Relationship between cold resistance,heading traits and ear primordia development of wheat cultivars

Summary For breeding early heading wheat cultivars with resistance to frost damage which are well adapted to dry areas of West Asia and North Africa, the relationships between winter hardiness, ear primordia development and heading traits, i.e. veernalization requirement, photoperiodic response and narrow-sense earliness, were assessed using a total of 30 genotypes of wheat (Triticum aestivum L.) grown in an experiment in Syria. The results of artificial freezing tests indicated that cultivars with good winter hardiness were to be found only in the winter wheat cultivars which required 50 or more days of vernalization treatment. These winter wheat cultivars did not initiate internode elongation without vernalization even at 95 days after planting. Thus their ear primordia were still underground and were protected from frost injury at this stage. Photoperiodic response and narrow-sense earliness were not associated with winter hardiness and earliness of internode elongation, but were related to the number of days to heading after planting. This indicated the possibility for breeding early heading cultivars with winter hardiness and tiller frost avoidance by combining high vernalization requirement, short narrow-sense earliness and neutral response to photoperiod.     

Effect of alien 5R(5A) chromosome substitution on ear-emergence time and winter hardiness in wheat-rye substitution lines

Ear emergence time and response to vernalization were investigated in 12 alien substitution lines in which a pair of chromosomes 5A of recipient spring wheat cultivars was replaced by a pair of chromosomes 5R of Siberian spring rye ‘Onokhoiskaya’. The recipients were 12 spring cultivars of common wheat, each carrying different Vrn genes. Spring rye ‘Onokhoiskaya’ had the Sp1 (now called Vrn-R1) gene for spring growth habit located on chromosome 5R, but its expression was weaker. The Vrn-R1 gene had no effect on growth habit, ear emergence time and response to vernalization in wheat-rye substitution lines. Ears emerged significantly later in the 5R(5A) alien substitution lines than in the recipient wheat cultivars with the Vrn-A1/Vrn-B1/vrn-D1 or Vrn-A1/vrn-B1/Vrn-D1 genotypes. No difference in ear emergence time was found between most of the 5R(5A) alien substitution lines and the cultivars carrying the recessive vrn-A1 gene. The presence of the Vrn2a and Vrn2b alleles at the Vrn2 (now called Vrn-B1) locus located on wheat chromosome 5B was confirmed.The replacement of chromosome 5A by chromosome 5R in wheat cultivars ‘Rang’ and ‘Mironovskaya Krupnozernaya’, which carries the single dominant gene Vrn-A1, converted them to winter growth habit. In field studies near Novosibirsk the winter hardiness of 5R(5A) wheat–rye substitution lines of ‘Rang’ and ‘Mironovskaya Krupnozernaya’ was increased by 20–47% and 27–34%, respectively, over the recurrent parents.     

Detection of an earliness per se quantitative trait locus in the proximal region of wheat chromosome 5AL

A homoeologous quantitative trait locus to that of eps5L on barley chromosome 5H was identified in a syntenic region of wheat chromosome 5A. Wheat single chromosome recombinant lines (SCRs) were developed from a cross between ‘Chinese Spring’(‘Cappelle-Desprez’ 5A) and ‘Chinese Spring’(Triticum spelta 5A), these were grown together with the parental controls under different vernalization and photoperiod regimes. The variation for ear emergence time accelerated heading induced by the T. spelta segment indicated an effect associated with the Xcdo412-Xbcd9 interval. Since no differences between the SCRs and controls in responses to vernalization and photoperiod treatments were detected, this effect was identified as an earliness per se gene, Q Eetocs-5 A.2, which may be homoeologous to the eps5L quantitative trait locus of barley. Xbcd926 has been found to be closely linked to the rice flowering time quantitative trait loci, QHd9a or FLTQ2, on chromosome 9, suggesting possible relationships among the quantitative trait loci across wheat, barley and rice genomes.     

Isolation of a fertile wheat-barley addition line carrying the entire barley chromosome 1H

The isolation of six of the seven possible additions of barley chromosomes to the wheat genome reported 18 years ago has made an important contribution to gene mapping in barley, first with genes controlling isozymes and more recently DNA (molecular) markers. A fertile addition line involving barley chromosome 1H,which carries genes controlling several characters of economic importance, could not be isolated at that time because it caused extreme meiotic abnormalities leading to complete sterility when added to wheat. Later the short arm of barley chromosome 1H was added to wheat as a fertile ditelosomic addition, but the non-availability of the entire barley chromosome 1H addition line has hampered the location of barley genes to the long arm of this chromosome. This problem has now been overcome cytogenetically as described herein. The resultant self-fertile disomic-monotelodisomic addition line carrying a pair of barley chromosome 6H and a heteromorphic 1H/1HS pair is more stable, and makes the wheat-barley addition line series complete for gene mapping work and will provide a vehicle for the possible transfer of useful genes from this barley chromosome to wheat.     

Isolation, identification and characterization of disomic and translocated barley chromosome addition lines of common wheat

Two disomic barley chromosome addition lines and five translocated chromosome addition lines of common wheat cultivar Shinchunaga were isolated. They were derived from a hybrid plant between Shinchunaga and cultivated barley Nyugoruden (New Golden) by backcrossing with wheat and self pollination. Barley chromosomes added to chromosome arms involved in the translocated chromosomes were identified by C-banding method and by crossing these lines with Chinese Spring/Betzes addition lines. Two disomic addition lines were identified to have chromosome 6 and 7 of barley, respectively. Two of the five translocated chromosome addition lines were clarified to have same chromosome constitution, 42 wheat chromosomes and a pair of translocated chromosomes constituted with a long arm of chromosome 5B of wheat and a short arm of chromosome 7 of barley. The other three lines could not be identified due to chromosome rearrangement. Performances of these seven lines on agronomic characters were examined. Addition of barley chromosome 7 induced early heading, and chromosome 6 showed lated heading. Almost all of the lines except that of chromosome 6 showed short culm length and all showed reduced number of tillers, spikelets and grains per ear, and low seed fertility. These lines would be useful for genetic analyses in wheat and barley and for induction of useful genes of barley into wheat. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of wheat chromosomes involved with different types of resistance against greenbug (Schizaphis graminum, Rond.) and the Russian wheat aphid (Diuraphis noxia, Mordvilko)

Two sets of intervarietal chromosome substitution lines in the recipient,susceptible cultivar ‘Chinese Spring’ were screened to identify the wheat chromosomes involved with antixenosis, antibiosis and tolerance resistance to greenbug and Russian wheat aphid. The amphiploid ‘Synthetic’ and the cultivar ‘Hope’ were the donor parents. Antixenosis, antibiosis and tolerance were evaluated with conventional tests in controlled environmental conditions using a clone of greenbug biotype C and a clone of RWA collected on wheat. Antixenosis against greenbug was accounted for by several chromosomes in both sets of substitution lines with chromosome 2B contributing the highest level of this type of resistance. The highest levels of antixenosis against RWA were associated with the group of chromosomes 7 of the substitutions CS/Syn set and the chromosome substitutions 2B, 6A and 7D of the CS/Hope set. Antibiosis against both aphids species was accounted for by several different chromosomes. The highest levels of antibiosis for most of RWA resistance traits were recorded from the 1B substitution line of the CS/Hope set. More than one gene appears to determine antibiosis. Tolerance to both greenbug and the RWA was significantly associated with chromosomes 1A,1D, and 6D in the CS/Syn set of substitutions. These lines showed enhanced plant growth under aphid infestation. The highest levels of antixenosis, antibiosis and tolerance against the two aphid species occurred mostly in different substitution lines. Consequently, the different types of resistance for both pests seem to be partially independent. Since different genes seem to be involved in at least several traits of the resistance categories against the two aphid species, such genes could be combined in new cultivars of wheat to broaden their genetic base of resistance against the greenbug and the RWA. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular mapping of genes involved in root hair formation in barley

In the presented study, the existing AFLP and SSR maps of barley were used to find chromosomal position of four genes controlling different stages of root hair development. Four barley mutants were used in the analysis: the root hairless mutant rhl1.b, mutant rhp1.b with root hair development blocked at the initial bulge formation, mutant rhi1.a with irregular pattern of sparsely located root hairs and mutant rhs1.a with very short root hairs. Each mutant was crossed with parents of ‘Steptoe’/‘Morex’ mapping population and F₂ progenies of crosses: mutant × ‘Steptoe’ and mutant × ‘Morex’ were analyzed for segregation of root hair phenotype and polymorphic AFLP and SSR markers. It was possible to map all the analyzed genes on barley chromosomes: rhl1 gene on the short arm of chromosome 7H, rhp1 gene on chromosome 1H, rhs1 locus in the pericentromeric region of chromosome 5H and rhi1 gene on the long arm of chromosome 6H. Subsequently, the Bulk Segregant Analysis and AFLP technique were used for saturation of the identified regions with new markers. The joint maps were constructed using as common points the SSR markers located in the target regions. Linkage maps of the regions around the four genes involved in the root hair formation in barley were composed of 8–11 markers and spanned over 16.1–49.0 cM. The distances between localized genes and the closest markers ranged from 1.0 to 3.8 cM. The identified chromosomal locations of genes can be used for their fine mapping and future map-based cloning.     

Genetic Control of Vernalization, Day-length Response, and Earliness per se by Homoeologous Group-3 Chromosomes in Wheat

To identify homoeologous group-3 chromosomes that carry genes for vernalization, day-length responses, and earliness per se, a series of aneuploid lines (mono-somics and tetrasomics) and chromosome-substitution lines in ‘Chinese Spring’ (CS) were surveyed under different vernalization and day-length regimes in controlled environments. The results indicated that genes on all three chromosomes of group 3 can have striking effects on ear-emergence time. The replacement of CS 3B by its homologues in ‘Lutescens 62’ and ‘Cheyenne’ produced an increased insensitivity to vernalization, while 3B homologues from ‘Ceska Presivka’ gave CS a remarkable sensitivity to vernalization. This provided evidence for multiple allelism at a new Vrn locus on chromosome 3B. A negative association between gene dosage and day-length response was found in CS 3D which was thought to carry a gene for promoting insensitivity to day-length. The behaviour of CS monosomic 3A and CS (Timstein 3A), in reducing numbers of days to heading independently of environmental stimuli, suggested the presence of earliness per se genes on this chromosome.     

The influence of a spring habit gene, Vrn-D1, on heading time in wheat

The adaptability of wheat cultivars to environmental conditions is known to be associated with a vernalization requirement, that is, spring/winter habit. To clarify the genetic effect of the spring habit gene, Vrn‐D1, on heading time in the field, recombinant inbred lines (RILs) with or without the Vrn‐D1 gene were produced from F₂ plants of the cross between ‘Nanbukomugi’ and ‘Nishikazekomugi’, non‐carrier and carrier cultivars of this gene, respectively. Using growth chambers with a controlled temperature and photoperiod, three components of heading time, i.e. vernalization requirement, photoperiodic sensitivity and narrow‐sense earliness (earliness per se), were evaluated in each RIL. RILs with the Vrn‐D1 gene (E lines) showed greatly reduced vernalization requirements and slightly shorter narrow‐sense earliness than RILs without Vrn‐D1 (L lines), although no difference in photoperiodic sensitivity was observed between the two groups. RILs were planted at four different sites in Japan and examined for their heading time in the field. E lines headed significantly earlier than L lines at all locations, indicating that the earliness of E lines is stable in various environmental conditions. These results indicated that spring habit caused by Vrn‐D1 gene, as well as narrow‐sense earliness, was responsible for heading time in the field.     

Genetic markers for doubled haploid response in barley

In order to analyse the genetic control of anther culture response in barley, a doubled-haploid (DH) population from the cross between a medium responsive cultivar ‘Dobla’ and the model cultivar ‘Igri’ was produced. A linkage map was constructed with 91 markers. A sub-population of 41 lines was characterised for different components of the anther culture response, and was used for quantitative trait loci (QTL) analysis. The vrs1 locus region on chromosome 2H, which determines inflorescence row type, was coincident with the largest putative QTL for number of embryos (nEMB) and albino plants. A region of chromosome 6H was associated with QTLs for nEMB and green plants. QTLs for number and percentage of green plants were located on the long arm of chromosome 5H. Therefore, new QTLs for main components of barley anther culture response were identified on chromosomes 2H, 5H and 6H, indicating that anther culture response in barley could be controlled by relative few genes of large effect. This work is a useful step towards the identification of new regions on the barley genome that could be associated with fundamental biological process implicated in the anther culture response.     

The detection of allelic variants at the recessive vrn loci of winter wheat

Substitution lines with reciprocal substitutions of chromosomes containing recessive alleles of the homoeologous group 5 chromosomeVrn genes between varieties of winter wheat with high vernalisation requirement (‘Mironovskaya 808’) and low vernalisation requirements (‘Bezostaya 1’) have been created. On this basis the genetic determination of vernalisation requirement was established. Substitution lines Mironovskaya 808 (Bezostaya 1 5A), Mironovskaya 808 (Bezostaya 1 5B), Mironovskaya 808 (Bezostaya 1 5D) and reciprocal substitution lines Bezostaya 1 (Mironovskaya 808 5A), Bezostaya 1 (Mironovskaya 808 5B) and Bezostaya 1 (Mironovskaya 808 5D) were grown under different durations of vernalisation (3, 4, 5, 6, 7 and 8 weeks) and their response was evaluated. Photoperiodic sensitivity of the original parental genotypes was also determined. Reciprocal substitution lines of the same chromosome that carries the same vrn allele responded differently to vernalisation deficit. Differences have been shown between all group 5 reciprocal substitutions. Lines carrying chromosomes 5A and 5D of Mironovskaya 808 had a high vernalisation requirement whereas lines carrying chromosome 5B of Bezostaya 1 (vrn2^B) had a low vernalisation requirement. The reciprocal lines had a reverse requirement. This explains the different vernalisation requirements of the original varieties: Mironovskaya 808 with a high vernalisation requirement carries two alleles (vrn1^M and vrn3^M) in its genotype that increase the vernalisation requirement, whereas Bezostaya 1 with a lower requirement for vernalisation contains only one such allele (vrn2^B). By combination of the alleles in the lines with the substitution of chromosome 5B carrying vrn2 allele that in both original genotypes work inversely to the other alleles, transgressive genotypes have been formed: genotype vrn1^M vrn2^B vrn3^M determines a higher vernalisation requirement than original variety Mironovskaya 808, and genotype vrn1^B vrn2^M vrn3^B determines a lower vernalisation requirement than the original Bezostaya 1. An incomplete vernalisation requirement prolonged the time to heading, with exponential dependence on the vernalisation deficit, or prevented heading altogether. The original varieties further differed in photoperiodic sensitivity (Mironovskaya 808 sensitive, Bezostaya 1 less sensitive) that also influenced the background of substitution lines. The impact of the background on the heading time showed itself by about one week difference between Mironovskaya 808 and Bezostaya 1 grown under 8 weeks vernalisation and normal photoperiod. The difference between the lines with Mironovskaya 808 background and the lines with Bezostaya 1 background was approximately the same and was not significantly changed in different vernalisation variants of the lines. This difference may be caused by different photoperiodic sensitivity of the original varieties, but also by other genes, such as genes of earliness per se. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of QEet.ocs-5A.1, a quantitative trait locus for ear emergence time on wheat chromosome 5AL

QEet.ocs‐5A.1, a quantitative trait locus controlling ear emergence time, has been detected on wheat chromosome 5AL using single chromosome recombinant lines (SCRs) developed from a cross between ‘Chinese Spring’ (CS) (‘Cappelle‐Desprez’ 5A) and CS (Triticum spelta 5A). This locus has little influence on grain yield and its components, and thus has breeding potential for changing ear emergence time without yield reduction. To characterize the phenotypic expression of QEet.ocs.1 and to test its interaction with the Vrn‐A1 gene for vernalization response, six near‐isogenic SCRs differing for these two gene regions were grown together with the parental controls under different vernalization and photoperiod regimes. The T. spelta allele of QEet.ocs.1 accelerated heading time when vernalization and photoperiod were satisfied, demonstrating that the function of this QTL is earliness per se. There was no interaction between Vrn‐A1 and QEet.ocs.1.     

Chromosomal regions associated with green plant regeneration in wheat (Triticum aestivum L.) anther culture

Genetic capacity for green plant regeneration in anther culture were mapped in a population comprising 50 doubled haploid lines from a cross between two wheat varieties ‘Ciano’ and ‘Walter’ with widely different capacity for green plant regeneration. Bulked segregant analysis with AFLP markers and composite interval mapping detected four QTLs for green plant percentage on chromosomes 2AL (QGpp.kvl-2A), 2BL (QGpp.kvl-2B.1 and QGpp.kvl-2B.2) and 5BL (QGpp.kvl-5B).The three QTLs detected on chromosome 2AL and 2BL all derived their alleles favouring green plant formation from the responsive parent ‘Ciano’.The remaining QTL on chromosome 5BL had the allele favouring green plants from the low responding parent ‘Walter’. In a multiple regression analysis the four QTLs could explain a total of 80% of the genotypic variation for green plant percentage. None of the chromosomal regions with QTLs for green plant percentage showed significant influence on either embryo formation or regeneration frequencies from the anther culture. The three major QTLs located on group two chromosomes were fixed in a second DH population derived from two parents ‘Ciano’ and ‘Benoist’,both with high capacity to produce green plants. A QTL explaining31.5% of the genetic variation for green plant formation were detected on chromosome 5BL in this cross as well. This revised version was published online in July 2006 with corrections to the Cover Date.     

Substituting Ability of Individual Barley Chromosomes for Wheat Chromosomes 1. Substitutions Involving Barley Chromosomes 1, 3 and 6

In order to determine the genetic relatedness of individual barley chromosomes to wheat chromosomes, ‘Betzes’ barley chromosomes 1, 3 and 6 were substituted for individual ‘Chinese Spring’ wheat chromosomes of homoeologous groups 7, 3 and 6, respectively. The substitution status of these lines has been confirmed using isozyme selective markers, chromosome pairing behaviour in F₁ hybrids between the substitution lines and the appropriate double ditelocentric stocks of wheat, and hybridization of cDNA probes to the genomic DNA digests of these substitution lines. Each of the three barley chromosomes provided genetic compensation for the wheat chromosomes they replaced in the substitution plants. From the basis of this compensation with respect to plant vigour and fertility, barley chromosomes 1, 3 and 6 have been designated 7H, 3H and 6H.     

Genetic analysis of glume colour in common wheat cultivars from the former USSR

Genotypes for the glume colour character have been studied in 27 cultivars of common wheat (Triticum aestivum L.) originated from old landraces, and 1 specimen of T. petropavlovskyi Udacz. et Migusch. by means of analysis of the F₂ populations. The following tester lines have been used: white-glumed ‘Novosibirskaya 67’ ‘Diamant I’, and ‘Federation’, carrying the Rg1 gene alone; lines RL5405 and near-isogenic ‘Saratovskaya 29’ *5 (T. timopheevii Zhuk./T. tauschii (Coss.) Schmal.), carrying Rg2; line (1A ‘CS’ × ‘Strela’) with Rg3. The red glume colour in 21 cultivars of Triticum aestivum and in the accession of T. petropavlovskyi has been shown to be determined by the single gene Rg1, located on chromosome 1B. Five cultivars carrying the gene Rg3 for red glumes on chromosome 1A have been revealed. The cultivars ‘Zhnitsa’ and ‘Iskra’ carry the gene Rg3 alone. The red glume colour in the cultivars ‘Milturum 321’, ‘Milturum 2078’, ‘Sredneural'skaya’ is controlled by two genes, Rg1 and Rg3. In two common wheat cultivars, ‘Sarrubra’ and ‘Krasnoyarskaya 1103’ the red glume colour is determined by Rg1, inherited from local populations (‘Turka’ and ‘Kubanka’ respectively) of tetraploid wheat T. durum Desf. var. hordeiforme Host. Wide occurrence of the Rg1 gene in common wheat has been confirmed. On the contrary, none of the investigated varieties carries the gene Rg2. This revised version was published online in July 2006 with corrections to the Cover Date.     

Substitution of Hordeum marinum ssp. gussoneanum chromosome 7HL into wheat homoeologous group-7

Ditelosomic (Dt) 7HL^mar(7D) and monotelosomic (Mt) 7HL^mar(7A) and 7HL^mar(7B) wheat–barley substitution lines were developed by crossing monosomic 7A, 7B and 7D lines of common wheat cv. Saratovskaya 29 with disomic wheat–barley addition lines (2n = 44) that carry telocentric chromosomes 7HL^mar from Hordeum marinum ssp. gussoneanum 4×. Genomic in situ hybridisation confirmed the presence of barley chromosomes in the wheat genome. The compensating ability of the telosome in each combination was assessed by its transmission rate to progenies of plants with 2n = 41 + t chromosomes. Seed set and transmission rates of the telosome depended on the identity of the competing wheat homoeologue. Of the three chromosomes wheat, the telosome 7HL^mar compensated better for chromosome 7D and poorly for 7B. These and other data are discussed with respect to the phylogenetic relationships between the wheat chromosomes of group 7 and the chromosome of H. marinum, and the practical utility of these lines for wheat improvement is evaluated.     

Genetic relationships between preharvest sprouting and dormancy in barley

Preharvest sprouting (PHS) and dormancy (DOR) can be problems in barley production and end use quality, especially for barley used for seed and malting. Three crosses previously analyzed for DOR inheritance, were reanalyzed for PHS and DOR inheritance using artificial rain to calculate sprout score (SSc) and measure alpha-amylase activity (AA). Germination percentage of untreated grain for DOR was also measured. The crosses are ‘Steptoe’/’Morex’ (previously published), ‘Harrington’/TR306, and ‘Triumph’/Morex. Among the three crosses, DOR QTLs were located to six and PHS QTLs to five chromosomes, respectively. Chromosome 6H was never implicated. Previously identified DOR QTLs were confirmed in each cross, and most PHS QTLs coincided with DOR QTLs, but not all. Unique PHS QTLs were identified on chromosomes 1H (AA), 2H (SSc, AA), 3H (SSc, AA), and 7H (SSc, AA) and unique DOR QTLs on 1H, 2H, and 7H. Results indicate that PHS susceptibility and DOR are not always represented by opposite alleles at a locus. Some QTL regions for a given trait are conserved across crosses and some are not. Several QTLs are suitable for marker-assisted selection to balance PHS and DOR in breeding new cultivars.     

Simplified culture method of detached ears and its application to vernalization in wheat

Summary The effects of the addition of sulfurous acid into culture solution and of cold treatment of the solution were examined to simplify the culture of detached wheat ears. In the simplified method, detached ears could be cultured at room temperature on the liquid medium containing 100 g/l sucrose and 0.075% sulfurous acid without any sterilization. The immature seeds in detached ears cultured by this method were treated with low temperature or with chemicals known to have vernalizing effect. The chemical treatment did not affect the chilling requirement of immature embryos, although photoperiodic response and narrow-sense earliness were reduced by kinetin and trypsin. The low temperature treatment drastically affected the chilling requirement, and fully vernalized mature seeds having normal germinability were obtained by treating the detached ears in culture with low temperature from 10 days after anthesis.     

Vernalization response and earliness per se in cultivars representing different eras of wheat breeding in Argentina

Argentine wheat cultivars are assumed to be essentially vernalization insensitive or very slightly sensitive. However, there are only speculations on this lack of vernalization requirement and a greater unawareness on the variation in earliness per se. The aims of this research have been to determine the extent of variability in vernalization requirement and earliness per se, and how the variability in both traits was produced by breeding programs, through the release of wheat cultivars from the 1930's to the 1990's in Argentina. Sixty-eight cultivars, selected among those of highest performance in each era, were evaluated under field and glasshouse conditions for their vernalization response and earliness per se. Forty per cent of the cultivars showed some vernalization response. There was a decrease in this requirement along the first decades of the analysed breeding period, likely in response to the considerable introgression of CIMMYT germplasm. This initial trend to release earlier cultivars was also evidenced in a clear decrease in earliness per se. As this tendency in both characteristics was reverted during the last two decades, it may denote that certain vernalization response and not extreme earliness per se, may contribute to achieve higher yield cultivars in our area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparative genetic mapping of loci affecting plant height and development in cereals

Restriction fragment length polymorphism (RFLP) mapping data for genes determining dwarfness (GA insensitive and GA sensitive), vernalisation response and photoperiodic response in wheat, rye and barley were compared and their homoeologous relationships discussed. The GA insensitive Rht genes of wheat are not related to the GA insensitive dwarfing genes of rye or barley; however, homoeology is present for two members of the GA sensitive dwarfing genes of wheat (Rht12) and rye (Ddw1), located on the translocated segments of the long arms of chromosomes 5A and 5R, respectively. The comparative mapping of the Triticeae group 5 vernalisation response genes of wheat, rye and barley, and the group 2 photoperiodic response genes of wheat and barley, show that both gene families are located in homoeologous regions of the particular chromosomes. This revised version was published online in August 2006 with corrections to the Cover Date.