Vrn-B1 Locus Research Articles

Marker-assisted development of wheat lines of the winter cultivar Bezostaya 1 and the effects of interaction between alleles of Vrn-A1L and Vrn-B1 loci on heading time

Marker-assisted development of wheat lines of the winter cultivar Bezostaya 1 and the effects of interaction between alleles of Vrn-A1L and Vrn-B1 loci on heading time

Evaluation of the Allelic Variations in Vernalisation (VRN1) and Photoperiod (PPD1) Genes and Genetic Diversity in a Spanish Spelt Wheat Collection.

Allelic variation within genes controlling the vernalisation requirement (VRN1) and photoperiod response (PPD1) determines the adaptation of wheat to different environmental growing conditions as well as influences other traits related to grain yield. This study aimed to screen a Spanish spelt wheat collection using gene-specific molecular markers for VRN-A1, VRN-B1, VRN-D1, and PPD-D1 loci and to phenotype for heading date (HD) in both field and greenhouse experiments under a long photoperiod and without vernalisation. Fifty-five spelt genotypes (91.7%) exhibited a spring growth habit, and all of them carried at least one dominant VRN1 allele, whereas five (8.3%) genotypes had a winter growth habit, and they carried the triple recessive allele combination. The Vrn-D1s was the most frequent allele in the studied set of spelt accessions, and it was found in combination with both the dominant Vrn-A1b and/or Vrn-B1a alleles in 88.3% of the spelt accessions tested. All spelt accessions carried the photoperiod-sensitive Ppd-D1b allele, which may explain the late heading of spelt germplasm compared to the commercial spring bread wheat Setenil used as a control. The least significant difference test showed significant differences between allelic combinations, the earliest accessions being those carrying two or three dominant alleles, followed by the one-gene combinations. In addition, the genetic diversity was evaluated through capillary electrophoresis using 15 wheat simple sequence repeat (SSR) markers. Most markers had high levels of polymorphism, producing 95 different alleles which ranged between 53 and 279 bp in size. Based on the polymorphic information content values obtained (from 0.51 to 0.97), 12 out of the 15 SSRs were catalogued as informative markers (values > 0.5). According to the dendrogram generated, the spelt accessions clustered as a separate group from the commercial bread wheat Setenil. Knowledge of VRN1 and PPD1 alleles, heading time, and genetic variability using SSR markers is valuable for spelt wheat breeding programs.

Allelic Variation Analysis at the Vernalization Response and Photoperiod Genes in Russian Wheat Varieties Identified Two Novel Alleles of Vrn-B3.

Heading time is an important agronomic trait affecting the adaptability and productivity of common wheat. In this study, 95 common wheat varieties from Russia and the late-maturing breeding line ‘Velut’ were tested for allelic diversity of genes having the strongest effect on heading. In this research, allelic variation at the Ppd-D1, Vrn-A1, Vrn-B1, Vrn-D1, and Vrn-B3 loci was tested. The Vrn-B1 and Vrn-B3 loci provided the largest contribution to genetic diversity. We found two novel allelic variants of the Vrn-B3 gene in the studied varieties. Ten varieties carried a 160 bp insertion in the promoter region, and the breeding line ‘Velut’ carried a 1617 bp insertion. These alleles were designated Vrn-B3e and Vrn-B3d, respectively. The analysis of the sequences showed the recent insertion of a retrotransposon homologous to the LTR retrotransposon (RLX_Hvul_Dacia_ RND-1) in the Vrn-B3d allele. Plants with the Vrn-B3e and the ‘Velut’ line with the Vrn-B3d allele headed later than the plants with the wild-type allele; among these plants, ‘Velut’ is the latest maturing wheat variety. Analysis of the gene expression of two groups of lines differing by the Vrn-B3 alleles (Vrn-B3d or vrn-B3) from the F2 population with ‘Velut’ as a parental line did not reveal a significant difference in the expression level between the groups. Additional research is required to study the reasons for the late maturation of the ‘Velut’ line. However, the studied wheat varieties could be used as a potential source of natural variation in genes controlling heading times.

Genetic analyses of native Fusarium head blight resistance in two spring wheat populations identifies QTL near the B1, Ppd-D1, Rht-1, Vrn-1, Fhb1, Fhb2, and Fhb5 loci.

QTL analyses of two bi-parental mapping populations with AC Barrie as a parent revealed numerous FHB-resistance QTL unique to each population and uncovered novel variation near Fhb1. Fusarium head blight (FHB) is a destructive disease of wheat worldwide, leading to severe yield and quality losses. The genetic basis of native FHB resistance was examined in two populations: a recombinant inbred line population from the cross Cutler/AC Barrie and a doubled haploid (DH) population from the cross AC Barrie/Reeder. Numerous QTL were detected among the two mapping populations with many being cross-specific. Photoperiod insensitivity at Ppd-D1 and dwarfing at Rht-B1 and Rht-D1 was associated with increased FHB susceptibility. Anthesis date QTL at or near the Vrn-A1 and Vrn-B1 loci co-located with major FHB-resistance QTL in the AC Barrie/Reeder population. The loci were epistatic for both traits, such that DH lines with both late alleles were considerably later to anthesis and had reduced FHB symptoms (i.e., responsible for the epistatic interaction). Interestingly, AC Barrie contributed FHB resistance near the Fhb1 locus in the Cutler population and susceptibility in the Reeder population. Analyses of the Fhb1 candidate genes PFT and TaHRC confirmed that AC Barrie, Cutler, and Reeder do not carry the Sumai-3 Fhb1 gene. Resistance QTL were also detected at the expected locations of Fhb2 and Fhb5. The native FHB-resistance QTL detected near Fhb1, Fhb2, and Fhb5 do not appear to be as effective as Fhb1, Fhb2, and Fhb5 from Sumai-3. The presence of awns segregated at the B1 awn inhibitor locus in both populations, but was only associated with FHB resistance in the Cutler/AC Barrie population suggesting linkage caused the association rather than pleiotropy.

Genomic selection for winter survival ability among a diverse collection of facultative and winter wheat genotypes

Winter survival ability is important for autumn sown winter wheat (Triticum aestivum L.) in regions with cold winters. Wheat vernalization and photoperiod genes influence adaptation by regulating the timing of the transition from vegetative to reproductive growth to protect the floral meristem from cold temperatures. We evaluated winter injury of 287 genotypes from the Facultative and Winter Wheat Observation Nursery (FAWWON) in six field environments over 3 years (2014 to 2016) in Colorado. Entries were genotyped using single-nucleotide polymorphisms (SNPs) obtained by genotyping by sequencing (GBS) and at known vernalization (Vrn-A1, Vrn-B1, and Vrn-D1) and photoperiod (Ppd-B1 and Ppd-D1) loci using Kompetitive Allele Specific PCR (KASP) assays. Winter injury was observed and visually scored in five of the six environments. Mean GS prediction accuracies across the five environments, obtained through ridge regression best linear unbiased prediction (RR-BLUP) using 23,269 SNPs alone as random effects, ranged from 0.26 ± 0.01 to 0.74 ± 0.00. Incorporation of alleles at Vrn-A1, Vrn-B1, and Vrn-D1 loci as fixed effects in the GS models together with GBS markers as random effects provided the highest prediction accuracy with mean GS accuracies ranging from 0.34 ± 0.01 to 0.78 ± 0.00 across the five environments. Genomic selection models incorporating photoperiod alleles as fixed effects rarely improved GS prediction accuracy of winter injury. Genomic selection models that incorporate both major and minor genetic factors that influence low-temperature tolerance improved the model predictions for identifying genotypes that are best adapted to regions where cold winter temperatures are an important production constraint.

Molecular characterization of a novel vernalization allele Vrn-B1d and its effect on heading time in Chinese wheat (Triticum aestivum L.) landrace Hongchunmai

Flowering time of wheat cultivars contributes greatly to the adaptability to environmental conditions and it is largely controlled by vernalization genes. In this study, 262 Chinese mini-core wheat cultivars were used to identify the allelic variation at VRN-B1 locus. A novel dominant allele Vrn-B1d was found in Chinese spring wheat landrace cultivar Hongchunmai. This allele contained several genetic divergence within the first intron comparing to the recessive allele vrn-B1, including one large 6850-bp deletion (670–7519 bp), one small 187-bp deletion (7851–8037 bp), one unique SNP (T to C, 7845 bp), and one 4-bp mutation (TTTT to ACAA, 7847–7850 bp). Meanwhile, it was also different from the three known dominant alleles at VRN-B1 locus. Two pairs of primers were designed to identify the novel allele Vrn-B1d and other four known alleles of VRN-B1. A multiplex PCR was established to discriminate all five alleles simultaneously. The greenhouse experiment with high temperature (non-vernalizing condition) and long light showed that F2 plants containing Vrn-B1d allele headed significantly earlier than those with recessive vrn-B1 allele, suggesting that Vrn-B1d is a dominant allele conferring the spring growth habit. This study provides a useful germplasm and molecular markers for wheat breeding.

Heading Date QTL in Winter Wheat (Triticum aestivum L.) Coincide with Major Developmental Genes VERNALIZATION1 and PHOTOPERIOD1.

In wheat (Triticum aestivum L.), time from planting to spike emergence is influenced by genes controlling vernalization requirement and photoperiod response. Characterizing the available genetic diversity of known and novel alleles of VERNALIZATION1 (VRN1) and PHOTOPERIOD1 (PPD1) in winter wheat can inform approaches for breeding climate resilient cultivars. This study identified QTL for heading date (HD) associated with multiple VRN1 and PPD1 loci in a population developed from a cross between two early flowering winter wheat cultivars. When the population was grown in the greenhouse after partial vernalization treatment, major heading date QTLs co-located with the VRN-A1 and VRN-B1 loci. Copy number variation at the VRN-A1 locus influenced HD such that RIL having three copies required longer cold exposure to transition to flowering than RIL having two VRN-A1 copies. Sequencing vrn-B1 winter alleles of the parents revealed multiple polymorphisms in the first intron that were the basis of mapping a major HD QTL coinciding with VRN-B1. A 36 bp deletion in the first intron of VRN-B1 was associated with earlier HD after partial vernalization in lines having either two or three haploid copies of VRN-A1. The VRN1 loci interacted significantly and influenced time to heading in field experiments in Louisiana, Georgia and North Carolina. The PPD1 loci were significant determinants of heading date in the fully vernalized treatment in the greenhouse and in all field environments. Heading date QTL were associated with alleles having large deletions in the upstream regions of PPD-A1 and PPD-D1 and with copy number variants at the PPD-B1 locus. The PPD-D1 locus was determined to have the largest genetic effect, followed by PPD-A1 and PPD-B1. Our results demonstrate that VRN1 and PPD1 alleles of varying strength allow fine tuning of flowering time in diverse winter wheat growing environments.

QTL and major genes influencing grain yield potential in soft red winter wheat adapted to the southern United States

The aim of this study was to identify quantitative trait locus (QTL) associated with grain yield (GY) in a recombinant inbred line (RIL) population from a cross between two elite soft red winter wheat (SRWW) cultivars (‘Pioneer 26R61’ and ‘AGS2000’). The RIL population was grown from 2011 to 2014 in 12 site-year combinations throughout the southeastern US. Overall, AGS2000 was the higher yielding parental line, out-performing 26R61 in seven of the 12 environments. Mean GY for the RILs ranged from 3.39 to 7.16 t ha−1 with significant genotype, environment and genotype by environmental interaction effects. Nine stable QTL were detected for yield, explaining up to 53 % of the phenotypic variation when fit into a multiple-QTL model. The QTL with the largest effect was detected at the Vrn-B1 locus with the short vernalization winter allele from AGS2000 favorable for yield. In addition, vrn-B1 acted additively with a region on chromosome 2B near the Ppd-B1 locus, indicating that a shorter vernalization requirement combined with the Ppd-B1b allele for photoperiod sensitivity may play a key role in adaptation of SRWW to the southern US. Single nucleotide polymorphism markers linked to additional QTL on chromosomes 3A and 3B were in agreement with a previous genome-wide association study in spring wheat, confirming the importance of these regions for yield across environments and germplasm pools. Overall the stable QTL were more predictive of GY compared to individual site-year QTL, indicating that a targeted QTL approach can be utilized by breeding programs to enrich for favorable loci.

Genetic variation for flowering time and height reducing genes and important traits in western Canadian spring wheat

Genetic variation is prerequisite for wheat improvement. High grain yield and protein content and early maturity are some of the major objectives in global as well as Canadian wheat breeding programs. We investigated genetic diversity for earliness related and plant height reducing (Rht) genes in 82 spring wheat cultivars, registered in western Canada, through eight diagnostic DNA markers. Allelic variation was observed at the Vrn-A1, Vrn-B1, Vrn-D1 and Ppd-D1 loci but not at Ppd-A1 and Ppd-B1 loci in the 82 cultivars. Spring type allele of Vrn-A1 was present in 94 % cultivars, whereas only two cultivars carried spring allele of Vrn-D1. Among the four earliness related genes, the most frequent combination was Vrn-A1a, Vrn-B1, vrn-D1 and Ppd-D1b, which was found in 32 cultivars. As for the Rht genes, eight cultivars had Rht-B1b and 13 cultivars had Rht-D1b. All cultivars carrying dominant allele of Vrn-B1, photoperiod-insensitive allele of Ppd-D1 and height reducing allele of Rht-1 had shorter plants and higher grain yield but lower grain protein content. Days to heading and maturity showed positive genetic (rg = 0.65) and phenotypic (rp = 0.44) correlation, and were also positively correlated with grain yield and kernel weight but negatively correlated with test weight and protein content. Plant height was positively correlated with grain protein content (rg = 0.53; rp = 0.42), but negatively correlated with grain yield (rg = −0.47; rp = −0.14). Grain yield and protein content showed negative genetic correlation (rg = −0.57). Among the sixty cultivars from Canada Western Red Spring Class released over 100 years, the newest cultivar yielded 23 % more grain and had 15 % higher grain protein than the oldest cultivar ‘Red Fife’. Breeders in western Canada have incorporated vernalization and photoperiod insensitive and Rht genes in modern cultivars to promote early maturity, to make use of off-season nurseries abroad, and to improve lodging tolerance.

Earliness per se quantitative trait loci and their interaction with Vrn-B1 locus in a spring wheat population

In the spring wheat-growing regions of western Canada, early maturity is an important trait for timely harvest to avoid frost damage, and associated harvest and post-harvest problems. Earliness is genetically regulated by vernalization, photoperiod, earliness per se genes, and complex gene interactions. In this study, we explored the effect of these gene complexes on the expression of 11 agronomic traits in the CDC Teal × CDC Go Canadian western red spring wheat-mapping population. The population of 187 recombinant inbred lines was genotyped with 341 DArT polymorphic markers and a functional Vrn-B1 marker, and phenotyped over 3 years in replicated trials. The dominant allele of Vrn-B1 reduced the number of days to heading, flowering and maturity, and increased leaf color concentration and plant height, but did not affect grain yield in the presence of common genetic backgrounds with dominant Vrn-A1a and Ppd-D1 alleles at two epistatic loci, Vrn-A1 and Ppd-D1. A total of 21 QTLs were identified for all phenotypic traits recorded, except plant height and grain protein content. Two earliness per se QTLs were mapped on chromosomes 1A (QEps.dms-1A) and 4A (QEps.dms-4A) in all three growing seasons, contributing 15–27 and 8–10 %, respectively, to the total genetic variation in days to maturity. The two earliness QTLs and Vrn-B1 exhibited additive interaction. Lines carrying dominant alleles at these three loci headed, flowered and matured 1.7, 1.9 and 4 days earlier, respectively, but yielded 0.43 t ha−1 less than lines with recessive alleles.

Allelic composition in the Vrn-A1, Vrn-B1, and Vrn-B3 genes of double haploid lines of hexaploid triticale

Vernalization genes are associated with the adaptation capability, heading dates, and yield potential of grain crops. The allelic composition in the Vrn-A1, Vrn-B1, and Vrn-B3 genes was defined in 42 lines of double haploids of hexaploid triticale, which were produced through in vitro anther culture. Two alleles (Vrn-A1a and vrn-A1) were found at the Vrn-A1[ital] locus and three alleles (Vrn-B1a, Vrn-B1c, and vrn-B1) were found at the Vrn-B1 locus. All double haploids carried the recessive allele at the Vrn-B3[ital] locus. Twelve lines of spring triticale were selected, and they were characterized by an allelic composition associated with early maturity and high potential of grain yield.

Allelic Variation of Rht-1, Vrn-1 and Ppd-1 in Korean Wheats and Its Effect on Agronomic Traits

The allelic variations at the Rht-1, Vrn-1 and Ppd-1 of 410 Korean wheat cultivars, including 111 Korean experimental lines, 238 Korean landraces and 61 North Korean collections, were investigated to provide the information of plant height and heading date and to elucidate the relationship between those traits and allelic variation of these genes because earliness is major consideration in Korean wheat production. All Korean wheats displayed vrn-A1 and Ppd-A1b alleles, while Rht-B1a, Rht-D1a, vrn-B1, Vrn-D1, Ppd-B1b and Ppd-D1a alleles were also predominantly found. Most Korean wheats carried both Rht-B1a and Rht-D1a alleles, both vrn-B1 and Vrn-D1 alleles, or both Ppd-B1b and Ppd-D1a alleles. The Rht-B1a, vrn-D1, Ppd-B1b and Ppd-D1b alleles were found to exhibit longer culm and spike length than their counterpart alleles. The Rht-B1a allele also showed longer spike length than Rht-B1b. Vrn-B1b and vrn-D1 alleles exhibited longer days to heading date than their counterpart alleles at the Vrn-B1 and Vrn-D1 loci. Lines carrying both Rht-B1b and Rht-D1b alleles displayed shorter culm and longer spike length and days to heading date than any other combination of alleles at the Rht-B1 and Rht-D1 loci. In contrast, lines carrying both Ppd-B1b and Ppd-D1b alleles exhibited longer culm and spike length than any other combination of alleles at the Ppd-B1 and Ppd-D1 loci.

VRN-1 gene- associated prerequisites of spring growth habit in wild tetraploid wheat T. dicoccoides and the diploid A genome species.

BackgroundIn order to clarify the origin of spring growth habit in modern domesticated wheat, allelic variability of the VRN-1 gene was investigated in a wide set of accessions of the wild tetraploid species Triticum dicoccoides (BBAA), together with diploid species T. monococcum, T. boeoticum and T. urartu, presumable donors of the A genome to polyploid wheats.ResultsNo significant variation was found at the VRN-B1 locus of T. dicoccoides, whereas at VRN-A1 a number of previously described alleles were found with small deletions in the promoter (VRN-A1b, VRN-A1d) or a large deletion in the first (1st) intron (VRN-A1L). The diploid A genome species were characterized by their own set of VRN-1 alleles including previously described VRN-A1f and VRN-A1h alleles with deletions in the promoter region and the VRN-A1ins allele containing a 0.5 kb insertion in the 1st intron. Based on the CAPS screening data, alleles VRN-A1f and VRN-A1ins were species-specific for T. monococcum, while allele VRN-A1h was specific for T. boeoticum. Different indels were revealed in both the promoter and 1st intron of the recessive VRN-A1u allele providing specific identification of T. urartu, the proposed donor of the A genome to modern wheat. We found that alleles VRN-A1b and VRN-A1h, previously described as dominant, have either no or weak association with spring growth habit, while in some diploid accessions this habit was associated with the recessive VRN-A1 allele.ConclusionsSpring growth habit in diploid wheats was only partially associated with indels in regulatory regions of the VRN-1 gene. An exception is T. monococcum where dominant mutations in both the promoter region and, especially, the 1st intron were selected during domestication resulting in a greater variety of spring forms. The wild tetraploid T. dicoccoides had a distinct set of VRN-A1 alleles compared to the diploids in this study, indicating an independent origin of spring tetraploid forms that likely occurred after combining of diploid genomes. These alleles were subsequently inherited by cultivated polyploid (tetraploid and hexaploid) descendants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0473-x) contains supplementary material, which is available to authorized users.

Characterization of wild emmer wheat Triticum dicoccoides germplasm for vernalization alleles

The flowering in winter and wild wheats is induced by extended exposure to cold temperatures, a process called vernalization while spring wheats do not have any such requirement. In the present study, we analyzed 45 accessions of wild emmer wheat T. dicoccoides for the allelic composition of the vernalization genes at VRN-A1 and VRN-B1 loci. Three gene based markers for VRN-A1 and two for VRN-B1 locus were used. Thirty five T. dicoccoides accessions had only winter type allele vrn-A1 at VRN-A1 locus. One accession each had VRN-A1a and Vrn-A1d allele, and two accessions each showed the presence of VRN-A1b and Vrn-A1c, potent spring type alleles. Three accessions, however, had multiple alleles at VRN-A1 locus. At the VRN-B1 locus 35 accessions had winter type allele vrn-B1 and 10 accession had dominant Vrn-B1 allele. These T. dicoccoides accessions constitute a very useful resource for incorporation of alternative vernalization alleles in the cultivated wheat gene pool for developing better adaptive wheat varieties.

Distribution of different Vrn-B1 alleles in hexaploid spring wheat germplasm

In wheat, the transition from the vegetative to reproductive stage is primarily controlled by the series of vernalisation (Vrn-1) genes located on the homoeologous group 5 chromosomes. Up to 2009, only two alleles at the Vrn-B1 locus were known: one dominant, spring, allele (now designated Vrn-B1a) and the other recessive, winter, (vrn-B1) allele. Recently, two additional dominant alleles, Vrn-B1b and Vrn-B1c, were described. In this study, we screened a range of hexaploid spring wheat germplasms for the presence of different Vrn-B1 alleles using new diagnostic molecular markers. Our results show that the Vrn-B1a allele was the most prevalent, being present in 55.3 % of the 2,495 accessions examined, followed by the recessive vrn-B1 allele, which occurred in 31.5 % of the accessions. The novel alleles Vrn-B1b and Vrn-B1c were found in 5.3 and 7.9 % of all accessions, respectively.

Molecular examination and genotype diversity of vernalization sensitivity and photoperiod response in old and modern bread wheat cultivars grown in Iran

Understanding the genetic factors governing developmental patterns and flowering time in breeding materials is required for the development of new wheat varieties for a specific environment. Iran is among the largest wheat producers in the arid and semi-arid regions of the Middle East and North Africa. The wheat germplasm grown in Iran is either developed nationally or is introduced from the CIMMYT global wheat program. For decades, the wheat breeding program in Iran focused on generating new varieties better able to grow in the predominant Iranian climatic conditions such as humidity at the reproductive stage, high temperature during reproductive stages (terminal heat stress), moderate temperature during the cropping season, and high probability of frost damage during early stages of growth. There have also been sub-programs aimed at developing drought and salinity-tolerant wheat cultivars in Iran. Knowledge of cultivars’ growth habits in Iran is currently limited to flowering in spring-sown nurseries. We identified allelic diversity in loci involved in vernalization response (Vrn) and photoperiod sensitivity (Ppd) in 60 bread wheat cultivars developed in Iran, CIMMYT, or ICARDA. This study revealed that the spring growth habit observed in most of the cultivars is conferred by a combination of recessive vrn-A1 and dominant Vrn-D1, Vrn-B1, and/or Vrn-B3 loci. This implies that most of the cultivars have minimal vernalization requirements for overwintering. Perhaps cold winters, even in the southern regions of Iran, provide sufficient vernalization conditions for cultivars possessing the recessive vrn-A1 allele. The germplasm investigated in this study revealed no evidence indicating selection for or against any specific Vrn and Ppd allele in our wheat breeding program.

Molecular genetical characterization of vernalization genesVrn-A1, Vrn-B1andVrn-D1in spring wheat germplasm from Russia and adjacent regions

We characterized a representative set of 42 spring wheat cultivars from Russia and adjacent regions for 3 Vrn loci. The 42 genotypes were screened, along with 3 genotypes of known Vrn genes, using previously published genome-specific polymerase chain reaction (PCR) primers designed for detecting the presence or absence of dominant or recessive alleles of the major Vrn loci: Vrn-A1, Vrn-B1 and Vrn-D1. The dominant promoter duplication allele Vrn-A1a was present in 28 of 42 cultivars, whereas the promoter deletion allele Vrn-A1b was present in only 1 of the Russian cultivars (Triticum aestivum L. ‘Pyrothrix 28’). The intron deletion allele Vrn-A1c was not present in any tested cultivar. The dominant Vrn-D1 allele was found in 1 of the cultivars. Thirteen of the spring wheat cultivars tested here carry the recessive vrn-A1 allele. However, for 6 cultivars, there were inconsistencies between PCR data and genetic segregation analysis, showing the presence of the dominant Vrn-A1 gene. No inconsistencies were found in the case of Vrn-B1 locus. A new combination of specific primers allowed amplification of the common Vrn-B1a allele along with the novel Vrn-B1c allele, which was present in 17 of the studied cultivars (40%). Twenty-five cultivars (59%) had dominant alleles of Vrn-A1a and Vrn-B1 in combination. We showed the predominance of the Vrn-B1c allele among cultivars with monogenic control of vernalization in West Siberia and Kazakhstan. In the absence of epistatic effects of Vrn-A1, this allele causes an earlier heading time compared to Vrn-B1a, thereby avoiding early fall frosts. Suggestions are made concerning the origin and distribution of the Vrn-B1c allele among Russian spring wheats.

Identification of a new Vrn-B1 allele using two near-isogenic wheat lines with difference in heading time

We conducted a molecular analysis of the Vrn-B1 gene in two near-isogenic lines (NILs) carrying the dominant Vrn-B1 S and Vrn-B1 Dm alleles from the Saratovskaya 29 and Diamant 2 cultivars, respectively. These lines are characterized by different times of ear emergence. PCR analysis and subsequent sequencing of the regulatory regions of Vrn-B1 revealed the full identity of the promoter region in both alleles. Simultaneously, we found significant differences in the structure of the first intron of the Vrn-B1 S allele when compared to Vrn-B1 Dm ; specifically, the deletion of 0.8 kb coupled with the duplication of 0.4 kb. We suggest that these changes in intron 1 of Vrn-B1 S caused earlier ear emergence in the corresponding NIL. The unusual structure of intron 1 within the Vrn-B1 S allele was described for the first time in this study. The allele Vrn-B1 Dm was almost identical with the previously studied sequence of the Vrn-B1a allele of T. aestivum, Triple Dirk B. We designated the new Vrn-B1 S allele as Vrn-B1c. PCR analysis of the Vrn-B1 gene in 26 spring wheat cultivars of both Russian and foreign breeding revealed that 16 of them contain the Vrn-B1a allele and 6 contain the Vrn-B1c allele. Other cultivars studied contained the recessive vrn-B1 gene, except for Novosibirskaya 67. This study demonstrates that the traditional system of Vrn-1 markers does not fully encompass the allelic diversity of these genes because none of the cultivars containing the Vrn-B1c allele gave a PCR product using the previously developed set of primers for identification of the Vrn-B1 locus. We showed that the newly characterized Vrn-B1c allele is widely distributed among different genotypes of spring wheat. The findings indicate the impact of structural changes in the first intron of Vrn-1 on the vernalization response and heading time.

Multiple allelism in theVrn-B1locus of common wheat

Two intervarietal substitution lines of common wheat cv. Sava bearing chromosome 5B from Saratovskaya 29 and Diamant 2 donors and two near-isogenic lines (NILs) of winter cv. Bezostaya 1 with the Vrn-B1 locus from the same donors were developed. Multiple allelism of the dominant Vrn-B1 locus was studied in these lines. It manifested itself as earing time variation in plants grown near Novosibirsk (West Siberia), Almaty (Kazakhstan), and in a greenhouse. One dominant allele, Vrn-B1S, having a stronger effect on earing time, was detected in Saratovskaya 29 and another, Vrn-B1Dm, in Diamant 2. The NILs and substitution lines are late-ripening. Lines with Vrn-B1S come to earing earlier than with Vrn-B1Dm.

Distribution and Selective Effects of Vrn-A1, Vrn-B1, and Vrn-D1 Genes in Derivative Varieties from Four Cornerstone Breeding Parents of Wheat in China

Vernalization, the process of a long exposure to low temperature to induce flowering in plants, is essential for plants to adapt to cold winters. The presence of vernalization genes Vrn-A1, -B1, and -D1 in four cornerstone breeding parents of wheat in China (Funo, Mentana, Yanda 1817, and Bima 4) and 322 derivative varieties (mostly winter wheat) from these parents were determined using PCR based molecular method. The frequencies of the VRN−1 genes in these derivative varieties were in order of Vrn-D1(67.1%) > Vrn-B1(19.6%) > Vrn-A1(5.3%), which are similar as the former conclusion that Vrn-D1 is associated with the latest heading time, Vrn-A1 the earliest, and Vrn-B1 intermediate values. The frequencies of Vrn-A1 and Vrn-B1 loci in the derivative varieties from winter wheat zones were higher than that from spring winter zones. Based on the wheat breeding history in China and the fact of non-random distribution of Vrn-A1 and Vrn-B1 in the derivative varieties from the four parents, there could be a strong selective effect on VRN−1 genes in different regions where the derivative varieties were cultivated.