Effect of VRN‐1 and PPD‐D1 genes on heading time in European bread wheat cultivars

The variation of the vernalization (VRN‐1) and photoperiod (PPD‐1) genes offers opportunities to adjust heading time and to maximize yield in crop species. The effect of these genes on heading time was studied based on a set of 245 predominantly spring cultivars of bread wheat from the main eco‐geographical regions of Europe. The genotypes were screened using previously published diagnostic molecular markers for detecting the dominant or recessive alleles of the major VRN‐1 loci such as: VRN‐A1, VRN‐B1, VRN‐D1 as well as PPD‐D1. We found that 91% of spring wheat cultivars contain the photoperiod sensitive PPD‐D1b allele. Photoperiod insensitive PPD‐D1a allele has been found mainly in southern region of Europe. For this region the monogenic control of vernalization by VRN‐B1 or VRN‐D1 dominant alleles is common, whereas in the remaining part of Europe, the combination of photoperiod sensitive PPD‐D1b allele with dominant VRN‐A1, VRN‐B1 and recessive vrn‐D1 alleles represents the most frequent genotype. Also, we revealed a significantly later (5–8 days) heading of the monogenically dominant genotypes at VRN‐B1 as compared to the digenic VRN‐A1 VRN‐B1 genotypes.     

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.     

Mapping of the Vrn-B1 gene in Triticum aestivum using microsatellite markers

An F₂ population segregating for the dominant gene Vrn‐B1 was developed from the cross of the substitution line ‘Diamant/'Miro‐novskaya 808 5A’ and the winter wheat cultivar ‘Bezostaya 1′. Microsatellite markers (Xgwm and Xbarc) with known map locations on chromosome 5B of common wheat were used for mapping the gene Vrn‐B1. Polymorphism between parental varieties was observed for 28 out of 34 microsatellite markers (82%). Applying the quantitative trait loci mapping approach, the target gene was mapped on the long arm of chromosome 5B, closely linked to Xgwm408. The map position of Vrn‐B1 suggests that the gene is homoeologous to other vernalization response genes located on the homoeologous group 5 chromosomes of wheat, rye and barley.     

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.     

Evaluation of cold hardiness in two sets of near-isogenic lines of wheat (Triticum aestivum) with polymorphic vernalization alleles

In wheat, variation at the orthologus Vrn‐1 loci, located on each of the three genomes, A, B and D, is responsible for vernalization response. A dominant Vrn‐1a allele on any of the three wheat genomes results in spring habit and the presence of recessive Vrn‐1b alleles on all three genomes results in winter habit. Two sets of near‐isogenic lines (NILs) were evaluated for DNA polymorphisms at their Vrn‐A1, B1 and D1 loci and for cold hardiness. Two winter wheat cultivars, ‘Daws’ and ‘Wanser’ were used as recurrent parents and ‘Triple Dirk’ NILs were used as donor parents for orthologous Vrn‐1 alleles. The NILs were analysed using molecular markers specific for each allele. Only 26 of 32 ‘Daws’ NILs and 23 of 32 ‘Wanser’ NILs had a plant growth habit that corresponded to the marker genotype for the markers used. Freezing tests were conducted in growth chambers programmed to cool to ?21.5°C. Relative area under the death progress curve (AUDPC), with a maximum value of 100 was used as a measure of death due to freezing. The average relative AUDPC of the spring habit ‘Daws’Vrn‐A1a NILs was 86.15; significantly greater than the corresponding winter habit ‘Daws’Vrn‐A1b NILs (42.98). In contrast, all the ‘Daws’Vrn‐A1bVrn‐B1aVrn‐D1b and Vrn‐A1bVrn‐B1bVrn‐D1a NILs (spring habit) had relative AUDPC values equal to those of their ‘Daws’ sister genotypes with Vrn‐A1bVrn‐B1bVrn‐D1b NILs (winter habit). The average AUDPC of spring and winter habit ‘Wanser’ NILs differed at all three Vrn‐A1, Vrn‐B1 and Vrn‐D1 locus comparisons. We conclude that ‘Daws’ and ‘Wanser’ have different background genetic interactions with the Vrn‐1 loci influencing cold hardiness. The marker for Vrn‐A1 is diagnostic for growth habit and cold hardiness but there is no relationship between the Vrn‐B1 and Vrn‐D1 markers and the cold tolerance of the NILs used in this study.     

Genetic and Molecular Characterization of Vernalization Genes Vrn‐A1, Vrn‐B1, and Vrn‐D1 in Spring Wheat Germplasm from the Pacific Northwest Region of the U.S.A.

The objective of this study was to determine the Vrn‐1 allelic composition of spring wheat germplasm from the Pacific Northwest region of the USA. Individual plants from 56 spring wheat lines were crossed to near‐isogenic tester lines carrying the dominant allele Vrn‐A1, Vrn‐B1 or Vrn‐D1. F₂ progeny were evaluated for growth habit in the field and Vrn‐1 allelic composition was determined through chi‐square analysis. Lines also were analysed with DNA sequence‐based Vrn‐1 allele‐specific markers. A majority of the germplasm carried the dominant allele Vrn‐A1a alone or in combination with Vrn‐B1, Vrn‐D1 or Vrn‐B3 alleles. Vrn‐B1 and Vrn‐D1 were almost always associated with other dominant Vrn‐1 allele(s). Based on DNA sequence analysis, a novel Vrn‐B1 allele referred to as Vrn‐B1b, which carried a single nucleotide polymorphism (SNP) and a 36 bp deletion, was identified in cultivar ‘Alpowa’. These results will be useful to wheat breeders for choosing parents with different Vrn‐1 alleles for crossing to maximize diversity at the Vrn‐1 loci with an expectation of identifying superior Vrn‐1 allelic combinations for cultivar improvement.     

Microsatellite monitoring of recombination around the Vrn-B1 locus of wheat during early backcross breeding

The length of chromosomal segments retained around the Vrn‐B1 gene controlling sensitivity to vernalization in wheat (Triticum aestivum L.) was studied in the first and third backcrosses by using microsatellite markers. Eleven polymorphic markers located on chromosome 5B were used for microsatellite analysis. It was shown in the first backcross that plants with a donor segment around the gene of interest not longer than 50% of chromosome 5B could be selected. When selection is not molecular‐marker assisted, the length of the chromosomal donor segment with the target gene may reach 94% of chromosome 5B even in plants of the third backcross generation. The considerable length differences in the 5B microsatellite loci between the winter and spring lines of wheat studied indicate that these markers are promising in marker‐assisted backcrossing or marker‐assisted selection for the Vrn‐B1 gene using different combinations of Spring and Winter genotypes.     

Developmental responses to vernalization in wheat deletion lines for chromosomes 5A and 5D

The aim of this investigation was to test the developmental patterns of deletion lines, generated for chromosome arms 5AL and 5DL in the variety ‘Chinese Spring’ (CS) under vernalized and non‐vernalized treatments. Plants were grown in controlled conditions under saturating daylength. Time to heading and the duration of particular phases before flowering were recorded, and leaf and spikelet production rates and numbers were analysed. The lines lacking Vrn‐A1 and Vrn‐D1 were delayed in time to heading under non‐vernalized conditions, because of the lengthening of the emergence to floral initiation phase (EM‐FI) and the terminal spikelet to heading phase (TS‐H). Differences in final leaf numbers corresponded to longer durations of the EM‐FI phase. The absence of Vrn‐A1 and Vrn‐D1 apparently decreased the number of spikelets by a lower primordium production rate, even though the duration of the FI‐TS phase was longer or equal to CS. The sensitivity to vernalization in lines where the Vrn genes were deleted was much higher.     

The influence of photoperiod on the Vrn-H2 locus (4H) which is a major determinant of plant development and reproductive fitness traits in a facultative × winter barley (Hordeum vulgare L.) mapping population

To determine the effect of Vrn‐H2 locus on plant developmental and agronomic traits, detailed controlled environment tests involving a factorial set of vernalization and photoperiod treatments were carried out using doubled haploid lines developed from a facultative (Vrn‐H2^?) × winter (Vrn‐H2⁺) barley cross. The allele phase at the Vrn‐H2 locus influenced heading date as well as the developmental and agronomic traits. The performance of Vrn‐H2⁺ lines was significantly influenced by vernalization: reproductive fitness traits showed significant decreases without vernalization. However, the effects of alleles at the Vrn‐H2 locus extended beyond simple satisfaction of the vernalization requirement. Vrn‐H2⁺ lines showed increased reproductive fitness compared with Vrn‐H2^? lines when vernalization was followed by a long photoperiod. The responses of the two Vrn‐H2 allele classes to photoperiod duration were quite different in terms of heading date, developmental and agronomic traits. These results suggest that alleles at the Vrn‐H2 locus – and/or tightly linked gene(s) – respond primarily to the exogenous signal of vernalization (temperature), but when the vernalization requirement has been fulfilled, they also respond to photoperiod duration.     

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.     

Growth habit in common wheat (Triticum aestivum L. em. Thell.)

Summary A study of the Vrn genotypes of 642 spring wheats supports the theory that only Vrn1, Vrn2 and Vrn3 exist in Tricticum aestivum. In none of the varieties investigated Vrn4 was present. Seven varieties, which according to literature carry Vrn4, showed to carry Vrn1, Vrn2 and/or Vrn3. Some varieties were mixtures of Vrn-genotypes, which could mislead geneticists in pooled data analysis. Other causes for misinterpretation of the data could be hybrid necrosis, hybrid dwarfness or a wrong determination of plants with a winter habitus. Only Hope was dominant on another Vrn locus. Its haploid Vrn-genotype is Vrn1 vrn2vrn3 Vrn5.     

小麦TaFT基因编码区序列多态性及其与开花期的关系

春化基因VRN-B3是小麦开花素基因TaFT,为探索该基因在品种间的保守性及其与小麦开花早晚的关系,根据TaFT基因序列(GenBank accession No.: DQ890162)设计特异PCR引物,扩增了13个品种中该基因的编码区。通过测序和序列比对,发现不同品种间该基因编码区的DNA序列存在多态性,序列翻译发现5个品种的表达产物FT蛋白发生变异。利用中国春的非整倍体材料将TaFT基因定位在7BS染色体上。参考品种的冬春性及开花时间,推测冬性品种正常的FT蛋白(同DQ890162翻译的氨基酸序列一致)可加速开花,FT蛋白变异则延迟开花;春性品种的FT蛋白变异与否对开花期影响不大,推测TaFT基因的效应可能被春性品种的显性春化基因所掩盖。     

Relative performance of Canadian spring wheat cultivars under organic and conventional field conditions

Producing higher yields under organic conditions is generally hampered by weeds and lesser nutrient supply. In wheat certain adaptive traits like early season vigour, taller plants, and shorter life cycle have been reported to help plants compete with weeds and produce satisfactory yields. In this experiment we tested the hypothesis ‘that early flowering and maturity conferred by insensitive vernalization alleles Vrn-A1a and/or Vrn-B1 has a yield advantage under organic conditions’ in Canadian spring wheat germplasm. We genotyped 32 cultivars for their vernalization gene composition (Vrn-A1a, Vrn-B1 and Vrn-D1) and studied these cultivars in organic and conventional management systems. We found 88 % of the cultivars possessed vernalization (Vrn) insensitive allele Vrn-A1a either alone or in combination with Vrn-B1. There were no differential affects between the cultivars having insensitive Vrn allele at either single locus (Vrn-A1a) or two (Vrn-A1a, Vrn-B1) under organic and conventional field conditions; except for days to maturity, where cultivars having only Vrn-A1a allele matured earlier. This earlier maturity did not translate to any yield advantage under organic field conditions. Overall, the cultivars grown under organic conditions were earlier flowering, lower yielding with lower test weight compared to the conventional management system. Significant cultivar × environment interactions were found for grain yield, grain protein content and grain fill rate. For grain protein content, cross-over interactions of the cultivars between the management systems were observed. Three cultivars (Marquis, Unity and Minnedosa) exhibited minimal comparative loss in grain yield and grain protein content under organic field conditions, and hence could potentially serve as parents for organic wheat breeding programs.     

Intrachromosomal mapping of genes for dwarfing (Rht12) and vernalization response (Vrn1) in wheat by using RFLP and microsatellite markers

For intrachromosomal mapping of the dominant GA-sensitive dwarfing gene Rht12 and the vernalization response gene Vrn1 on chromosome 5 A, an F₂ population was established using a wide (synthetic) wheat cross. In addition to restriction fragment length polymorphism (RFLP) probes four microsatellite markers were incorporated. Rht12 was mapped distally to four RFLP loci (Xmwg616, Xpsr164, Xwg114, Xpsr1201) and three microsatellite markers (Xgwm179, Xgwm410, Xgwm291), known to be located on the segment of chromosome SAL which was ancestrally translocated and is homoeologous to Triticeae 4 L. The map position of Rht12 suggests that it is homoeologous to the dominant GA-sensitive dwarfing gene Ddw1, present on chromosome 5RL. The vernalization response gene Vrn1 showed linkage to Xwg644, as might be expected from comparative maps.     

Adaptation and ecological differentiation in wheat with special reference to geographical variation of growth habit and Vrn genotype

Geographical variation of growth habit was studied for 749 landraces from various parts of the world, with special reference to their adaptation and ecogeographical differentiation. The total frequency of spring‐type landraces was 49.9%, and varied between localities. Spring‐type landraces were frequent in two distinct areas where the average January temperature was either below ‐7°C or above 4°C, with winter‐type landraces in areas from ‐7°C to 4°C. These results indicated that geographical variation of growth habit is closely related to the degree of winter coldness. An analysis of the Vrn genotype for 216 spring‐type landraces demonstrated the uneven distribution of four Vrn genes, with Vrn4 being the least frequent. The adaptive Vrn genotype was different between localities. Genotypes carrying Vrn‐A1 and additional Vrn gene(s) were frequent in two distinct areas where the average January temperature was either below ‐7°C or over 10°C, while genotypes with any of three Vrn genes, except Vrn‐A1, adapted to areas with temperatures from 4°C to 10°C. Therefore, it was concluded that the adaptability of wheat landraces differed depending on their growth habit and Vrn genotype, and that ecotypes with different Vrn genotypes were allopatrically distributed as a result of adaptation to different winter temperature. However, the differential distribution of Vrn‐B1, Vrn‐D1 and Vrn4 could not be explained by their adaptability, and might reflect the polyphyletic origin of common wheat.     

Identifying AFLP and microsatellite markers for vernalization response gene Vrn-B1 in hexaploid wheat using reciprocal mapping populations

Marker‐assisted selection may be useful for combining specific vernalization response (Vrn) alleles into a single wheat genotype for yield enhancement; however, DNA markers are only available for two of the three genes identified to date. The objectives of this study were to investigate reciprocal effects on days to heading using F₂ populations generated by cross‐hybridizing near‐isogenic lines (NILs) carrying spring (Vrn‐B1; TDB) and winter (vrn‐B1; TDC) alleles, and to identify markers linked to Vrn‐B1 through genetic linkage analysis. Heading data were recorded for 91 and 89 progeny from reciprocal mapping populations TDB/TDC and TDC/TDB, respectively, and significant (P < 0.0001) reciprocal and dominance effects were detected. Among 207 amplified fragment length polymorphisms primer pairs and seven wheat microsatellite markers screened, two and one, respectively, were linked distally to Vrn‐B1 on wheat chromosome 5BL. Microsatellite Xgwm408 was most closely linked to Vrn‐B1 at 3.9 and 1.1 cM in the TDB/TDC and TDC/TDB map, respectively. Reciprocal differences in recombination distances emphasize the importance of female parent choice when generating mapping populations. Molecular markers are now available for three Vrn loci in wheat.     

Genetic control of flowering time and its component processes in subterranean clover (Trifolium subterraneum L.)

Summary The inheritance of flowering time and its component processes, vernalization and photoperiod response, were studied in two crosses of subterranean clover (Trifolium subterraneum L.) using a field sowing and four controlled environment sowings with different combinations of vernalization and photoperiod. Time to flowering was under polygenic control and was highly heritable. For both vernalization and photoperiod response, there was dominance for a low response, or earliness. A simple genetic control was indicated for photoperiod response. The results for vernalization response were not clear cut, although the character appeared to be under polygenic control. An interaction between vernalization and photoperiod response was evident in three of the four cultivars studied. This made it impossible to separate the effect of these two component processes and complicated the study of their inheritance. Node of first flower on the main stem was closely related to flowering time and its use led to similar conclusions in the inheritance studies.     

小麦TaFT基因编码区序列多态性及其与开花期的关系

春化基因VRN-B3是小麦开花素基因TaFT,为探索该基因在品种间的保守性及其与小麦开花早晚的关系,根据TaFT基因序列(GenBank accession No.: DQ890162)设计特异PCR引物,扩增了13个品种中该基因的编码区。通过测序和序列比对,发现不同品种间该基因编码区的DNA序列存在多态性,序列翻译发现5个品种的表达产物FT蛋白发生变异。利用中国春的非整倍体材料将TaFT基因定位在7BS染色体上。参考品种的冬春性及开花时间,推测冬性品种正常的FT蛋白(同DQ890162翻译的氨基酸序列一致)可加速开花,FT蛋白变异则延迟开花;春性品种的FT蛋白变异与否对开花期影响不大,推测TaFT基因的效应可能被春性品种的显性春化基因所掩盖。