Characterization of ω-secalin genes from rye, triticale, and a wheat 1BL/1RS translocation line

Sixty-two DNA sequences for the coding regions of omega-secalin (ω-secalin) genes have been characterized from rye (Secale cereale L.), hexaploid and octoploid triticale (× Triticosecale Wittmack), and wheat (Triticum aestivum L.) 1BL/1RS translocation line. Only 19 out of the 62 ω-secalin gene sequences were full-length open reading frames (ORFs), which can be expressed into functional proteins. The other 43 DNA sequences were pseudogenes, as their ORFs were interrupted by one or a few stop codons or frameshift mutations. The 19 ω-secalin genes have a typical primary structure, which is different from wheat gliadins. There was no cysteine residue in ω-secalin proteins, and the potential celiac disease (CD) toxic epitope (PQQP) was identified to appear frequently in the repetitive domains. The ω-secalin genes from various cereal species shared high homology in their gene sequences. The ω-secalin gene family has involved fewer variations after the integration of the rye R chromosome or whole genome into the wheat or triticale genome. The higher Ka/Ks ratio (i.e. non-synonymous to synonymous substitutions per site) in ω-secalin pseudogenes than in ω-secalin ORFs indicate that the pseudogenes may be subject to a reduced selection pressure. Based on the conserved sequences of ω-secalin genes, it will be possible to manipulate the expression of this gene family in rye, triticale, or wheat 1BL/1RS translocation lines, to reduce its negative effects on grain quality.     

Molecular cytogenetic characterization of the spring triticale line 131/7 carrying a rye—wheat translocation

The chromosomal composition of the spring triticale line 131/7 carrying a rye—wheat translocation was studied using GISH, C-banding, and SSR analysis. The complex analysis revealed the presence of a pair of 2D chromosomes and T2RS.2RL-2BL translocation in the genome of the hexaploid triticale line 131/7. The break point in the translocated chromosome is between the markers Xwmc592 and Xwmc441, loci 63.9 cM and 76.8 cM on the linkage map (Wheat, Consensus SSR, 2004 NA-SSR-2004-2B) and in the region C-2BL2-0.36 on the physical map (Wheat, Physic al, SSR). The analysis of the line enables its use in breeding programs and in genetic studies.     

Chromosomal location of genes for stem rust resistance derived from ‘Waldron’ wheat

The chromosomal locations of genes for resistance to stem rust (Puccinia graminis Pers.: Pers. f. sp. tritici Eriks. & E. Henn.) in the wheat (Triticum aestivum L.) cultivar ‘Waldron’ (WDR) were determined by monosomic analyses. Wheat lines WDR-B1, -C2, -E4, and -F1,which have single genes for resistance to stem rust derived previously from WDR sel. ‘Little Club’, were crossed onto a complete set of 21 ‘Chinese Spring’ monosomics. The F₂ and backcross-F₁ (BC₁F₁) seedlings from each of the 84 crosses were tested for reaction to culture 111-SS2 (CRL-LCBB) of stem rust, and a few selected segregants were analyzed cytologically for chromosome number. The F₂ from 2 crosses of WDR-C2, -E4 and -F1 and the BC₁F₁ from 2 crosses of WDR-F1 were tested also with culture Or11c (CRL-QBCN). Significant deviations from disomic ratios towards monosomic ratios in the F₂ and BC₁F₁ were used to determine which chromosomes carried the genes for resistance. Cytological analyses of certain BC₁F₁ and susceptible F₂ plants were used to help identify the location of the genes for rust resistance. WDR-B1 has a gene, herein designated Sr41, for resistance on chromosome 4D. WDR-C2 has a gene on chromosome 7 A that may be the same as one previously designated SrWld2. WDR-E4 has a gene on chromosome 2A, possibly SrWld1, which is effective against most or all North American stem rust cultures. WDR-F1 has a gene on chromosome 6B that is the same as or similar to Sr11.     

Wheat lines monogenic for resistance to stem rust from the wheat cultivar ‘Waldron’

The Triticum aestivum L. cultivar ‘Waldron’ has long lasting resistance to most North American stem rust (Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. and E. Henn.) isolates. The objective of this research was to develop wheat lines monogenic for resistance to stem rust from ‘Waldron’ using allelism tests and tests for reaction to a series of ten stem rust cultures having a range of virulences. Twelve lines homozygous for single resistance genes were selected as parents of a diallel cross to test for allelism among genes for resistance. We identified 6 lines or groups of lines (WDR-A1, the WDR-B1 and WDR-B2 group, the WDR-C1 and WDR-C2 group, WDR-D1, the WDR-E1, WDR-E2, WDR-E3, and WDR-E4 group, and WDR-F1) that carried different single genes for resistance from ‘Waldron’. A seventh line (WDR-G1) probably has two genes for resistance, one in common with WDR-C1 and WDR-C2. The gene in the WDR-E group is probably the same as SrWld1, and the one in WDR-F1 the same as Sri11. ‘Waldron’ probably has two or more genes for resistance to stem rust that previous genetic studies did not detect.     

Characterization of a wheat–Thinopyrum bessarabicum (T2JS-2BS·2BL) translocation line

Thinopyrum bessarabicum (2n = 2x = 14, JJ or E^bE^b) is an important genetic resource for wheat improvement due to its salinity tolerance and disease resistance. Development of wheat–Th. bessarabicum translocation lines will facilitate its practical utilization in wheat improvement. In this study, a novel wheat–Th. bessarabicum translocation line T2JS-2BS·2BL, which carries a segment of Th. bessarabicum chromosome arm 2JS was identified and further characterized using sequential chromosome C-banding, genomic in situ hybridization (GISH), dual-color fluorescent in situ hybridization (FISH) and DNA markers. The translocation breakpoint was mapped within bin C-2BS1-0.53 of chromosome 2B through marker analysis. Compared to the Chinese Spring (CS) parent and to CS-type lines, the translocation line has more fertile spikes per plant, longer spikes, more grains per spike and higher yield per plant, which suggests that the alien segment carries yield-related genes. However, plants with the translocation are also taller, head later and have lower 1,000-kernel weight than CS or CS-type lines. By using markers specific to the barley photoperiod response gene Ppd-H1, it was determined that the late heading date was conferred by a recessive allele located on the 2JS segment. In addition, four markers specific for the translocated segment were identified, which can be used for marker-aided screening.     

Markers to a common bunt resistance gene derived from ‘Blizzard’ wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) and mapped to chromosome arm 1BS

Common bunt, caused by Tilletia caries (DC.) Tul. &; C. Tul. and T. laevis J.G Kuhn, is an economically important disease of wheat (Triticum aestivum L.) worldwide. The resistance in the winter wheat cultivar ‘Blizzard’ is effective against known races of common bunt in western Canada. The incorporation of resistance from Blizzard into field-ready cultivars may be accelerated through the use of molecular markers. Using the maize pollen method, a doubled haploid population of 147 lines was developed from the F₁ of the second backcross of Blizzard (resistant) by breeding line ‘8405-JC3C’ (susceptible). Doubled haploid lines were inoculated at seeding with race T19 or T19 and L16 and disease reaction was examined under controlled conditions in 1999 and natural conditions in 2002, and 2003. Resistant:susceptible-doubled haploid lines segregated in a 1:1 ratio for bunt reaction, indicating single major gene segregation. Microsatellite primers polymorphic on the parents were screened on the population. Initial qualitative segregation analysis indicated that the wheat microsatellite markers Xgwm374, Xbarc128 and Xgwm264, located on wheat chromosome 1BS, were significantly linked to the resistance locus. Qualitative results were confirmed with quantitative trait locus analysis. The genetic distance, calculated with JoinMap^®, between the bunt resistance locus and overlapping markers Xgwm374, Xgwm264 and Xbarc128 was 3.9 cM. The three markers were validated on doubled haploid populations BW337/P9502&;DAF1BB and Blizzard/P9514-AR17A3E evaluated for common bunt reaction in the growth chamber in 2007. These markers will be useful in selecting for the common bunt resistance from Blizzard and assist in identifying the resistance among potential new sources of resistance.     

Genetics and mapping of seedling resistance to Ug99 stem rust in Canadian wheat cultivars ‘Peace’ and ‘AC Cadillac’

Stem rust (caused by Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.) has re-emerged as a threat to wheat production with the evolution of new pathogen races, namely TTKSK (Ug99) and its variants, in Africa. Deployment of resistant wheat cultivars has provided long-term control of stem rust. Identification of new resistance genes will contribute to future cultivars with broad resistance to stem rust. The related Canadian cultivars Peace and AC Cadillac show resistance to Ug99 at the seedling stage and in the field. The purpose of this study was to elucidate the inheritance and genetically map resistance to Ug99 in these two cultivars. Two populations were produced, an F_2:3 population from LMPG/AC Cadillac and a doubled haploid (DH) population from RL6071/Peace. Both populations showed segregation at the seedling stage for a single stem rust resistance (Sr) gene, temporarily named SrCad. SrCad was mapped to chromosome 6DS in both populations with microsatellite markers and a marker (FSD_RSA) that is tightly linked to the common bunt resistance gene Bt10. FSD_RSA was the closest marker to SrCad (≈1.6 cM). Evaluation of the RL6071/Peace DH population and a second DH population, AC Karma/87E03-S2B1, in Kenya showed that the combination of SrCad and leaf rust resistance gene Lr34 provided a high level of resistance to Ug99-type races in the field, whereas in the absence of Lr34 SrCad conferred moderate resistance. A survey confirmed that SrCad is the basis for all of the seedling resistance to Ug99 in Canadian wheat cultivars. While further study is needed to determine the relationship between SrCad and other Sr genes on chromosome 6DS, SrCad represents a valuable genetic resource for producing stem rust resistant wheat cultivars.     

Quantifying the Extent of Lateral Gene Transfer Required to Avert a ‘Genome of Eden’

The complex pattern of presence and absence of many genes across different species provides tantalising clues as to how genes evolved through the processes of gene genesis, gene loss, and lateral gene transfer (LGT). The extent of LGT, particularly in prokaryotes, and its implications for creating a ‘network of life’ rather than a ‘tree of life’ is controversial. In this paper, we formally model the problem of quantifying LGT, and provide exact mathematical bounds, and new computational results. In particular, we investigate the computational complexity of quantifying the extent of LGT under the simple models of gene genesis, loss, and transfer on which a recent heuristic analysis of biological data relied. Our approach takes advantage of a relationship between LGT optimization and graph-theoretical concepts such as tree width and network flow.     

The assignment of a Thinopyrum distichum (Thunb.) Löve-derived translocation to the long arm of wheat chromosome 7D using endopeptidase polymorphisms

Summary Endopeptidase zymograms of the translocation line Indis revealed the presence of several major and minor bands that had differential expression in coleoptile and seed tissues. While Indis lacks Ep-D1a, which is present in the parental cultivar Inia 66, it also may not express any of the Th. distichum bands. The Indis zymogram was found to be identical to that of an isogenic line of Inia 66 possessing Lr19. Since the absence of an Ep-D1a product appears to be linked to the 7DL translocation, it is possible to use the null condition as a marker for both the Lr19 or Indis translocations. The Indis translocation also did not show recombination with the cn-D1 chlorophyl mutant on 7DL, confirming that a part of 7D was involved. The results of a telocentric mapping experiment involving the 7D telosomes indicated that in Indis a chromosome segment from Th. distichum replaced a large section of 7DL of Inia 66.     

Localization of a novel recessive powdery mildew resistance gene from common wheat line RD30 in the terminal region of chromosome 7AL

Segregation analysis of resistance to powdery mildew in a F₂ progeny from the cross Chinese Spring (CS) × TA2682c revealed the inheritance of a dominant and a recessive powdery mildew resistance gene. Selfing of susceptible F₂ individuals allowed the establishment of a mapping population segregating exclusively for the recessive resistance gene. The extracted resistant derivative showing full resistance to each of 11 wheat powdery mildew isolates was designated RD30. Amplified fragment length polymorphism (AFLP) analysis of bulked segregants from F₃s showing the homozygous susceptible and resistant phenotypes revealed an AFLP marker that was associated with the recessive resistance gene in repulsion phase. Following the assignment of this AFLP marker to wheat chromosome 7A by means of CS nullitetrasomics, an inspection of simple sequence repeat (SSR) loci evenly spaced along chromosome 7A showed that the recessive resistance gene maps to the distal region of chromosome 7AL. On the basis of its close linkage to the Pm1 locus, as inferred from connecting partial genetic maps of 7AL of populations CS × TA2682c and CS × Virest (Pm1e), and its unique disease response pattern, the recessive resistance gene in RD30 was considered to be novel and tentatively designated mlRD30.Communicated by C. Möllers     

Genetic analysis of adult plant,quantitative resistance to stripe rust in wheat cultivar ‘Stephens’ in multi-environment trials

The wheat (Triticum aestivum L.) cultivar ‘Stephens’ has been grown commercially in the USA Pacific Northwest for 30 years. The durable resistance of ‘Stephens’ to stripe rust (Puccinia striiformis f. sp. tritici) was believed to be due to a combination of seedling and adult plant resistance genes. Multilocation field trials, diversity array technology (DArT), and simple sequence repeat (SSR) markers were used to identify quantitative trait loci (QTL) for resistance. Recombinant inbred lines were assessed for stripe rust response in eight locations/years, five in 2008 and three in 2009. The data from Mt. Vernon, WA, differed from all other environments, and composite interval mapping (CIM) identified three QTL, QYrst.orr-1AL, QYrst.orr-4BS, and QYrpl.orr-6AL, which accounted for 12, 11, and 6% of the phenotypic variance, respectively. CIM across the remaining six environments identified four main QTL. Two QTL, QYrst.orr-2BS.2 and QYrst.orr-7AS, were detected in five of six environments and explained 11 and 15% of the phenotypic variance, respectively. Two other QTL, QYrst.orr-2AS and QYrpl.orr-4BL, were detected across four and three of six environments, and explained 19 and 9% of the phenotypic variance, respectively. The susceptible parent ‘Platte’ contributed QYrpl.orr-4BL and QYrpl.orr-6AL, with the remaining QTL originating from ‘Stephens’. For each environment, additional minor QTL were detected, each accounting for 6–10% of the phenotypic variance. Different QTL with moderate effects were identified in both ‘Stephens’ and ‘Platte’. Significant QTL × environment interactions were evident, suggesting that specificity to plant stage, pathogen genotype, and/or temperature was important.     

Genetic engineering of Plum pox virus resistance: ‘HoneySweet’ plum—from concept to product

Sharka disease, caused by Plum pox virus (PPV) was first recorded in Bulgaria during the early twentieth century and since that first report, the disease has progressively spread throughout Europe and more recently to Asia, Africa, North and South America. Few PPV resistance genes have been found to naturally occur in Prunus and this has led to the investigation of biotech approaches to the development of resistance through genetic engineering (GE). A notable example of the utility of this approach is ‘HoneySweet’ plum. PPV protection in this case is based on RNA interference (RNAi) and resistance has been shown to be highly effective, stable, durable, and heritable as a dominant trait. Extensive testing and risk assessment of ‘HoneySweet’ in laboratory, greenhouse and in the field for over 20 years has demonstrated not only the effectiveness but also the safety of the technology. ‘HoneySweet’ has been cleared for cultivation in the USA. By the appropriate regulatory agencies. The development and regulatory approval of ‘HoneySweet’ demonstrate the ability of RNAi technology to contribute to the sustainability of stone fruit production in regions impacted by PPV. Although it has taken almost 100 years since the identification of sharka, we are now able to effectively protect stone fruit species against this disease through the application of GE.     

Powdery mildew resistance and Lr34/Yr18 genes for durable resistance to leaf and stripe rust cosegregate at a locus on the short arm of chromosome 7D of wheat

The incorporation of effective and durable disease resistance is an important breeding objective for wheat improvement. The leaf rust resistance gene Lr34 and stripe rust resistance gene Yr18 are effective at the adult plant stage and have provided moderate levels of durable resistance to leaf rust caused by Puccinia triticina Eriks. and to stripe rust caused by Puccinia striiformis Westend. f. sp. tritici. These genes have not been separated by recombination and map to chromosome 7DS in wheat. In a population of 110 F₇ lines derived from a Thatcher × Thatcher isogenic line with Lr34/Yr18, field resistance to leaf rust conferred by Lr34 and to stripe rust resistance conferred by Yr18 cosegregated with adult plant resistance to powdery mildew caused by Blumeria graminis (DC) EO Speer f. sp. tritici. Lr34 and Yr18 were previously shown to be associated with enhanced stem rust resistance and tolerance to barley yellow dwarf virus infection. This chromosomal region in wheat has now been linked with resistance to five different pathogens. The Lr34/Yr18 phenotypes and associated powdery mildew resistance were mapped to a single locus flanked by microsatellite loci Xgwm1220 and Xgwm295 on chromosome 7DS.     

Molecular characterization of a wheat–Psathyrostachys huashanica Keng 2Ns disomic addition line with resistance to stripe rust

We characterized a wheat–Psathyrostachys huashanica derived line 3-6-4-1 based on genomic in situ hybridization (GISH), molecular marker analysis, and agronomic trait evaluations. The GISH investigations showed that the 3-6-4-1 contained 42 wheat chromosomes and a pair of P. huashanica chromosomes. The homoeologous relationships of the introduced P. huashanica chromosomes were determined using EST-STS multiple loci markers from seven wheat homoeologous groups in the parents and the addition line. Twelve EST-STS markers located on the homoeologous group 2 chromosomes of wheat amplified polymorphic bands in 3-6-4-1, which were unique to P. huashanica. An introduced Ns chromosome pair that belonged to homoeologous group 2 was identified using chromosome-specific markers. Inoculation with isolates of the stripe rust pathotypes, CYR31, CYR32, and SY11-14, and mixed races (CYR31, CYR32, and SY11-14) in the seeding and adult stage, respectively, showed that 3-6-4-1 was generally resistant to stripe rust, which was probably attributable to its P. huashanica parent. We also compared a complete set of wheat–P. huashanica disomic addition lines (1Ns–7Ns, 2n = 44 = 22II) to assess their agronomic traits and morphological characteristics, which showed that 3-6-4-1 had improved spike traits compared with its parents. The P. huashanica 2Ns chromosome-specific molecular markers in 3-6-4-1 could be useful for marker-assisted selection in breeding programs to combat stripe rust. This line can be used as a donor source to introduce novel excellent genes from P. huashanica into wheat to widen its genetic diversity, thereby providing new germplasms for wheat breeding.     

Design of a structural motif ‘dendroid’ to mimic protein: Protein interactions via intramolecular self-organisation

Summary The design and synthesis of a structural motif which can mimic protein-protein interactions is described. These moieties, termed asdendroids (Greekdendron, a tree), are low-molecular-weight structures which are based on self-organising dendritic polymers.     

Transfer of a Dwarf Gene from Brassica rapa to Oilseed B. napus, Effects on Agronomic Traits, and Development of a ‘Perfect’ Marker for Selection

Lodging can be a serious problem in oilseed Brassica napus. Dwarf genes have been used to reduce lodging in other crops, and their use in wheat and rice was a major factor in the success of the ‘Green Revolution’. We previously reported on a single, semi-dominant, gibberellin insensitive dwarf mutant of B. rapa (Brrga1-d), and provided evidence for homology of this gene to the wheat ‘Green Revolution’ dwarf gene. In this paper, we report using interspecific hybridization of B. rapa and B. oleracea and embryo rescue to resynthesize B. napus containing the Brrga1-d dwarf gene. The dwarf gene was backcrossed into two parents of a commercial hybrid combination and evaluated as inbred and hybrid lines in field experiments. The Brrga1-d gene reduced plant height and lodging in inbred and hybrid lines of B. napus, even when present as a single dose in heterozygous genotypes. Seed yields of inbred lines homozygous for Brrga1-d were reduced compared to near isogenic wild-type inbreds, presumably due to damage by insects caused by a slight delay in flowering time. However, yields of hybrids that were homozygous or heterozygous for Brrga1-d were similar to those of near isogenic wild-type hybrids. In addition, we report on a ‘perfect’ PCR marker for selection of the Brrga1-d gene that is based on detecting the nucleotide mutation causing the dwarf phenotype.     

Synthesis of hexaploid (AABBCC) somatic hybrids: a bridging material for transfer of ‘tour’ cytoplasmic male sterility to different Brassica species

Most of the alloplasmic cytoplasmic male sterility (CMS) systems are known to be associated with a number of floral abnormalities that result from nuclear-cytoplasmic incompatibilities. One such system, tour, which is derived from Brassica tournefortii, induces additional floral abnormalities and causes chlorosis in Brassica spp. While the restorer for this CMS has been reported to be present in B. napus, in B. juncea, where the abnormalities are more pronounced, no restorer has yet been identified. Rectification of these floral abnormalities through mitochondrial recombinations and chloroplast replacement might result in the improvement of this CMS system. As organelle recombinations can possibly be achieved only by somatic cell hybridization, fusion experiments were carried out between hygromycin-resistant B. juncea AABB carrying tour cytoplasm and phosphinotricin-resistant, normal B. oleracea CC to generate AABBCC hexaploid somatic hybrids. The presence of selectable marker genes facilitated the selection of hybrids in large numbers. The resulting hybrids showed wide variation in floral morphology and organelle composition. Regenerants with normal, male-sterile flowers having recombinant tour-or oleracea-type mitochondria and oleracea-type chloroplasts were obtained. Hybrids with male-fertile flowers were also obtained that had recombined tour mitochondria. The AABBCC hexaploid hybrids synthesized in the present study were successfully utilized as a bridging material for transferring variability in the organelle genome simultaneously to all the digenomic Brassica species, and all of these hybrids are now being stabilized through repeated backcrosses to the allopolyploid crop brassicas.     

Loci underlying resistance to manganese toxicity mapped in a soybean recombinant inbred line population of ‘Essex2019; x ‘Forrest’

Resistance to manganese toxicity is associated with some soybean (Glycine max) cultivars grown on acidic soils or in hydroponics. Previously random amplified polymorphic DNA (RAPD) markers had seemed to identify 4 quantitative trait loci (QTL), regions that might underlie resistance to manganese toxicity in a recombinant inbred line (RIL) population derived from ‘Essex’ x ‘Forrest’. Our objective was to identify microsatellite markers linked to these, or additional, QTL for resistance to manganese toxicity in a separate assay. Two hundred and forty microsatellite markers and 100 RILs were used to construct a map. The response of five plants per genotype to manganese was measured by leaf chlorosis (scored from 0–5) and root necrosis (scored from 0–5) from 7–28 days after treatment with 125 μM of manganese in hydroponics. The experiment was repeated. ANOVA and MapMaker/QTL were used to identify regions underlying the responses. Three genomic regions on different linkage groups were found to contain QTL for resistance to necrosis during manganese toxicity. The regions located on linkage groups C2 (BARC__S att291),I(BARC__S att239)andG(OP__O EO2)wereeachsignificantlyassociated(P<0.005, R ²=20%) with root necrosis at 7 days after treatment. The regions all derived the beneficial allele from Essex. One of the previously identified RAPD associated root necrosis QTL was identified in this new study. However, no QTL for leaf chlorosis were detected (P<0.005) and none of the RAPD identified leaf chlorosis QTL could be identified. We conclude that root and leaf resistance to manganese toxicity are environmentally sensitive quantitative traits determined by separate loci of different number and magnitude of effect.     

Quantitative trait loci for resistance to spot blotch caused by Bipolarissorokiniana in wheat (T.aestivum L.) lines ‘Ning 8201’ and ‘Chirya 3’

Spot blotch caused by Bipolaris sorokiniana is a destructive disease of wheat in warm and humid wheat growing regions of the world. To identify quantitative trait loci (QTLs) for spot blotch resistance, two mapping populations were developed by making the crosses between common susceptible cultivar ‘Sonalika’ with the resistant breeding lines ‘Ning 8201’ and ‘Chirya 3’. Single seed descent derived F₆, F₇, F₈ lines of the first cross ‘Ning 8201’ × ‘Sonalika’ were evaluated for resistance to spot blotch in three blocks in each of the 3 years. After screening of 388 pairs of simple sequence repeat primers between the two parents, 119 polymorphic markers were used to genotype the mapping population. Four QTLs were identified on the chromosomes 2AS, 2BS, 5BL and 7DS and explained 62.9% of phenotypic variation in a simultaneous fit. The QTL on chromosome 2A was detected only in 1 year and explained 22.7% of phenotypic variation. In the second cross (‘Chirya 3’ × ‘Sonalika’), F₇ and F₈ population were evaluated in three blocks in each of the 2 years. In this population, five QTLs were identified on chromosomes 2BS, 2DS, 3BS, 7BS and 7DS. The QTLs identified in the ‘Chirya 3’ × ‘Sonalika’ population explained 43.4% of phenotypic variation in a simultaneous fit. The alleles for reduced disease severity in both the populations were derived from the respective resistant parent. The QTLs QSb.bhu-2B and QSb.bhu-7D from both populations were placed in the same deletion bins, 2BS1-0.53-0.75 and 7DS5-0.36-0.61, respectively. The closely linked markers Xgwm148 to the QTL on chromosome 2B and Xgwm111 to the QTL on chromosome 7D are potentially diagnostic markers for spot blotch resistance.     

Advanced backcross quantitative trait locus analysis in winter wheat: Dissection of stripe rust seedling resistance and identification of favorable exotic alleles originated from a primary hexaploid wheat (Triticum turgidum ssp. dicoccoides?×?Aegilops tauschii)

Stripe rust (Puccinia striiformis W.) causes a range of disease symptoms in hexaploid wheat. We have utilized the AB-QTL (advanced backcross quantitative trait locus) strategy for the genetic dissection of complex disease resistance against stripe rust. An advanced backcross population designated Z86 was made by crossing the winter wheat cultivar Zentos (Triticum aestivum L.) and the primary (exotic) synthetic wheat accession Syn86L (T. turgidum ssp. dicoccoides?×?Aegilops tauschii). The population Z86, containing 150 BC2F3 lines, was inoculated with the stripe rust isolate R108E141. The disease symptoms were subjected to QTL analysis by using a genetic map based on 118 simple sequence repeat markers. This analysis revealed six QTL effects that were located on chromosomes 1B, 2B, 6B, 7B, 1D and 4D. At four loci, the exotic alleles were associated to increased resistance against stripe rust. The strongest effect, QYrs.Z86-1B, was detected on the short arm of chromosome 1B. Here, the introgression of the exotic allele resulted in 86% enhancement of resistance which explained 37.2% of the genetic variance (R ²). The second favorable effect of an exotic allele was detected on chromosome 1D at QYrs.Z86-1D, which accounted for 72% increase in resistance and explained 18.4% of the R ². Each of the exotic allele at QTL QYrs.Z86-6B and QYrs.Z86-7B accounted for around 60% enhancement of resistance against stripe rust. At QTL QYrs.Z86-2B and QYrs.Z86-4D, the relative performance of the exotic alleles was inferior due to the pre-eminence of the elite alleles which ranged from 67 to 72%. In addition, QTL analysis revealed four QTL by marker interaction effects. In most cases, the interaction between the elite and exotic alleles brought up resistance in the mixed background of BC2F3 lines. The data presented here provide valuable new genetic resources to be used for stripe rust resistance breeding as well as to isolate new alleles of exotic origin.