Hexaploid Wheat Cultivars Research Articles

Transient changes in wheat endosperm polymeric proteins during the later stages of grain development

End-use quality of wheat depends mainly on the composition of the storage proteins. These proteins undergo changes during grain development. This study was carried out to examine modifications in the polymeric protein fraction at different days post anthesis (DPA) and to determine whether these changes are cultivar dependent. Endosperm proteins of three hexaploid wheat cultivars harvested at different stages of maturity and extracted sequentially from distal half kernels showed quantitative and qualitative changes when separated in a 7.5–9.0% gradient polyacrylamide gel system. Sudden qualitative changes were observed at a later stage of seed development (35 DPA) in all tested cultivars. Most qualitative changes occurred in proteins of molecular weight 60–90 kDa and least in proteins above 90 kDa. An intense 60-kDa band appeared in the 35-DPA sample of Columbus; this band faded as the grain approached full maturity (40 DPA). Key words: Developmental changes, electrophoresis, gluten proteins, seed ripening

Attempted transfer of leaf rust resistance from Triticum monococcum and durum wheat to hexaploid wheat

An attempt was made to transfer leaf rust resistance from diploid Triticum monococcum, an autotetraploid of the T. monococcum accession, and durum cultivars Medora and Stewart to hexaploid wheat cultivars Thatcher and RL6058 (Lr34). A single gene for leaf rust resistance which was the same as Lr33 (RL6057) was transferred from the durum cultivars to hexaploid wheat. The gene transferred in crosses involving autotetraploid T. monococcum was also Lr33, but since Lr33 is on chromosome 1B, it was probably not from T. monococcum. This gene was not the same as the T. monococcum-derived gene in RL6137 (Tc*6/TMR5-J14-12-24). Using RL6058 (Lr34) as the recurrent parent appeared to facilitate the interspecific transfer of resistance since resistance was expressed in the first backcross generation involving RL6058 but not Thatcher. Key words: leaf rust resistance, wheat, Triticum aestivum

Increase of inheritable polymorphisms of arbitrary primed PCR products on DGGE gels

Single 10-mer primers of arbitrary sequence were used to amplify, by polymerase chain reaction (PCR), random genomic regions of two closely related hexaploid wheat cultivars. Polymorphic bands between the two genomes were visualized on both agarose and denaturing gradient gel electrophoresis (DGGE) gels. There was approximately a four-fold increase in inheritable polymorphisms when the PCR fragments were separated on DGGE gels.

Some Aspects of Photoperiodism in Wheat and Its Wild Relatives

Experiments with plants grown in controlled environment conditions examine three aspects of photoperiodism in wheat. A survey of the flowering responses of 20 genotypes of diploid, tetraploid and hexaploid wheat cultivars and wild relatives to growth under three daylengths (8, 12, 16 h) after three durations of vernalisation (0, 4, 10 weeks at 20�C) showed that all were long-day plants and many responded to vernalisation. The requirement for long days was most stringent among the diploid progenitors and most relaxed among the hexaploid cultivars. However, not even the earliest flowering spring wheat cultivars (among eight) were entirely daylength-neutral. Minimum times to inflorescence initiation appeared to be determined independently of the responses to daylength. Whereas leaf initiation and appearance rates were hardly influenced by daylength, the rate of spikelet initiation responded to it from the beginning of floral induction, well before the appearance of double ridges. Comparison of the times to double ridges among near-isogenic lines of four spring wheat cultivars (Ciano 67, Yaqui 50, Rescue and April Bearded) showed that each of the three dwarfing genes Rht1, Rht2 and Rht3 advanced inflorescence initiation but without changing the response to daylength.

Differences in the heat-shock response between thermotolerant and thermosusceptible cultivars of hexaploid wheat

Heat-shock protein (HSP) gene expression in two wheat lines cv 'Mustang' (heat-tolerant) and cv 'Sturdy' (heat-susceptible) were analyzed to determine if wheat genotypes differing in heat tolerance also differ in in-vitro HSP synthesis (translatable HSP mRNAs) and steady-state levels of HSP mRNA. Several sets of mRNA were isolated from seedling leaf tissues which had been heat-stressed at 37 °C for various time intervals. These mRNAs were hybridized with HSP cDNA or genomic DNA probes (HSP17, 26, 70, 98, and ubiquitin). Protein profiles were compared using in-vitro translation and 2-D gels. The Northern slot-blot data from the heat-stress treatment provide evidence that the heat-tolerant cv 'Mustang' synthesized low molecular weight (LMW) HSP mRNA earlier during exposure to heat shock and at a higher level than did the heat-susceptible cv 'Sturdy'. This was especially true for the chloroplast-localized HSP. The protein profiles shown by 2-D gel analysis revealed that there were not only quantitative differences of individual HSPs between the two wheat lines, but also some unique HSPs which were only found in the 'Mustang' HSP profiles. The high level of RFLP between the two wheat lines was revealed by Southern blot hybridization utilizing a HSP17 probe. These data provide a molecular basis for further genetic analysis of the role of HSP genes in thermal tolerance in wheat.

A Strategy to Identify Probes that Detect a High Degree of Polymorphism in Bread Wheat

Although the genetic linkage map of Triticum tauschil, the D-genome progenitor of wheat its available, its use for linkage analysis of hexaploid wheat chromosome regions is hampered by the lack of polymorphism in wheat. Here we describe a strategy to identity probes that detect a high degree of polymorphism in wheat. The strategy involves the use of DNA probes that detect null alleles. About 16% of the Pstl genomic clones from Triticum tauschil detect null alleles in the species. The probes that detect null alleles reveal high degree of polymorphism among hexaploid wheat cultivars. The probes selected following this strategy are expected to detect null alleles throughout the tribe Triticeae, therefore, reveal high degree of polymorphism.

Induced Mutations of a Genetic Suppressor of Resistance to Wheat Stem Rust

A genetic suppressor of resistance to stem rust, Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn., of wheat (Triticum aestivum L.) is on the long arm of chromosome 7D. Mutation or inactivation of the suppressor gene would allow expression of the suppressed resistance genes already present in hexaploid wheat or of resistance genes transferred to wheat from diploid or tetraploid relatives. Our objective was to induce a mutation of the suppressor gene and describe its inheritance. Seed treatment of the hexaploid wheat cultivar Canthatch (CTH) with ethyl methanesulfonate produced 15 stem rust‐resistant mutants. The mutant lines were tested for reaction to 13 races of stem rust, and crossed with CTH and 7D aneuploids of CTH and ‘Chinese Spring’ (CS). Parental, F1, F2, and F3 seedlings were tested for reaction to race CRL‐QSH of stem rust. Similarity among the 15 mutants in reactions to 13 races of stem rust indicated that each of the mutants had a similar genetic alteration resulting in an inactivated or deleted suppressor gene. The suppressor gene mutations showed incomplete dominance and monogenic inheritance in crosses with CTH. One mutant was ditelosomic 7DS and lacked the suppressor gene. Allelism tests indicated that the mutated gene(s) in the other 14 mutants were at or near the same locus on 7DL. Crosses between the mutants and CS monosomic 7D or CS ditelosomic 7DS indicated that CTH may have three recessive genes for resistance that were inhibited by the suppressor. The mutant lines may permit the use of the suppressed genes for stem rust resistance in hexaploid wheat and related species to breed hexaploid wheat cultivars with improved resistance.

Agronomical performance and breeding value of selected strains of diploid wheat, Triticum monococcum

Twenty-one germplasm accessions and breeding lines of einkorn wheat (Triticum monococcum ssp. monococcum and ssp. sinskajae) were grown at two sites in Italy and evaluated for various field and seed characteristics. Grain yields of germplasm accessions were relatively high (317–3238 kg/ha), but distinctly lower than those of four modern cultivars of tetraploid (T. turgidum ssp. durum) and hexaploid wheat (T. aestivum ssp. Aestivum) included in the experiments as controls. As expected, all Einkorns-including some substantially higher yielding crossbred lines (3415–4362 kg/ha)-were defective for one or more agronomically relevant features. However, a few of the accessions examined were found to contain, as a group, practically all the genes needed to breed monococcums having the main field attributes of a modern wheat cultivar: high yielding capacity, good threshability, large kernel size, earliness, short stature and adequate lodging resistance. Still higher yielding diploid wheats, more responsive to improved growing conditions and of better seed quality, could probably be obtained from crosses with wild monococcums bearing mostly two-seeded florets and with accessions producing less slender-shaped kernels. Some of the Einkorns examined were found to carry minor genes for easy threshing which might enhance the efficacy of the major gene for soft glumes carried by T. monococcum ssp. sinskajae, a partially free-threshing diploid wheat taxon. Seed protein percentage of monococcums was markedly higher than that of durum and bread wheat cultivars even in those cases where their grain yields surpassed those of the polyploid checks. The possibilities offered by diploid wheat in the exploitation of novel endosperm mutants and F1 hybrid vigour, as well as in the fields of celiac disease, crop diversification and resistance to agro-biological stresses are discussed. Breeding priorities and strategies are also proposed.

Confirmation of a 4BL/5RL Wheat‐Rye Chromosome Translocation Line in the Wheat Cultivar ‘Viking’ Showing High Copper Efficiency

AbstractThe N‐ and C‐banding patterns of the chromosomes of the hexaploid wheat cultivar ‘Viking’, and the hairy‐necked line derived from it, were described. Except for chromosome 4B (formerly 4A), no significant variation in banding patterns were found between the two genotypes. In addition to a 5BS.7BS (5BL.7BL) translocation in both genotypes, the presence of a small 5RL rye segment in a terminal position on the long arm of chromosome 4B was suggested by banding and confirmed by meiotic analysis, and by the hairy neck marker as well as by rye‐specific leaf esterase bands in the translocation line. The translocation breakpoint is presumed to be located in the distal 4BL2.2 and/or 5RL2.3 band. The hairy‐necked ‘Viking’ was shown to be copper efficient. Its utilization in wheat breeding programmes is proposed.

Reproductive Behavior of Hexaploid/Diploid Wheat Hybrids 1

AbstractThe bottleneck restricting introgression of useful genes directly from diploid into hexaploid wheats is the low number of BC1F1 seeds obtained. In crosses between hexaploid wheat (Triticum aestivum L.; AABBDD) and Aegilops squarrosa L. (DD) or T. urartu Thum. (AA), this bottleneck may be overcome simply by pollinating a sufficient number of F1 spikes. However, hybrids between hexaploid wheat cultivars (T. aestivum) and T. monococcum L. (AA) generally are highly female‐sterile, often having no pistils. One T. monococcum accession, PI 355520, when crossed with T. aestivum, produced hybrids with female fertility in the same range as that of T. aestivum/A. squarrosa or T. aestivum/T. urartu hybrids, ca. 0.5 to 1.0 backcross seed per spike. We found that female fertility was controlled by two duplicate genes in PI 355520, and that this accession can be used as a bridging parent to introgress genes from other T. monococcum accessions into hexaploid wheat. Pairing of homologous chromosomes was less frequent and weaker in such crosses than in T. aestivum/A. squarrosa crosses, but homoeologous bivalents occurred at a rate of almost 0.5 II per cell. Restitution division was detected in crosses involving all three diploid species and was confirmed cytologically in crosses with PI 355520. Chromosome numbers of BC1F1 plants ranged from 35 to 67; plants with 49 or more chromosomes occurred at frequencies of 0.09 to 0.21 among progeny of A. squarrosa and T. urartu and 0.29 in progeny of T. aestivum/T. monococcum crosses involving PI 355520. These results are consistent with those of previous studies, demonstrating the potential of direct Hexaploid/diploid crosses for rapidly introgressing useful genes into Hexaploid wheat with minimum disturbance of the background genotype.

Screening Spring Wheat Genotypes (Triticum sp.) for Seedling Emergence under Optimal and Suboptimal Temperature Conditions

Ninety six tetraplold spring wheat genotypes and six hexaploid wheat cultivars were allowed to germinate in four growth chambers set at temperature regimes of 5°C, 10°C, 15°C, and 20°C. Temperature had a strong effect on seedling emergence time of all genotypes. This effect was much more dramatic at the lower than at the higher temperature values. Optimum temperature conditions (15°C and 20°C) were associated with smaller genetic variances for seedling emergence time. The 15°C and 20°C did not statistically differ in their effccts on emergence time. The 5°C and 10°C treatments can be successfully used to screen genotypes for their cold tolerance because of much larger genetic variances. Genotypes were classified into three categories according to their cold tolerance: tolerant, intermediate, and susceptible. Hexaploid genotypes were the most cold tolerant in this wheat population. The most cold tolerant tetraploid genotypes are 1460, Adamello, Creso, Echiopia Komugi 72-201, Kunduru 1149, Kyperounda, Latino, Mindum, and Norba. The emergence time of these 9 tetraploid genotypes was cornparable to that of the hexaploid genotypes. Under low temperature conditons some spring wheat genotypes performed simllarly as the winter types suggesting that cold torelance during seedling emergence is independent of varnalization requirement. There was no genotype x temperature interactionindicating that selection for cold tolerance is effective. The 10°C can be successfully used to screen genotypes for their cold tolerance durlng the emergence growth phase.

Transfer to hexaploid wheat of linked genes for adult-plant leaf rust and seedling stem rust resistance from an amphiploid of Aegilops speltoides × Triticum monococcum

A partially dominant gene for adult-plant leaf rust resistance together with a linked, partially dominant gene for stem rust resistance were transferred to the hexaploid wheat cultivar 'Marquis' from an amphiploid of Aegilops speltoides × Triticum monococcum by direct crossing and backcrossing. Pathological evidence indicated that the alien resistance genes were derived from Ae. speltoides. Differential transmission of the resistance genes through the male gametes occurred in hexaploid hybrids involving the resistant 'Marquis' stock and resulted in distorted segregation ratios. In heterozygotes, pairing between the chromosome arm with the alien segment and the corresponding arm of the normal wheat chromosome was greatly reduced. The apparent close linkage between the two resistance genes, 3 ± 1.07 crossover units, was misleading because of this decrease in pairing in the presence of the 5B diploidizing mechanism. The newly identified gene for adult-plant leaf rust resistance, located on chromosome 2B, is different from adult-plant resistance genes Lr12, Lr13, and Lr22 and from that in the hexaploid accession PI250413; it has been designated Lr35. It is not known whether the newly transferred gene for stem rust resistance differs from Sr32, also derived from Ae. speltoides and located on chromosomes 2B.Key words: hexaploid, Triticum, Aegilops, aneuploid, Puccinia graminis, Puccinia recondita.

Two-step one-dimensional SDS-PAGE analysis of LMW subunits of glutelin

A collection of 222 hexaploid wheat cultivars (including the 207 cultivars studied by Gupta and Shepherd in 1988) from 32 countries was analyzed for variation in the banding patterns of LMW subunits of glutenin using a modified two-step 1-D SDS-PAGE. Seventy percent ethanol at high temperature (≥50 °C) was used to selectively dissolve the native glutenins containing A, B, and C subunits and not the albumins and globulins (non-prolamins). This procedure allowed the glutenin subunits A, B and C to be separated in a background free of albumins and globulins, which normally overlap the B and C subunits (LMW subunits of glutenin). Although 40 different B and C subunits were detected, except where the cultivars carried a 1BL-1RS translocation or 1B/1R substitution, each cultivar exhibited from 7 to 16 subunits. These subunits could be divided into 20 band patterns which fell into three groups on the basis of their mutual exclusiveness, with 6, 9, and 5 patterns. Analysis of substitution lines revealed that the different patterns in these groups are controlled by genes on chromosomes 1A, 1B, and 1D, respectively. The least number of subunits was controlled by chromosome 1A and approximately 40% of the cultivars did not contain any band controlled by this chromosome. Thirteen of the cultivars were found to consist of two biotypes with respect to LMW subunits of glutenin. The genetic, evolutionary, and technological implications of these findings are discussed.

Chromosomal location of genes controlling heat shock proteins in hexaploid wheat

The low molecular weight heat shock protein (HSP) profiles of the hexaploid wheat cultivar "Chinese Spring" and its ditelosomic series were characterized by isoelectric focusing polyacrylamide gel electrophoresis of denatured in vivo radiolabeled proteins. Comparisons of the ditelosomics (DTs) to the euploid "Chinese Spring" enabled the assignment of genes controlling 9 of the 13 targeted HSPs to seven chromosome arms. There did not appear to be a genome-specific action in the regulation of expression of these HSPs. There did appear to be a higher frequency of controlling genes within homoeologous DT lines 3, 4 and 7. Significant variation in protein quantity was evident among the DT lines for some HSPs, while other HSPs were remarkably stable in their expression across all DTs examined. The results are useful in identifying specific DT lines for the investigation of HSP functions in hexaploid wheat.

Rht1 and Rht2 Semidwarf Genes Effect on Hybrid Vigor and Agronomic Traits of Wheat

The ‘Norin 10’ dwarfing genes, Rhtl and Rht2, have been an effective source of stature control in commercial cultivars of hexaploid wheat (Triticum aestivum L.). Various and conflicting studies have reported on the yield effects associated with these genes. The present study was undertaken to examine pleiotropic effects on yield and yield related characters in inbreds and F1 hybrids near‐isogenic for Rht1 and Rht2. Isogenic series for six diverse cultivars at three levels of dwarfing; tall (no Rht alleles), semidwarf (2 Rht alleles), and double‐dwarf (4 Rht alleles) were intercrossed in all possible combinations within each dwarfing level, without reciprocals, to construct three near‐isogenic series of 15 F1 hybrids. Parents and hybrids were grown in replicated field trials in each of two locations for two years. Mean grain yield of all genotypes declined significantly as a linear function of the number of Rht genes. Negative effects of Rht were a consequence of significantly reduced kernel weights that were not offset by other yield components. Midparent heterosis for one measure of yield was greatest for tall hybrids (14%), followed by semidwarfs (10%), and double‐dwarfs (2%). The Norin 10 Rht alleles appear to limit the expression of hybrid vigor.

Cytological characterization, powdery mildew resistance and storage protein composition of tetraploid and hexaploid 1BL/1RS wheat-rye translocation lines

Progenies of a tetraploid 1BL/1RS wheat-rye translocation line, CV 256, selected from the cross 'Cando' x 'Veery', were analyzed by means of Giemsa C-banding. CV 256 is cytologically stable for the presence of the 1BL/1RS translocation but still segregating for A- and B-genome chromosomes of 'Cando' and 'Veery'. In CV 256, nucleolar activity of the 1RS NOR locus is suppressed, as judged by the absence of a secondary constriction in that rye segment and the capability of organizing nucleoli. PAGE analysis of prolamins confirmed the presence of two 1RS secalins in all single seeds analyzed. SDS-PAGE analysis of reduced glutenins of single seeds indicated that some seeds contained the 'Cando' Glu-B1 locus (subunits 6+8), some contained the 'Veery' Glu-B1 locus (subunits 7+9) while others contained all four subunits, indicating that the material was heterozygous. Pm8 resistance is expressed in the tetraploid 1BL/1RS translocation line based on the reactions of six well-defined powdery mildew isolates. However, Pm8 resistance is not expressed in the hexaploid wheat cultivars 'Olymp', 'Heinrich' and 'Florida', which also contain the 1BL/1RS translocation. Obviously, the existence of the 1BL/1RS translocation is not a proof for the expression of the associated genes. PAGE results did not show a clear linkage between powdery mildew resistance and the presence of 1RS secalins.

Identification of new mitochondrial genome organizations in wheat plants regenerated from somatic tissue cultures

Plants have been regenerated from short-and long-term in vitro somatic tissue cultures made from immature embryos of the hexaploid wheat cultivar "Chinese Spring". The mitochondrial genome organization of each regenerated plantlet was studied, after one selfing, by probing Sal I-restricted total DNA with cloned Sal I fragments of wheat mitochondrial DNA derived from a segment of the genome, which displays marked structural changes in response to in vitro culture. Short-term in vitro cultures give rise to regenerated plants whose mitochondrial genome organization is either close to that of the parental cultivar or to that of embryogenic callus cultures, except for a single plant which has an organization resembling that of short-term non-embryogenic cultures. In contrast, all but one of the plants regenerated from long-term cultures exhibited a mitochondrial genome organization similar to that of long-term nonembryogenic cultures. In addition, extra labelled bands were detected in some of the regenerated plants with two of the probes used. These results emphasize the importance of the duration of the in vitro step preceding the regeneration process: the longer it is, the higher the probability is of obtaining mitochondrial DNA variability in regenerated plants. Furthermore, since increasing the duration of the in vitro stetp results in the production of regenerated plants with a mitochondrial genome organization resembling that of non-embryogenic tissue cultures, the question is thus raised as to whether regeneration from long-term cultures is suitable for use in plant breeding.

Salt‐tolerant Triticum×Lophopyrum derivatives limit the accumulation of sodium and chloride ions under saline‐stress

Abstract. Cultivars of hexaploid wheat (Triticum aestivum cvs. Chinese Spring or PI 178704) and derivatives containing chromosomes from both a cultivar and a wild, salt‐tolerant species (Lophopyrum elongatum or L. ponticum) were compared to determine differences in growth, ion transport and ion accumulation under salt‐stress. Two experiments were conducted in which plants were grown under saline and non‐saline conditions and harvested at various lime intervals throughout ontogeny. Under salt‐stress the growth rate of the cultivars, as compared to the growth rate of the derivatives, decreased more rapidly later in development. Transport rates from root to shoot of Na+ and Cl− reached higher levels in the cultivars. The cultivars accumulated more Na+ and Cl− and relatively less K+ in the shoot. The K+/Na+ ratio was higher in the derivatives than in the cultivars from which they were derived. The addition of chromosomes from Lophopyrum species into wheat altered ion accumulation, growth rates, and ion transport rates from root to shoot.

Heterochromatin differentiation and phylogenetic relationship of the A genomes in diploid and polyploid wheats

Heterochromatin differentiation, including band size, sites, and Giemsa staining intensity, was analyzed by the HKG (HCl-KOH-Giemsa) banding technique in the A genomes of 21 diploid (Triticum urartu, T. boeoticum and T. monococcum), 13 tetraploid (T. araraticum, T. timopheevi, T. dicoccoides and T. turgidum var. Dicoccon, Polonicum), and 7 cultivars of hexaploid (T. aestivum) wheats from different germplasm collections. Among wild and cultivated diploid taxa, heterochromatin was located mainly at centromeric regions, but the size and staining intensity were distinct and some accessions' genomes had interstitial and telomeric bands. Among wild and cultivated polyploid wheats, heterochromatin exhibited bifurcated differentiation. Heterochromatinization occurred in chromosomes 4A(t) and 7A(t) and in smaller amounts in 2A(t), 3A(t), 5A(t), and 6A(t) within the genomes of the tetraploid Timopheevi group (T. araraticum, and T. timopheevi) and vice versa within those of the Emmer group (T. dicoccoides and T. turgidum). Similar divergence patterns occurred among chromosome 4A(a) and 7A(a) of cultivars of hexaploid wheat (T. aestivum). These dynamic processes could be related to geographic distribution and to natural and artifical selection. Comparison of the A genomes of diploid wheats with those of polyploid wheats shows that the A genomes in existing diploid wheats could not be the direct donors of those in polyploid wheats, but that the extant taxa of diploids and polyploids probably have a common origin and share a common A-genomelike ancestor.

DNase I sensitivity of ribosomal RNA Genes in chromatin and nucleolar dominance in wheat

Ribosomal RNA genes at different nucleolar organizer (NOR) loci in hexaploid wheat are expressed at different levels. The degree of expression of a particular organizer depends on the genetic background, especially on the presence of other NOR loci. For example, when chromosome 1U of Aegilops umbellulata is introduced into the hexaploid wheat cultivar “Chinese Spring” the A. umbellulata NOR accounts for most of the nucleolar activity and seems to suppress the activity of the wheat NOR loci. Even in wild-type “Chinese Spring”, the NOR on chromosome 1B is partially dominant to that on chromosome 6B, since the 1B locus is more active in spite of having fewer genes. We have previously shown that these and other examples of nucleolar dominance in wheat are associated with undermethylation of cytosine residues in certain regions of the dominant rDNA. Here, we show that rRNA genes at dominant loci are organized in a chromatin conformation that renders them more sensitive to DNase I digestion than other rRNA genes. In addition, we have mapped several DNase I-hypersensitive sites in the intergenic spacer region of the rDNA repeating unit. Some of these sites are located near the initiation region for the 45 S rRNA precursor, while others are associated with a series of short direct repeats 5′ to the 45 S rRNA initiation site. The results are discussed in terms of a model in which repeated sequences in the wheat intergenic DNA are presumed to function as upstream promoters and transcriptional enhancers similar to those in Xenopus.