Development of a wheat genotype combining the recessive crossability alleles kr1kr1kr2kr2 and the 1BL.1RS translocation, for the rapid enrichment of 1RS with new allelic variation

The main objective of the present work was to develop a wheat genotype containing both the recessive crossability alleles (kr1kr1kr2kr2), allowing high crossability between 6x wheat and diploid rye, and the 1BL.1RS wheat/rye translocation chromosome. This wheat genotype could be used as a recipient partner in wheat–rye crosses for the efficient introduction of new allelic variation into 1RS in translocation wheats. After crossing the wheat cultivars ‘Mv Magdaléna’ and ‘Mv Béres’, which carry the 1BL.1RS translocation involving the 1RS chromosome arm from ‘Petkus’, with the line ‘Mv9 kr1’, 117 F₂ plants were analysed for crossability, ten of which had higher than 50% seed set with rye and thus presumably carried the kr1kr1kr2kr2 alleles. Four of the ten plants contained the 1BL.1RS translocation in the disomic condition as detected by genomic in situ hybridization (GISH). The wheat × rye F₁ hybrids produced between these lines and the rye cultivar ‘Kriszta’ were analysed in meiosis using GISH. 1BL.1RS/1R chromosome pairing was detected in 62.4% of the pollen mother cells. The use of fluorescent in situ hybridization (FISH) with the repetitive DNA probes pSc119.2, Afa family and pTa71 allowed the 1R and 1BL.1RS chromosomes to be identified. The presence of the 1RS arm from ‘Kriszta’ besides that of ‘Petkus’ was demonstrated in the F₁ hybrids using the rye SSR markers RMS13 and SCM9. In four of the 22 BC₁ progenies analysed, only ‘Kriszta’-specific bands were observed with these markers, though the presence of the 1BL.1RS translocation was detected using GISH. It can be concluded that recombination occurred between the ‘Petkus’ and ‘Kriszta’ 1RS chromosome arms in the translocated chromosome in these plants.     

Identification of novel QTLs for seedling and adult plant leaf rust resistance in a wheat doubled haploid population

Pyramiding of genes that confer partial resistance is a method for developing wheat (Triticum aestivum L.) cultivars with durable resistance to leaf rust caused by Puccinia triticina. In this research, a doubled haploid population derived from the cross between the synthetic hexaploid wheat (SHW) (×Aegilotriticum spp.) line TA4152-60 and the North Dakota breeding line ND495 was used for identifying genes conferring partial resistance to leaf rust in both the adult plant and seedling stages. Five QTLs located on chromosome arms 3AL, 3BL, 4DL, 5BL and 6BL were associated with adult plant resistance with the latter four representing novel leaf rust resistance QTLs. Resistance effects of the 4DL QTL were contributed by ND495 and the effects of the other QTLs were contributed by the SHW line. The QTL on chromosome arm 3AL had large effects and also conferred seedling resistance to leaf rust races MJBJ, TDBG and MFPS. The other major QTL, which was on chromosome arm 3BL, conferred seedling resistance to race MFPS and was involved in a significant interaction with a locus on chromosome arm 5DS. The QTLs and the associated molecular markers identified in this research can be used to develop wheat cultivars with potentially durable leaf rust resistance.     

Development of consistently crossable wheat genotypes for alien wheat gene transfer through fine-mapping of the <Emphasis Type="Italic">Kr1</Emphasis> locus

Breeders can force sexual hybridisation between wheat and related grass species to produce interspecific hybrids containing a dihaploid set of wheat and related chromosomes. This facilitates the introgression of desirable genes into wheat from the secondary gene pool. However, most elite European wheat varieties carry genes that suppress crossability, making the transfer of novel traits from exotic germplasm into elite wheat varieties difficult or impossible. Previous studies have identified at least five crossability loci in wheat. Here, the crossability locus with the largest effect, Kr1 on chromosome arm 5BL, was fine-mapped by developing a series of recombinant substitution lines in which the genome of the normally non-crossable wheat variety ‘Hobbit sib’ carries a recombinant 5BL chromosome arm containing segments from the crossable variety ‘Chinese Spring’. These recombinant lines were scored for their ability to cross with rye over four seasons. Analysis revealed at least two regions on 5BL affecting crossability, including the Kr1 locus. However, the ability to set seed is highly dependent on prevailing environmental conditions. Typically, even crossable wheat lines exhibit little or no seed set when crossed with rye in winter, but show up to 90% seed set from similar crosses made in summer. By recombining different combinations of the two regions affecting crossability, wheat lines that consistently exhibit up to 50% seed set, whether crossed in the UK winter or summer conditions, were generated, thus creating a very important tool for increasing the efficiency of alien wheat transfer programmes.     

Production of a new wheat line possessing the 1BL.1RS wheat-rye translocation derived from Korean rye cultivar Paldanghomil

The 1BL.1RS translocations between wheat (Triticum aestivum L.) and rye (Secale cereale L.) are widely used in bread wheat breeding programs, but all modern wheat cultivars with the 1BL.1RS have shown genetic vulnerability due to one rye source – a German cultivar, Petkus. We have developed, a new 1BL.1RS wheat-rye translocation line from the backcross of the F₁ hybrid of wheat cv. Olmil and rye cv. Paldanghomil, both cultivars from Korea. The GISH technique was applied to identify the presence of rye chromatin in 467 BC₁F₆ lines selected from 77 BC₁F₅ lines. Only one line, Yw62–11, showed wheat-rye translocated chromosomes, with a somatic chromosome number of 2n=42. C-banding patterns revealed that the translocated chromosome was 1BL.1RS, showing prominent bands in the terminal and sub-terminal regions of the short arm as well as in the centromeric region and terminal region of the long arm. This new 1BL.1RS translocation line formed 21 bivalents like common wheat at meiotic metaphase I, thereby showing complete homology. Received: 28 February 2001 / Accepted: 17 April 2001     

Description and mapping of the resistance of DBA/2 mice to TNF-induced lethal shock

In our search for genes that inhibit the inflammatory effects of TNF without diminishing its antitumor capacities we found that, compared with C57BL/6 mice, DBA/2 mice exhibit a dominant resistance to TNF-induced lethality. Tumor-bearing (C57BL/6 x DBA/2)(BXD)F(1) mice completely survived an otherwise lethal TNF/IFN-gamma-antitumor therapy with complete regression of the tumor. This was not the case for C57BL/6 mice. Genetic linkage analysis revealed that TNF resistance is linked to a major locus on distal chromosome 6 and a minor locus on chromosome 17. Compared with littermate controls, chromosome substitution mice carrying a DBA/2 chromosome 6 in a C57BL/6 background were significantly protected against TNF and TNF/IFN-gamma, albeit less so than DBA/2 mice. Definition of a critical region of 13 Mb on chromosome 6 was the highest mapping resolution obtained. Further analysis of candidate genes may provide a powerful tool to control TNF-induced pathologies in humans.     

Hypothesis: Transgene establishment in wild relatives of wheat can be prevented by utilizing the Ph1 gene as a senso stricto chaperon to prevent homoeologous recombination

Durum and bread wheat need transgenic traits such as herbicide and disease resistance due to recent evolution of herbicide resistant grass weeds and an intractable new strain of stem rust. Transgenic wheat varieties have not been commercialized partly due to potential transgene movement to wild/weedy relatives, which occurs naturally to closely related Aegilops and other spp. Recombination does not occur in the F₁ hybrid between wheat and its relatives due to the presence of the Ph1 gene on wheat chromosome arm 5BL, which acts as a chaperone, preventing promiscuous homoeologous pairing to similar, but not homologous chromosomes of the wild/weedy species. Thus recombination must occur during backcrossing after the wheat Ph1 gene has been eliminated. Based on these findings, we speculate that Ph1 could be used to prevent gene introgression into weedy relatives. We propose two methods to prevent such transgene establishment: (1) link the transgene in proximity to the wheat Ph1 gene and (2) insert the transgene in tandem with the lethal barnase on any chromosome arm other than 5BL, and insert barstar, which suppresses barnase on chromosome arm 5BL in proximity to Ph1. The presence of Ph1 in backcross plants containing 5BL will prevent the homoeologous establishment of barnase coupled to the desired transgene in the wild population. 5BL itself will be eliminated during repeated backcrossing to the wild parent, and progeny bearing the desired transgene in tandem with barnase but without the Ph1-barstar complex will die.     

Rye Pm8 and wheat Pm3 are orthologous genes and show evolutionary conservation of resistance function against powdery mildew

The improvement of wheat through breeding has relied strongly on the use of genetic material from related wild and domesticated grass species. The 1RS chromosome arm from rye was introgressed into wheat and crossed into many wheat lines, as it improves yield and fungal disease resistance. Pm8 is a powdery mildew resistance gene on 1RS which, after widespread agricultural cultivation, is now widely overcome by adapted mildew races. Here we show by homology‐based cloning and subsequent physical and genetic mapping that Pm8 is the rye orthologue of the Pm3 allelic series of mildew resistance genes in wheat. The cloned gene was functionally validated as Pm8 by transient, single‐cell expression analysis and stable transformation. Sequence analysis revealed a complex mosaic of ancient haplotypes among Pm3‐ and Pm8‐like genes from different members of the Triticeae. These results show that the two genes have evolved independently after the divergence of the species 7.5 million years ago and kept their function in mildew resistance. During this long time span the co‐evolving pathogens have not overcome these genes, which is in strong contrast to the breakdown of Pm8 resistance since its introduction into commercial wheat 70 years ago. Sequence comparison revealed that evolutionary pressure acted on the same subdomains and sequence features of the two orthologous genes. This suggests that they recognize directly or indirectly the same pathogen effectors that have been conserved in the powdery mildews of wheat and rye.     

Visualization of Secale cereale DNA in wheat germ plasm by fluorescent in situ hybridization

Homozygous wheat/rye (1BL/1RS or 1AS/ 1RL) translocation lines have significantly contributed to wheat production, and several other wheat/rye translocation lines show a potential promise against biotic and abiotic stresses. Detecting the presence of rye at the chromosome level is feasible by C-banding and isozyme protocols, but the diagnostic strength of genomic in situ hybridization for eventually analyzing smaller DNA introgressions has greater significance. As a first step we have applied the genomic in situ hybridization technique to detect rye chromosomes in a wheat background using germ plasm of agricultural significance. By this method rye contributions to the translocations 1BL/1RS, 1AL/1RS, 5AS/5RL and 6BS/6RL could be identified. Differential labelling has further enabled the detection of rye and Thinopyrum bessarabicum chromosomes in a trigeneric hybrid of Triticum aestivum/Th. bessarabicum//Secale cereale.     

Genetic mapping of Dn7, a rye gene conferring resistance to the Russian wheat aphid in wheat

The Russian wheat aphid is a significant pest problem in wheat and barley in North America. Genetic resistance in wheat is the most effective and economical means to control the damage caused by the aphid. Dn7 is a rye gene located on chromosome 1RS that confers resistance to the Russian wheat aphid. The gene was previously transferred from rye into a wheat background via a 1RS/1BL translocation. This study was conducted to genetically map Dn7 and to characterize the type of resistance the gene confers. The resistant line '94M370' was crossed with a susceptible wheat cultivar that also contains a pair of 1RS/1BL translocation chromosomes. The F₂ progeny from this cross segregated for resistance in a ratio of 3 resistant: 1 susceptible, indicating a single dominant gene. One-hundred and eleven RFLP markers previously mapped on wheat chromosomes 1A, 1B and 1D, barley chromosome 1H and rye chromosome 1R, were used to screen the parents for polymorphism. A genetic map containing six markers linked to Dn7, encompassing 28.2 cM, was constructed. The markers flanking Dn7 were Xbcd1434 and XksuD14, which mapped 1.4 cM and 7.4 cM from Dn7, respectively. Dn7 confers antixenosis, and provides a higher level of resistance than that provided by Dn4. The applications of Dn7 and the linked markers in wheat breeding are discussed.Communicated by J. Dvorak     

Genetic analysis of anther culture response in wheat using aneuploid,chromosome substitution and translocation lines

Summary Marked effects of genotype on wheat anther culture response have been observed. Genetic factors have been recognised to be one of the major contributors to in vitro responses of cultured wheat tissues. In wheat anther culture, embryo induction, plant regeneration and albina/green ratio have been determined to be heritable traits. Using Chinese Spring (CS) monosomic 1D, single chromosome substitution lines of chromosome 5B or chromosome arm 5BL from Chinese Spring into six varieties, and F₁ hybrids heterozygous for the 1B chromosome structure (1BL-1BS/1BL-1RS), the anther culture response was studied: genes on CS1D chromosome and 5BL chromosome arm increases the embryo frequency; gene(s) involved in regeneration ability are located on the 1RS chromosome arm; a gene increasing albina frequency is located on Chinese Spring 5B chromosome. Our results support the fact that without gametic selection, a differential development occurred from the particular classes of microspores carrying genes for higher regeneration ability. Moreover, in some crosses, a few genes with major effects were involved in determination of anther culture response.     

A Mutant with Expression Deletion of Gene Sec-1 in a 1RS.1BL Line and Its Effect on Production Quality of Wheat

The chromosome arm 1RS of rye (Secale cereal L.) has been used worldwide as a source of genes for agronomic and resistant improvement. However, the 1RS arm in wheat has end-use quality defects that are partially attributable to the presence of ω-secalins, which are encoded by genes at the Sec-1 locus. Various attempts in removing the Sec-1 genes from the 1RS.1BL translocation chromosome have been made. In the present study, two new primary 1RS.1BL translocation lines, T917-26 and T917-15, were developed from a cross between wheat variety “{"type":"entrez-nucleotide","attrs":{"text":"A42912","term_id":"2298361"}}A42912” and Chinese local rye “Weining.” The lines T917-15 and T917-26 carried a pair of intact and homogeneous 1RS.1BL chromosomes. The line T917-26 also harbored an expression deletion of some genes at the Sec-1 locus, which originated from a mutation that occurred simultaneously with wheat-rye chromosome translocations. These results suggest that the accompanying mutations of the evolutionarily significant translocations are remarkable resources for plant improvement. Comparison of translocation lines with its wheat parent showed improvements in the end-use quality parameters, which included protein content (PC), water absorption (WA), sodium dodecyl sulfate sedimentation (SDSS), wet gluten (WG), dry gluten (DG) and dough stickiness (DS), whereas significant reduction in gluten index (GI) and stability time (ST) were observed. These findings indicate that 1RS in wheat has produced a higher amount of protein, although these comprised worse compositions. However, in the T917-26 line that harbored an expression deletion mutation in the Sec-1 genes, the quality parameters were markedly improved relative to its sister line, T917-15, especially for GI and DS (P < 0.05). These results indicated that expression deletion of Sec-1 genes significantly improves the end-use quality of wheat cultivars harboring the 1RS.1BL translocation. Strategies to remove the Sec-1 genes from the 1RS.1BL translocation in wheat improvement are discussed.     

The influence of 5-azacytidine on the condensation of the short arm of rye chromosome 1R in Triticum aestivum L. root tip meristematic nuclei

This paper describes the effects of 5-azacytidine on the condensation state of rye (Secale cereale L.) chromatin introduced into the wheat genome (Triticum aestivum L. cv. Beaver). The wheat cultivar Beaver carries a translocation between the short arm of rye chromosome 1R (1RS) and the long arm of wheat chromosome 1B (1BL/1RS). 1RS can be detected using genomic in situ hybridisation and carries a ribosomal DNA (rDNA) locus that can be simultaneously detected using multiple labelling strategies. The rDNA locus divides 1RS into a distal region that is gene rich and a proximal region that is gene poor and highly methylated. 1RS also carries a large block of subtelomeric heterochromatin. The drug, which acts to inhibit DNA methylation in plants, has three pronounced effects on interphase nuclei. (1) It induces aberrant condensation of the rye subtelomeric heterochromatin and in many cases induces sister chromatid separation in the subtelomeric heterochromatin of G2 nuclei. (2) Nuclei trisomic for 1RS are observed at low frequency in treated material and are probably a consequence of aberrant sister chromatid separation or condensation. (3) The drug alters normal condensation of 1RS euchromatin. However, contrary to expectation the effect is not simply to induce decondensation. The proximal region of the arm actually condenses at low levels of drug administration while the distal region remains unaltered or increases its decondensation state. Increasing the concentration of 5-azacytidine induces a biphasic response and at the highest concentration used all regions of the arm show signs of decondensation. Thus the influence of the drug on chromatin condensation depends on the genomic structure. Received: 14 July 1997; in revised form: 26 August 1997 / Accepted: 27 August 1997     

Genetic analysis of resistance to yellow rust in hexaploid wheat using a mixture model for multiple crosses

DNA-based molecular markers have been used in numerous studies for tagging specific genes in wheat for subsequent use in marker-assisted selection. Usually in plant breeding, procedures for mapping genes are based on analysis of a single segregating population. However, breeding programmes routinely evaluate large numbers of progeny derived from multiple-related crosses with some parental lines shared. In most such related crosses, the number of progeny is quite small. Thus, statistical techniques for detecting quantitative trait loci (QTLs) using data from conventional multi-cross breeding programmes are interesting. The objective of this study is to present a mixture model for QTL mapping in crosses of multiple inbred varieties with non-normal phenotype distributions and to use this model to map QTLs for yellow rust resistance in elite wheat breeding material. Three doubled haploid populations consisting of 41, 42 and 55 lines, respectively, originating from four parental varieties were studied. Multi-cross QTL analysis with three specific pathogen isolates of Puccinia striiformis f. sp. tritici and a mixture of the isolates revealed QTLs for resistance at four different genomic locations. These QTLs were found on chromosome 2AL, 2AS, 2BL and 6BL and explained between 21 and 41% of the phenotypic variation. Two of these QTLs, one on the long arm of chromosome 2A and one on the short arm of chromosome 2A were identical to the known yellow rust resistance genes Yr32 and Yr17, respectively, whereas the QTLs located on the long arms of chromosomes 2B and 6B may reflect types of resistance to yellow rust, which have not previously been mapped.     

1BL/1RS translocation in durum wheat and its effect on end use quality traits

The gluten proteins document the genotypic identity of a wheat variety, in addition to providing valuable clues about its ancestry and technological properties. In this study, an Indian durum wheat genotype B662 was identified to carry 1BL/1RS translocation and characterized further for its effect on end use quality traits. Comparison of the end use quality traits of B662 with five other durum cultivars without 1BL/1RS, showed decreased gluten content, lower swelling index of glutenins and low MSDS-SV indicating that, B662 with 1BL/1RS is not good for pasta making. In F_2:3 seeds from a durum wheat cross between the 1BL/1RS cultivar B662 and HI8498 without the translocation, the secalin Sec-1 loci segregated in theoretically expected 3:1 proportion and were inherited as a block of the rye chromosome arm. The analysis of F_2:3 harvests for the two most important durum wheat quality tests showed that the presence of 1BL/1RS translocation did not alter the grain protein content values, but was associated with significant reduction of micro SDS-sedimentation volume indicating inferior quality, thus limiting the commercial exploitation of durum wheat genotypes with 1BL/1RS translocation. The cautious use of rye translocation in Indian durum wheat breeding is suggested.     

The powdery mildew resistance gene Pm8 derived from rye is suppressed by its wheat ortholog Pm3

The powdery mildew resistance gene Pm8 derived from rye is located on a 1BL.1RS chromosome translocation in wheat. However, some wheat lines with this translocation do not show resistance to isolates of the wheat powdery mildew pathogen avirulent to Pm8 due to an unknown genetically dominant suppression mechanism. Here we show that lines with suppressed Pm8 activity contain an intact and expressed Pm8 gene. Therefore, the absence of Pm8 function in certain 1BL.1RS‐containing wheat lines is not the result of gene loss or mutation but is based on suppression. The wheat gene Pm3, an ortholog of rye Pm8, suppressed Pm8‐mediated powdery mildew resistance in lines containing Pm8 in a transient single‐cell expression assay. This result was further confirmed in transgenic lines with combined Pm8 and Pm3 transgenes. Expression analysis revealed that suppression is not the result of gene silencing, either in wheat 1BL.1RS translocation lines carrying Pm8 or in transgenic genotypes with both Pm8 and Pm3 alleles. In addition, a similar abundance of the PM8 and PM3 proteins in single or double homozygous transgenic lines suggested that a post‐translational mechanism is involved in suppression of Pm8. Co‐expression of Pm8 and Pm3 genes in Nicotiana benthamiana leaves followed by co‐immunoprecipitation analysis showed that the two proteins interact. Therefore, the formation of a heteromeric protein complex might result in inefficient or absent signal transmission for the defense reaction. These data provide a molecular explanation for the suppression of resistance genes in certain genetic backgrounds and suggest ways to circumvent it in future plant breeding.     

小麦主栽品种中的1RS分布和兰考90(6)系列白粉病新抗源

利用黑麦染色体臂1RS的特异性PCR标记,对黄淮麦区138个小麦主栽品种、系进行了PCR扩增,结果表明：有42．0%的小麦品种、系携带1RS染色体臂。以六倍体小黑麦Mzalenod Beer为黑麦染色体供体,培育的兰考90(6)系列小麦品系是新的小麦-黑麦1BL／1RS易位系。这些品系对小麦白粉病具有很高的抗性,是小麦抗白粉病育种的新抗源。对兰考90(6)系列品系白粉病抗性进行了研究,结果表明,兰考90(6)系列品系的抗谱与许多已经知道的小麦抗白粉病基因的抗谱不同,并具有数量抗性特点。     

小麦遗传背景对黑麦抗叶锈基因Lr26的抗性表达的影响

利用1套从小麦纯系和黑麦自交系培育出的1R附加系、代换系和易位系,研究了1RS上的抗叶锈基因Lr26在小麦中的表达。结果发现,1R二体附加系和纯合1RS/1BL易位系高抗小麦叶锈病;而其小麦亲本、1R(1B)代换系和1BS/1RL易位系重感叶锈病。这一结果指出了黑麦染色体臂1RS上的抗小麦叶锈病基因Lr26在小麦中的表达受小麦染色体臂1BL上的基因的强烈影响,指出了外源基因在小麦中的表达可受染色体臂或基因水平上的相互作用的制约。文中讨论了外源基因与小麦遗传背景相互作用在小麦育种中的意义。     

黑麦碱基因（Sec–1）表达缺失的1RS／1BL易位系的鉴定

用改良的Giemsa C－带技术、DNA原位杂交和酸性聚丙烯酰胺凝胶电泳（A-PAGE）对来源于小麦品种绵阳11与不同黑麦自交系远缘杂交获得的高代株系（BC1F7）的染色体结构和醇溶蛋白进行了研究。结果发现,在鉴定的200个株系中,有45个株系经C-带和A-PAGE检测均一致地发现它们含有一对1RS /1BL易位染色体,而一个株系843-1-1,C-带鉴定、原位杂交结果均证明它含有一对1RS/1BL易位染色体,但A-PAGE醇溶蛋白图谱却不具有黑麦1RS染色体臂的黑麦碱特征带,而表达出既不同于黑麦碱又不同于亲本绵阳11的醇溶蛋白带型。这一结果表明,利用不同的黑麦亲本资源,可以获得黑麦碱基因Sec-1表达缺失的新的1RS/1BL易位系。这种新的1RS/1BL易位系缺失了影响小麦品质的黑麦碱蛋白,因此是进一步研究1RS/1BL 易位对小麦品质影响的珍贵材料。研究指出,在利用外源基因的植物育种中,外源种供体材料的遗传多样性是值得重视的基因资源。     

Genetic analysis of leaf rust resistance genes and associated markers in the durable resistant wheat cultivar Sinvalocho MA

In the cross of the durable leaf rust resistant wheat Sinvalocho MA and the susceptible line Gama6, four specific genes were identified: the seedling resistance gene Lr3, the adult plant resistance (APR) genes LrSV1 and LrSV2 coming from Sinvalocho MA, and the seedling resistance gene LrG6 coming from Gama6. Lr3 was previously mapped on 6BL in the same cross. LrSV1 was mapped on chromosome 2DS where resistance genes Lr22a and Lr22b have been reported. Results from rust reaction have shown that LrSV1 from Sinvalocho is not the same allele as Lr22b and an allelism test with Lr22a showed that they could be alleles or closely linked genes. LrSV1 was mapped in an 8.5-cM interval delimited by markers gwm296 distal and gwm261 proximal. Adult gene LrSV2 was mapped on chromosome 3BS, cosegregating with gwm533 in a 7.2-cM interval encompassed by markers gwm389 and gwm493, where other disease resistance genes are located, such as seedling gene Lr27 for leaf rust, Sr2 for stem rust, QTL Qfhs.ndsu-3BS for resistance to Fusarium gramineum and wheat powdery mildew resistance. The gene LrG6 was mapped on chromosome 2BL, with the closest marker gwm382 at 0.6 cM. Lines carrying LrSV1, LrSV2 and LrG6 tested under field natural infection conditions, showed low disease infection type and severity, suggesting that this kind of resistance can be explained by additive effects of APR and seedling resistance genes. The identification of new sources of resistance from South American land races and old varieties, supported by modern DNA technology, contributes to sustainability of agriculture through plant breeding.     

Centromere structure and function analysis in wheat–rye translocation lines

1RS.1BL translocations are centric translocations formed by misdivision and have been used extensively in wheat breeding. However, the role that the centromere plays in the formation of 1RS.1BL translocations is still unclear. Fluorescence in situ hybridization (FISH) was applied to detect the fine structures of the centromeres in 130 1RS.1BL translocation cultivars. Immuno‐FISH, chromatin immunoprecipitation (ChIP)‐qPCR and RT‐PCR were used to investigate the functions of the hybrid centromeres in 1RS.1BL translocations. New 1R translocations with different centromere structures were created by misdivision and pollen irradiation to elucidate the role that the centromere plays in the formation of 1RS.1BL translocations. We found that all of the 1RS.1BL translocations detected contained hybrid centromeres and that wheat‐derived CENH3 bound to both the wheat and rye centromeres in the 1RS.1BL translocation chromosomes. Moreover, a rye centromere‐specific retrotransposon was actively transcribed in 1RS.1BL translocations. The frequencies of new 1RS hybrid centromere translocations and group‐1 chromosome translocations were higher during 1R misdivision. Our study demonstrates the hybrid nature of the centromere in 1RS.1BL translocations. New 1R translocations with different centromere structures were created to help understand the fusion centromere used for wheat breeding and for use as breeding material for the improvement of wheat.