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.     

Control of ear emergence time by chromosome 3A of wheat

Chromosome 3A of wheat is known to carry earliness per se genes. To determine the number of genes and their arm location, ear emergence time under a controlled environment was nvestigated using ditelosomic lines and homozygous recombinant substitution lines developed between chromosome 3A homologues from (Timstein) and (Chinese Spring) (CS) in a CS genetic background. Because the ear emergence distribution was discontinuous and two separate modes were produced, the 86 recombinant lines could be divided into 21 lines as the early ‘Timstein’3A type and 65 lines as the late CS type. This agrees with the 1:3 independent segregation of two genes both located on chromosome 3A. Therefore, two hypotheses can be proposed, either CS(‘Timstein’ 3A) carries two genes and both are necessary to give early ear emergence, or one gene for early ear emergence is present on (Timstein) 3A, but a suppressor is on CS 3A. The behaviour of ditelosomic 3AL and 3AS lines, with an ear emergence time identical to that of CS, suggested that one gene is located on the long arm and the other is on the short arm.     

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.     

Effects of barley chromosome on heading characters in wheat-barley chromosome addition lines

Heading time in cereals is a composite character determined by vernalization requirement, photoperiodic sensitivity and narrow-sense earliness. To study the effects of added barley chromosomes on the heading characters in wheat, two sets of wheat-barley chromosome addition lines, i.e., ‘Betzes’ barley chromosomes 2H to 7H added to ’Chinese Spring‘ wheat (CS-Be2H to CS-Be7H) and ‘New Golden’ barley chromosomes 5H and 6H added to ‘Shinchunaga’ wheat (Shi-NG5H, Shi-NG6H), were examined for their heading characters. All barley chromosomes except Be6H affected vernalization requirement and/or narrow-sense earliness in CS or Shi. Be5H chromosome also slightly increased the photoperiodic sensitivity of CS. Shi-NG5H addition line showed significantly decreased vernalization requirement in comparison with Shi, whereas CS-Be5H did not show any difference from CS. The F₁ hybrid of the cross, Shi-NG5H × CS-Be5H, exhibited the same level of vernalization insensitivity as the Shi-NG5H addition line, and plants with and without a vernalization requirement segregated in a 1 : 3 ratio in the F₂ generation. These observations, together with previous reports, suggest that the decreased vernalization requirement in the Shi-NG5H addition line was caused by the presence of a major dominant gene for spring habit, Sh₂, located on the NG5H barley chromosome. Furthermore, this study revealed that the Sh₂ gene in barley has a similar but weaker effect than the wheat vernalization insensitive gene, Vrn1, on the vernalization response in wheat. This revised version was published online in July 2006 with corrections to the Cover Date.     

Multivariate analysis of traits determining adaptation in cultivated barley

Thirty‐nine barley varieties of different origin, representing different growth types, were included in a series of experiments aimed at analysing the variability in vernalization response, photoperiod sensitivity and earliness per se and establishing the types of ecoclimatic adaptability using multivariate analysis. In the case of spring barley varieties there was no correlation between any of the three traits. For winter barleys, a negative correlation was found between photoperiod sensitivity and vernalization response and between photoperiod sensitivity and earliness per se. Vernalization response and earliness per se showed a positive correlation. Among the winter barley varieties large variations were apparent in photoperiod sensitivity, vernalization response and earliness per se, which resulted in a tremendous variation in flowering patterns and frost tolerance. Between the spring barley varieties only wider variations in photoperiod sensitivity were detected. Based on the cluster analysis, the 39 varieties could be separated into seven groups. The spring barley varieties were placed in two groups, and the winter barleys in five groups representing different adaptational types. Among these five groups two represented the two opposing extreme combinations of photoperiod sensitivity and vernalization response. The combination of large photoperiod sensitivity and no vernalization response resulted in better frost tolerance than did the combination of photoperiod insensitivity and large vernalization response.     

Detection of chromosomes carrying genes for seed dormancy of wheat using the backcross reciprocal monosomic method

Preharvest sprouting (PHS) in wheat represents a major constraint to the production of high‐quality grain. Genetic variation for tolerance to PHS is associated with seed dormancy. The present study was initiated to detect homologous chromosome variation associated with seed dormancy genes in a PHS tolerant cultivar ‘Zenkojikomugi’ (Zen) and ‘Chinese Spring’ (CS) using the backcross reciprocal monosomic method. The most striking effect on variation in seed dormancy was associated with chromosome 3A, and followed by group 4 chromosomes. These chromosomes of Zen increased dormancy compared with the respective CS homologues. Chromosomes 2D and 7D of Zen, and 6A of CS seemed to contribute smaller positive effects on dormancy. Chromosomes 2A of CS and Zen, as well as 3B, were equally effective in enhancing dormancy. The chromosome 3 A factors were independent of the grain‐colour gene R‐A1 because Zen was found to carry the white‐grained R‐A1a allele, which was identical to that of CS, and there was no difference in dormancy between the reciprocal F₁ seeds.     

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.     

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

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

Identification of RFLP markers linked with heading date and its heterosis in hexaploid wheat

Recombinant inbred lines (RILs) from a cross between hexaploid wheat (T. aestivum cv. Chinese Spring (CS) and T. spelta (Sp)) were used for RFLP analysis of heading date and heterosis. Fourteen RFLP markers linking with heading date were identified; two were localized on chromosome 1A, one on 2A, three on 2B, one on 2D, four on 5A, two on 7A and one unlinked but reported to be on group 2. All of these markers may be attributable to genes for earliness per se. However, the markers in the chromosomes of 1A and 7A are new to this study. RILs were crossed with (tim)-CS, the alloplasmic CS with T. timopheevi cytoplasm, and the heterosis from earlier-parent and mid-parents were calculated for the F₁s to examine the heterotic effect toward earliness on heading date. Five and two RFLP markers were associated with heterosis from the earlier-parent and mid-parents, respectively. They were distributed on the chromosomes of homoeologous groups 1 and 2. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Chromosomal location of genes affecting tissue-culture response in wheat

Six ‘Chinese Spring/Triticum spelta’ substitution lines for chromosomes 1A, 1D (duplicates), 3D (duplicates), 6D, and one ‘Chinese Spring/ Marquis’ substitution line for chromosome 2B were studied for tissue-culture response (TCR). The results reported here indicate that chromosomes 2B and 6D are critical for TCR, whereas chromosome ID affects callus weight only. Chromosomes 1A and 3D were not found to be critical, however, these chromosomes may carry genes with minor effects.     

The influence of flowering time genes on environmental adaptability in European wheats

Summary In order to obtain high levels of environmental adaptability in wheat varieties it is essential they flower at times appropriate to particular environmental conditions. The influence of three distinct genetic systems that together determine time of flowering is reviewed here.Vernalization genes are seen to be particularly important to winter wheats for their direct or indirect effects on winter hardiness. Vernalization genes play a minor role in determining flowering time in autumn sown winter wheats but insensitivity is essential if spring sown wheats are to flower.Day length sensitive photoperiod genes play a major role in determining flowering time and adaptability of autumn sown wheats. Insensitivity can promote yield advantages of over 35% in Southern European environments. 15% in Central Europe and offers benefits even in the UK. At present only a single allele of Ppd1 appears to have been introduced into commercial European wheat varieties. The merits of alternative Ppd1 alleles or different loci are discussed.The influence of earliness per se genes that determine flowering time independently of environmental stimuli is less well documented than the effect of photoperiod and vernalization genes. It is likely that genes on chromosomes belonging to groups 2, 3, 4, 6 and 7 may act to modify flowering time independently of environmental stimuli probably by determining numbers of vegetative and floral primordia being initiated or the rate of initiation of the primordia. Earliness per se genes appear to be widespread in European wheats and play a significant role in determining the exact time plants flower.     

Genetic analysis of agronomic and fibre traits using four interspecific chromosome substitution lines in cotton

Backcrossed chromosome substitution lines (CS‐B) have been developed with a homologous pair of chromosomes or chromosome arms of Gossypium barbadense (3‐79) germplasm substituted for the homologous Gossypium hirsutum(TM‐1) chromosomes or chromosome segments. We report on agronomic and fibre trait performance of four backcrossed chromosome or chromosome arm substitution lines including chromosomes 01, 11sh (chromosome 11 short arm), 12 sh and 26 Lo (chromosome 26 long arm). Data for agronomic and fibre traits were collected from replicated field experiments at two different locations in 2 years, and analysed under an additive dominance genetic model. CS‐B 12sh had higher, while CS‐B 01 and CS‐B 26Lo had lower boll weight than TM‐1. The presence of significant negative additive effects for micronaire with CS‐B 01 and significant positive additive effects for elongation and fibre strength with CS‐B 11sh suggested the substituted chromosome arms of 3‐79 in these CS‐B lines were more likely carrying genes causing these effects. Results revealed that several CS‐B lines had significant homozygous and heterozygous dominance effects for different agronomic and fibre traits suggesting that specific CS‐B lines may be useful for improving agronomic and fibre traits in hybrid cottons. These CS‐B lines also provide novel genetic resources for improving upland cotton germplasm.     

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.     

Chromosomal Assignment of Three Enzyme Coding Loci (Icd1, Nad-Mdh1 and Aco1) Using Primary Trisomics in Beet (Beta vulgaris L.)

Resistance to Septoria nodorum was investigated in seedlings of an amphiploid generated from Triticum dicoccum Shübl. and Aegilops squarrosa Tausch, and in a series of substitution lines of single chromosomes from this synthetic hexaploid into Triticum aestivum cv. ‘Chinese Spring’ in three tests to determine the chromosomal location of resistance. From the Ae. squarrosa parent (D genome), chromosome 5D was found to confer a high level of resistance, reducing lesion cover to near that of the amphiploid in the three tests. Chromosomes 3D, and to a lesser extent, 7D were also found to confer significant resistance to the amphiploid. Three chromosomes, 2A, 3B and 5A, from the T. dicoccum parent (AB genomes) also conferred resistance but to a lesser extent than 7D. Two chromosomes, 2B and 2D, caused a significant decrease in resistance. ‘Chinese Spring’ may thus carry genes for resistance to S. nodorum on these chromosomes which are absent in the synthetic hexaploid.     

Waiting for fine times: genetics of flowering time in wheat

To maximise yield potential in any environment, wheat cultivars musthave an appropriate flowering time and life cycle duration which`fine-tunes' the life cycle to the target environment. This in turn, requiresa detailed knowledge of the genetical control of the key components of thelife cycle. This paper discusses our current knowledge of the geneticalcontrol of the three key groups of genes controlling life-cycle duration inwheat, namely those controlling vernalization response, photoperiodresponse and developmental rate (`earliness per se', Eps genes).It also discusses how our ability to carry out comparative mapping of thesegenes across Triticeae species, and particularly with barley, is indicatingnew target genes for discovery in wheat. Major genes controllingvernalization response, the Vrn-1 series, have now been located bothgenetically and physically on the long arms of the homoeologous group fivechromosomes. These genes are homoeologous to each other and to thevernalization genes on chromosomes 5H of barley and 5R of rye.Comparative analysis with barley also indicates that other series ofvernalization response genes may exit on chromosomes of homoeologousgroups 4 (4B, 4D, 5A) and 1. The major genes controlling photoperiodresponse in wheat, the Ppd-1 genes, are located on the homoeologousgroup 2 chromosomes, and are homoeologous to a gene on barleychromosome 2H. Mapping in barley also indicates a photoperiod responselocus on barley 1H and 6H, indicating that a homoeologous series shouldexist on wheat group 1 and 6 chromosomes. In wheat, only a few`earliness per se loci have been located, such as on chromosomes ofhomoeologous group 2. However, in barley, all chromosomes appear tocarry such loci, indicating that several series of loci that affectdevelopmental rate independent of environment remain to be discovered.Overall, comparative studies indicate that there are probably twenty-fiveloci controlling the duration of the life-cycle, Vrn, Ppd and Eps genes, that remain to be mapped in wheat. There are major gaps inour knowledge of the detailed physiological effects of genes discovered todate on the timing of the life cycle from different sowing dates. This isbeing addressed by studying the phenology of isogenic and deletion lines inboth field and controlled environmental conditions. This has indicated thatthe vernalization genes have major effects on the rate of primodiaproduction, whilst the photoperiod genes affect the timing of terminalspikelet production and stem elongation, and these effects interact withsowing date.     

Genetic Analysis of Chromosome 2D of Wheat

The Yugoslavian varieties ‘Novosadska Rana 1’ and ‘Sava’ are shown by monosomic comparisons to carry weak height promoters on chromosome 2D characteristic of the ‘Akakomugi’ gene for reduced height, Rht8. Reciprocal monosomic crosses between ‘Bersee’ and ‘Sava’ demonstrate ‘Sava’ chromosome 2D reduces height by about 16 cms, accelerates ear emergence by about 9 days and increases yield through increased grain number and grain size. Recombinant lines developed for chromosome 2D suggest that this chromosome in Mediterranean wheats carries three genes, Rht8, Ppd1 and Yr16, important to their adaptation. Rht8 and Ppd1, a gene for day length insensitivity together reduce height. Ppd1 and, to a minor degree, either yr16, the susceptible allele of a gene for adult plant resistance to yellow rust or a closely linked gene, accelerate time to flowering and thereby avoid desiccating Yugoslavian summer conditions. The same genes reduce spikelets numbers but this is offset by increased floret fertility producing an overall increase in the number of grains per ear. Ppd1 also by avoiding desiccating conditions increases gram size and together with either yr16 or the closely linked fertility gene increases ear and plant yields.     

Pleiotropic Effects of Genes for Reduced Height (Rht) and Day-Length Insensitivity (Ppd) on Yield and its Components for Wheat Grown in Middle Europe

Under field conditions in Germany over three growing seasons the pleiotropic effects on yield and its components of four sets of near isogenic lines carrying the GA insensitive dwarfing alleles Rht1, Rht2, Rht3, Rht1+2, Rht2+3 or rht (tall) in four different genetical backgrounds were examined together with 24 single chromosome recombinant lines segregating for the GA sensitive dwarfing gene Rht8 and the gene for day-length insensitivity Ppd1 in a ‘Cappelle-Desprez’ background. For the GA insensitive semi-dwarfs it was shown that in all three years a higher number of grains per ear was accompanied by a lower grain weight. Depending on the climatic conditions in a particular year, the increase in grain number was sufficient to compensate for the reduction in grain size and resulted in higher yields. For the Ppd1 allele yield advantages were found for wheats grown under environmental conditions of middle Europe.     

Temperature as a component of the expression of developmental responses in wheat

Summary Studies were made of days to ear emergence under the constant temperatures of 9, 14, 19 and 25°C and 16 h photoperiod in three sets of wheat lines each possessing genotypes differing for developmental responses.Days to ear emergence in three near-isogenic lines of the wheat cultivar Triple Dirk, which differed for vernalization response, increased as the strength of the response increased. At the four temperatures Triple Dirk D (Vrn 1 vrn 2) was not significantly different from normal Triple Dirk (Vrn 1 Vrn 2) but Triple Dirk B (vrn 1 Vrn 2) was significantly (P=0.01) later than normal Triple Dirk at each temperature. This indicates that the vrn 1 allele confers stronger vernalization response than vrn 2 over the range of temperatures (9–24°C). However, Triple Dirk C (vrn 1 vrn 2) failed to head after 120 days at each temperature indicating strong interaction between vrn 1 and vrn 2 with each other (and possibly the Triple Dirk back-ground) to give a much stronger vernalization response than predictions from additivity of their individual effects.The second set comprised the four Chinese Spring/Thatcher chromosome substitution lines CS/T 3B, 6B, 7B and 5D, plus Chinese Spring and Thatcher, and were grown in the unvernalized condition. CS/T 5D was similar in days to ear emergence as Chinese Spring at all four temperatures but the other three lines were earlier to ear emergence, particularly as the temperature increased. Days to ear emergence was fastest at 14°C in all lines, except CS/T 3B, in which it decreased progressively from 9 to 24°C.The third set of Chinese Spring and Thatcher and the homoeologous group 2 chromosomes of Thatcher substituted in Chinese Spring, the group which is considered to be involved in the control of photoperiod sensitivity. The three substitution lines responded differently to temperature compared with Chinese Spring and with each other, with chromosome 2D being the least, and chromosome 2B the most, responsive to temperature.     

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.