Assessment of genetic diversity among Syrian durum (<Emphasis Type="Italic">Triticum</Emphasis> ssp. <Emphasis Type="Italic">durum</Emphasis>) and bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) using SSR markers

Genetic diversity among 49 wheat varieties (37 durum and 12 bread wheat) was assayed using 32 microsatellites representing 34 loci covering almost the whole wheat genome. The polymorphic information content (PIC) across the tested loci ranged from 0 to 0.88 with average values of 0.57 and 0.65 for durum and bread wheat respectively. B-genome had the highest mean number of alleles (10.91) followed by A genome (8.3) whereas D genome had the lowest number (4.73). The correlation between PIC and allele number was significant in all genome groups accounting for 0.87, 074 and 0.84 for A, B and D genomes respectively, and over all genomes, the correlation was higher in tetraploid (0.8) than in hexaploid wheat varieties (0.5). The cluster analysis discriminated all varieties and clearly divided the two ploidy levels into two separate clusters that reflect the differences in genetic diversity within each cluster. This study demonstrates that microsatellites markers have unique advantages compared to other molecular and biochemical fingerprinting techniques in revealing the genetic diversity in Syrian wheat varieties that is crucial for wheat improvement.     

Asymmetric somatic hybridization between wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>) and <Emphasis Type="Italic">Avena sativa</Emphasis> L.

Protoplasts from cell suspensions of young-embryo-derived calli, whichwere non- regenerable for long-term subculture and protoplasts from embryogenic calli with the regeneration capacity of 75% of the same wheat Jinan 177, were mixed as recipient. Protoplasts from embryogenic calli of Avena sativa (with the regeneration capacity of less than 10%) irradiated with UV at an intensity of300 μW/cm2 for 30 s, 1 min, 2 min, 3 min, 5 min were used as the donor. Protoplasts of the recipient and the donor were fused by PEG method. Many calli and normal green plants were regenerated at high frequency, and were verified as somatic hybrids by chromosome counting, isozyme, 5S rDNA spacer sequence analysis and GISH (genomic in situ hybridization). Fusion combination between protoplasts either from the cell suspensions or from the calli and UV-treated Avena sativa protoplasts could not regenerate green plants.     

Chromosomal localization of aromatic alcohol dehydrogenase fast-migrating isoenzyme <Emphasis Type="Italic">Aadh1F</Emphasis> (<Emphasis Type="Italic">CAD1-F</Emphasis>) gene in <Emphasis Type="Italic">Triticum aestivum</Emphasis> L. bread wheat

Differences in isoenzyme pattern of aromatic alcohol dehydrogenase, NADP-AADH or CAD, were found in the Triticum aestivum L. winter bread wheat cultivars by the method of electrophoresis in the starch gel. A standard three-component spectrum is present in the cv. Zitnica (former Yugoslavia); additional fact-migrating isoenzymes appear in the cv. Novosibirskaya 9 (Institute of Cytology and Genetics, Siberian Branch, Russian Academy of Sciences, Russia). The presence of fast-migrating CAD isoenzymes is designated as FF phenotype; their absence, as 00 phenotype. Hybridological analysis was carried out; the excess of “null” genotypes was found in F₂ progenies. Hybridization with nulli-tetrasomic lines of the chromosomes of the fifth homeologous group was conducted for the gene localization. The segregation analysis demonstrated the most probable localization of the CAD1-F gene in the chromosome 5A. The plants with FF and 00 genotypes differed in a number of chemical and anatomical traits, as well as in grain productivity. The results obtained are discussed in connection with the function of this enzyme in the wheat plant tissues.     

Expression and functional analysis of <Emphasis Type="Italic">TaASY1</Emphasis> during meiosis of bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>)

Background  

Pairing and synapsis of homologous chromosomes is required for normal chromosome segregation and the exchange of genetic material via recombination during meiosis. Synapsis is complete at pachytene following the formation of a tri-partite proteinaceous structure known as the synaptonemal complex (SC). In yeast, HOP1 is essential for formation of the SC, and localises along chromosome axes during prophase I. Homologues in Arabidopsis (AtASY1), Brassica (BoASY1) and rice (OsPAIR2) have been isolated through analysis of mutants that display decreased fertility due to severely reduced synapsis of homologous chromosomes. Analysis of these genes has indicated that they play a similar role to HOP1 in pairing and formation of the SC through localisation to axial/lateral elements of the SC.     

Structure and expression of the <Emphasis Type="Italic">TaGW7</Emphasis> in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

OsGW7 (also known as OsGL7) is homologous to the Arabidopsis thaliana gene that encodes LONGIFOLIA protein, which regulates cell elongation, and is involved in regulating grain length in rice. However, our knowledge on its ortholog in wheat, TaGW7, is limited. In this study, we identified and mapped TaGW7 in wheat, characterized its nucleotide and protein structures, predicted the cis-elements of its promoter, and analysed its expression patterns. The GW7 orthologs in barley (HvGW7), rice (OsGW7), and Brachypodium distachyon (BdGW7) were also identified for comparative analyses. TaGW7 mapped onto the short arms of group 2 chromosomes (2AS, 2BS, and 2DS). Multiple alignments indicated GW7 possesses five exons and four introns in all but two of the species analysed. An exon–intron junction composed of introns 3–4 and exons 4–5 was highly conserved. GW7 has a conserved domain (DUF 4378) and two neighbouring low complexity regions. GW7 was mainly expressed in wheat spikes and stems, in barley seedling crowns, and in rice anthers and embryo-sacs during early development. Drought and heat significantly increased and decreased GW7 expression in wheat, respectively. In barley, GW7 was significantly down-regulated in paleae and awns but up-regulated in seeds under drought treatment and down-regulated under Fusarium and stem rust inoculation. In rice, OsGW7 expression differed significantly under drought treatments. Collectively, these results provide insights into GW7 structure and expression in wheat, barley and rice. The GW7 sequence structure and expression data are the foundation for manipulating GW7 and uncovering its roles in plants.     

The parameters of grain filling and yield components in common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) and durum wheat (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L. var. <Emphasis Type="Italic">durum</Emphasis>)

Final grain dry weight, a component of yield in wheat, is dependent on the duration and the rate of grain filling. The purpose of the study was to compare the grain filling patterns between common wheat, (Triticum aestivum L.), and durum wheat, (Triticum turgidum L. var. durum), and investigate relationships among grain filling parameters, yield components and the yield itself. The most important variables in differentiating among grain filling curves were final grain dry weight (W) for common wheat genotypes and grain filling rate (R) for durum wheat genotypes; however, in all cases the sets of variables important in differentiating among grain filling curves were extended to either two or all three parameters. Furthermore, in one out of three environmental conditions and for both groups of genotypes, the most important parameter in the set was grain filling duration (T). It indicates significant impact of environmental conditions on dry matter accumulation and the mutual effect of grain filling duration and its rate on the final grain dry weight. The medium early anthesis date could be associated with further grain weight and yield improvements in wheat. Grain filling of earlier genotypes occurs in more temperate environments, which provides enough time for gradual grain fill and avoids the extremes of temperature and the stress of dry conditions.     

Evidence of intralocus recombination at the <Emphasis Type="Italic">Glu-3</Emphasis> loci in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Key message

Recombination at the Glu-3 loci was identified, and strong genetic linkage was observed only between the amplicons representing i-type and s-type genes located, respectively, at the Glu-A3 and Glu-B3 loci.

Abstract

The low-molecular weight glutenin subunits (LMW-GSs) are one of the major components of wheat seed storage proteins and play a critical role in the determination of wheat end-use quality. The genes encoding this class of proteins are located at the orthologous Glu-3 loci (Glu-A3, Glu-B3, and Glu-D3). Due to the complexity of these chromosomal regions and the high sequence similarity between different LMW-GS genes, their organization and recombination characteristics are still incompletely understood. This study examined intralocus recombination at the Glu-3 loci in two recombinant inbred line (RIL) and one doubled haploid (DH) population, all segregating for the Glu-A3, Glu-B3, and Glu-D3 loci. The analysis was conducted using a gene marker system that consists of the amplification of the complete set of the LMW-GS genes and their visualization by capillary electrophoresis. Recombinant marker haplotypes were detected in all three populations with different recombination rates depending on the locus and the population. No recombination was observed between the amplicons representing i-type and s-type LMW-GS genes located, respectively, at the Glu-A3 and Glu-B3 loci, indicating tight linkage between these genes. Results of this study contribute to better understanding the genetic linkage and recombination between different LMW-GS genes, the structure of the Glu-3 loci, and the development of more specific molecular markers that better represent the genetic diversity of these loci. In this way, a more precise analysis of the contribution of various LMW-GSs to end-use quality of wheat may be achieved.

     

Features of alloplasmic wheat-barley substitution and addition lines (<Emphasis Type="Italic">Hordeum marinum</Emphasis> subsp. <Emphasis Type="Italic">gussoneanum</Emphasis>)-<Emphasis Type="Italic">Triticum aestivum</Emphasis>

Two alloplasmic wheat-barley substitution lines were studied: a line replaced at three pairs of chromosomes 1H ^mar (1B), 5H ^mar (5D), and 7H ^mar (7D), and the disomic-substituted line 7H ^mar (7D). The lines were constructed on the basis of individual plants from BC₁F₈ and BC₂F₆ progeny of barley-wheat hybrids (H. marinum subsp. gussoneanum Hudson (= H. geniculatum All.) (2n = 28) × T. aestivum L.) (2n = 42) (Pyrotrix 28), respectively. Moreover, the alloplasmic wheat-barley ditelosomic addition line 7HL ^mar isolated among plants from the BC₁F₆ progeny of a barley-wheat amphiploid was studied, which in this work corresponds to BC₂F₁₀ and BC₂F₁₁ progeny. It was ascertained that when grown in the field, these alloplasmic lines manifest stable self-fertility. Plants of the given lines are characterized by low height, shortened ears, the fewer number of stems and ears, and of spikelets in the ear, by decreased grain productivity and weight of 1000 grains, in comparison with the common wheat cultivar Pyrotrix 28. The inhibition of trait expression in alloplasmic wheat-barley substitution and addition lines may be connected not only with the influence of wild barley chromosomes functioning in the genotypic environment of common wheat, but also with the effect of the barley cytoplasm. The alloplasmic line with substitution of chromosomes 1H ^mar (1B), 5H ^mar (5D), and 7H ^mar (7D) or the alloplasmic line 5HL ^mar with ditelosomic addition have, in comparison with the common wheat cultivar Pyrotrix 28, an increased grain protein content, which is explained by the effect of wild barley H. marinum subsp. gussoneanum chromosomes.     

<Emphasis Type="Italic">STAYGREEN</Emphasis> (<Emphasis Type="Italic">CsSGR</Emphasis>) is a candidate for the anthracnose (<Emphasis Type="Italic">Colletotrichum orbiculare</Emphasis>) resistance locus <Emphasis Type="Italic">cla</Emphasis> in Gy14 cucumber

Key message

Map-based cloning identified a candidate gene for resistance to the anthracnose fungal pathogen Colletotrichum orbiculare in cucumber, which reveals a novel function for the highly conserved STAYGREEN family genes for host disease resistance in plants.

Abstract

Colletotrichum orbiculare is a hemibiotrophic fungal pathogen that causes anthracnose disease in cucumber and other cucurbit crops. No host resistance genes against the anthracnose pathogens have been cloned in crop plants. Here, we reported fine mapping and cloning of a resistance gene to the race 1 anthracnose pathogen in cucumber inbred lines Gy14 and WI 2757. Phenotypic and QTL analysis in multiple populations revealed that a single recessive gene, cla, was underlying anthracnose resistance in both lines, but WI2757 carried an additional minor-effect QTL. Fine mapping using 150 Gy14?×?9930 recombinant inbred lines and 1043 F₂ individuals delimited the cla locus into a 32 kb region in cucumber Chromosome 5 with three predicted genes. Multiple lines of evidence suggested that the cucumber STAYGREEN (CsSGR) gene is a candidate for the anthracnose resistance locus. A single nucleotide mutation in the third exon of CsSGR resulted in the substitution of Glutamine in 9930 to Arginine in Gy14 in CsSGR protein which seems responsible for the differential anthracnose inoculation responses between Gy14 and 9930. Quantitative real-time PCR analysis indicated that CsSGR was significantly upregulated upon anthracnose pathogen inoculation in the susceptible 9930, while its expression was much lower in the resistant Gy14. Investigation of allelic diversities in natural cucumber populations revealed that the resistance allele in almost all improved cultivars or breeding lines of the U.S. origin was derived from PI 197087. This work reveals an unknown function for the highly conserved STAYGREEN (SGR) family genes for host disease resistance in plants.

     

Genetic architecture of seed longevity in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

The deterioration in the quality of ex situ conserved seed over time reflects a combination of both physical and chemical changes. Intraspecific variation for longevity is, at least in part, under genetic control. Here, the grain of 183 bread wheat accessions maintained under low-temperature storage at the IPK-Gatersleben genebank over some decades have been tested for their viability, along with that of fresh grain subjected to two standard artificial ageing procedures. A phenotype–genotype association analysis, conducted to reveal the genetic basis of the observed variation between accessions, implicated many regions of the genome, underling the genetic complexity of the trait. Some, but not all, of these regions were associated with variation for both natural and experimental ageing, implying some non-congruency obtains between these two forms of testing for longevity. The genes underlying longevity appear to be independent of known genes determining dormancy and pre-harvest sprouting.     

A high-density microsatellite consensus map for bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

A microsatellite consensus map was constructed by joining four independent genetic maps of bread wheat. Three of the maps were F₁-derived, doubled-haploid line populations and the fourth population was Synthetic × Opata, an F₆-derived, recombinant-inbred line population. Microsatellite markers from different research groups including the Wheat Microsatellite Consortium, GWM, GDM, CFA, CFD, and BARC were used in the mapping. A sufficient number of common loci between genetic maps, ranging from 52 to 232 loci, were mapped on different populations to facilitate joining the maps. Four genetic maps were developed using MapMaker V3.0 and JoinMap V3.0. The software CMap, a comparative map viewer, was used to align the four maps and identify potential errors based on consensus. JoinMap V3.0 was used to calculate marker order and recombination distances based on the consensus of the four maps. A total of 1,235 microsatellite loci were mapped, covering 2,569 cM, giving an average interval distance of 2.2 cM. This consensus map represents the highest-density public microsatellite map of wheat and is accompanied by an allele database showing the parent allele sizes for every marker mapped. This enables users to predict allele sizes in new breeding populations and develop molecular breeding and genomics strategies.Electronic Supplementary Material Supplementary material is available for this article at     

Flow karyotyping and chromosome sorting in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Previously, we reported on the development of procedures for chromosome analysis and sorting using flow cytometry (flow cytogenetics) in bread wheat. That study indicated the possibility of sorting large quantities of intact chromosomes, and their suitability for analysis at the molecular level. However, due to the lack of sufficient differences in size between individual chromosomes, only chromosome 3B could be sorted into a high-purity fraction. The present study aimed to identify wheat stocks that could be used to sort other chromosomes. An analysis of 58 varieties and landraces demonstrated a remarkable reproducibility and sensitivity of flow cytometry for the detection of numerical and structural chromosome changes. Changes in flow karyotype, diagnostic for the presence of the 1BL·1RS translocation, have been found and lines from which translocation chromosomes 5BL·7BL and 4AL·4AS-5BL could be sorted have been identified. Furthermore, wheat lines have been identified which can be used for sorting chromosomes 4B, 4D, 5D and 6D. The ability to sort any single arm of the hexaploid wheat karyotype, either in the form of a ditelosome or a isochromosome, has also been demonstrated. Thus, although originally considered recalcitrant, wheat seems to be suitable for the development of flow cytogenetics and the technology can be applied to the physical mapping of DNA sequences, the targeted isolation of molecular makers and the construction of chromosome- and arm-specific DNA libraries. These approaches should facilitate the analysis of the complex genome of hexaploid bread wheat.     

Salt stress reveals differential physiological,biochemical and molecular responses in <Emphasis Type="Italic">T. monococcum</Emphasis> and <Emphasis Type="Italic">T. durum</Emphasis> wheat genotypes

Salt stress responses implicate a complex mechanism and differ from plant species to another. In this study, we analyzed the physiological, biochemical and molecular responses to salt stress of the diploid wheat (T. monococcum) and compared to the tetraploid wheat (T. durum). Our results showed that the diploid wheat cultivar (cv. Turkey) is relatively tolerant to different salt stress conditions than the tetraploid wheat cultivar (cv. Om Rabia3). This tolerance was manifested by significant germination, plant growth and uptake of water generating cell turgor and development. Moreover, total chlorophyll content was higher in the diploid wheat than that in the tetraploid wheat. The Na⁺ content in leaf blade of the cv. Om Rabia3 was significantly higher than that of the cv. Turkey, suggesting that the diploid cultivar accumulates less toxic sodium in the photosynthetic tissues. This mechanism could be explained by the recirculation of the toxic ions Na⁺ into the xylem sap by SOS1 protein, which coordinates with HKT-like proteins to reduce the accumulation of Na⁺ ions in leaf blade. Interestingly, the expression of the three genes SOS1, HKT and NHX was enhanced under salinity especially in leaf blade of the cv. Turkey. Moreover, this wheat cultivar induced the antioxidative enzymes CAT and SOD activity more efficiently than the other cultivar.     

Over-expressing a UDP-glucosyltransferase gene (<Emphasis Type="Italic">Ta-UGT</Emphasis><Subscript><Emphasis Type="Italic">3</Emphasis></Subscript>) enhances <Emphasis Type="Italic">Fusarium</Emphasis> Head Blight resistance of wheat

Wheat Fusarium Head Blight (FHB), mainly caused by Fusarium graminearum (F.g), is a destructive fungal disease worldwide. FHB can not only cause considerable reduction in yield, but more seriously, can contaminate grain by trichothecene toxins released by the fungus. Here, we report new insights into the function and underlying mechanisms of a UDP-glycosyltransferase gene, Ta-UGT ₃ , that is involved in FHB resistance in wheat. In our previous study, Ta-UGT ₃ was found to enhance host tolerance against deoxynivalenol (DON) in Arabidopsis. In this study, four transgenic lines over-expressing Ta-UGT ₃ in a FHB highly susceptible wheat variety, Alondra’s, were obtained and characterized. 3 years of assays using single floret inoculation with F.g indicated that all four transgenic lines exhibited significantly enhanced type II resistance to FHB and less DON accumulation in the grains compared to the untransformed control. Histological observation using GFP labelled F.g was in agreement with the above test results since over-expression of Ta-UGT ₃ dramatically inhibited expansion of F.g. To explore the putative mechanism of resistance mediated by Ta-UGT ₃ , microarray analysis, qRT-PCR and hormone measurements were performed. Microarray analysis showed that DON up-regulated genes, such as TaNPR1, in the susceptible control, and down-regulated genes in F.g inoculated transgenic lines, while qRT-PCR showed that some defence related genes were up-regulated in F.g inoculated transgenic lines. Ta-UGT ₃ over-expression also changed the contents of the endogenous hormones SA and JA in the spikes. These data suggest that Ta-UGT ₃ positively regulates the defence responses to F.g, perhaps by regulating defence-related and DON-induced downstream genes.     

Allelic variations in <Emphasis Type="Italic">Glu-1</Emphasis> and <Emphasis Type="Italic">Glu-3</Emphasis> loci of historical and modern Iranian bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivars

Proline and glutamine-rich wheat seed endosperm proteins are collectively referred to as prolamins. They are comprised of HMW-GSs, LMW-GSs and gliadins. HMW-GSs are major determinants of gluten elasticity and LMW-GSs considerably affect dough extensibility and maximum dough resistance. The inheritance of glutenin subunits follows Mendelian genetics with multiple alleles in each locus. Identification of the banding patterns of glutenin subunits could be used as an estimate for screening high quality wheat germplasm. Here, by means of a two-step 1D-SDS-PAGE procedure, we identified the allelic variations in high and low-molecular-weight glutenin subunits in 65 hexaploid wheat (Triticum aestivum L.) cultivars representing a historical trend in the cultivars introduced or released in Iran from the years 1940 to 1990. Distinct alleles 17 and 19 were detected for Glu-1 and Glu-3 loci, respectively. The allelic frequencies at the Glu-1 loci demonstrated unimodal distributions. At Glu-A1, Glu-B1 and Glu-D1, we found that the most frequent alleles were the null, 7 + 8, 2 + 12 alleles, respectively, in Iranian wheat cultivars. In contrast, Glu-3 loci showed bimodal or trimodal distributions. At Glu-A3, themost frequent alleles were c and e. At Glu-B3 the most frequent alleles were a, b and c. At Glu-D3 locus, the alleles b and a, were the most and the second most frequent alleles in Iranian wheat cultivars. This led to a significantly higher Nei coefficient of genetic variations in Glu-3 loci (0.756) as compared to Glu-1 loci (0.547). At Glu-3 loci, we observed relatively high quality alleles in Glu-A3 and Glu-D3 loci and low quality alleles at Glu-B3 locus.     

Genome-wide association mapping of resistance to eyespot disease (<Emphasis Type="Italic">Pseudocercosporella herpotrichoides</Emphasis>) in European winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) and fine-mapping of <Emphasis Type="Italic">Pch1</Emphasis>

Key message

Genotypes with recombination events in the Triticum ventricosum introgression on chromosome 7D allowed to fine-map resistance gene Pch1, the main source of eyespot resistance in European winter wheat cultivars.

Abstract

Eyespot (also called Strawbreaker) is a common and serious fungal disease of winter wheat caused by the necrotrophic fungi Oculimacula yallundae and Oculimacula acuformis (former name Pseudocercosporella herpotrichoides). A genome-wide association study (GWAS) for eyespot was performed with 732 microsatellite markers (SSR) and 7761 mapped SNP markers derived from the 90 K iSELECT wheat array using a panel of 168 European winter wheat varieties as well as three spring wheat varieties and phenotypic evaluation of eyespot in field tests in three environments. Best linear unbiased estimations (BLUEs) were calculated across all trials and ranged from 1.20 (most resistant) to 5.73 (most susceptible) with an average value of 4.24 and a heritability of H ² = 0.91. A total of 108 SSR and 235 SNP marker–trait associations (MTAs) were identified by considering associations with a ?log₁₀ (P value) ≥3.0. Significant MTAs for eyespot-score BLUEs were found on chromosomes 1D, 2A, 2D, 3D, 5A, 5D, 6A, 7A and 7D for the SSR markers and chromosomes 1B, 2A, 2B, 2D, 3B and 7D for the SNP markers. For 18 varieties (10.5%), a highly resistant phenotype was detected that was linked to the presence of the resistance gene Pch1 on chromosome 7D. The identification of genotypes with recombination events in the introgressed genomic segment from Triticum ventricosum harboring the Pch1 resistance gene on chromosome 7DL allowed the fine-mapping of this gene using additional SNP markers and a potential candidate gene Traes_7DL_973A33763 coding for a CC-NBS-LRR class protein was identified.

     

Genetic mapping of stem rust resistance gene <Emphasis Type="Italic">Sr13</Emphasis> in tetraploid wheat (<Emphasis Type="Italic">Triticum turgidum</Emphasis> ssp. <Emphasis Type="Italic">durum</Emphasis> L.)

Wheat stem rust caused by Puccinia graminis f. sp. tritici, can cause significant yield losses. To combat the disease, breeders have deployed resistance genes both individually and in combinations to increase resistance durability. A new race, TTKSK (Ug99), identified in Uganda in 1999 is virulent on most of the resistance genes currently deployed, and is rapidly spreading to other regions of the world. It is therefore important to identify, map, and deploy resistance genes that are still effective against TTKSK. One of these resistance genes, Sr13, was previously assigned to the long arm of chromosome 6A, but its precise map location was not known. In this study, the genome location of Sr13 was determined in four tetraploid wheat (T. turgidum ssp. durum) mapping populations involving the TTKSK resistant varieties Kronos, Kofa, Medora and Sceptre. Our results showed that resistance was linked to common molecular markers in all four populations, suggesting that these durum lines carry the same resistance gene. Based on its chromosome location and infection types against different races of stem rust, this gene is postulated to be Sr13. Sr13 was mapped within a 1.2–2.8 cM interval (depending on the mapping population) between EST markers CD926040 and BE471213, which corresponds to a 285-kb region in rice chromosome 2, and a 3.1-Mb region in Brachypodium chromosome 3. These maps will be the foundation for developing high-density maps, identifying diagnostic markers, and positional cloning of Sr13.     

Comparative analysis of the differential regeneration response of various genotypes of <Emphasis Type="Italic">Triticum aestivum</Emphasis>, <Emphasis Type="Italic">Triticum durum</Emphasis> and <Emphasis Type="Italic">Triticum dicoccum</Emphasis>

An efficient genotype independent, in vitro regeneration system was developed for nine popular Indian wheat cultivars, three each of Triticum aestivum L. viz., CPAN1676, HD2329 and PBW343, Triticum durum Desf. viz., PDW215, PDW233 and WH896, and Triticum dicoccum Schrank. Schubl. viz., DDK1001, DDK1025 and DDK1029, by manipulating the concentration and time of exposure to the growth regulator, thidiazuron (TDZ). A total of 18 (for immature inflorescence and embryo explant) and six (for mature embryo explant) different combinations of growth regulators were tried for callusing and regeneration, respectively. Media combination with low concentration of TDZ (2.2 μM) in combination to auxin and/or cytokinin (depending upon culture stage), was found to be effective for immature and mature explants. Compact, nodular and highly embryogenic calli were obtained by using immature embryo, immature inflorescence and mature embryo explants, and regeneration frequency up to 25 shoots/explant with an overall 80% regeneration was achieved. Comparable regeneration frequency was achieved for mature embryo explants. No separate hormone combination for rooting was required and plantlets ready to transfer to soil could be obtained in a short period of 8–10 weeks. This protocol can be used for raising transgenic plants for functional genomics analysis of agronomically important traits in the three species of wheat.     

Overexpression of <Emphasis Type="Italic">AtHDG11</Emphasis> enhanced drought tolerance in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Drought is one of the major abiotic stresses restricting the yield of wheat (Triticum aestivum L.). Breeding wheat varieties with drought tolerance is an effective and durable way to fight against drought. Here we reported introduction of AtHDG11 into wheat via Agrobacterium-mediated transformation and analyzed the morphological and physiological characteristics of T2 generation transgenic lines under drought stress. With drought treatment for 30 days, transgenic plants showed significantly improved drought tolerance. Compared with controls, the transgenic lines displayed lower stomatal density, lower water loss rate, more proline accumulation and increased activities of catalase and superoxide dismutase. Without irrigation after booting stage, the photosynthetic parameters, such as net photosynthesis rate, water use efficiency and efficiency of excitation energy, were increased in transgenic lines, while transpiration rate was decreased. Moreover, the kernel yield of transgenic lines was also improved under drought condition. Taken together, our data demonstrate that AtHDG11 has great potential in genetic improvement of drought tolerance of wheat.