Cultivar Chinese Spring Research Articles

Development of a deletion and genetic linkage map for the 5A and 5B chromosomes of wheat (Triticum aestivum)

The aims of the present study were to provide deletion maps for wheat ( Triticum aestivum L.) chromosomes 5A and 5B and a detailed genetic map of chromosome 5A enriched with popular microsatellite markers, which could be compared with other existing maps and useful for mapping major genes and quantitative traits loci (QTL). Physical mapping of 165 gSSR and EST-SSR markers was conducted by amplifying each primer pair on Chinese Spring, aneuploid lines, and deletion lines for the homoeologous group 5 chromosomes. A recombinant inbred line (RIL) mapping population that is recombinant for only chromosome 5A was obtained by crossing the wheat cultivar Chinese Spring and the disomic substitution line Chinese Spring-5A dicoccoides and was used to develop a genetic linkage map of chromosome 5A. A total of 67 markers were found polymorphic between the parental lines and were mapped in the RIL population. Sixty-three loci and the Q gene were clustered in three linkage groups ordered at a minimum LOD score of 5, while four loci remained unlinked. The whole genetic 5A chromosome map covered 420.2 cM, distributed among three linkage groups of 189.3, 35.4, and 195.5 cM. The EST sequences located on chromosomes 5A and 5B were used for comparative analysis against Brachypodium distachyon (L.) P. Beauv. and rice ( Oryza sativa L.) genomes to resolve orthologous relationships among the genomes of wheat and the two model species.

Molecular marker-based detection of Ph1b mutation to increase homoeologous pairing in wheat (Triticum aestivum)

Despite the close relationship between three genomes of wheat, meiosis in wheat is characterized by formation of bivalents only. The homologous pairing of polyploidy wheat is controlled by Ph1 (pairing homologous) locus located on long arm of chromosome 5B which suppresses pairing and recombination between homoeologous chromosomes. However, similar genes have also been identified in T. turgidum and T. timopheevii with lesser impact. Cytogenetic manipulations for suppressing the Ph1 pairing regulation would be necessary to bring about the desired chromosome pairing and hence alien gene transfers into cultivated wheat. In the present study, PCR based marker was used to transfer the recessive mutation in Ph1 locus (Ph1b) from bread wheat cultivar Chinese Spring to Indian bread and durum wheat cultivars. The availability of Ph1b locus in Indian wheat genetic background will help in transfer of alien genes of economic and agronomic importance.

Diversification of three APETALA1/FRUITFULL-like genes in wheat

The genomes of grass family species have three paralogs of APETALA1/FRUITFULL (AP1/FUL)-like genes (FUL1, FUL2 and FUL3) that are derived from the FUL lineage. In this study, we focus on the different roles of the wheat AP1/FUL-like genes, WFUL1 (identical to VRN1), WFUL2 and WFUL3, during the transition from vegetative to reproductive growth. Sequence analysis indicated that there was a high level of variability in the amino acid sequence of the C-domain among three WFUL genes. Expression analyses using the spring wheat cultivar Chinese Spring indicated that WFUL1/VRN1 was expressed in leaves as well as spike primordia of non-vernalized plants at the vegetative stage just before phase transition, while WFUL2 and WFUL3 were not expressed in leaves. This result indicates that WFUL1/VRN1 performs a distinct role in leaves before phase transition. In young spikes, WFUL1/VRN1 and WFUL3 were expressed in all developing Xoral organs, whereas WFUL2 expression was restricted in the Xoral organs to the lemma and palea. Furthermore, yeast two-hybrid and three-hybrid analyses revealed that WFUL2, but not WFUL1/VRN1 or WFUL3, interacted with class B and class E proteins. These results suggest that WFUL2 of wheat has class A functions in specifying the identities of Xoral meristems and outer Xoral organs (lemma and palea) through collaboration with class B and class E genes.

Comparative proteomic analysis of salt response proteins in seedling roots of two wheat varieties

A comparative proteomic analysis was made of salt response in seedling roots of wheat cultivars Jing-411 (salt tolerant) and Chinese Spring (salt sensitive) subjected to a range of salt stress concentrations (0.5%, 1.5% and 2.5%) for 2 days. One hundred and ninety eight differentially expressed protein spots (DEPs) were located with at least two-fold differences in abundance on 2-DE maps, of which 144 were identified by MALDI-TOF-TOF MS. These proteins were involved primarily in carbon metabolism (31.9%), detoxification and defense (12.5%), chaperones (5.6%) and signal transduction (4.9%). Comparative analysis showed that 41 DEPs were salt responsive with significant expression changes in both varieties under salt stress, and 99 (52 in Jing-411 and 47 in Chinese Spring) were variety specific. Only 15 and 9 DEPs in Jing-411 and Chinese Spring, respectively, were up-regulated in abundance under all three salt concentrations. All dynamics of the DEPs were analyzed across all treatments. Some salt responsive DEPs, such as guanine nucleotide-binding protein subunit beta-like protein, RuBisCO large subunit-binding protein subunit alpha and pathogenesis related protein 10, were up-regulated significantly in Jing-411 under all salt concentrations, whereas they were down-regulated in salinity-stressed Chinese Spring.

Protein disulphide isomerase promoter sequence analysis of Triticum urartu, Aegilops speltoides and Aegilops tauschii

Protein disulphide isomerase (PDI) catalyses the formation, reduction and isomerization of disulphide bonds in the newly synthesized secretory proteins. Plant PDIs have been shown to be involved in the folding and deposition of seed storage proteins, which makes this enzyme particularly interesting in wheat, as flour quality is strongly affected by composition and structure of seed storage proteins. In hexaploid wheat cultivar (AABBDD) Chinese Spring (CS), the genomic, complementary DNA and promoter sequences of the three homoeologous gene encoding PDI had been isolated and characterized in a previous study revealing high levels of sequence conservation. In this study, we report the isolation and sequencing of a ~700 bp region, comprising ~600 bp of the putative promoter region and 88 bp of the first exon of the typical PDI gene, in five accessions each from Triticum urartu (AA), Aegilops speltoides (BB) and Aegilops tauschii (DD). Sequence analysis indicated large variation among sequences belonging to the different genomes, while close similarity was found within each species and with the corresponding homoeologous PDI sequences of Triticum aestivum cv. CS (AABBDD) resulting in an overall high conservation of the regulatory motifs conferring endosperm-specific expression.

Meiotic behaviour of tetraploid wheats (Triticum turgidum L.) and their synthetic hexaploid wheat derivates influenced by meiotic restitution and heat stress

Meiotic restitution is considered to be a common mechanism of polyploidization in plants and hence is one of the most important processes in plant speciation. Meiotic behaviour of plant chromosomes is influenced by both genetic and environmental factors. In this study, the meiotic behaviour of cereal crops was investigated, which includes tetraploid wheat genotypes (with and without the meiotic restitution trait) and their derivates (synthetic hexaploid wheats and a doubled haploid (DH) line), grown at two planting dates in the field. In addition, two local landraces of emmer wheat (Triticum turgidum ssp. dicoccum), one wheat cultivar (Chinese spring), one DH triticale cultivar (Eleanor) and one rye accession were included. Immature spikes of mid-autumn and end-winter sowing plants were collected in April and May 2008, respectively, fixed in Carnoy's solution and stained with hematoxylin. Pollen mother cells (PMCs) from anthers at different stages of meiotic process were analysed for their chromosomal behaviour and irregularities. Meiotic aberrations such as laggards, chromosome bridges, micronuclei, abnormal cytokines, chromatin pulling and meiotic restitution were observed and the studied genotypes were accordingly ranked as follows: triticale > synthetic hexaploid wheats > tetraploid wheats possessing meiotic restitution > tetraploid wheats lacking meiotic restitution > rye. The results indicated that the samples that had been planted in the autumn, thus experiencing an optimum temperature level at the flowering stage, exhibited less meiotic irregularities than winter planting samples that encountered heat stress at the flowering period.

Chromosomal location and molecular mapping of a tan spot resistance gene in the winter wheat cultivar Red Chief

The winter wheat cultivar Red Chief has been identified as the wheat cultivar most resistant to Pyrenophora tritici-repentis (Ptr). This study was undertaken to determine the inheritance, chromosomal location and molecular mapping of a tan spot resistance gene in Red Chief. χ² analysis of the F2 segregation data of the hybrids between 21 monosomic lines of the susceptible wheat cultivar Chinese Spring and the resistant cultivar Red Chief revealed that tan spot resistance in cv. Red Chief is controlled by a single recessive gene located on chromosome 3A. Linkage analysis using SSR markers in the Red Chief/Chinese Spring F2 population showed that the tsr4 gene is clustered in the region around Xgwm2a, on the short arm of chromosome 3A. This marker has also been identified as the closest marker to the tsr3 locus on chromosome 3D in synthetic wheat lines. Validation analysis of this marker for the tsr3 and tsr4 genes using 28 resistant and 6 susceptible genotypes indicated that the 120 bp allele (the tsr3 gene) specific fragment was observed in 11 resistant genotypes, including the three synthetic lines XX41, XX45 and XX110, while the 130 bp allele was amplified only in cv. Red Chief and Dashen. Xgwm2a can be used to trace the presence of the target gene in successive backcross generations and pyramiding of the tsr3 & tsr4 genes into a commonly grown and adaptable cultivar.

Physical mapping of puroindoline b-2 genes and molecular characterization of a novel variant in durum wheat (Triticum turgidum L.)

The puroindoline genes (Pina and Pinb) are the functional components of the common or bread wheat (Triticum aestivum L.) grain hardness locus that are responsible for kernel texture. In this study, four puroindoline b-2 variants were physically mapped using nulli-tetrosomic lines of bread wheat cultivar Chinese Spring and substitution lines of durum wheat (Triticum turgidum L.) cultivar Langdon. Results indicated that Pinb-2v1 was on 7D of Chinese Spring, Pinb-2v2 on 7B of Chinese Spring, Pinb-2v3 on 7B of Chinese Spring and Langdon, and Pinb-2v4 on 7A of Chinese Spring and Langdon. A new puroindoline b-2 variant, designated Pinb-2v5, was identified at the puroindoline b-2 locus of durum wheat cultivar Langdon, with a difference of only five single nucelotide polymorphisms compared with Pinb-2v4. Sequencing results indicated that, in comparison with the Pinb-2v3 sequence (AM99733 and GQ496618 with one base-pair modification of G to T at 6th position, designated Pinb-2v3a) in bread wheat cultivar Witchta, the coding region of Pinb-2v3 in 12 durum wheat cultivars had a single nucleotide change from T to C at the 311th position, resulting in a corresponding amino acid change from valine to alanine at the 104th position. This new allele was designated Pinb-2v3b. The study of puroindoline b-2 gene polymorphism in CIMMYT and Italian durum wheat germplasm and discovery of a novel puroindoline b-2 variant could provide useful information for further understanding the molecular and genetic basis of kernel hardness and illustrating gene duplication events in wheat.

Chromosomal location of specific and nonspecific components of polygenic resistance to brown rust in common wheat

The genetic nature of polygenic resistance of common wheat to a causative agent of brown rust was studied. It was established, using ditelosomic lines (DT) of the cultivar Chinese Spring, that the majority of examined chromosome arms participate in differential interactions with the pathogen during formation of basic traits of polygenic resistance: the number of pustules (NP) per 1 cm2 of leaf area, the mean spore formation ability of pustule (MSFAP), the mean spore formation ability of fungus per unit of leaf area (MSFAULA). When parameters of spore formation were estimated in the pathogen, it was detected that DT lines 2BL and 5DL did not differentially interact with fungal genotypes carrying different virulence genes. Consequently, minor genes located on 2BS and 5DS arms carry a specific component ofpolygenic resistance. In this model experiment, we confirmed for the first time the hypothesis that polygenic (horizontal) resistance involves two components: a specific component, which is overcome by the pathogen, and a nonspecific component mediating the prolonged resistance.

Molecular mapping of powdery mildew resistance gene PmHNK in winter wheat (Triticum aestivum L.) cultivar Zhoumai 22

The Chinese winter wheat cultivar Zhoumai 22 is highly resistant to powdery mildew. The objectives of this study were to map a powdery mildew resistance gene in Zhoumai 22 using molecular markers and investigate its allelism with Pm13. A total of 278 F2 and 30 BC1 plants, and 143 F3 lines derived from the cross between resistant cultivar Zhoumai 22 and susceptible cultivar Chinese Spring were used for resistance gene tagging. The 137 F2 plants from the cross Zhoumai 22/2761-5 (Pm13) were employed for the allelic test of the resistance genes. Two hundred and ten simple sequence repeat (SSR) markers were used to test the two parents, and resistant and susceptible bulks. Subsequently, seven polymorphic markers were used for genotyping the F2 and F3 populations. The results indicated that the powdery mildew resistance in Zhoumai 22 was conferred by a single dominant gene, designated PmHNK tentatively, flanked by seven SSR markers Xgwm299, Xgwm108, Xbarc77, Xbarc84, Xwmc326, Xwmc291 and Xwmc687 on chromosome 3BL. The resistance gene was closely linked to Xwmc291 and Xgwm108, with genetic distances of 3.8 and 10.3 cM, respectively, and located on the chromosome bin 3BL-7-0.63-1.0 in the test with a set of deletion lines. Seedling tests with seven isolates of Blumeriagraminis f. sp. tritici (Bgt) and allellic test indicated that PmHNK is different from Pm13, and Pm41 seems also to be different from PmHNK due to its origin from T. dicoccoides and molecular evidence. These results indicate that PmHNK is likely to be a novel powdery mildew resistance gene in wheat.

Potential new genes for resistance to Mycosphaerella graminicola identified in Triticum aestivum × Lophopyrum elongatum disomic substitution lines

Lophopyrum species carry many desirable agronomic traits, including disease resistance, which can be transferred to wheat by interspecific hybridization. To identify potentially new genes for disease and insect resistance carried by individual Lophopyrum chromosomes, 19 of 21 possible wheat cultivar Chinese Spring × Lophopyrum elongatum disomic substitution lines were tested for resistance to barley yellow dwarf virus (BYDV), cereal yellow dwarf virus (CYDV), the Hessian fly Mayetiola destructor, and the fungal pathogens Blumeria graminis and Mycosphaerella graminicola (asexual stage: Septoria tritici). Low resistance to BYDV occurred in some of the disomic substitution lines, but viral titers were significantly higher than those of two Lophopyrum species tested. This suggested that genes on more than one Lophopyrum chromosome are required for complete resistance to this virus. A potentially new gene for resistance to CYDV was detected on wheatgrass chromosome 3E. All of the substitution lines were susceptible to Mayetiola destructor and one strain of B. graminis. Disomic substitution lines containing wheatgrass chromosomes 1E and 6E were significantly more resistant to M. graminicola compared to Chinese Spring. Although neither chromosome by itself conferred resistance as high as that in the wheatgrass parent, they do appear to contain potentially new genes for resistance against this pathogen that could be useful for future plant-improvement programs.

EST mining for structure and expression of genes in the region of the wheat high-molecular-weight glutenin loci

An in-depth analysis was carried out with expressed sequence tags (ESTs) for genes in and near the HMW-GS loci. Considerations for using ESTs are discussed, including the occurrence of chimeric and aberrant HMW-GS ESTs. Complete gene sequences demonstrated the feasibility of constructing accurate full-length coding regions from EST assemblies and found, or supported, errors in several previously reported HMW-GS gene sequences. New complete HMW-GS gene sequences are reported for the cultivars Chinese Spring and Glenlea. The Ay subunit gene, which is considered null in cultivated wheats, was shown to transcribe in at least two germplasms. Analyses support the conclusion that of the five known genes within this genomic region, the two HMW-GS genes and the globulin gene are highly expressed. The other two genes, encoding a receptor kinase and a protein kinase, have one and no identifiable wheat EST, respectively, although ESTs are found for the orthologous genes in barley. The ESTs of all five genes within the HMW-GS region are either definitely associated with the endosperm or possibly originate from imbibed seed, suggesting the four distinct gene classes in this region are part of a seed or endosperm chromatin domain. EST resources were also used to determine relative abundance of ESTs for all classes of wheat prolamines and indicated differential levels of expression both among germplasms and among the three genomes of hexaploid wheats.

Transcriptional profiling in response to terminal drought stress reveals differential responses along the wheat genome

BackgroundWater stress during grain filling has a marked effect on grain yield, leading to a reduced endosperm cell number and thus sink capacity to accumulate dry matter. The bread wheat cultivar Chinese Spring (CS), a Chinese Spring terminal deletion line (CS_5AL-10) and the durum wheat cultivar Creso were subjected to transcriptional profiling after exposure to mild and severe drought stress at the grain filling stage to find evidences of differential stress responses associated to different wheat genome regions.ResultsThe transcriptome analysis of Creso, CS and its deletion line revealed 8,552 non redundant probe sets with different expression levels, mainly due to the comparisons between the two species. The drought treatments modified the expression of 3,056 probe sets. Besides a set of genes showing a similar drought response in Creso and CS, cluster analysis revealed several drought response features that can be associated to the different genomic structure of Creso, CS and CS_5AL-10. Some drought-related genes were expressed at lower level (or not expressed) in Creso (which lacks the D genome) or in the CS_5AL-10 deletion line compared to CS. The chromosome location of a set of these genes was confirmed by PCR-based mapping on the D genome (or the 5AL-10 region). Many clusters were characterized by different level of expression in Creso, CS and CS_AL-10, suggesting that the different genome organization of the three genotypes may affect plant adaptation to stress. Clusters with similar expression trend were grouped and functional classified to mine the biological mean of their activation or repression. Genes involved in ABA, proline, glycine-betaine and sorbitol pathways were found up-regulated by drought stress. Furthermore, the enhanced expression of a set of transposons and retrotransposons was detected in CS_5AL-10.ConclusionBread and durum wheat genotypes were characterized by a different physiological reaction to water stress and by a substantially different molecular response. The genome organization accounted for differences in the expression level of hundreds of genes located on the D genome or controlled by regulators located on the D genome. When a genomic stress (deletion of a chromosomal region) was combined with low water availability, a molecular response based on the activation of transposons and retrotransposons was observed.

Hybridization, fertility and herbicide resistance of hybrids between wheat andAegilops biuncialis

Genetically modified crops are now grown worldwide and their area of cultivation is increasing yearly. Although transgenic crops offer benefits, several risks have been identified associated with their cultivation. One such risk is their potential for hybridization with wild species, and weed-related species, and the possible escape and subsequent introgression of the transgenes into these species. Transgenic wheat varieties are being successfully developed and field-tested, primarily on herbicide-tolerant wheat. If genetically modified herbicide-tolerant wheat is commercialized in the near future this may result in the escape of the inserted gene from the crop and its incorporation into closely related wild species. This fact could give a competitive advantage to the recipients. For risk assessment purposes it is necessary to determine the frequency of crop-wild transgene flow and the fertility of hybrids. Most wheat-wild hybridization studies have been conducted with the purpose of breeding with wheat acting as the female parent in crosses, but very limited information is available focused on hybrid production with wheat as the male parent. Here, we studied (1) the potential hybridization between wheat and the wild related Aegilops biuncialis, and (2) the fertility of the hybrids. Hybridization was quantified in crossing experiments over 5 years in a greenhouse using three wheat cultivars as pollen donors and emasculated plants of one A. biuncialis population as pollen recipients. Hybridization was estimated as the ratio of number of seeds set to the number of flowers pollinated in percentage terms. Our results show that hybrids between wheat and A. biuncialis are formed easily, with hybridization rates ranging from 8.5 to 75%. The fertility of the hybrids, measured as the number of seeds per spikelet (%), was also evaluated by self-pollination and by backcrossing. Most of the hybrids were self-sterile but 11 F2 seeds were obtained from 191 A. biuncialis-wheat hybrids. However, backcrossing seeds were found in all BC1 combinations at average rates of 3.7% (0–19.6%) for greenhouse experiments, and 4.6% (0–28.9%) for field experiments. In subsequent generations, although few plants were available, BC1F1 exhibited a certain degree of fertility, up to 3.57% with the cultivar Chinese Spring. F1 and BC1 were also checked for resistance to the herbicide difenzoquat that was present in the parental wheat, while A. biuncialis was susceptible. Difenzoquat resistance was maintained in the F1 hybrids and also in the derived BC1 plants. This information on hybridization and fertility of the first A. biuncialis-wheat hybrid generations could be an initial step to assess the relative advantage of hybridization in the adaptive ability of A. biuncialis and hybrid derivatives and the impact thereof on the environment and agricultural system. This needs to be studied in depth when wheat and A. biuncialis share habitat.

Orf260cra, a Novel Mitochondrial Gene, is Associated with the Homeotic Transformation of Stamens into Pistil-Like Structures (Pistillody) in Alloplasmic Wheat

Homeotic transformation of stamens into pistil-like structures (pistillody) can occur in cytoplasmic substitution (alloplasmic) lines of bread wheat (Triticum aestivum) that have the cytoplasm of the related species, Aegilops crassa. Previously we showed that pistillody results from altered patterns of expression of class B MADS-box genes mediated by mitochondrial gene(s) in the Ae. crassa cytoplasm. The wheat cultivar Chinese Spring does not show pistillody when Ae. crassa cytoplasm is introduced. The absence of an effect is due to a single dominant gene (designated Rfd1) located on the long arm of chromosome 7B. To identify the mitochondrial gene involved in pistillody induction, we performed a subtraction analysis using cDNAs derived from young spikes of a pistillody line and a normal line. We found that mitochondrial cDNA clone R04 was abundant in the young spikes of the pistillody line but was down-regulated in the normal line that carried nuclear Rfd1. Sequencing of the full-length cDNA corresponding to clone R04 showed that two genes were present, cox I (cytochrome c oxidase subunit I) and orf260(cra). orf260(cra) shows high sequence similarity to orf256, the T. timopheevii mitochondrial gene responsible for cytoplasmic male sterility (CMS). orf260(cra) was also present in the cytoplasms of Ae. juvenalis and Ae. vavilovii, which induce pistillody, but not in the cytoplasms of other species not associated with pistillody. Furthermore, Western blot analysis revealed that the ORF260cra protein was more abundant in the pistillody line than in the normal line. We suggest therefore that orf260(cra) is associated with pistillody induction.

Registration of a Hexaploid Wheat Translocation Line Carrying a Short Segment of Chromosome 5Am including Softness Genes Pina and Pinb from Triticum monococcum

Translocation line T5AmS‐5AS·5AL R#45 (Reg. No. GP‐839, PI 651012) carries the distal region of Triticum monococcum L. chromosome 5AmS translocated into the 5AS chromosome of T. aestivum L. cultivar Chinese Spring. This translocation line was developed in collaboration with the Instituto de Recursos Biológicos, INTA, Argentina, and the University of California, Davis, CA. The distal T. monococcum 5AmS segment in T5AmS‐5AS·5AL R#45 is approximately 8 cM long and carries the active softness genes Pina and Pinb in the genetic background of Chinese Spring. This translocation replaced the deleted Pina and Pinb puroindoline genes from T. aestivum by the functional orthologs from T. monococcum, significantly reducing the hardness of the grain. Translocation line T5AmS‐5AS·5AL R#45 has a shorter segment of T. monococcum chromosome 5Am relative to previous translocations, minimizing linkage drag and the probability of negative effects associated with the introgression of alien genes.

Homoeologous Group-5 Chromosome Effects on the Ability of Durum and Bread Wheats to Produce Haploids

Haploid plants have proved to be useful tools in basic cytogenetic studies. Maize-mediated chromosome elimination provides the method of choice for haploid production in disomic polyploids like wheat (Triticum aestivum L.). Different chromosomes may have varying effects on haploid production. Previously, we studied the effect of the substitution of bread wheat chromosome 5D for 5B on durum wheat's ability to produce haploids via hybridization with maize (Zea mays L.). In the present study, we have investigated the effects of all homoeologous group-5 chromosomes on induction of haploidy in both durum wheat [using the cultivar Langdon and its disomic substitution lines, 5D(5A) and 5D(5B)], and bread wheat (using the cultivar Chinese Spring and its nullisomic-tetrasomic lines, N5A-T5D, N5D-T5A, N5A-T5B, N5B-T5A, N5B-T5D, and N5D-T5B). All these materials were crossed with maize, using the techniques standardized earlier. Although the overall production of haploids was low, the durum disomic substitution 5D(5B) gave a higher yield of haploid plantlets compared with 5D(5A). Among the nullitetras, N5B-T5D and N5B-T5A were the best producers of haploid plantlets, but N5B-T5D was better of these two (χ2 = 5.4297; p = 0.0198). Thus, among these cytogenetic stocks, tetrasomy for chromosome 5D combined with nullisomy for 5B seemed to increase the production of haploids. It would appear that chromosome 5D of bread wheat has genes for haploidy induction and further research along these lines may unravel any such haploidy-inducing genetic mechanism(s).

Mapping barley genes to chromosome arms by transcript profiling of wheat–barley ditelosomic chromosome addition lines

Wheat-barley disomic and ditelosomic chromosome addition lines have been used as genetic tools for a range of applications since their development in the 1980s. In the present study, we used the Affymetrix Barley1 GeneChip for comparative transcript analysis of the barley cultivar Betzes, the wheat cultivar Chinese Spring, and Chinese Spring - Betzes ditelosomic chromosome addition lines to physically map barley genes to their respective chromosome arm locations. We mapped 1257 barley genes to chromosome arms 1HS, 2HS, 2HL, 3HS, 3HL, 4HS, 4HL, 5HS, 5HL, 7HS, and 7HL based on their transcript levels in the ditelosomic addition lines. The number of genes assigned to individual chromosome arms ranged from 24 to 197. We validated the physical locations of the genes through comparison with our previous chromosome-based physical mapping, comparative in silico mapping with rice and wheat, and single feature polymorphism (SFP) analysis. We found our physical mapping of barley genes to chromosome arms to be consistent with our previous physical mapping to whole chromosomes. In silico comparative mapping of barley genes assigned to chromosome arms revealed that the average genomic synteny to wheat and rice chromosome arms was 63.2% and 65.5%, respectively. In the 1257 mapped genes, we identified SFPs in 924 genes between the appropriate ditelosomic line and Chinese Spring that supported physical map placements. We also identified a single small rearrangement event between rice chromosome 9 and barley chromosome 4H that accounts for the loss of synteny for several genes.

Introgression of the reduced height gene Rht10 from the wheat cultivar Ai-Bian 1 into the triticale genotype

A gene determining reduced height, Rht10, from the wheat cultivar Ai-Bian 1 was introgressed into the triticale genotype. Initially, Ai-Bian 1 was crossed with the wheat cultivar Chinese Spring (CS), a carrier of Kr genes, to overcome the uncrossability of this cultivar with rye. Amphidiploids were produced by hybridizing the F2 (CS x Ai-Bian 1) plants displaying reduced height (at the level of Ai-Bian 1) with rye. Free pollination of F1 (F2 of CS x Ai-Bian 1) x Saratovskaya 7 with triticale pollen gave fertile viable hybrids; the majority of hybrids were phenotypically closer to octoploid triticale; however, the variants intermediate between octo- and hexaploids were also present. The height of amphidiploids varied from 40 to 90 cm, and the grain yield per spike amounted on the average to 11.7--24.7 grains, which exceeded essentially this value in F1 plants.

Wheat pollen dispersal under semiarid field conditions: potential outcrossing with Triticum aestivum and Triticum turgidum

Isolation distance is the main barrier to crop-to-crop gene-flow. A 3-year study assessed the maximum potential outcrossing under field conditions between two wheat cultivars (Triticum aestivum L.) and between wheat and durum wheat (Triticum turgidum L. var. durum). Outcrossing was measured by seed set on emasculated recipient plants placed at four sides with different distances from a 3 m × 3 m T. aestivum (cultivar Chinese Spring) pollen source. Frequencies of seed set at 0 m distance were 45% (37–56%) for T. aestivum cultivars and 18% (5–30%) with T. turgidum. These values agree with hybridization in non-limiting pollen conditions measured by manual crosses in greenhouse. The number of pollen grains and the outcrossing frequencies decreased at increasing distances influenced by the prevailing wind direction. Under semiarid conditions of this assay, viable pollen was found 14 m from the pollen source, with a maximum distance of 8 m at which cross-pollination decreases below 1%. Ambient conditions affect pollen viability, hybridization and pollen dispersal. Data presented in this paper emphasize the major role played by environmental conditions in outcrossing. Data obtained in one area may therefore not coincide with the prevailing situation in different locations and climates.