Differential effects of cultivated and wild barley 5H chromosomes on heading characters in wheat-barley chromosome addition lines

Wheat (Triticum aestivum L.)-barley (Hordeum vulgare L.) chromosome addition lines are possible vehicles for transferring barley genes into wheat. The barley 5H chromosome has genetic effects on the heading characters in wheat-barley addition lines: accelerating narrow-sense earliness, decreasing vernalization requirement and/or increasing photoperiodic sensitivity. To elucidate the effects of different 5H chromosomes under an identical wheat genetic background, two wheat-barley addition lines, i.e. cultivated barley 'New Golden' 5H chromosome added to 'Shinchunaga' wheat (Shi-NG5H) and wild barley H. vulgare ssp. spontaneum 5H chromosome added to 'Shinchunaga' wheat (Shi-Spn5H), were examined for their heading characters. The addition line Shi-NG5H showed a significantly lower vernalization requirement in comparison with 'Shinchunaga' wheat, whereas Shi-Spn5H did not. Furthermore, both NG5H and Spn5H chromosomes shortened narrow-sense earliness and increased photoperiodic sensitivity in wheat, but the effects of Spn5H were weaker than those of NG5H. The fact that NG5H and Spn5H showed differential effects on heading characters in wheat demonstrated that the heading characters were altered by the function of the barley genes located on 5H chromosomes, not merely by the aneuploid effect alone.     

Segregation analysis of heading traits in hexaploid wheat utilizing recombinant inbred lines

The purpose of this study was to analyze the genetic segregation of heading traits in wheat using recombinant inbred lines (RILs) of hexaploid wheat, derived from Triticum aestivum cv. Chinese Spring and T. spelta var. duhameliamum. The population was examined under controlled environmental conditions as well as in the field. This strategy differentiated the effect of three genetic factors (vernalization requirement, photoperiod sensitivity and narrow-sense earliness) and identified their interactions. Correlation analysis showed that photoperiod sensitivity and narrow-sense earliness are critical for heading time in the field. Single-marker analysis using 322 molecular markers segregating among RIL detected a total of 38 linked markers for each genetic factor and heading in the field. In interval analysis, two Vrn genes (Vrn-B1 and Vrn-D1) and Ppd-B1 were mapped on chromosomes 5B, 5D and 2B, respectively. It was noticed that Vrn-B1 on 5B from the spelt wheat conferred a strong-spring habit equivalent to the homologous Vrn-A1. Quantitative trait locus analysis also showed that Ppd-B1 was not detected under the short-day condition without vernalization treatment, and that there were two types of genes for photoperiod sensitivity, dependent on and independent of vernalization treatment.     

Geographical variation in heading traits in wild emmer wheat, Triticum dicoccoides. I. Variation in vernalization response and ecological differentiation

 Geographical variation in vernalization response and narrow-sense earliness was investigated for accessions of wild emmer wheat, Triticum dicoccoides, collected in Israel. Wide variation between and within populations was observed in both characters. The analysis of vernalization response showed that 2 accessions from Tabigha were of a strong spring growth habit, and thus wild emmer wheat was classified into four types, i.e., strongly spring type, moderately spring type, moderately winter type, and strongly winter type, according to their vernalization response. Whereas winter types were frequently found in most populations except that of Tabigha, the distribution of spring types was sporadic and restricted to warmer areas. It was thus suggested that spring type in T. dicoccoides might have evolved from a winter prototype as an adaptation to warmer conditions. Within moderately winter and moderately spring types, quantitative differences in vernalization response, measured as Dof₇₀/Dof₂₀ and Dof₂₀/Dof₀, were observed between populations. Inter- and intra-population variation in vernalization response could be explained to some extent by the difference in growing conditions at each habitat. It was clearly indicated that environmental heterogeneity caused ecogenetic differentiation in wild emmer wheat in Israel. Wild emmer wheat also varied considerably for narrow-sense earliness, ranging from 32.9 days to 69.5 days among accessions. However, it was difficult to explain its geographical variation simply by a linear relationship with environmental factors, and a nonlinear relationship and/or unknown microgeographic heterogeneity may be responsible. Received: 18 March 1996/Accepted: 13 December 1996     

Two-gene systems of vernalization requirement and narrow-sense earliness in einkorn wheat.

The genetic segregation of the heading trait was analyzed using a recombinant inbred line (RIL) of einkorn wheat, RILWA-1, derived from cultivated Triticum monococcum L., and wild-type T. boeoticum Boiss. The latency to heading was examined in 115 lines under controlled environmental conditions, as well as in the field, and the degrees of narrow-sense earliness and vernalization requirement were evaluated for quantitative trait locus (QTL) analysis. Single-marker analysis using 107 RFLP markers segregating in RILWA-1 detected 20 linking markers for heading factors. In all marker loci, the alleles for early heading were conferred by T. monococcum. In interval analysis of chromosome 5Am, two vernalization genes, Vrn-Am1 and Vrn-Am2, were precisely mapped to the Xcdo504-Xpsr426 interval on the central region of the long arm and to the Xwg114-Xwec87 interval on its distal region, respectively. Interval analysis also showed that two genes for narrow-sense earliness, designated Nse-3Am and Nse-5Am, were located on chromosome 3Am and 5Am, respectively. It was noticed that heading time in the field was determined mainly by Nse-3Am, suggesting that narrow-sense earliness is critical for heading in the field in einkorn wheat.     

Genome-wide association analysis to identify chromosomal regions determining components of earliness in wheat

The modification of flowering date is considered an important way to escape the current or future climatic constraints that affect wheat crops. A better understanding of its genetic bases would enable a more efficient and rapid modification through breeding. The objective of this study was to identify chromosomal regions associated with earliness in wheat. A 227-wheat core collection chosen to be highly contrasted for earliness was characterized for heading date. Experiments were conducted in controlled conditions and in the field for 3 years to break down earliness in the component traits: photoperiod sensitivity, vernalization requirement and narrow-sense earliness. Whole-genome association mapping was carried out using 760 molecular markers and taking into account the five ancestral group structure. We identified 62 markers individually associated to earliness components corresponding to 33 chromosomal regions. In addition, we identified 15 other significant markers and seven more regions by testing marker pair interactions. Co-localizations were observed with the Ppd-1, Vrn-1 and Rht-1 candidate genes. Using an independent set of lines to validate the model built for heading date, we were able to explain 34% of the variation using the structure and the significant markers. Results were compared with already published data using bi-parental populations giving an insight into the genetic architecture of flowering time in wheat.     

FT genome A and D polymorphisms are associated with the variation of earliness components in hexaploid wheat

The transition from vegetative to floral meristems in higher plants is determined by the coincidence of internal and environmental signals. Contrary to the photoperiod pathway, convergent evolution of the cold-dependent pathway has implicated different genes between dicots and monocots. Whereas no association between natural variation in vernalization requirement and Flowering time locus T (FT) gene polymorphism has been described in Arabidopsis, recent studies in Triticeae suggest implication of orthologous copies of FT in the cold response. In our study, we show that nucleotide polymorphisms on A and D copies of the wheat FT gene were associated with variations for heading date in a collection of 239 lines representing diverse geographical origins and status (landraces, old or recent cultivars). Interestingly, polymorphisms in the non-coding intronic region were strongly associated to flowering variation observed on plants grown without vernalization. But differently from VRN1, no epistatic interaction between FT homeologous copies was revealed. In agreement with the results of association study, the A and D copies of FT were mapped in regions including major QTLs for earliness traits in hexaploid wheat. This work, by identifying additional homeoalleles involved in wheat vernalization pathway, will contribute to a better understanding of the control of flowering, hence providing tools for the breeding of varieties with enhanced adaptation to changing environments. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Genetics of Heading Time in Wheat (TRITICUM AESTIVUM L.). I. the Inheritance of Photoperiodic Response

The inheritance of photoperiodic response was studied in crosses involving four spring wheats (Sonora 64, Pitic 62, Justin and Thatcher) and three winter wheats (Blackhull, Early Blackhull and Extra Early Blackhull). The parental cultivars were classified into a photoperiod-sensitive group (Justin, Thatcher, Blackhull and Early Blackhull) and a relatively photoperiod-insensitive group (Sonora 64, Pitic 62 and Extra Early Blackhull) based on their heading response when vernalized and grown under different daylength regimes.-F(1) data indicated that daylength insensitivity is not always dominant over day-length sensitivity and that the dominance relationship with respect to photoperiodic response depends on the alleles present in the parents. The heading patterns after vernalization and growth under short days of F(1), F(2), F(3) and backcross generations of a 4-parent diallel cross involving Justin, Sonora 64, Extra Early Blackhull and Blackhull could be satisfactorily explained on the basis of two major loci with three alleles at each locus. The genotype for each parent was suggested in terms of these loci. Genes with minor effects also influenced the photoperiodic response in a quantitative manner.-Diallel cross analysis of the number of days to heading (log scale) indicated significant additive and dominance genetic variances, a high average degree of dominance for earliness (photoperiod insensitivity) and a preponderance of recessive alleles in the parents acting in the direction of lateness (photoperiod sensitivity). Estimation of the genetic components of variation contained in the generation means of individual crosses (untransformed data) showed that, besides additivity and dominance, epistasis was also an important factor in the genetic control of photoperiodic response in wheat.     

Rapid differentiation of experimental populations of wheat for heading time in response to local climatic conditions

BACKGROUND AND AIMS: Dynamic management (DM) of genetic resources aims at maintaining genetic variability between different populations evolving under natural selection in contrasting environments. In 1984, this strategy was applied in a pilot experiment on wheat (Triticum aestivum). Spatio-temporal evolution of earliness and its components (partial vernalization sensitivity, daylength sensitivity and earliness per se that determines flowering time independently of environmental stimuli) was investigated in this multisite and long-term experiment. METHODS: Heading time of six populations from the tenth generation was evaluated under different vernalization and photoperiodic conditions. KEY RESULTS: Although temporal evolution during ten generations was not significant, populations of generation 10 were genetically differentiated according to a north-south latitudinal trend for two components out of three: partial vernalization sensitivity and narrow-sense earliness. CONCLUSIONS: It is concluded that local climatic conditions greatly influenced the evolution of population earliness, thus being a major factor of differentiation in the DM system. Accordingly, a substantial proportion (approximately 25 %) of genetic variance was distributed among populations, suggesting that diversity was on average conserved during evolution but was differently distributed by natural selection (and possibly drift). Earliness is a complex trait and each genetic factor is controlled by multiple homeoalleles; the next step will be to look for spatial divergence in allele frequencies.     

Wheat SOC1 functions independently of WAP1/VRN1, an integrator of vernalization and photoperiod flowering promotion pathways

Heading time in bread wheat ( Triticum aestivum L.) is determined by three characters – vernalization requirement, photoperiodic sensitivity and narrow-sense earliness (earliness per se) – which are involved in the phase transition from vegetative to reproductive growth. The wheat APETALA1 ( AP1 )-like MADS-box gene, wheat AP1 ( WAP1 , identical with VRN1 ), has been identified as an integrator of vernalization and photoperiod flowering promotion pathways. A MADS-box gene, SUPPRESSOR OF OVEREXPRESSION OF CO 1 ( SOC1 ) is an integrator of flowering pathways in Arabidopsis . In this study, we isolated a wheat ortholog of SOC1 , wheat SOC1 ( WSOC1 ), and investigated its relationship to WAP1 in the flowering pathway. WSOC1 is expressed in young spikes but preferentially expressed in leaves. Expression starts before the phase transition and is maintained during the reproductive growth phase. Overexpression of WSOC1 in transgenic Arabidopsis plants caused early flowering under short-day conditions, suggesting that WSOC1 functions as a flowering activator in Arabidopsis . WSOC1 expression is affected neither by vernalization nor photoperiod, whereas it is induced by gibberellin at the seedling stage. Furthermore, WSOC1 is expressed in transgenic wheat plants in which WAP1 expression is cosuppressed. These findings indicate that WSOC1 acts in a pathway different from the WAP1 -related vernalization and photoperiod pathways.     

Genetics of Heading Time in Wheat (TRITICUM AESTIVUM L.). II. the Inheritance of Vernalization Response

The inheritance of vernalization response was studied in crosses involving four spring wheats (Sonora 64 (S), Pitic 62 (P), Justin (J) and Thatcher (T)) and three winter wheats (Blackhull (B), Early Blackhull (E) and Extra Early Blackhull (EE)).—All winter cultivars were highly responsive to vernalization, and Pitic 62 was the only spring cultivar whose time to heading was significantly accelerated following cold treatments. When vernalized and grown under long days, spring and winter cultivars became comparable in their heading response, indicating that cold requirement is the major attribute differentiating the heading behavior of true spring and true winter wheats.—Inheritance of growth habit in the F₁ generation of a five-parent diallel cross showed dominance of the spring character in all spring x winter crosses. Depending on the cross, one or two duplicate major genes governing growth habit were detected in F₂, F₃ and backcross generations grown in the field under long days in the absence of vernalizing temperatures. In some spring x winter crosses most of the variation in heading time among spring segregates could be attributed to the effects of major genes conditioning growth habit. In other crosses the heading patterns appeared more complex, indicating that genes with smaller effects are also involved in the control of heading response under spring or summer environments.—Evidence was presented supporting the hypothesis that the cultivar Pitic 62 carries a different allele at one of the two major loci governing its spring habit. This allele was associated with some response to vernalization and acted as a dominant gene determining earliness under low temperature vernalization, but as a partially recessive gene determining lateness in the absence of vernalizing temperatures. Genotypes were assigned to five cultivars as follows: S, CC DD; P, CC D'D'; J, cc DD; B and EE, cc dd.—The presence of major and minor genes and of multiple alleles governing response to photoperiod and vernalization was discussed in relation to the genetic manipulation of the heading response and to breeding wheat cultivars with specific or broad adaptation.     

Most significant genome regions involved in the control of earliness traits in bread wheat, as revealed by QTL meta-analysis

Earliness is one of the most important adaptation traits in plant breeding. Our purpose was to identify the genome regions of bread wheat involved in the control of earliness and its three components: photoperiod sensitivity (PS), vernalization requirement (VR) and intrinsic earliness (IE). A QTL meta-analysis was carried out to examine the replicability of QTL across 13 independent studies and to propose meta-QTL (MQTL). Initial QTL were projected on a recent consensus map (2004). Quality criteria were proposed to assess the reliability of this projection. These criteria were based on the distances between markers in the QTL regions. Chromosomes of groups 2 and 5 had a greater incidence on earliness control as they carry the known, major genes Ppd and Vrn. Other chromosome regions played an intermediate role in earliness control: 4A [heading date (HD) Meta-QTL], 4B (HD MQTL), 2B (VR MQTL) and 5B (IE MQTL). Markers at this four MQTL should prove helpful in marker-assisted selection, to better control earliness.     

Deciphering the genetics of flowering time by an association study on candidate genes in bread wheat (Triticum aestivum L.)

Earliness is very important for the adaptation of wheat to environmental conditions and the achievement of high grain yield. A detailed knowledge of key genetic components of the life cycle would enable an easier control by the breeders. The objective of the study was to investigate the effect of candidate genes on flowering time. Using a collection of hexaploid wheat composed of 235 lines from diverse geographical origins, we conducted an association study for six candidate genes for flowering time and its components (vernalization sensitivity and earliness per se). The effect on the variation of earliness components of polymorphisms within the copies of each gene was tested in ANOVA models accounting for the underlying genetic structure. The collection was structured in five groups that minimized the residual covariance. Vernalization requirement and lateness tend to increase according to the mean latitude of each group. Heading date for an autumnal sowing was mainly determined by the earliness per se. Except for the Constans (CO) gene orthologous of the barley HvCO3, all gene polymorphisms had a significant impact on earliness components. The three traits used to quantify vernalization requirement were primarily associated with polymorphisms at Vrn-1 and then at Vrn-3 and Luminidependens (LD) genes. We found a good correspondence between spring/winter types and genotypes at the three homeologous copies of Vrn-1. Earliness per se was mainly explained by polymorphisms at Vrn-3 and to a lesser extent at Vrn-1, Hd-1 and Gigantea (GI) genes. Vernalization requirement and earliness as a function of geographical origin, as well as the possible role of the breeding practices in the geographical distribution of the alleles and the hypothetical adaptive value of the candidate genes, are discussed.     

小麦抽穗期的遗传控制

春化反应、光周期反应和早熟性本身是影响小麦抽穗期的三种重要因素,它们的作用和互作可以调节生育期以应付不同的环境胁迫。小麦抽穗期的遗传控制非常复杂,本文对多年来的研究进展进行了详细的综述。 Abstract:Responses to vernalization,photoperiod and earliness per se are three important factors affecting heading time in wheat.Their actions and interactions may adjust the phasic development of wheat to avoid environmental stress.The genetic control of heading time in wheat is very complex,and this paper summarizes its research progress in details.     

Genotype Differences in Photoperiodic Sensitivity and Vernalization Response in Wheat

The regression of final leaf number on leaf number at transferfrom an 8 h to an 18 h photoperiod was used to compare the photoperiodicresponse of eight locally-adapted lines of wheat. Comparisonsof such regressions in the vernalized and univernalized conditionsenabled detection of the presence or absence of a significantcultivar vernalization response and comparisons of differingresponses between cultivars. Prior vernalization generally did not significantly alter the‘rate’ of photoperiodic response, as the slope ofthe LNT/FLN regression, indicating a certain physiological independenceof vernalization and photoperiodic responses in wheat. Differences, both in photoperiodic and vernalization responseof the eight wheats studied have been discussed in terms ofadaptability and breeding for maturity alteration in wheat.Evidence has been produced for the possible existence of a thirdfactor influencing developmental processes associated with floweringin wheat.     

小麦发育过程及生育期机理模型的研究I.建模的基本设想与模型的描述

将小麦发育的温度效应曲线化,以发育生理生态过程为基础,利用作物生理发育时间(Physiological Development Time,简称PDT)为尺度,提出系统地预测小麦顶端发育阶段和物候生育期的模拟模型.预测的顶端发育阶段包括单棱期、二棱期、小花原基分化期、雌雄蕊原基分化期、药隔期、四分体期、抽穗期.物候发育阶段包括种子萌发、出苗期、分蘖期、越冬期、返青期、拔节期、孕穗期、抽穗期、开花期、灌浆期、成熟期.模型中用来描述特定品种发育遗传差异的参数有温度敏感性、生理春化时间、光周期敏感性和基本早熟性,分别体现了不同品种小麦在热效应、春化作用、光周期反应以及最早开花时间这四方面的遗传特性,共同决定了不同品种到达各发育阶段的生理发育时间     

Genome-wide association study of heading and flowering dates and construction of its prediction equation in Chinese common wheat

Heading date is one of the most important traits in wheat breeding as it affects adaptation and yield potential. A genome-wide association study (GWAS) using the 90 K iSelect SNP genotyping assay indicated that a total of 306 loci were significantly associated with heading and flowering dates in 13 environments in Chinese common wheat from the Yellow and Huai wheat region. Of these, 105 loci were significantly correlated with both heading and flowering dates and were found in clusters on chromosomes 2, 5, 6, and 7. Based on differences in distribution of the vernalization and photoperiod genes among chromosomes, arms, or block regions, 13 novel, environmentally stable genetic loci were associated with heading and flowering dates, including RAC875_c41145_189 on 1DS, RAC875_c50422_299 on 2BL, and RAC875_c48703_148 on 2DS, that accounted for more than 20% phenotypic variance explained (PVE) of the heading/flowering date in at least four environments. GWAS and t test of a combination of SNPs and vernalization and photoperiod alleles indicated that the Vrn-B1, Vrn-D1, and Ppd-D1 genes significantly affect heading and flowering dates in Chinese common wheat. Based on the association of heading and flowering dates with the vernalization and photoperiod alleles at seven loci and three significant SNPs, optimal linear regression equations were established, which show that of the seven loci, the Ppd-D1 gene plays the most important role in modulating heading and flowering dates in Chinese wheat, followed by Vrn-B1 and Vrn-D1. Additionally, three novel genetic loci (RAC875_c41145_189, Excalibur_c60164_137, and RAC875_c50422_299) also show important effect on heading and flowering dates. Therefore, Ppd-D1, Vrn-B1, Vrn-D1, and the novel genetic loci should be further investigated in terms of improving heading and flowering dates in Chinese wheat. Further quantitative analysis of an F₁₀ recombinant inbred lines population identified a major QTL that controls heading and flowering dates within the Ppd-D1 locus with PVEs of 28.4% and 34.0%, respectively; this QTL was also significantly associated with spike length, peduncle length, fertile spikelets number, cold resistance, and tiller number.     

A genome‐wide association study of 23 agronomic traits in Chinese wheat landraces

Uncovering the genetic basis of agronomic traits in wheat landraces is important for ensuring global food security via the development of improved varieties. Here, 723 wheat landraces from 10 Chinese agro‐ecological zones were evaluated for 23 agronomic traits in six environments. All accessions could be clustered into five subgroups based on phenotypic data via discriminant function analysis, which was highly consistent with genotypic classification. A genome‐wide association study was conducted for these traits using 52 303 DArT‐seq markers to identify marker‐trait associations and candidate genes. Using both the general linear model and the mixed linear model, 149 significant markers were identified for 21 agronomic traits based on best linear unbiased prediction values. Considering the linkage disequilibrium decay distance in this study, significant markers within 10 cM were combined as a quantitative trait locus (QTL), with a total of 29 QTL identified for 15 traits. Of these, five QTL for heading date, flag leaf width, peduncle length, and thousand kernel weight had been reported previously. Twenty‐five candidate genes associated with significant markers were identified. These included the known vernalization genes VRN‐B1 and vrn‐B3 and the photoperiod response genes Ppd and PRR. Overall, this study should be helpful in elucidating the underlying genetic mechanisms of complex agronomic traits and performing marker‐assisted selection in wheat.     

Detection and mapping of QTL for earliness components in a bread wheat recombinant inbred lines population

Earliness, an adaptative trait and factor of variation for agronomic characters, is a major trait in plant breeding. Its constituent traits, photoperiod sensitivity (PS), vernalization requirement (VR) and intrinsic earliness (IE), are largely under independent genetic controls. Mapping of major genes and quantitative trait loci (QTL) controlling these components is in progress. Most of the studies focusing on earliness considered it as a whole or through one (or two) of its components. The purpose of this study was to detect and map QTL for the three traits together through an experimental design combining field trials and controlled growth conditions. QTL were mapped in a population of F₇ recombinant inbred lines derived by single-seed descent from a cross between two French varieties, Renan and Récital. A map was previously constructed, based on 194 lines and 254 markers, covering about 77% of the genome. Globally, 13 QTL with a LOD>2.5 were detected, of which four control PS, five control VR and four control IE. Two major photoperiod sensitive QTL, together explaining more than 31% of the phenotypic variation, were mapped on chromosomes 2B and 2D, at the same position as the two major genes Ppd-B1 and Ppd-D1. One major VR QTL explaining (depending on the year) 21.8–39.6% of the phenotypic variation was mapped on 5A. Among the other QTL, two QTL of PS and VR not referenced so far were detected on 5A and 6D, respectively. A VR QTL already detected on 2B in a connected population was confirmed.