Genotyping of Triticum durum Desf. wheat accessions from the VIR collection based on the loci determining the rate of development and sensitivity to photoperiod (Vrn, Ppd)

Photoperiod sensitivity in rice cultivars is defined when the cultivar begins anthesis on a relatively invariant date, varying by < 7days, regardless of the date of sowing or germination. While the date of flowering in photoperiod sensitive (PPS) rice cultivars is characteristically determined by the day length, especially during the short-day season (September-December), the response of the flower opening time (FOT) to photoperiod remains hitherto unexplored. This paper examines whether day length restrains year-to-year variation in FOT in PPS cultivars. We examined 105 PPS and 173 photoperiod insensitive (PPI) cultivars grown in different years and estimated their year-to-year FOT difference (or FOTD) and the year-to-year difference of sunrise to anthesis duration (or SADD). Wilcoxon signed rank test and bootstrap test were then performed to test whether these descriptors significantly differed between PPS and PPI groups of cultivars. The means of FOTD and SADD were detected to be significantly less in the PPS group than in the PPI group of cultivars, indicating significantly lesser variability of FOT in PPS than in PPI cultivars. This is the first report of a strong restraining influence of photoperiod on FOT variability in PPS cultivars.

Hemp (Cannabis sativa L.) is an extraordinarily versatile crop, with applications ranging from medicinal compounds to seed oil and fibre products. Cannabis sativa is a short-day plant, and its flowering is highly controlled by photoperiod. However, substantial genetic variation exists for photoperiod sensitivity in C. sativa, and photoperiod-insensitive ("autoflower") cultivars are available. Using a bi-parental mapping population and bulked segregant analysis, we identified Autoflower2, a 0.5 Mbp locus significantly associated with photoperiod-insensitive flowering in hemp. Autoflower2 contains an ortholog of the central flowering time regulator FLOWERING LOCUS T (FT) from Arabidopsis thaliana which we termed CsFT1. We identified extensive sequence divergence between alleles of CsFT1 from photoperiod-sensitive and insensitive cultivars of C. sativa, including a duplication of CsFT1 and sequence differences, especially in introns. Furthermore, we observed higher expression of one of the CsFT1 copies found in the photoperiod-insensitive cultivar. Genotyping of several mapping populations and a diversity panel confirmed a correlation between CsFT1 alleles and photoperiod response, affirming that at least two independent loci involved in the photoperiodic control of flowering, Autoflower1 and Autoflower2, exist in the C. sativa gene pool. This study reveals the multiple independent origins of photoperiod insensitivity in C. sativa, supporting the likelihood of a complex domestication history in this species. By integrating the genetic relaxation of photoperiod sensitivity into novel C. sativa cultivars, expansion to higher latitudes will be permitted, thus allowing the full potential of this versatile crop to be reached.

Purpose. Identification and evaluation of the frequencies of dominant and recessive alleles of the Ppd-A1 gene in winter and spring durum wheat varieties of different geographical origins. Methods. DNA isolation, allele-specific PCR, electrophoresis in agarose and polyacrylamide gels and statistical analysis were used in the research. Results. Using diagnostic molecular markers, the genotypes of 81 spring and winter durum wheat varieties from different geographical origins were identified by alleles of the Ppd-A1 gene, which determines differences in photoperiodic sensitivity. Four alleles were found in spring varieties and three in winter varieties (the dominant allele Ppd-A1a.2 was absent). The recessive allele Ppd-A1_del303 was not found in any of the examined varieties. Conclusions. No significant differences were found between winter and spring genotypes in the frequency of one or the other allele. In winter and spring varieties, the recessive allele Ppd-A1_del2ex7 is the most frequent (68.5 and 47.9%, respectively). The recessive allele Ppd-A1b is significantly lower in winter varieties and almost identical in spring varieties. The frequencies of the dominant alleles Ppd-A1a.2 and Ppd-A1a.3 are lower than the two above and generally very low. The Ppd-A1a.2 allele was detected only in the Georgian variety ‘Merliuri’ (spring type); Ppd-A1a.3 – in the Ukrainian varieties ‘Luhanska 7’, ‘Metyska’ (spring) and ‘Koralovyi’ (winter). The possibility of using varieties carrying the dominant alleles Ppd-A1a.2 and Ppd-A1a.3 as donors in hard winter wheat bree­ding programmes is currently being discussed, in order to increase their adaptive potential in conditions of drought and high temperatures and to increase grain yield. The use of marker analysis will ensure the selection of breeding material with the optimal combination of alleles of the Ppd-A1a gene.

BackgroundVernalization genes VRN1 play a major role in the transition from vegetative to reproductive growth in wheat. In di-, tetra- and hexaploid wheats the presence of a dominant allele of at least one VRN1 gene homologue (Vrn-A1, Vrn-B1, Vrn-G1 or Vrn-D1) determines the spring growth habit. Allelic variation between the Vrn-1 and vrn-1 alleles relies on mutations in the promoter region or the first intron. The origin and variability of the dominant VRN1 alleles, determining the spring growth habit in tetraploid wheat species have been poorly studied.ResultsHere we analyzed the growth habit of 228 tetraploid wheat species accessions and 25 % of them were spring type. We analyzed the promoter and first intron regions of VRN1 genes in 57 spring accessions of tetraploid wheats. The spring growth habit of most studied spring accessions was determined by previously identified dominant alleles of VRN1 genes. Genetic experiments proof the dominant inheritance of Vrn-A1d allele which was widely distributed across the accessions of Triticum dicoccoides. Two novel alleles were discovered and designated as Vrn-A1b.7 and Vrn-B1dic. Vrn-A1b.7 had deletions of 20 bp located 137 bp upstream of the start codon and mutations within the VRN-box when compared to the recessive allele of vrn-A1. So far the Vrn-A1d allele was identified only in spring accessions of the T. dicoccoides and T. turgidum species. Vrn-B1dic was identified in T. dicoccoides IG46225 and had 11 % sequence dissimilarity in comparison to the promoter of vrn-B1. The presence of Vrn-A1b.7 and Vrn-B1dic alleles is a predicted cause of the spring growth habit of studied accessions of tetraploid species. Three spring accessions T. aethiopicum K-19059, T. turanicum K-31693 and T. turgidum cv. Blancal possess recessive alleles of both VRN-A1 and VRN-B1 genes. Further investigations are required to determine the source of spring growth habit of these accessions.ConclusionsNew allelic variants of the VRN-A1 and VRN-B1 genes were identified in spring accessions of tetraploid wheats. The origin and evolution of VRN-A1 alleles in di- and tetraploid wheat species was discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0924-z) contains supplementary material, which is available to authorized users.

Knowledge of the extent and pattern of genetic diversity within and among populations is crucial to identify useful breeding materials and design appropriate collection and conservation strategies. Genetic diversity of 160 durum wheat (Triticum durum Desf) accessions was studied using 15 morpho-agronomic traits. The field studies for morphological characterization were undertaken at Adadi Maryam and Ginchi locations using randomized complete block design with two replications. The average linkage technique of clustering produced a more understandable portrayal of the 160 durum wheat accessions and released varieties by grouping them into seven clusters with inter-cluster D2 values ranged from 13.72 to 235. The highest genetic distances (253) was observed between cluster five (improved varieties) and cluster three accessions. The minimum genetic distance (13.72) was observed between cluster one and two both are landrace collections. Five of the 15 principal components accounted for more than 76.98% of the total variation in the Ethiopian durum wheat genotypes. The first principal components accounted for 32% of the total differences. In this study, there is a moderate genetic diversity between landraces collected from Tigray, Gonder, and Wello. Landraces from these areas can be used as a source of important pre-breeding material for future breeding programs. Key words: Landraces, durum wheat varieties, genetic distances, correlation, genetic diversity, morphological characters.

Wheat adaptability to a wide range of environmental conditions is mostly determined by allelic diversity within genes controlling vernalization requirement (Vrn-1) and photoperiod sensitivity (Ppd-1). We characterized a panel of 151 durum wheat Mediterranean landraces and 20 representative locally adapted modern cultivars for their allelic composition at Vrn-1 and Ppd-1 gene using diagnostic molecular markers and studied their association with the time needed to reach six growth stages under field conditions over 6 years. Compared with the more diverse and representative landrace collection, the set of modern cultivars were characterized by a reduction of 50% in the number of allelic variants at the Vrn-A1 and Vrn-B1 genes, and the high frequency of mutant alleles conferring photoperiod insensitivity at Ppd-A1, which resulted on a shorter cycle length. Vrn-A1 played a greater role than Vrn-B1 in regulating crop development (Vrn-A1 > Vrn-B1). The results suggest that mutations in the Vrn-A1 gene may have been the most important in establishing the spring growth habit of Mediterranean landraces and modern durum cultivars. The allele Vrn-A1d, found in 10 landraces, delayed development. The relative effects of single Vrn-A1 alleles on delaying the development of the landraces were vrn-A1 = Vrn-A1d > Vrn-A1b > Vrn-A1c. Allele vrn-B1 was present in all except two landraces and in all modern cultivars. The null allele at Ppd-A1 (a deletion first observed in the French bread wheat cultivar ‘Capelle-Desprez’) was found for the first time in durum wheat in the present study that identified it in 30 landraces from 13 Mediterranean countries. Allele Ppd-A1a (GS105) was detected in both germplasm types, while the allele Ppd-A1a (GS100) was found only in modern North American and Spanish cultivars. The relative effect of single Ppd-A1 alleles on extending phenological development was Ppd-A1(DelCD) > Ppd-A1b > Ppd-A1a (GS105) > Ppd-A1a (GS100). Sixteen Vrn-1+Ppd-1 allelic combinations were found in landraces and six in modern cultivars, but only three were common to both panels. Differences in the number of days to reach anthesis were 10 days in landraces and 3 days in modern cultivars. Interactive effects between Vrn-1 and Ppd-1 genes were detected.

The main yield components in durum wheat are grain number per unit area (GN) and thousand kernel weight (TKW), both of which are affected by environmental conditions. The most critical developmental stage for their determination is flowering time, which partly depends on photoperiod sensitivity genes at Ppd-1 loci. Fifteen field experiments, involving 23 spring durum wheat genotypes containing all known allelic variants at the PHOTOPERIOD RESPONSE LOCUS (Ppd-A1 and Ppd-B1) were carried out at three sites at latitudes ranging from 41° to 27° N (Spain, Mexico-north, and Mexico-south, the latter in spring planting). Allele GS100 at Ppd-A1, which causes photoperiod insensitivity and results in early-flowering genotypes, tended to increase TKW and yield, albeit not substantially. Allele Ppd-B1a, also causing photoperiod insensitivity, did not affect flowering time or grain yield. Genotypes carrying the Ppd-B1b allele conferring photoperiod sensitivity had consistently higher GN, which did not translate into higher yield due to under-compensation in TKW. This increased GN was due to a greater number of grains spike-1 as a result of a higher number of spikelets spike-1. Daylength from double ridge to terminal spikelet stage was strongly and positively associated with the number of spikelets spike-1 in Spain. This association was not found in the Mexico sites, thereby indicating that Ppd-B1b had an intrinsic effect on spikelets spike-1 independently of environmental cues. Our results suggest that, in environments where yield is limited by the incapacity to produce a high GN, selecting for Ppd-B1b may be advisable.

With 2 tables AbstractDifferences in photoperiod sensitivity are widely used in wheat breeding to provide adaptation to diverse agronomic environments. Two photoperiod insensitive (PI) mutations in the A genome (Ppd‐A1a alleles) were previously identified using near‐isogenic lines of tetraploid durum wheat. We show that these Ppd‐A1a alleles predominate in modern durum wheat but are absent from wild tetraploid wheat and from conventional hexaploid wheat, suggesting they were selected for improved adaptation during durum cultivation. To increase genetic diversity in hexaploid wheat, synthetic hexaploid wheat lines were developed at CIMMYT by hybridizing elite durum lines with Aegilops tauschii accessions. Ppd‐A1a alleles from durum wheat were found in 71.4% of 447 synthetic hexaploids and 9.6% of 115 advanced selections. Backcrosses to hexaploid wheat showed that the durum Ppd‐A1a alleles conferred a PI phenotype and that one allele was intermediate between known B and D genome mutations, providing a new source of flowering time variation in hexaploid wheat and the potential for novel combinations of PI alleles.

BackgroundDurum wheat (Triticum durum Desf.) is a tetraploid cereal grown in the medium to low-precipitation areas of the Mediterranean Basin, North America and South-West Asia. Genomics applications in durum wheat have the potential to boost exploitation of genetic resources and to advance understanding of the genetics of important complex traits (e.g. resilience to environmental and biotic stresses). A dense and accurate consensus map specific for T. durum will greatly facilitate genetic mapping, functional genomics and marker-assisted improvement.ResultsHigh quality genotypic data from six core recombinant inbred line populations were used to obtain a consensus framework map of 598 simple sequence repeats (SSR) and Diversity Array Technology® (DArT) anchor markers (common across populations). Interpolation of unique markers from 14 maps allowed us to position a total of 2,575 markers in a consensus map of 2,463 cM. The T. durum A and B genomes were covered in their near totality based on the reference SSR hexaploid wheat map. The consensus locus order compared to those of the single component maps showed good correspondence, (average Spearman’s rank correlation rho ρ value of 0.96). Differences in marker order and local recombination rate were observed between the durum and hexaploid wheat consensus maps. The consensus map was used to carry out a whole-genome search for genetic differentiation signatures and association to heading date in a panel of 183 accessions adapted to the Mediterranean areas. Linkage disequilibrium was found to decay below the r2 threshold = 0.3 within 2.20 cM, on average. Strong molecular differentiations among sub-populations were mapped to 87 chromosome regions. A genome-wide association scan for heading date from 27 field trials in the Mediterranean Basin and in Mexico yielded 50 chromosome regions with evidences of association in multiple environments.ConclusionsThe consensus map presented here was used as a reference for genetic diversity and mapping analyses in T. durum, providing nearly complete genome coverage and even marker density. Markers previously mapped in hexaploid wheat constitute a strong link between the two species. The consensus map provides the basis for high-density single nucleotide polymorphic (SNP) marker implementation in durum wheat.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-873) contains supplementary material, which is available to authorized users.

Profiles of vitamin B and E in wheat grass and grain of einkorn (Triticum monococcum spp. monococcum), emmer (Triticum dicoccum ssp. dicoccum Schrank.), durum (Triticum durum Desf.), and bread wheat (Triticum aestivum L.) cultivars by LC-ESI-MS/MS analysis

The durum wheat varieties from Ukraine, Russia, and Kazakhstan are characterized by the specific allelic composition of the VRN genes that sharply distinguish them from the Triticum durum varieties from other countries. For numerous varieties, the VRN alleles which previously were not found in tetraploid wheat were identified. The ability of wheat to adapt to a wide range of environmental conditions is mostly determined by the allelic diversity within genes regulating the vernalization requirement (VRN) and photoperiod response (PPD). In the present study, allelic variation in the VRN1, VRN3, and PPD-A1 genes was investigated for 134 varieties of Triticum durum from different eco-geographic areas. It was shown that varieties from Russia and Ukraine have a specific allelic composition at the VRN genes, which in quantity and quality differed from European and American cultivars. A large number of varieties of T. durum from Russia carry the dominant Vrn-A1a.1 allele, previously identified mainly in hexaploid wheat. For some varieties from Eastern Europe and Asia, Vrn-A1i and vrn-A1b.3 recently revealed in wheat were also identified. Polymorphism of the VRN-B1 promoter region, distinguishing all three variants of this sequence (VRN-B1.f, VRN-B1.s, and VRN-B1.m), was detected. It was found that the dominant Vrn-B1c allele is commonly found in varieties of T. durum from Russia and Ukraine, but not Europe or USA. Furthermore, many Ukrainian and Russian varieties carry the dominant alleles of the both VRN-A1 and VRN-B1 genes simultaneously, while varieties from Europe and America carry the dominant allele of VRN-A1 alone. Finally, a high frequency of the Vrn-B3a allele, which previously was found only in some accessions of hexaploid wheat, was observed for varieties from Ukraine and Russia. It was revealed that the Ukrainian pool of T. durum varieties is currently the largest genetic source of the dominant Vrn-B3a allele in wheat in the worldwide.

Soybean (Glycine max (L.) Merr.) is a typical short-day and thermophilic crop. Absence of or low sensitivity to photoperiod is necessary for short-day crops to adapt to high latitudes. Photoperiod insensitivity in soybeans is controlled by two genetic systems and involves three important maturity genes: E1, a repressor for two soybean orthologs of Arabidopsis FLOWERING LOCUS T, and E3 and E4, which are phytochrome A genes. The aim of this work was to investigate the role of four maturity genes (E1 through E4) on the yield components, seed quality and on phasic development of near isogenic by E genes lines of soybean: short-day (SD) lines with genotype e1E2E3E4e5E7, e1E2E3e4e5E7, E1e2e3E4e5E7 and photoperiodic insensitive (PPI) lines with genotype e1e2E3E4e5E7, e1e2e3E4e5E7 under a long photoperiod (the natural day length of 50 latitude) conditions and short day conditions. The results of the study showed that soybean development processes under conditions of different day lengths depend on the dominant/recessive state of the main maturity genes. In addition, the response to the photoperiod depends on certain combinations of genes. SD lines began flowering on average 16.9% later under the conditions of a natural long photoperiod. Dominant alleles of genes E1 and E3 extended the pre- and post-flowering phases under conditions of exposure to long and short photoperiods. The dominant allele of the E1 gene delayed the onset of flowering by an average of 26.9%, and the period of full maturity by 39.8% compared to the recessive e1. The dominant allele of the E3 gene, compared to the recessive e3, lengthened the transition to flowering by an average of 16.1%, and the period of full ripeness by 27.1%. The dominant allele of the E2 gene lengthened the duration of the vegetative phase by 20% under the conditions of a long photoperiod. No significant influence of the dominant E4 allele on the duration of the vegetative and generative phases of soybean development was found in our study. PPI lines begin flowering under the conditions of a long and short photoperiod at the same time, but the phases of flowering and full seed maturity in the line with genotype e1e2e3E4e5E7 occurred earlier, due to the loss of the photoperiod sensitivity of the E3 gene. PPI line with genotype e1e2e3E4e5E7 proved to be the most insensitive line to the effect of different photoperiod durations among the studied lines. It was shown that the dominant alleles of E1–E4 maturity genes reduced the parameters of seed weight per plant and the weight of 1000 seeds under the conditions of a natural long photoperiod in comparison with recessive alleles of these genes. The maximum weight of seeds per plant and the weight of 1000 seeds were recorded in the PPI line with genotype e1e2e3E4e5E7. It should be noted that the dominant alleles E1 and E3 increased yield under conditions of a short photoperiod. Maturity genes had different effects on the biochemical composition of seeds. It was shown that soybean lines with dominant E1, E2 and E4 genes showed a higher content of starch and a lower content of total nitrogen and oil in seeds under natural photoperiod conditions compared to lines with recessive alleles of these genes. The dominant E3 allele reduced the oil content and did not affect the starch and total nitrogen content of seeds under long day conditions compared to the recessive e3 allele. The analysis of the effect of photoperiod on the timing of phenophases, yield structure indicators and biochemical composition of seeds in soybean plants with different sensitivity to photoperiod showed that the PPI line with the genotype e1e2e3E4e5E7 was the most adapted to the natural conditions of 50 degrees latitude. The PPI line with the genotype e1e2e3E4e5E7 was characterized by the shortest phases of days from sowing to flowering and full maturity. As a result, this line had the shortest growing season without reducing the yield and seed quality. Clearly, photoperiod had strong effects on all stages of plant reproduction and often acted indirectly, as shown by delayed responses expressed in later phases of development. The obtained results can be useful for the selection of soybean cultivars adapted to the climatic conditions of cultivation of Kharkiv region.

SUMMARYUnderstanding the effect of genetic factors controlling flowering time is essential to fine-tune crop development to each target environment and to maximize yield. A set of 35 durum wheat genotypes of spring growth-habit involving different allelic combinations at Ppd-A1 and Ppd-B1 genes was grown for 2 years at four sites at latitudes ranging from 19°N to 41°N. The emergence-flowering period was reduced from north to south. The frequency in the collection of the insensitive allele GS-105 at Ppd-A1 was greater (34%) than that of allele GS-100 (20%). Genotypes that flowered earlier due to the presence of alleles causing photoperiod insensitivity extended their grain-filling period, but less than the shortening in flowering time. The effect of the allele conferring photoperiod sensitivity at Ppd-A1 was stronger than that at Ppd-B1 (Ppd-A1b &gt; Ppd-B1b). The effect of photoperiod insensitivity alleles was classified as GS-100 &gt; GS-105 &gt; Ppd-B1a. The phenotypic expression of alleles conferring photoperiod insensitivity at Ppd-A1 increased at sites with average day length from emergence to flowering lower than 12 h. An interaction effect was found between Ppd-A1 and Ppd-B1. Differences between allelic combinations in flowering time accounted for c. 66% of the variability induced by the genotype effect, with the remaining 34% being explained by genes controlling earliness per se. The shortest flowering time across sites corresponded to the allelic combination GS-100/Ppd-B1a, which reduced flowering time by 11 days irrespective of the Ppd-A1b/Ppd-B1b combination. The current study marks a further step towards elucidation of the phenotypic expression of genes regulating photoperiod sensitivity and their interaction with the environment.

Tolerance to soil acidity constraints differ greatly among small grain species. However, information is lacking on the response of durum wheat to acid soil stress. The agribotanical traits of two common (Triticum aestivum L.) and two durum wheat (Triticum durum Desf.) cultivars, grown in limed and unlimed soil in a greenhouse, were measured after 32 weeks. Soil acidity had a greater influence on the agribotanical traits of the durum cultivars. The acid soil stress was severe on spike number, above ground yield and grain yield and less severe on harvest index, plant height and spike length. All cultivars had higher grain yields in limed than unlimed soil, however, the differences were only significant for the durum wheats. The two cultivars of the tetraploid (durum) wheat were more susceptible to soil acidity constraints than the two hexaploid (common) wheat cultivars.

Mol Gen Genomics (2005) 273: 54–65 DOI 10.1007/s00438-004-1095-4 O R I GI N A L P A P E R Daolin Fu AE Pe´ter Szu } cs AE Liuling Yan Marcelo Helguera AE Jeffrey S. Skinner Jarislav von Zitzewitz AE Patrick M. Hayes Jorge Dubcovsky Large deletions within the first intron in VRN-1 are associated with spring growth habit in barley and wheat Received: 15 September 2004 / Accepted: 22 November 2004 / Published online: 3 February 2005 Springer-Verlag 2005 Abstract The broad adaptability of wheat and barley is in part attributable to their flexible growth habit, in that spring forms have recurrently evolved from the ancestral winter growth habit. In diploid wheat and barley growth habit is determined by allelic variation at the VRN-1 and/or VRN-2 loci, whereas in the polyploid wheat species it is determined primarily by allelic variation at VRN-1. Dominant Vrn-A1 alleles for spring growth habit are frequently associated with mutations in the promoter region in diploid wheat and in the A genome of common wheat. However, several dominant Vrn-A1, Vrn-B1, Vrn-D1 (common wheat) and Vrn-H1 (barley) alleles show no polymorphisms in the promoter region relative to their respective recessive alleles. In this study, we sequenced the complete VRN-1 gene from these accessions and found that all of them have large dele- tions within the first intron, which overlap in a 4-kb region. Furthermore, a 2.8-kb segment within the 4-kb region showed high sequence conservation among the different recessive alleles. PCR markers for these dele- tions showed that similar deletions were present in all the accessions with known Vrn-B1 and Vrn-D1 alleles, and in 51 hexaploid spring wheat accessions previously shown to have no polymorphisms in the VRN-A1 pro- moter region. Twenty-four tetraploid wheat accessions Communicated by W.R. McCombie D. Fu AE L. Yan AE J. Dubcovsky (&) Department of Plant Sciences, University of California, One Shields Av, Davis, CA 95616, USA P. Szu } cs Agricultural Research Institute of the Hungarian Academy of Sciences, 2462 Martonva´sa´r, Hungary M. Helguera EEA INTA Marcos Jua´rez, CC 21, 2580 Marcos Jua´rez, Argentina J. S. Skinner AE J. von Zitzewitz AE P. M. Hayes Department of Crop and Soil Science and Horticulture, Oregon State University, Corvallis, OR 97331, USA had a similar deletion in VRN-A1 intron 1. We hypothesize that the 2.8-kb conserved region includes regulatory elements important for the vernalization requirement. Epistatic interactions between VRN-H2 and the VRN-H1 allele with the intron 1 deletion suggest that the deleted region may include a recognition site for the flowering repression mediated by the product of the VRN-H2 gene of barley. Keywords Wheat AE Barley AE Vernalization AE VRN-1 AE Allelic variation Introduction Many cereal crops, such as wheat, barley and oat, are divided into spring and winter types based on their growth habit. Winter varieties require an extended per- iod of exposure to cold in order to flower, a process known as vernalization. Vernalization is defined as ‘‘the acquisition or acceleration of the ability to flower by a chilling treatment’’ (Chouard 1960). The physiology of vernalization has been studied extensively in cereals, but only a few genes from this molecular pathway are cur- rently known (Yan et al. 2003, 2004b). In wheat and barley, the determination of the ver- nalization requirement involves an epistatic interaction between the genetic loci VRN-1 and VRN-2 (Takahashi and Yasuda 1971; Tranquilli and Dubcovsky 2000). Positional cloning of these two genes from diploid wheat (Triticum monococcum L., 2n=14, genome A m A m ) re- vealed that VRN-1 encodes a MADS-box transcription factor that is orthologous to the Arabidopsis meristem identity gene APETALA1 (Yan et al. 2003), while the VRN-2 gene codes for a zinc finger-CCT domain tran- scription factor with no clear orthologues in Arabidopsis or rice (Yan et al. 2004b). The VRN-1 gene is dominant for the spring growth habit and it is up-regulated by vernalization in winter lines (Danyluk et al. 2003; Tre- vaskis et al. 2003; Yan et al. 2003), whereas the VRN-2