Synthetic Hexaploid Wheat Research Articles

RAPD and SSR based genetic diversity analysis of elite-2 set of synthetic hexaploid wheats.

Synthetic hexaploid wheats are artificially reconstituted hexaploid wheats that possess high genetic variation which could be utilized for the development of new improved wheat varieties. One such group of synthetic wheats is called the Elite-II set of synthetic wheats that are derived from crossing durum wheat with different Aegilops tauschii wheats. In the current study genetic diversity was investigated among 18 Elite-II synthetic hexaploid wheat lines at DNA level. Two types of molecular markers i.e. RAPD and SSR were used for this purpose. Both types of markers proved useful in estimating the overall genetic diversity among these lines. Based on RAPD data range of genetic distances in these lines was from 0 to 100 percent. Seven D-genome specific SSRs were also used to get further estimation of the genetic diversity contributed by Aegilops tauschii parent. On the basis of results obtained it is inferred that the Aegilops tauschi accessions used in the production of these synthetic lines were genetically different and they contributed to the enhancement of genetic variation in the synthetic lines. These results could be helpful for future genome mapping programs. The overall extensive genitive diversity indicates that these lines are good candidates for development of improved wheat varieties by crossing with cultivated wheat varieties.

Evolution of physiological responses to salt stress in hexaploid wheat.

Hexaploid bread wheat (Triticum aestivum L., genome BBAADD) is generally more salt tolerant than its tetraploid wheat progenitor (Triticum turgidum L.). However, little is known about the physiological basis of this trait or about the relative contributions of allohexaploidization and subsequent evolutionary genetic changes on the trait development. Here, we compared the salt tolerance of a synthetic allohexaploid wheat (neo-6x) with its tetraploid (T. turgidum; BBAA) and diploid (Aegilops tauschii; DD) parents, as well as a natural hexaploid bread wheat (nat-6x). We studied 92 morphophysiological traits and analyzed homeologous gene expression of a major salt-tolerance gene High-Affinity K(+) Transporter 1;5 (HKT1;5). We observed that under salt stress, neo-6x exhibited higher fitness than both of its parental genotypes due to inheritance of favorable traits like higher germination rate from the 4x parent and the stronger root Na(+) retention capacity from the 2x parent. Moreover, expression of the D-subgenome HKT1;5 homeolog, which is responsible for Na(+) removal from the xylem vessels, showed an immediate transcriptional reprogramming following allohexaploidization, i.e., from constitutive high basal expression in Ae. tauschii (2x) to salt-induced expression in neo-6x. This phenomenon was also witnessed in the nat-6x. An integrated analysis of 92 traits showed that, under salt-stress conditions, neo-6x resembled more closely the 2x than the 4x parent, suggesting that the salt stress induces enhanced expressivity of the D-subgenome homeologs in the synthetic hexaploid wheat. Collectively, the results suggest that condition-dependent functionalization of the subgenomes might have contributed to the wide-ranging adaptability of natural hexaploid wheat.

Identification of New Sources of Resistance to Septoria Tritici Blotch Caused by Zymoseptoria tritici

AbstractTwenty‐nine synthetic hexaploid wheats (SHWs) were evaluated for resistance to five isolates of Zymoseptoria tritici, a devastating wheat pathogen worldwide. The five Z. tritici isolates varied in their virulence spectra towards wheat genotypes, indicating that they have distinct set of avirulence genes. New isolate‐specific resistances were identified that could be used in wheat breeding programmes. Comparing with the previous studies, the number of specific resistances identified in this study is considerable. Among 150 interactions, 78 isolate‐specific resistances were identified. Interestingly, 21 wheat genotypes showed specific responses to one or more isolates tested. Of these, 12 genotypes were highly resistant to all isolates, indicating that they possess known or novel effective resistance genes. The Stb15 and Stb16/Stb17 are effective resistance genes towards isolates used in this study, indicating that the conferred resistance in these genotypes is due to the presence of either of these genes in combination or individually. Alternatively, they may carry novel broad‐spectrum resistance gene(s) that their identification is of interest. Our data suggest that the presence of complete resistance to various Z. tritici isolates in SHWs justifies the need for more in‐depth research to characterize the likely novel genes.

Genome-wide association for grain morphology in synthetic hexaploid wheats using digital imaging analysis.

BackgroundGrain size and shape greatly influence grain weight which ultimately enhances grain yield in wheat. Digital imaging (DI) based phenomic characterization can capture the three dimensional variation in grain size and shape than has hitherto been possible. In this study, we report the results from using digital imaging of grain size and shape to understand the relationship among different components of this trait, their contribution to enhance grain weight, and to identify genomic regions (QTLs) controlling grain morphology using genome wide association mapping with high density diversity array technology (DArT) and allele-specific markers.ResultsSignificant positive correlations were observed between grain weight and grain size measurements such as grain length (r = 0.43), width, thickness (r = 0.64) and factor from density (FFD) (r = 0.69). A total of 231 synthetic hexaploid wheats (SHWs) were grouped into five different sub-clusters by Bayesian structure analysis using unlinked DArT markers. Linkage disequilibrium (LD) decay was observed among DArT loci > 10 cM distance and approximately 28% marker pairs were in significant LD. In total, 197 loci over 60 chromosomal regions and 79 loci over 31 chromosomal regions were associated with grain morphology by genome wide analysis using general linear model (GLM) and mixed linear model (MLM) approaches, respectively. They were mainly distributed on homoeologous group 2, 3, 6 and 7 chromosomes. Twenty eight marker-trait associations (MTAs) on the D genome chromosomes 2D, 3D and 6D may carry novel alleles with potential to enhance grain weight due to the use of untapped wild accessions of Aegilops tauschii. Statistical simulations showed that favorable alleles for thousand kernel weight (TKW), grain length, width and thickness have additive genetic effects. Allelic variations for known genes controlling grain size and weight, viz. TaCwi-2A, TaSus-2B, TaCKX6-3D and TaGw2-6A, were also associated with TKW, grain width and thickness. In silico functional analysis predicted a range of biological functions for 32 DArT loci and receptor like kinase, known to affect plant development, appeared to be common protein family encoded by several loci responsible for grain size and shape.ConclusionConclusively, we demonstrated the application and integration of multiple approaches including high throughput phenotyping using DI, genome wide association studies (GWAS) and in silico functional analysis of candidate loci to analyze target traits, and identify candidate genomic regions underlying these traits. These approaches provided great opportunity to understand the breeding value of SHWs for improving grain weight and enhanced our deep understanding on molecular genetics of grain weight in wheat.

QTL for resistance to root lesion nematode (Pratylenchus thornei) from a synthetic hexaploid wheat source.

A whole genome average interval mapping approach identified eight QTL associated with P. thornei resistance in a DH population from a cross between the synthetic-derived wheat Sokoll and cultivar Krichauff. Pratylenchus thornei are migratory nematodes that feed and reproduce within the wheat root cortex, causing cell death (lesions) resulting in severe yield reductions globally. Genotypic selection using molecular markers closely linked to Pratylenchus resistance genes will accelerate the development of new resistant cultivars by reducing the need for laborious and expensive resistance phenotyping. A doubled haploid wheat population (150 lines) from a cross between the synthetic-derived cultivar Sokoll (P. thornei resistant) and cultivar Krichauff (P. thornei moderately susceptible) was used to identify quantitative trait loci (QTL) associated with P. thornei resistance. The resistance identified in the glasshouse was validated in a field trial. A genetic map was constructed using Diversity Array Technology and the QTL regions identified were further targeted with simple sequence repeat (SSR) and single-nucleotide polymorphism (SNP) markers. Six significant and two suggestive P. thornei resistance QTL were detected using a whole genome average interval mapping approach. Three QTL were identified on chromosome 2B, two on chromosome 6D, and a single QTL on each of chromosomes 2A, 2D and 5D. The QTL on chromosomes 2BS and 6DS mapped to locations previously identified to be associated with Pratylenchus resistance. Together, the QTL on 2B (QRlnt.sk-2B.1-2B.3) and 6D (QRlnt.sk-6D.1 and 6D.2) explained 30 and 48% of the genotypic variation, respectively. Flanking PCR-based markers based on SSRs and SNPs were developed for the major QTL on 2B and 6D and provide a cost-effective high-throughput tool for marker-assisted breeding of wheat with improved P. thornei resistance.

QTL mapping for physiological maturity in synthetic hexaploid wheat (Triticum aestivum L.) under drought stress

QTL mapping for physiological maturity in synthetic hexaploid wheat (Triticum aestivum L.) under drought stress

Identification of quantitative trait loci for abscisic acid responsiveness in the D-genome of hexaploid wheat

In crop species such as wheat, abiotic stresses and preharvest sprouting reduce grain yield and quality. The plant hormone abscisic acid (ABA) plays important roles in abiotic stress tolerance and seed dormancy. In previous studies, we evaluated ABA responsiveness of 67 Aegilops tauschii accessions and their synthetic hexaploid wheat lines, finding wide variation that was due to the D-genome. In this study, quantitative trait locus (QTL) analysis was performed using an F2 population derived from crosses of highly ABA-responsive and less-responsive synthetic wheat lines. A significant QTL was detected on chromosome 6D, in a similar location to that reported for ABA responsiveness using recombinant inbred lines derived from common wheat cultivars Mironovskaya 808 and Chinese Spring. A comparative map and physiological and expression analyses of the 6D QTL suggested that this locus involved in line differences among wheat synthetics is different from that involved in cultivar differences in common wheat. The common wheat 6D QTL was found to affect seed dormancy and the regulation of cold-responsive/late embryogenesis abundant genes during dehydration. However, in synthetic wheat, we failed to detect any association of ABA responsiveness with abiotic stress tolerance or seed dormancy, at least under our experimental conditions. Development of near-isogenic lines will be important for functional analyses of the synthetic wheat 6D QTL.

Identification of a robust molecular marker for the detection of the stem rust resistance gene Sr45 in common wheat

Fine mapping of the Ug99 effective stem rust resistance gene Sr45 introgressed into common wheat from the D -genome goatgrass Aegilops tauschii. Stem rust resistance gene Sr45, discovered in Aegilops tauschii, the progenitor of the D -genome of wheat, is effective against commercially important Puccinia graminis f. sp. tritici races prevalent in Australia, South Africa and the Ug99 race group. A synthetic hexaploid wheat (RL5406) generated by crossing Ae. tauschii accession RL5289 (carrying Sr45 and the leaf rust resistance gene Lr21) with a tetraploid experimental line 'TetraCanthatch' was previously used as the source in the transfer of these rust resistance genes to other hexaploid cultivars. Previous genetic studies on hexaploid wheats mapped Sr45 on the short arm of chromosome 1D with the following gene order: centromere-Sr45-Sr33-Lr21-telomere. To identify closely linked markers, we fine mapped the Sr45 region in a large mapping population generated by crossing CS1D5406 (disomic substitution line with chromosome 1D of RL5406 substituted for Chinese Spring 1D) with Chinese Spring. Closely linked markers based on 1DS-specific microsatellites, expressed sequence tags and AFLP were useful in the delineation of the Sr45 region. Sequences from an AFLP marker amplified a fragment that was linked with Sr45 at a distance of 0.39cM. The fragment was located in a bacterial artificial chromosome clone of contig (ctg)2981 of the Ae. tauschii accession AL8/78 physical map. A PCR marker derived from clone MI221O11 of ctg2981 amplified 1DS-specific sequence that harboured an 18-bp indel polymorphism that specifically tagged the Sr45 carrying haplotype. This new Sr45 marker can be combined with a previously reported marker for Lr21, which will facilitate selecting Sr45 and Lr21 in breeding populations.

Comparison of Grain Zinc and Iron Concentration between Synthetic Hexaploid Wheats and Their Parents

Deficiencies of iron (Fe) and zinc (Zn) in human food afflict a large proportion of the world’s population. Wheat is a major food source of minerals. One way to enhance bread wheat’s ability to enrich these minerals would be to take advantage of diversity of wild species by creating synthetic hexaploid wheat (SW). In this study, two minerals (Fe and Zn) concentrated in the grain of Aegilops tauschii Coss. (2n = 2x = 14, DD), Triticum turgidum L. (2n = 4x = 28, AABB), and 33 lines of their corresponding SW (2n = 2x = 42, AABBDD) were evaluated. The results showed that Fe concentration was decreased in most of SW lines compared with their parental Aegilops tauschii accessions, while Zn concentration was greatly increased in most of SW lines compared with their parental Aegilops tauschii accessions. Aegilops tauschii had stronger Fe enrichment than Triticum turgidum while they expressed the same ability for Zn enrichment. The genotypic variance based on their physiological performance was analyzed. SW lines showed less genotypic variance of Fe and Zn concentration than Aegilops tauschii. SW lines showed less genotypic variance of Fe concentration than Triticum turgidum L. lines while they had more genotypic variance of Zn concentration than Triticum turgidum L. lines. Regardless of the fact that the traits expressed in wild relatives of wheat may not predict the traits that will be expressed in SW lines derived from them, production of SW could be a powerful method creating genotypes with enhanced trait expression.

Preferential retention of chromosome regions in derived synthetic wheat lines: a source of novel alleles for wheat improvement

Synthetic hexaploid wheats (SHWs) and their synthetic derivative lines (SDLs) are being used as a means of introducing novel genetic variation into bread wheat (BW). Phenotypic information for days to flowering, height, grain weight and grain yield was collected from multiple environments for three SDL families, each with ~50 lines, and their elite BW parents. In general, the SDLs were earlier flowering and taller with larger grain size, but similar grain yield to the BWs. The three SDL families and their SHW and BW parents were genotyped using mapped DArT (diversity arrays technology) markers. Within each SDL family, SHW-specific DArT markers were used to identify SHW-derived chromosomal regions that appeared to be preferentially retained in the SDL families, as determined by retention at frequencies >0.25, the expected frequency for Mendelian segregation. Regions on chromosomes 2BS and 7BL appeared to be preferentially retained in all three SDL families, while regions on chromosomes 1AL, 1BS, 3BS, 5AS, 5BL, and 7AS were preferentially retained in two of the three SDL families. Other regions were preferentially retained in single families only, including some regions located on the D genome. Single-marker regression analysis was performed using the preferentially retained markers and identified markers and regions that were significantly associated with one or more of the four traits measured. Comparative mapping also indicates that these preferentially retained markers and chromosome regions may co-locate with previously identified QTLs for anthesis, height, grain weight and/or grain yield. Therefore, SHWs may contain novel alleles at these loci in these regions for these traits, which may provide a selective advantage to the SDLs. This approach could provide a useful method for identifying chromosomal regions of interest with potentially novel alleles for introgression for further BW improvement.

QTL analysis of genetic loci affecting domestication-related spike characters in common wheat.

Domestication-related changes that govern a spike morphology suitable for seed harvesting in cereals have resulted from mutation and selection of the genes. A synthetic hexaploid wheat (S-6214, genome AABBDD) produced by a cross between durum wheat (AABB) and wild goat grass (DD) showed partial non-domestication-related phenotypes due to genetic effects of the wild goat grass genome. Quantitative trait loci (QTLs) affecting wheat domestication-related spike characters including spike threshability, rachis fragility and spike compactness were investigated in F2 progeny of a cross between Chinese Spring (CS) wheat (AABBDD) and S-6214. Of 15 relevant QTLs identified, eight seemed to be consistent with peaks previously reported in wheat, while four QTL regions were novel. Four QTLs that affected spike threshability were localized to chromosomes 2BS, 2DS, 4D and 5DS. The QTL on 2DS probably represents the tenacious glume gene, Tg-D1. Based on its map position, the QTL located on 2BS coincides with Ppd-B1 and seems to be a homoeolocus of the soft glume gene. Two novel QTLs were detected on 4D and 5DS, and their goat grass alleles increased glume tenacity. Three novel QTLs located on 2DL, 3DL and 4D for rachis fragility were found. Based on the map position, the QTL on 3DL seems different from Br1 and Br2 loci and its CS allele appears to promote the generation of barrel-type diaspores. Three disarticulation types of spikelets were found in F2 individuals: wedge-type, barrel-type and both types. Among eight QTL peaks that governed spike morphology, six, located on 2AS, 2BS, 2DS, 4AL and 5AL, coincided with ones previously reported. A QTL for spike compactness on 5AL was distinct from the Q gene. A novel QTL that controls spike length was detected on 5DL. Complex genetic interactions between genetic background and the action of each gene were suggested.

QTLs for Waterlogging Tolerance at Germination and Seedling Stages in Population of Recombinant Inbred Lines Derived from a Cross Between Synthetic and Cultivated Wheat Genotypes

Waterlogging is a widespread limiting factor for wheat production throughout the world. To identify quantitative trait loci (QTLs) associated with waterlogging tolerance at early stages of growth, survival rate (SR), germination rate index (GRI), leaf chlorophyll content index (CCI), root length index (RLI), plant height index (PHI), root dry weight index (RDWI), shoot dry weight index (SDWI), and total dry weight index (DWI) were assessed using the International Triticeae Mapping Initiative (ITMI) population W7984/Opata85. Significant and positive correlations were detected for all traits in this population except RLI. A total of 32 QTLs were associated with waterlogging tolerance on all chromosomes except 3A, 3D, 4B, 5A, 5D, 6A, and 6D. Some of the QTLs explained large proportions of the phenotypic variance. One of these is the QTL for GRI on 7A, which explained 23.92% of the phenotypic variation. Of them, 22 alleles from the synthetic hexaploid wheat W7984 contributed positively. These results suggested that synthetic hexaploid wheat W7984 is an important genetic resource for waterlogging tolerance in wheat. These alleles conferring waterlogging tolerance at early stages of growth in wheat could be utilized in wheat breeding for improving waterlogging tolerance.

Identification of molecular marker linked to stem rust resistance gene in synthetic hexapolid lines of wheat (Triticum aestvium L.)

In order to enrich the molecular markers linked to wheat stem rust resistance gene and to facilitate the marker-assisted selection in breeding programme, bulk segregation analysis was carried out for gene tagging using F2 segregating population derived from cross between wheat synthetic 4 line with resistant gene (Sr gene carrier) and a common wheat variety Agra local (susceptible to wheat stem rust). This Sr gene carrier synthetic 4 was derived between a cross Triticum turgidum (AABB) and Triticum tauschii (DD). A total of 35 SSR primers covering D and B Genome on the basis of chromosomal location of resistance genes were screened. The SSR marker namely Xgwon106, Xgwm432, Xgwm533 and Xgwm369 have revealed polymorphism among the parents used for study. The SSR Xgwm 533 was found to be putative linked with stem rust resistance gene while the marker Xgwm 389 was co- segregating with Xgwm 533. Marker Xgwm 533 and Xgwm 389 were taken from B genome. Hence, the stem rust resistance gene presumed to be located on 3-B genome of wheat. The use of these markers in combination with others markers could better predict the presence of stem rust resistance gene in wheat genome. Key words: Stem rust (Puccinia graminis f.sp. tritici), molecular tagging, bulk segregation analysis, synthetic hexaploid wheat, SSR primers.

Quality of synthetic hexaploid wheat containing null alleles at Glu-A1 and Glu-B1 loci

Triticum turgidum ssp. dicoccon PI94668 and PI349045 were identified as containing null alleles at Glu-A1 and Glu-B1 loci in previous investigation. Sequencing of the respective HMW-GS genes Ax, Bx, Ay and By in both accessions indicated equal DNA lengths with gene silencing caused by 1 to 4 in-frame stop codon(s) in the open reading frames. Six synthetic hexaploid wheat lines were produced by crossing PI94668 or PI349045 with six Aegilops tauschii by spontaneous chromosome doubling of unreduced gametes. As expected, these amphiploids had three different HMW-GS: Dx 3.1(t) + Dy11(*t), Dx2.1(t) +10(t) and Dx2(t) +Dy12(t) in Glu-D1 but double nulls in Glu-A1 and Glu-B1. Quality tests showed that most quality parameters in two T. turgidum ssp. dicoccon parents were very low due to the lack of HMW-GSs. However, incorporation of HMW-GS from Ae. tauschii in six synthetic hexaploid wheat lines significantly increased most quality related parameters. The potential values of these wheat lines in improving the quality of wheat are discussed.

Selection of the Wheat Genotypes and Related Species with Resistance to Mycosphaerella Graminicola

During 2008-2012, field tests of resistance to Mycosphaerella graminicola (Fuckel) J. Schröt. were conducted on a set of selected wheat varieties and related forms. Various M. graminicola isolates obtained from the Crop Research Institute in Prague were used for infection. Resistance of genotypes to three different isolates was tested in each year with the exception of 2009 and 2010, when identical isolates were used. A variant without artificial infection was used as control. Assorted varieties of winter and spring wheat, synthetic hexaploid wheat (SW), tritordeum (×Tritordeum Ascherson et Graebner), and one sample of haynaldoticum (×Haynaldoticum sardoum Meletti et Onnis) were tested. The aim was to select potential donors of resistance. The average infection rate for the set of spring wheat varieties over the 5 years was 6.7% (con-trol 0.5%), for tritordeum it was 0.3% (control 0.1%), for SW it was 0.7% (control 0.1%), and for haynaldoticum it was 1.7% (control 0.2%). The infection of winter wheat was 18.6% (control 3.8%). High average resistance was found in tritordeum, haynaldoticum, and some forms of SW. Lower resistance was found in conventional wheat varieties. The results were influenced by the degree of isolate virulence, growing season, and developmental stages of plants at the time of inoculation.

Characterization of Triticum timopheevii Zhuk. gene bank accessions for the development of synthetic amphiploid wheat lines

In recent years 56 accessions of Triticum timopheevii Zhuk. (2n=4x=28, AtAtGG) were characterized for the main phenotypic and resistance characters. Among these accessions 38 originated from the base species together with subspecies and varietas forms thereof, and 18 belong to the subspecies armeniacum group. After the evaluation of field assessment data gathered over 12 years, the most promising 11 accessions were selected for a crossability trial with cultivated einkorn. As a result of this trial, the accession with the highest seed set (Acc. No.: MVGB845) was chosen for the development of a new synthetic amphiploid using the same semi-dwarf line of diploid cultivated einkorn (Triticum monococcum L. ssp. monococcum 1T-1, 2n=2x=14, AmAm) as in the crossability trial. This einkorn line was bred in Martonvásár, and has both outstanding resistance and other promising phenotypic and agronomic characters.After crossing the accession MVGB845 with 1T-1, the triploid hybrids were treated with colchicine to obtain fertile progenies with a doubled genome. The newly developed synthetic hexaploid wheat breeding stock (named Triticum timococcum Kost., 2n=6x=42, AtAtGGAmAm) could ease the introgression of valuable resistance genes into bread wheat at the hexaploid level (bridge-crossing).The aim of the present research was to redevelop Triticum timococcum based on a detailed characterization of gene bank accessions, and to introduce this new material into wheat breeding.

Conditional QTL mapping for waterlogging tolerance in two RILs populations of wheat

Waterlogging is a widespread limiting factor for wheat production throughout the world, specially irrigated and high rainfall environments. Only few studies reported QTLs for waterlogging tolerance. To identify quantitative trait loci (QTLs) for waterlogging tolerance, root dry weight index (RDWI), shoot dry weight index (SDWI), total dry weight index (TDWI) were measured at seedling stage in two unrelated recombinant inbred lines (RILs) populations. These populations were International Triticeae Mapping Initiative (ITMI) population ‘W7984 / Opata85’, and ‘SHW-L1 × Chuanmai 32’ (SC) population. Conditional QTL mapping and unconditional QTL mapping were studied to dissect the genetic relationship between TDWI and its components of SDWI and TDWI. Total of 36 QTLs for waterlogging tolerance in ITMI population and 10 QTLs in SC population were identified in present study. Of them, 17 alleles from synthetic hexaploid wheat ‘W7984’ and 3 alleles from synthetic hexaploid wheat ‘SHW-L1’ contribute positively to waterlogging tolerance. Combinations of conditional and unconditional mapping methods indicate that SDWI showed tighter genetic correlation with TDWI than RDWI. This QTL identification study and dissection provide theoretical basis and application foundation to Marker-assisted selection (MAS) of waterlogging tolerance improvement in wheat.

Production of hexaploid triticale by a synthetic hexaploid wheat-rye hybrid method

Hexaploid triticale, including its primary and secondary forms, is an important forage crop and a promising energy plant. Primary forms are usually developed by crossing Triticum turgidum L. with rye, with secondary forms obtained by crossing primary hexaploid triticale and/or hexaploid wheat with octoploid triticale. In this study, we developed an effective method for production of hexaploid triticale via hybridization of synthetic hexaploid wheat (SHW) with rye. The three employed SHW lines were derived from hybridization of T. turgidum with Aegilops tauschii Cosson, and inherited meiotic restitution genes, which can promote the formation of functional gametes in haploid status, from their T. turgidum parents. Although the resulting tetraploid F-1 hybrids with rye (genome ABDR) produced amphiploids (octoploid triticale) and partial amphiploids, the final hybrid products obtained through fertility selection over several generations were hexaploids. These hexaploids were the result of preferential elimination of D-genome chromosomes. In addition to complete hexaploid triticale with 28 intact A/B and 14 intact R chromosomes, we obtained hexaploid triticales with other chromosome constitutions, including monosomic, substitution, and translocation lines. Chromosomes 2D and 5D from the wild species A. tauschii were incorporated into the hexaploid triticales. Out of eight analyzed stable lines derived from three different SHW-L1/rye F-1 plants, we observed four lines with small-fragment translocations between wheat and rye chromosomes. Rapid production of hexaploid triticales using this method involves two factors: (1) hybridization between hexaploid wheat with a meiotic restitution gene(s) and rye and (2) selection for good fertility during F-3 and subsequent generations.

Strategy for exploiting exotic germplasm using genetic, morphological, and environmental diversity: the Aegilops tauschii Coss. example

Hexaploid bread wheat evolved from a rare hybridisation, which resulted in a loss of genetic diversity in the wheat D-genome with respect to the ancestral donor, Aegilops tauschii. Novel genetic variation can be introduced into modern wheat by recreating the above hybridisation; however, the information associated with the Ae. tauschii accessions in germplasm collections is limited, making rational selection of accessions into a re-synthesis programme difficult. We describe methodologies to identify novel diversity from Ae. tauschii accessions that combines Bayesian analysis of genotypic data, sub-species diversity and geographic information that summarises variation in climate and habitat at the collection point for each accession. Comparisons were made between diversity discovered amongst a panel of Ae. tauschii accessions, bread wheat varieties and lines from the CIMMYT synthetic hexaploid wheat programme. The selection of Ae. tauschii accessions based on differing approaches had significant effect on diversity within each set. Our results suggest that a strategy that combines several criteria will be most effective in maximising the sampled variation across multiple parameters. The analysis of multiple layers of variation in ex situ Ae. tauschii collections allows for an informed and rational approach to the inclusion of wild relatives into crop breeding programmes.

Short, natural, and extended photoperiod response in BC2F4 lines of bread wheat with different Photoperiod-1 (Ppd-1) alleles

Flowering is a critical period in the life cycle of flowering plant species, resulting in an irreversible commitment of significant resources. Wheat is photoperiod sensitive, flowering only when daylength surpasses a critical length; however, photoperiod insensitivity (PI) has been selected by plant breeders for >40 years to enhance yield in certain environments. Control of flowering time has been greatly facilitated by the development of molecular markers for the Photoperiod-1 (Ppd-1) homeoloci, on the group 2 chromosomes. In the current study, an allelic series of BC2F4 lines in the winter wheat cultivars 'Robigus' and 'Alchemy' was developed to elucidate the influence on flowering of eight gene variants from the B- and D-genomes of bread wheat and the A-genome of durum wheat. Allele effects were tested in short, natural, and extended photoperiods in the field and controlled environments. Across genetic background and treatment, the D-genome PI allele, Ppd-D1a, had a more potent effect on reducing flowering time than Ppd-B1a. However, there was significant donor allele effect for both Ppd-D1a and Ppd-B1a, suggesting the presence of linked modifier genes and/or additional sources of latent sensitivity. Development of Ppd-A1a BC2F4 lines derived from synthetic hexaploid wheat provided an opportunity to compare directly the flowering time effect of the A-genome allele from durum with the B- and D-genome variants from bread wheat for the first time. Analyses indicated that the reducing effect of Ppd-A1a is comparable with that of Ppd-D1a, confirming it as a useful alternative source of PI.