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.     

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.     

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.     

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.     

Alteration of wheat vernalization requirement by alien chromosome-mediated transposition of MITE

Under the changing climate, early flowering is advantageous to escape terminal heat and drought. Previously during evaluation of 14 chromosome introgression lines (ILs), we found three ILs that flowered a month earlier than their wheat background Chinese Spring (CS). This paper describes the cause of the early flowering in the ILs and provides insight into the evolution of spring wheat from the winter wheat. We used specific molecular markers for Vrn genes to determine its allelic composition. Phenotypic evaluations carried out under field conditions and in a growth chamber. Unlike the winter vrn-A1 allele of CS, the spring Vrn-A1 allele of the ILs had insertions of 222 and 131-bp miniature inverted-repeat transposable element (MITE) in the promoter region. Sequence analysis indicated that the 222-bp insertion is similar to an insertion in the spring genotype, Triple Dirk D. Our results ruled out any possibility of outcrossing or contamination. Without vernalization, Vrn-A1 is highly expressed in the ILs compared to CS. We attribute the early flowering of the ILs to the insertion of the MITE in the promoter of Vrn-A1. The alien chromosome might mediate this insertion.     

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.     

A reciprocal F1 monosomic analysis of the genetic control of time of ear emergence,number of leaves and number of spikelets in wheat (Triticum aestivum L.)

Summary A reciprocal F₁ monosomic analysis of chromosomal differences between Spica and Bersée was carried out under controlled environment conditions. Chromosomes associated with differences in days to ear emergence, number of leaves and number of spikelets were identified. The results indicated that chromosome 2B of Spica carries a photoperiod insensitivity allele at the Ppd ₂ locus. Both Spica and Bersée appear to have a vernalization insensitity allele at the Vrn ₂ locus on chromosome 5B. On chromosome 3A, 4B, 4D and 6B factors were found with major effects on earliness per se, diffeences in ear emergence and number of spikelets which were independent of photoperiod and vernalization. The possibility that these factors influence growth rate is discussed.     

Variation of PGM and IDH isozymes for identification of alfalfa varieties

Growth habit, heading date and Vrn genotypewere examined for wheat landraces cultivated in China,Korea and Japan, to study their ecogeographicaldifferentiation in east Asia. Spring type landracesaccounted for 43.6% of the whole, and the frequencyvaried between the localities, being closely relatedto the degree of winter coldness. Spring typelandraces mainly adapted to north and south Chinawhere average January temperature is under –7 ^°Cand over 4 ^°C, respectively. On the contrary,winter type adapted to areas of average Januarytemperature from –7 ^°C to 4 ^°C. As toheading date, significant difference was not observedbetween spring and winter type landraces but betweenlocalities, and those cultivated in north China weresignificantly later in heading. It is thereforeindicated that spring type mainly adapts to areaswhere wheat is sown in spring to avoid frost injury,and where winter temperature is not low enough tovernalize winter type wheat. Genetic analysis forspring type landraces showed that the relativefrequency of four Vrn genes was different witheach other. Vrn3 was most widely and frequentlyfound among the four genes, followed by Vrn1 andVrn2. Only seven landraces proved to be thecarrier of Vrn4. The frequency was alsodifferent between localities. Genotype with Vrn1plus other dominant gene(s) adapted to spring sowingto avoid severely cold winter in north China, whilegenotype with only Vrn3 adapted to winter sowingin south China and southwest Japan. It is thereforeconcluded that at least three ecotypes, differing ingrowth habit and Vrn genotype, areallopatrically distributed in east Asia, as a resultof adaptation to winter coldness in each locality.     

Vernalization gene combination to maximize grain yield in bread wheat (Triticum aestivum L.) in diverse environments

The major vernalisation genes of VRN1 are well understood at the molecular level. However, their quantitative contributions to flowering time and grain yield related traits are not clear. In this study, we used a double haploid population (225 lines) of Westonia × Kauz in which the Vrn-A1a (Westonia), Vrn-B1a (Westonia) and Vrn-D1a (Kauz) were segregating, and a high resolution genetic map of 1,159 loci, to determine the quantitative contributions of Vrn-A1a, Vrn-B1a and Vrn-D1a for the days to anthesis and grain yield related traits in diverse environments. The major quantitative trait loci (QTL) of spikelet number per spike and days to anthesis were contributed by the winter alleles of VRN1. The QTL of the time of grain filling were contributed by the spring alleles of VRN1. The wild genotype (vrn-A1vrn-B1vrn-D1) showed the latest flowering, the highest spikelet number per spike, lowest peduncle proportion and thousand grain weight in three environmental analyses, and the largest spikelet number per spike, which resulted in high kernel number per spike (KN) and grain weight (GW) in well-watered environments. One QTL of KN was located on 5B, contributed by winter allele of vrn-B1 in three environmental analyses, and one GW QTL was detected on 5A, contributed by the spring allele of Vrn-A1a in a drought environment. The results indicated that the genotype Vrn-A1avrn-B1Vrn-D1a would shorten the time to anthesis and give high GW and KN in drought environments. The early anthesis associated phenotype, peduncle proportion would provide an indicator in breeding programs.     

Measurement of response to vernalization in Australian wheats with winter habit

Summary Development in wheat is strongly controlled by sensitivity to vernalization and photoperiod, and to a lesser degree by non-vernalizing temperature and intrinsic earliness. A method to measure effect of vernalization in wheats with winter habit is described. Twenty seven wheats with winter habit and eight with spring/facultative habit were studied, comprising breeding lines and cultivars with maturities suited to south-central New South Wales. Effect of vernalization on the development of these wheats was quantified by integrating responses to vernalizing treatments of differing duration. Intrinsic earliness was measured as time for vernalized seedlings to grow to ear emergece in an 18h photoperiod with day/night temperature of 21/16°C, and response to photoperiod as the difference in time to ear emergence between 9 and 18h daylengths. Integrated response to vernalization is sensitive to both cumulative and thresh-hold responses and is applicable to wheats of all habit type. Integrated response to vernalization and intrinsic earliness were positively associated within wheats with winter habit. Wheats were largely of restricted origin, so that there were few allelic differences at Vrn loci to disrupt this association, which suggests intrinsic earliness may modify response to vernalization. Though integrated response to vernalization was measured with artificial treatments, it was strongly associated with ear emergence for wheats with winter habit when grown at a site in New South Wales.     

Chromosome location of genes affecting polyphenol oxidase activity in seeds of common and durum wheat

This study used cytogenetic stocks to investigate the chromosomal location of genes responsible for polyphenol oxidase (PPO) activity in common and durum wheat seeds. Substitution lines of chromosome 2A of hexaploid varieties ‘Cheyenne’, ‘Thatcher’ and ‘Timstein’ in ‘Chinese Spring’ showed significantly higher PPO activity than all other substitution lines of the same variety, with the exception of substitutions of ‘Cheyenne’ chromosome 3A and ‘Thatcher’ chromosome 4B. Substitution lines of chromosome 2A of Triticum turgidum var. dicoccoides and of chromosome 2D of ‘Chinese Spring’ into the tetraploid variety ‘Langdon’ showed a significant increase in PPO activity relative to all other substitution lines in Langdon. The gene(s) responsible for high PPO activity in chromosome 2D from ‘Chinese Spring’ was mapped on the long arm within a deletion that represents 24% of the distal part of the arm. This study shows that genes located in homoeologous group 2 play a major role in the activity of PPO in wheat.     

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.     

Molecular and physical mapping of genes affecting awning in wheat

Quantitative trait loci (QTL) for three traits related to awning (awn length at the base, the middle and the top of the ear) in wheat were mapped in a doubled‐haploid line (DH) population derived from the cross between the cultivars ‘Courtot’ (awned) and ‘Chinese Spring’ (awnless) and grown in Clermont‐Ferrand, France, under natural field conditions. A molecular marker linkage map of this cross that was previously constructed based on 187 DH lines and 550 markers was used for the QTL mapping. The genome was well covered (more than 95%) and a set of anchor loci regularly spaced (one marker every 20.8 cM) was chosen for marker regression analysis. For each trait, only two consistent QTL were identified with individual effects ranging from 8.5 to 45.9% of the total phenotypic variation. These two QTL cosegregated with the genes Hd on chromosome 4A and B2 on chromosome 6B, which are known to inhibit awning. The results were confirmed using ‘Chinese Spring’ deletion lines of these two chromosomes, which have awned spikes, while ‘Chinese Spring’ is usually awnless. No quantitative trait locus was detected on chromosome 5A where the B1 awn‐inhibitor gene is located, suggesting that both ‘Courtot’ and ‘Chinese Spring’ have the same allelic constitution at this locus. The occurrence of awned speltoid spikes on the deletion lines of this chromosome suggests that ‘Chinese Spring’ and ‘Courtot’ have the dominant B1 allele, indicating that B1 alone has insufficient effect to induce complete awn inhibition.     

The relationships of hardening period and the expression of frost resistance in chromosome substitution lines of wheat

Summary The highly frost resistant wheat variety Cheyenne (donor) and the poorly frost resistant variety Chinese Spring (recipient) were frozen at –9° C and –11° C at various stages of hardening, as were a number of substitution lines of these two varieties (CS/Ch 3A, CS/Ch 5A, CS/Ch 7A, CS/Ch 2B, CS/Ch 4B, CS/Ch 5B, CS/Ch 4D, CS/Ch 5D). Chromosomes 5A, 5B, 5D, 4B and 7A of Cheyenne increased the frost resistance of the recipient variety to varying extents. However, the frost resistance changed not only as a function of the different chromosomes, but also as a function of the duration of hardening, indicating that genes responsible for frost resistance are expressed differently during different phases of the hardening process.     

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.     

Genes for frost resistance in wheat

Wheat varieties differ in their responses to low temperatures. Geneticstudies on frost resistance in wheat are difficult because the effects arequantitative in nature and thus require precise genetic material andreproducible experimental conditions. The detailed diallel analyses indicatedthat the inheritance of frost resistance is polygenic and mostly additive.Nevertheless, studies using monosomic, ditelosomic and substitution lineshave identified specific chromosomes that carry genes responsible for frostresistance. In particular, the chromosomes 5A and 5D appear to carrymajor genes. Using molecular markers (RFLP, AFLP) and recombinantsubstitution lines it was shown that the Vrn-A1 (vernalization) and Fr1 (frost resistance) loci were located closely linked on the distal portionof the long arm of 5A, but recombination between them was found (cM = 2). The RFLP markers Xpsr426 and Xwg644 were tightlylinked to the Vrn-A1 locus. Loci Vrn-D1 and Fr2are located on the long arm of 5D. Fr2 and Vrn-D1 arehomoeologous to Fr1 and Vrn-A1. A physical map of theVrn-A1 and Fr1 genes was constructed on chromosome 5Ausing deletion lines. This cytogenetically based physical map could be usefulin further work on genome mapping and gene cloning.     

The effect of the homoeologous group 5 chromosomes with different vrn loci on growth phases and quantitative characters of wheat

The differences between effects of homoeologous group 5 chromosomes on growth phases and agronomic characters were studied by using reciprocal substitution lines between a winter wheat cultivar with a high vernalization requirement (Mironovskaya 808) and one with lowvernalization requirement (Bezostaya 1), in which the presence of different recessive vrn alleles is supposed. The two cultivars and the substitution lines Mironovskaya 808 (Bezostaya 1 5A), Mironovskaya 808 (Bezostaya 1 5B), Mironovskaya 808 (Bezostaya 1 5D), Bezostaya1 (Mironovskaya 808 5A), Bezostaya 1 (Mironovskaya 808 5B),Bezostaya 1 (Mironovskaya 808 5D) were grown at 10 different sowing dates. The results showed that differences between the homoeologous group 5 chromosomes of Mironovskaya 808 and those of Bezostaya 1influenced the growth phases in addition to the impact by the genetic background and sowing date. We inferred from the analysis and comparison of their effect on vernalization response that vrn loci on these chromosomes influence growth phases. It is probably due to pleiotropic effects of the loci. The rare occurrence of significant interactions between group 5 chromosomes × sowing dates probably indicates independence of their effect. Agronomic characters were also markedly influenced by sowing date and the difference in backgrounds between Mironovskaya 808 and Bezostaya 1. A significant impact by at least two of the chromosomes on almost all studied characters was detected. The chromosomes affected the combined characters in the order5D>5B>5A and the positive value of the differences suggests that a content of Mironovskaya 808 chromosomes is more advantageous. It was possible to find certain indices in some agronomic traits, supporting the idea that the expression of some characters can also be connected to vernalization requirement and thus to the expression of the vrn loci. This supposition is most probable in the number of tillers and number of spikes. In some traits significant interactions occurred between homoeologous group 5 chromosomes × genetic background. Sporadic and low significance between homoeologous group 5 chromosomes × sowing dates suggest that the genetic effect of these chromosomes is independent of environmental conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of the genetic variation in the effect of temperature and daylength on bolting of Brassica campestris L.

Summary Effects of temperature and daylength on the bolting of a number of B. campestris accessions were investigated both in the open and in the IVT phytotron. From the results it was concluded that low temperature and genotype are the predominant factors with respect to bolting. Daylength has rather limited influence. One cultivar bolted more than 12 weeks earlier at 10 and 14°C than at 18°C. On the other hand some cultivars did not require vernalization at all.At 14°C and short daylength, depending on genotype, the period of time between sowing and 50% bolting ranged from 8 to 30 weeks. At this temperature the stimulating effect of long day (24 h), depending again on the genotype, ranged from 0 to 4 weeks. The genotypes most resistant to bolting appeared to be the stubble turnips (B. campestris ssp. rapa).In terms of seed(ling) vernalization at 5°C the cold requirement ranged from 0 to more than 3 weeks, depending on the genotype. The required vernalization periods at 5°C can be used as a criterion in screening for resistance to bolting.     

The physiology of variation in the time of ear emergence among wheat varieties from different regions of the world

Summary Differences in response to photoperiod and vernalization and genetic variation independent of photoperiod and vernalization (earliness per se), affecting time of ear emergence of wheat, were identified in controlled environment experiments with 33 varieties of diverse geographical origin. The results were compared with an analysis of time of ear emergence of 10409 T. aestivum accessions from the USDA Small Grain Collection grown from autumn sowings in Pendleton, Oregon, and spring sowings in Fargo, North Dakota. The effect of differences in photoperiod and vernalization sensitivity on time of ear emergence was similar to the effect of earliness per se, both under controlled environment conditions and in the field. Most of the accessions from low latitude regions reached ear emergence rapidly owing to their insensitivity to photoperiod and vernalization and earliness per se factors accelerating ear emergence. Lateness was common among accessions from Northern Europe, Afghanistan and Turkey, which was due to sensitivity to photoperiod and vernalization, and to earliness per se factors delaying ear emergence. The physiological basis of earliness per se is discussed.     

Factors affecting haploid production in wheat using the Hordeum bulbosum system. 3. Post-fertilization effects on embryo survival

Summary An investigation was made of factors affecting the frequency of development of fertilized ovules following wheat x Hordeum bulbosum hybridizations. Seed survival, a term used here to represent the relationship between seed set and fertilization, was shown to vary between the wheat genotypes tested, but was unrelated to the crossability genes present within the wheat genotype. A high seed survival was obtained in crosses involving the variety TH3929 and the single chromosome substitution line, Chinese Spring (Hope 5B). Chinese Spring showed a poor seed survival. Some influence of the H. bulbosum genotype on seed survival was detected. The two environmental factors studied, namely the post-pollination application of gibberellic acid and the ambient temperature, were both shown to affect seed survival. The application of gibberellic acid immediately after pollination or 1 and 2 days after pollination improved seed survival, although the extent of the response was dependent upon the number and timing of the application(s). A genotype-dependent response to the ambient temperature was observed, TH3929 showing a slight but insignificant reduction and Chinese Spring a significant improvement in seed survival with an increase in temperature from 20°C to 26°C. The physiological processes which may be influenced by GA and the ambient temperature and may thereby affect seed survival are discussed.