Development and application of a new codominant PCR marker for detecting 1BL·1RS wheat–rye chromosome translocations

The 1BL·1RS translocation has been widely used in wheat breeding programmes throughout the world. Unfortunately, this translocation has frequently resulted in unsatisfactory grain processing quality. Two primer combinations derived from the published sequence of a ω‐secalin gene on 1RS gave polymerase chain reaction (PCR) fragments 0.4 and 1.1 kb in size. Both fragments can be used to quickly detect 1BL·1RS translocations. By combining the PCR assay resulting in the 1.1‐kb fragment from 1RS and a PCR assay resulting in a 0.6‐kb fragment from the Glu‐B3 gene on 1BS, plants homozygous for the 1BL 1RS could clearly be distinguished from the heterozygous ones. This codominant marker was successfully applied to genotype a segregating F₂ population and a local cultivar collection.     

Molecular marker-facilitated pyramiding of different genes for powdery mildew resistance in wheat

Breeding durable resistance to pathogens and pests is a major task for modern plant breeders and pyramiding different resistance genes into a genotype is one way of achieving this. Three powdery mildew resistance gene combinations, Pm2+Pm4a, Pm2+Pm21, Pm4a+Pm21 were successfully integrated into an elite wheat cultivar ‘Yang047′. Double homozygotes were selected from a small F₂ population with the help of molecular markers. As the parents were near‐isogenic lines (NILs) of ‘Yang158′, the progenies showed good uniformity in morphological and other non‐resistance agronomic traits. The present work illustrates the bright prospects for the utilization of molecular markers in breeding for host resistance.     

An STS marker distinguishing the rye-derived powdery mildew resistance alleles at the Pm8/Pm17 locus of common wheat

A sequence‐tagged site marker has been developed from restriction fragment length polymorphism marker probe IAG95 for the rye‐derived powdery mildew resistance Pm8/Pm17 locus of common wheat. This polymerase chain reaction marker enables the amplification of DNA fragments with different sizes from T1AL.1RS and T1BL.1RS wheat‐rye translocation cultivars with chromatin from ‘Insave’ and ‘Petkus’ rye, respectively, and therefore will be very useful in distinguishing Pm8‐carrying cultivars from Pm17‐carrying cultivars. Results obtained with that marker were compared with resistance tests performed on detached primary leaves of 29 wheat lines from two populations derived from doubled haploid production. The molecular assay corresponded well with the resistance tests in all the lines, and therefore will be helpful for the identification of Pm17 in lines in which other Pm genes or quantitative trait loci are present.     

Evidence of allelism between genes Pm8 and Pm17 and chromosomal location of powdery mildew and leaf rust resistance genes in the common wheat cultivar'Amigo'

TIBL-1RS wheat-rye translocation cultivars utilized in wheat programmes worldwide carry powdery mildew resistance gene Pm8. Cultivar‘Amigo’possesses resistance gene Pm17 on its TIAL-1RS translocated chromosome. To be able to use Pm17efficiently in breeding programmes, this gene was transferred to a TIBL-1RS translocation in line Helami-105, and allelism between Pm8 and Pm17was studied. The progenies of the hybrids in the F₂ generation and F₃ families provided evidence that the two genes are allelic. Genetic studies using monosomic analyses confirmed that in cultivar‘Amigo', Pm17 and leaf rust resistance gene Lr24 are located on a translocated chromosome involving 1 A and 1B, respectively.     

Novel complementary genes for adult plant leaf rust resistance in a wheat stock carrying the 1BL-1RS translocation

The wheat-rye translocation (IBL-IRS) that carries the tightly linked genes Lr26/Sr31/Yr9, has been widely exploited in the development of wheat cultivars worldwide. This resistance, however, has become ineffective owing to the evolution of new pathotypes of Puccinia recondita that neutralize the resistance of Lr26. Inheritance studies on ‘Federation4′/‘Kavkaz’ revealed complementary genes derived separately from ‘Federation’ and ‘Kavkaz’ for adult plant resistance. This previously undescribed source of resistance appears to be widely effective and could therefore be used to broaden the genetic base for resistance in India. Its effectiveness in other geographical areas is unknown.     

Genetic mapping of sequence-specific PCR-based markers on the short arm of the 1BL.1RS wheat-rye translocation

Wheat cultivars carrying the 1BL.1RStranslocation were crossed with newly synthesised octoploid triticale lines involving four rye genotypes having ο-secalin banding patterns different from each other and from that of the 1BL.1RS translocation. Homologous recombination was expected between the short arm of the 1R chromosomes of the rye genotypes and the 1RS arm of the 1BL.1RSwheat/rye translocation. Seven sequence-specific PCR-based markers:Xiag95, RMS13, Bmac0213, GPI, Xpsr960, 5Sand SCM9, and ο-secalinproteins were used to detect recombination events in the BC₁F₂ generation. Segregation analysis demonstrated that a barley SSR marker (Bmac0213) locus was present on the 1RS chromosome arm. Of 834plants tested in four different BC₁F₂ populations, 246individuals were found to carry recombined1BL.1RS translocation chromosomes. Genetic linkage analysis was performed on the eight markers in the four different mapping populations. The physical positions of the markers are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of resistance gene analogue markers closely linked to wheat powdery mildew resistance gene Pm31

Specific oligonucleotide primers, designed for the sequences of known plant disease resistance genes, were used to amplify resistance gene analogues (RGAs) from wheat genomic DNA. This method was applied in a bulked segregant analysis to screen for the RGA markers linked to the powdery mildew resistance gene Pm31, introgressed into common wheat from wild emmer. Two RGA markers (RGA200 and RGA390) were found to be closely linked to Pm31 and completely co‐segregating with the marker allele of Xpsp3029 linked to Pm31, with a genetic distance of 0.6 cM. These two RGA markers were then integrated into the formerly established microsatellite map of Pm31 region. The result showed the effectiveness of the RGA approach for developing molecular markers linked to disease resistance genes and demonstrated the efficiency of denaturing polyacrylamide‐gel electrophoresis for detecting polymerase chain reaction polymorphism.     

Mapping of the Vrn-B1 gene in Triticum aestivum using microsatellite markers

An F₂ population segregating for the dominant gene Vrn‐B1 was developed from the cross of the substitution line ‘Diamant/'Miro‐novskaya 808 5A’ and the winter wheat cultivar ‘Bezostaya 1′. Microsatellite markers (Xgwm and Xbarc) with known map locations on chromosome 5B of common wheat were used for mapping the gene Vrn‐B1. Polymorphism between parental varieties was observed for 28 out of 34 microsatellite markers (82%). Applying the quantitative trait loci mapping approach, the target gene was mapped on the long arm of chromosome 5B, closely linked to Xgwm408. The map position of Vrn‐B1 suggests that the gene is homoeologous to other vernalization response genes located on the homoeologous group 5 chromosomes of wheat, rye and barley.     

Chromosomal location of genes for resistance to powdery mildew in common wheat (Triticum aestivum L. em Thell.). 9. Gene MlZec1 from the Triticum dicoccoides-derived wheat line Zecoi-1

The Triticum dicoccoides-derived wheat line Zecoi-1 provides effective protection against powdery mildew. F₃ segregation analysis of Chinese Spring × Zecoi-1 hybrids showed that resistance in line Zecoi-1 is controlled by a single dominant gene. Amplified fragment length polymorphism (AFLP) analysis of bulked segregants from F₃s showing the homozygous resistant and susceptible phenotypes identified eight markers, of which four were associated with the resistance allele in repulsion phase. Following the assignment of these four repulsion phase AFLP markers to wheat chromosome 2B with the aid of Chinese Spring nulli-tetrasomic lines, they were physically mapped in the terminal breakpoint interval 0.89 (2BL-6)–1.00 (telomere) of chromosome 2BL. Genetic and physical mapping of simple sequence repeat markers from the distal half of chromosome 2BL located the wild emmer-derived powdery mildew resistance gene distal of breakpoint 0.89 in deletion line 2BL-6. Based on disease response patterns, genomic origin and chromosomal location the resistance gene in Zecoi-1 is temporarily designated MlZec1.     

Molecular markers linked to the Aegilops variabilis-derived root-knot nematode resistance gene Rkn-mn1 in wheat

Aegilops variabilis no. 1 is the only known source of resistance to the root‐knot nematode Meloidogyne naasi in wheat. Previous studies showed that a dominant gene, Rkn‐mn1, was transferred to a wheat translocation line from the donor Ae. variabilis. Random amplified polymorphic DNA (RAPD) analysis was performed on the wheat cultivar ‘Lutin’, on Ae. variabilis, on a resistant disomic addition line and on a resistant translocation line. For genetic and molecular studies, 114‐117 BC₃F₂ plants and F₃‐derived families were tested. Five DNA and one isozyme marker were linked to Rkn‐mn1. Three RAPD markers flanking the Rkn‐mn1 locus were mapped at 0 cM (OpY16_‐1065), 0.8 cM (OpB12_‐1320) and 1.7 cM (OpN20_‐1235), respectively. Since the Rkn‐mn1 gene remained effective, its introduction into different wheat cultivars by marker‐assisted selection is suggested.     

Characterization of three wheat cultivars possessing new 1BL.1RS wheat-rye translocations

The wheat-rye 1BL.1RS translocation chromosomes have been used widely around the world in commercial wheat ( Triticum aestivum L.) production because of the presence of several disease resistance genes and a yield enhancement factor on the rye ( Secale cereale L.) chromosome. However, the recent reports of the loss of complete effectiveness of the disease resistance genes on the most commonly used 1BL.1RS chromosome have highlighted the need to seek and deploy additional sources of disease resistance genes. Three new sibling wheat cultivars, 'CN12', 'CN17' and 'CN18', were developed carrying 1RS arms derived from the rye inbred line L155. Genomic in situ hybridization and C-banding analysis revealed that all the three cultivars contained the rye chromosome 1RS arm fused to the wheat 1BL wheat chromosome arm. The three cultivars displayed high yields and high resistance to local powdery mildew and stripe rust pathotypes. Fluorescence in situ hybridization analysis indicated the different structure of 1BL.1RS chromosome between 'CN18' and the other two cultivars. The present study provides a new 1RS resource for wheat improvement.     

Detection of molecular markers linked to the durable adult plant stripe rust resistance gene Yr18 in bread wheat (Triticum aestivum L.)

Stripe rust of wheat caused by Puccinia striiformis West. f. sp. tritici presents a serious problem for wheat production worldwide, and identification and deployment of resistance sources to it are key objectives for many wheat breeders. Here we report the detection of simple sequence repeat (SSR) markers linked to the durable adult plant resistance of cv. ‘Otane’, which has conferred this resistance since its release in New Zealand in 1984. A double haploid population from a cross between ‘Otane’ and the susceptible cv. Tiritea’ was visually assessed for adult plant infection types (IT) in the glasshouse and field, and for final disease severity in the field against stripe rust pathotype 106E139A⁺. At least three resistance loci controlled adult plant resistance to stripe rust in this population. Quantitative trait loci (QTL) mapping results revealed that two of these, one on chromosome 7DS corresponds to the durable adult plant resistance gene Yr18 and other on chromosome 5DL were contributed from ‘Otane’; while the remaining one on chromosome 7BL, was contributed from the susceptible ‘Tiritea’. Interval mapping placed the ‘Otane’‐resistant segment near the centromere of chromosome 7DS at a distance of 7 cM from the SSR marker gwm44. The stability of QTL in the two environments is discussed. SSR gwm44 is potentially a candidate marker for identifying the durable resistance gene Yr18 in breeding programmes.     

Genetic, agronomic and quality comparisons of two 1AL.1RS. wheat-rye chromosomal translocations

The 1AL.1RS wheat-rye chromosomal translocation originally found in ‘Amigo’ wheat possesses resistance genes for stem rust, powdery mildew and greenbug biotypes B and C, but also has a negative effect on wheat processing quality. Recently, a second 1AL.1RS translocation carrying Gb6, a gene conferring resistance to greenbug biotypes B, C, E, G and I, was identified in the wheat germplasm line ‘GRS1201′. Protein analytical methods, and the DNA polymerase chain reaction were used to identify markers capable of differentiating the 1RS chromosome arms derived from ‘Amigo’ and ‘GRS1201′. The secalin proteins encoded by genes on 1RS chromosome arms differed in ‘Amigo’ and ‘GRS1201′. A 70 kDa secalin was found in the ‘Amigo’1AL.1RS, but did not occur in the ‘GRS1201’1AL.1RS. Polymorphisms detected by PCR primers derived from a family of moderately repetitive rye DNA sequences also differentiated the two translocations. When ‘GRS1201’was mated with a non-1RS wheat, no recombinants between 1RS markers were observed. In crosses between 1RS and non-1RS parents, both DNA markers and secalins would be useful as selectable markers for 1RS-derived greenbug resistance. Recombination between 1RS markers did occur when 1RS from ‘Amigo’ and 1RS from ‘GRS1201’were combined, but in such intermatings, the molecular markers described herein could still be used to develop a population enriched in lines carrying Gb6. No differences in grain yield or grain and flour quality characteristics were observed when lines carrying 1RS from ‘Amigo’ were compared with lines with 1RS from ‘GRS1201′. Hence, differences in secalin composition did not result in differential quality effects. When compared with sister lines with 1AL.1AS derived from the wheat cultivar ‘Redland’, lines with ‘GRS1201’had equal grain yield, but produced flours with significantly shorter mix times, weaker doughs, and lower sodium dodecyl sulphate sedimentation volumes.     

Mapping QTL involved in adult plant resistance to powdery mildew in the winter wheat line RE714 in two susceptible genetic backgrounds

The objective was to study the genetic basis of adult plant resistance to powdery mildew of the winter wheat line RE714 by quantitative trait loci (QTL) analysis and to investigate the stability of the QTL detected in two different genetic backgrounds. Two DH populations from the crosses between RE714 and the susceptible parents ‘Festin’ and ‘Hardi’ were used. Reaction of the DH lines to powdery mildew was assessed in different environments in Belgium under natural disease infection. Considering both populations and according to the environment tested, one to seven QTL were detected. Among them, residual effects of the race‐specific resistance genes Pm4b and MIRE were found. Two major QTL were very stable (on chromosome 5D and at the MIRE locus), since they were detected in both populations and over all environments tested. The QTL detected varied according to the susceptible parent used, and a residual effect at the Pm4b gene was not observed with the genetic background of ‘Hardi’.     

Chromosomal locations in common wheat of three new leaf rust resistance genes from Triticum monococcum

Monosomic analysis was conducted to determine chromosomal locations of three new leaf rust resistance genes recently transferred to common wheat (Triticum aestivum) from T. monococcum. The resistance gene in wheat germplasm line KS92WGRC23 was transferred from T. monococcum ssp. monococcum. The resistance genes found in KS93U3 and KS96WGRC34 were transferred from T. monococcum ssp. aegilopoides. Allelism tests showed that the three resistance genes were unlinked. The three lines were crossed with each of the seven A-genome Wichita monosomic lines. The leaf rust resistance genes in KS92WGRC23, KS93U3, and KS96WGRC34 were located on chromosomes 6A, 1A, and 5A, respectively, by monosomic analysis. These results demonstrate that the three new genes derived from T. monococcum are each different. They also differ from previously reported Lr genes. This information on chromosome location and the development of mapping populations will facilitate molecular tagging of the new genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

PCR-based markers for detection of different sources of 1AL.1RS and 1BL.1RS wheat–rye translocations in wheat background

The rye ( Secale cereale L.) chromosome arm 1RS is one of the most successfully used alien resources in wheat ( Triticum aestivum L.) improvement, and it is still being widely utilized by many breeding programmes. With increasing application of marker-assisted selection in wheat breeding, development of an efficient molecular marker system to monitor and track 1AL.1RS and 1BL.1RS wheat–rye translocations is of practical value. In this study, we systematically evaluated the utility of eight rye-specific molecular markers in detecting 1RS chromatins with different origins in diverse wheat genetic backgrounds. Two such markers, PAWS5/S6 and SCM9 were identified that were able to differentiate multiple sources of wheat–rye translocations involving 1RS. A duplex polymerase chain reaction (PCR) procedure was developed with two rye-specific markers PAWS5/S6 and RIS and tested in a set of representative wheat lines. The two rye-specific markers and the duplex PCR procedure established in this study provided a useful tool in marker-assisted selection of materials containing desirable 1RS chromatin in wheat breeding.     

Mapping quantitative trait loci in wheat for resistance against greenbug and Russian wheat aphid

Breeding for genetic resistance against greenbug and Russian wheat aphid (RWA) is the most effective way of controlling these widespread pests in wheat. Earlier work had shown that chromosome 7D of a synthetic hexaploid wheat, ‘Synthetic’ (T. dicoccoides × Ae. squarrosa) (AABB × DD) gave resistance when transferred into the genetic background of an aphid‐susceptible cultivar, ‘Chinese Spring’, as the recipient. To map the genes involved, a set of 103 doubled haploid recombinant substitution lines was obtained from crossing the 7D substitution line with the recipient, and used to determine the number and chromosomal location of quantitative trait loci (QTL) controlling antixenosis and antibiosis types of resistance. Antixenosis to RWA was significantly associated with marker loci Xpsr687 on 7DS, and Xgwm437 on 7DL. Antibiosis to greenbug was associated with marker loci Xpsr490, Rc3 (on 7DS), Xgwm44, Xgwm111, Xgwm437, Xgwm121 and D67 (on 7DL). Similarly, antibiosis to RWA was linked to loci Xpsr490, Rc3, Xgwm44, Xgwm437 and Xgwm121. At least two QTL in repulsion phase, one close to the centromere either on the 7DS or 7DL arms, and a second distal on 7DL could explain antibiosis to RWA and, partially, this mechanism against greenbug.