp-1 gene sequences. The present study reports the production of novel wheat-S. africanum chromosome 5R(a) stripe rust resistant derivatives and new rye-specific molecular markers, which may find application in future use of wild Secale genome resources for grain quality studies and disease resistance breeding.

The creation of new aneuploid lines of the cotton (Gossypium hirsutum L.) with identification of chromosomes by translocation and SSR-markers

The use of monosomic lines significantly increases the effectiveness of molecular-genetic analysis and the development of superior quality breeding lines via substitutions by alien chromosomes. A complete set of aneuploid series for each cotton chromosome was required. Simple sequence repeats (SSR) have been applied as useful markers for understanding cotton genetics. Several DNA markers have already been assigned to the individual chromosomes of Gossypium hirsutum. The primary objective of this paper is to report the creation of new monosomic lines and the use of chromosome specific simple sequence repeat (SSR) markers and translocation lines for chromosome identification to confirm chromosome specificity of monosomic lines in the Uzbek collection. Here, we summarize data on the development of a monosomic stock collection of cotton (G. hirsutum L.) from Uzbekistan, including the origin of 95 primary monosomics, their cytogenetic characteristics, morphological features and their identification by translocation tests and chromosome SSR-markers. Our results indicated several different monosomic lines identified by chromosomes 2, 4, 6 and telosome 11 of the At subgenome and chromosomes 18 and 22 of the Dt subgenome, 22 monosomes were identified as duplicates of three monosomes (chromosomes 2, 4 and 6). Chromosome 4 of the At subgenome was recovered more frequently (18 times) than chromosome 2 of the At subgenome (4 times) and chromosome 6 of the At subgenome (3 times) during pollen irradiation at different doses and in the progeny of the desynaptic plants. These lines will be useful for molecular mapping and enhancement of Upland cotton.

Identification of wheat-Agropyron cristatum 6P translocation lines and localization of 6P-specific EST markers

To improve genetic diversity of wheat and produce chromosome translocation lines with chromatin from Agropyron cristatum, this study screened progenies of a wheat line SM2-244 known to carry a reciprocal wheat-A. cristatum 5A. 6P chromosome translocation with increased fertile tiller number and grain number per spike. Genomic in situ hybridization (GISH) showed that these progenies contained four new types of translocation chromosomes, labeled as TC-A, TC-L, TC-S and TC-T. The long arm of chromosome 6P originally present in the 5A. 6P translocation was subdivided into three segments between relative arm length points 0–0.32, 0.32–0.69, 0.69–1 on the centromere to telomere axis. Screening with 6P-specific EST markers allocated 24, 30, 20 and 56 EST markers to segments C-6PL-0.32, 6PL-0.32-0.69, 6PL-0.69-1, and 6PS, respectively, and markers specific to individual arms were also identified. This study provides experimental resources and tools for mining of desirable genes on the A. cristatum chromosome 6P that can be exploited in wheat breeding.

Evaluation of wheat chromosome translocation lines for high temperature stress tolerance at grain filling stage.

High temperature (HT, heat) stress is detrimental to wheat (Triticum aestivum L.) production. Wild relatives of bread wheat may offer sources of HT stress tolerance genes because they grow in stressed habitats. Wheat chromosome translocation lines, produced by introgressing small segments of chromosome from wild relatives to bread wheat, were evaluated for tolerance to HT stress during the grain filling stage. Sixteen translocation lines and four wheat cultivars were grown at optimum temperature (OT) of 22/14°C (day/night). Ten days after anthesis, half of the plants were exposed to HT stress of 34/26°C for 16 d, and other half remained at OT. Results showed that HT stress decreased grain yield by 43% compared with OT. Decrease in individual grain weight (by 44%) was the main reason for yield decline at HT. High temperature stress had adverse effects on leaf chlorophyll content and Fv/Fm; and a significant decrease in Fv/Fm was associated with a decline in individual grain weight. Based on the heat response (heat susceptibility indices, HSIs) of physiological and yield traits to each other and to yield HSI, TA5594, TA5617, and TA5088 were highly tolerant and TA5637 and TA5640 were highly susceptible to HT stress. Our results suggest that change in Fv/Fm is a highly useful trait in screening genotypes for HT stress tolerance. This study showed that there is genetic variability among wheat chromosome translocation lines for HT stress tolerance at the grain filling stage and we suggest further screening of a larger set of translocation lines.

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.

Chromosome changes after polyploidization in Triticeae

AbstractChromosome changes are common in Triticeae, and they occur widely in natural and resynthesized polyploidy. Two important factors, nucleocytoplasmic interaction (internal) and the environment (external), can significantly influence chromosome changes after polyploidization. And chromosomal DNA changes play key roles during the initial formation, gradual stabilization, and establishment of polyploids. Hybrid breeding between common wheat and related wild species of Triticeae is an example of polyploidization, and many of the chromosome changes occurring after hybridization could be useful for improving wheat varieties. The famous chromosomal translocation 1BL/1RS that occurred after ancestral hybridization between wheat and rye is distributed widely among modern wheat varieties and makes a big contribution to wheat breeding; xiaoyan 6 is a similarly distant hybridization between wheat and Agropyron elongatum (Host) P. Beauv. in China. This chromosome translocation line was cultivated as the main variety in Shaanxi Province for 16 years and has also been used as a core parent for wheat breeding in China during the past 20 years because of its outstanding merits.

Cytogenetic and molecular identification of small-segment chromosome translocation lines from wheat-rye substitution lines to create wheat germplasm with beneficial traits

ABSTRACTIntergeneric crop plant hybrid lines with small-segment chromosome translocations are very useful in plant genetic research and breeding. In this study, to create small-segment chromosome translocations with beneficial agronomic characters, the progeny of wheat-rye substitution lines 5R/5A and 6R/6A were selected from generations F2 to F5 for rye-specific characteristics. A PCR primer and specific simple sequence repeat marker for rye were used in F5 populations to detect rye chromatin and to amplify a specific chromosome band in six translocation lines (06-6-5, 06-6-6, 06-6-9, 6-26-1, 7-23, and 7-33). Fragment pSc119.1 cloned from 7-33 had 99% homology with the big ear gene sequence (GenBank AF512607.1) in wheat. The six lines were further characterized via pollen mother cell meiosis analysis for genetic stability, and chromosome C-banding and genomic in situ hybridization for rye chromatin. The results show that line 7-33 was still within the 5R/5A substitution lines and possessed the big ear gene. The other lines all contained small-segment rye chromosome translocations. The results indicated that substitution line hybridization is an effective method for creating small-segment chromosome translocations with useful agronomic traits. Trials for these six wheat-rye translocation lines are justified because they possess many important stably-inherited agronomic characters, including disease resistance and improved yield.

Retraction Note: Analysis of DNA methylation polymorphism in a set of stable chromosome translocation lines

Retraction Note: Analysis of DNA methylation polymorphism in a set of stable chromosome translocation lines

Tracing the location of powdery mildew resistance-related gene Stpk-V by FISH with a TAC clone in Triticum aestivum-Haynaldia villosa alien chromosome lines

Bacterial artificial chromosomes (BACs) or yeast artificial chromosomes (YACs) containing large inserts as probes for fluorescence in situ hybridization (FISH) have been used in the physical mapping of specific DNA sequences, especially for single- or low-copy sequences. Our earlier study identified Stpk-V, a powdery mildew resistance-related gene located on the 6VS chromosome arm of the wild grass Haynaldia villosa (tribe Triticeae), and obtained several Triticum aestivum-H. villosa alien chromosome lines carrying the Stpk-V gene. However, the precise physical location of the Stpk-V gene on chromosome 6VS is not known. In this study, we used TAC-FISH with TAC15 as the probe coupled with sequential genomic in situ hybridization (GISH) to determine the physical location of the Stpk-V gene in different T. aestivum-H. villosa 6V alien chromosome lines, including addition, substitution and translocation lines. The result indicated that the fraction length of the Stpk-V locus is 0.575±0.035 on the 6V chromosome short arm and this was confirmed by FISH using TAC15 as the probe for tracing the Stpk-V gene in other genetic stocks. The cytological mapping strategies used in this study will be of benefit for tracing the alien gene location in the course of introducing desirable traits from wild species.

Molecular cytogenetic characterization of a new wheat–rye 4R chromosome translocation line resistant to powdery mildew

Rye is an important and valuable gene resource for wheat improvement. However, due to extensive growing of cultivars with disease resistance genes from short arm of rye chromosome 1R and coevolution of pathogen virulence and host resistance, these cultivars successively lost resistance to pathogens. Identification and deployment of new resistance gene sources in rye are, therefore, of especial importance and urgency. A new wheat-rye line, designated as WR41-1, was produced through distant hybridization and chromosome engineering protocols between common wheat cultivar Xiaoyan 6 and rye cultivar German White. It was proved to be a new wheat-rye T4BL·4RL and T7AS·4RS translocation line using sequential genomic in situ hybridization (GISH), multicolor fluorescence in situ hybridization (mc-FISH), and expressed sequence tag-simple sequence repeat (EST-SSR) marker analysis. WR41-1 showed high levels of resistance to powdery mildew (Blumeria graminis f. sp. tritici, Bgt) pathogens prevalent in China at the adult growth stage and 13 of 23 Bgt isolates tested at the seedling stage. According to its resistant pattern to 23 different Bgt isolates, WR41-1 may possess new gene(s) for resistance to powdery mildew, which differed from previously identified and known powdery mildew genes from rye (Pm7, Pm8, Pm17, and Pm20). In addition, WR41-1 was cytologically stable, had a desirable fertility, and is expected to be useful in wheat improvement.

Production of hexaploid triticale by a synthetic hexaploid wheat-rye hybrid method

Hexaploid triticale, including its primary and secondary forms, is an important forage crop and a promising energy plant. Primary forms are usually developed by crossing Triticum turgidum L. with rye, with secondary forms obtained by crossing primary hexaploid triticale and/or hexaploid wheat with octoploid triticale. In this study, we developed an effective method for production of hexaploid triticale via hybridization of synthetic hexaploid wheat (SHW) with rye. The three employed SHW lines were derived from hybridization of T. turgidum with Aegilops tauschii Cosson, and inherited meiotic restitution genes, which can promote the formation of functional gametes in haploid status, from their T. turgidum parents. Although the resulting tetraploid F-1 hybrids with rye (genome ABDR) produced amphiploids (octoploid triticale) and partial amphiploids, the final hybrid products obtained through fertility selection over several generations were hexaploids. These hexaploids were the result of preferential elimination of D-genome chromosomes. In addition to complete hexaploid triticale with 28 intact A/B and 14 intact R chromosomes, we obtained hexaploid triticales with other chromosome constitutions, including monosomic, substitution, and translocation lines. Chromosomes 2D and 5D from the wild species A. tauschii were incorporated into the hexaploid triticales. Out of eight analyzed stable lines derived from three different SHW-L1/rye F-1 plants, we observed four lines with small-fragment translocations between wheat and rye chromosomes. Rapid production of hexaploid triticales using this method involves two factors: (1) hybridization between hexaploid wheat with a meiotic restitution gene(s) and rye and (2) selection for good fertility during F-3 and subsequent generations.