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.     

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.     

Geographical variation in heading characters among wheat landraces,Triticum aestivum L., and its implication for their adaptability

Summary Heading time and its constituent traits, photoperiodic response, narrow-sense earliness and vernalization requirement, were surveyed for 158 wheat landraces. Wide varietal variation was observed in each character. Nearly half of the variation for each character was explained by a geographical difference in origin. Based on these data and the growing environments in each locality, we analyzed adaptation strategy, seen as the adjustment of heading time in terms of differences in the constituent traits, both individually and combined. The difference among localities indicated that wheat landraces had been selected for early heading as an adaptation strategy to water stress and/or high temperature in early summer. This change was caused by a reduction in photoperiodic response and narrow-sense earliness. The vernalization requirement was also reduced for adaptation to relatively mild winters. Adaptation strategy deduced from the variation within each locality was also different amongst localities. In the central region of wheat evolution, where wide variations existed in both photoperiodic response and narrow-sense earliness, the late-heading trait was achieved by either one of these traits individually or both of them combined. On the contrary, in the eastern and the western regions, wide variation in heading time was achieved by the unique combination of photoperiodic response and narrowsense earliness. A sampling strategy for wheat germ plasm is also discussed.     

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.     

The chromosome region including the earliness per se locus Eps-Am1 affects the duration of early developmental phases and spikelet number in diploid wheat

Earliness per se genes are those that regulate flowering time independently of vernalization and photoperiod, and are important for the fine tuning of flowering time and for the wide adaptation of wheat to different environments. The earliness per se locus Eps-A(m)1 was recently mapped within a 0.8 cM interval on chromosome 1A(m)L of diploid wheat Triticum monococcum L., and it was shown that its effect was modulated by temperature. In this study, this precise mapping information was used to characterize the effect of the Eps-A(m)1 region on both duration of different developmental phases and spikelet number. Near isogenic lines (NILs) carrying the Eps-A(m)1-l allele from the cultivated accession DV92 had significantly longer vegetative and spike development phases (P<0.0001) than NILs carrying the Eps-A(m)1-e allele from the wild accession G3116. These differences were paralleled by a significant increase in the number of spikelets per spike, in both greenhouse and field experiments (P<0.0001). Significant interactions between temperature and Eps-A(m)1 alleles were detected for heading time (P<0.0001) but not for spikelet number (P=0.67). Experiments using NILs homozygous for chromosomes with recombination events within the 0.8 cM Eps-A(m)1 region showed that the differences in number of spikelets per spike were linked to the differences in heading time controlled by the Eps-A(m)1 locus. These results indicate that the differences in these two traits are either pleiotropic effects of a single gene or the effect of closely linked genes. A similar effect on spikelet number was detected in the distal region of chromosome 1AL in common wheat (T. aestivum L.).     

Characterization of three VERNALIZATION INSENSITIVE3-like (VIL) homologs in wild wheat, Aegilops tauschii Coss

Control of flowering time is an adaptive trait of plants for different growth habitats. A vernalization requirement is a major genetic component determining wheat flowering time. Arabidopsis VERNALIZATION INSENSITIVE3 (VIN3) and VIN3-like 1 (VIL1) play critical roles in the vernalization pathway of flowering, and three wheat VIL homologs are upregulated by vernalization in einkorn wheat. To study the relationship between vernalization and wheat VIL homologs in Aegilops tauschii, the D-genome progenitor of common wheat, we isolated three cDNAs orthologous to the einkorn wheat VIL genes. The three Ae. tauschii VIL genes showed many single nucleotide polymorphisms including non-synonymous substitutions relative to the einkorn orthologs. In addition, high rates of non-synonymous and synonymous substitutions were revealed by intraspecific variation analysis of the AetVIL sequences, suggesting adaptive evolution at the AetVIL loci. Quantitative RT-PCR analysis was conducted to examine the time course of expression of the VIL genes during vernalization. Of the three AetVIL genes, AetVIL2 was upregulated after one week of low-temperature treatment, and its expression pattern was distinct for winter and spring habit accessions. These observations strongly suggest that AetVIL2 is associated with the vernalization-responsive pathway in Ae. tauschii.     

The einkorn wheat (Triticum monococcum) mutant, maintained vegetative phase, is caused by a deletion in the VRN1 gene

The einkorn wheat (Triticum monococcum) mutant, maintained vegetative phase (mvp), was induced by nitrogen ion-beam treatment and was identified by its inability to transit from the vegetative to reproductive phase. In our previous study, we showed that WAP1 (wheat APETALA1) is a key gene in the regulatory pathway that controls phase transition from vegetative to reproductive growth in common wheat. WAP1 is an ortholog of the VRN1 gene that is responsible for vernalization insensitivity in einkorn wheat. The mvp mutation resulted from deletion of the VRN1 coding and promoter regions, demonstrating that WAP1/VRN1 is an indispensable gene for phase transition in wheat. Expression analysis of flowering-related genes in mvp plants indicated that wheat GIGANTIA (GI), CONSTANS (CO) and SUPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) genes either act upstream of or in a different pathway to WAP1/VRN1.     

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.     

Mapping genes affecting flowering time and frost resistance on chromosome 5B of wheat

Two populations of single chromosome recombinant lines were used to map genes controlling flowering time on chromosome 5B of wheat, and one of the populations was also used to map a new frost resistance gene. Genetic maps were developed, mainly using microsatellite markers, and QTL analysis was applied to phenotypic data on the performance of each population collected from growth-room tests of flowering time and frost tolerance. Using a recombinant substitution-line mapping population derived from a cross between the substitution-line 'Chinese Spring' ('Cheyenne' 5B) and 'Chinese Spring' (CS), the gene Vrn-B1, affecting vernalization response, an earliness per se locus, Eps-5BL1, and a gene, Fr-B1, affecting frost resistance, were mapped. Using a 'Hobbit Sib' ('Chinese Spring' 5BL) x 'Hobbit Sib' recombinant substitution line mapping population, an earliness per se locus, Eps-5BL2 was mapped. The Vrn-B1 locus was mapped on the distal portion of the long arm of chromosome 5B, to a region syntenous with the segments of chromosomes 5A and 5D containing Vrn-A1 and Vrn-D1 loci, respectively. The two Eps-5BL loci were mapped close to the centromere with a 16-cM distance from each other, one in agreement with the position of a homoeologous locus previously mapped on chromosome 5H of barley, and suggested by the response of 'Chinese Spring' deletion lines. The Fr-B1 gene was mapped on the long arm of chromosome 5B, 40 cM from the centromeric marker. Previous comparative mapping data with rice chromosome 9 would suggest that this gene could be orthologous to the other Fr genes mapped previously by us on chromosomes 5A or 5D of wheat, although in a more proximal position. This study completes the mapping of these homoeoallelic series of vernalization requirement genes and frost resistance genes on the chromosomes of the homoeologous group 5 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.     

栽培一粒小麦3AA30中抗白粉病基因的鉴定及分子标记定位

栽培一粒小麦是普通小麦的近缘种,遗传多样性丰富,蕴含丰富的抗病基因,是小麦抗病性改良的重要资源。本文对栽培一粒小麦抗白粉病材料3AA30的抗白粉病基因进行了遗传分析和分子标记定位。结果表明,3AA30中含有一个隐性抗白粉病基因,暂命名为ml3AA30,找到了5个与该基因连锁的SSR分子标记Xgwm6、Xcfd39、Xcfa2185、Xcfa2141、Xcfa2155及2个STS标记Xmag2170、Xmag1491,并构建了ml3AA30的遗传连锁图,将该基因定位在小麦5A染色体长臂上。本研究为小麦抗病育种提供了新的抗源材料。     

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     

Detection of the quantitative trait loci for α-amylase activity on a high-density genetic map of rye and comparison of their localization to loci controlling preharvest sprouting and earliness

The objectives of the research were to determine the position of quantitative trait loci (QTL) for α-amylase activity on the genetic map of a rye recombinant inbred line population-S120?×?S76-and to compare them to known QTL for preharvest sprouting and heading earliness. Fourteen QTL for α-amylase activity on all seven chromosomes were identified. The detected QTL were responsible for 6.09-23.32% of α-amylase activity variation. The lowest LOD value (2.22) was achieved by locus QAa4R-M3 and the highest (7.79) by locus QAa7R-M1. Some QTL intervals for features of interest overlapped partially or completely. There were six overlapping QTL for α-amylase activity and preharvest sprouting (on 1R, 3R, 4R, 6R, 7R) and the same number for preharvest sprouting and heading earliness (on 1R, 2R, 6R, 7R). Furthermore, there was one interval partially common to all three traits, mapped on the long arm of chromosome 1R. Testing of lines originating from hybrid breeding programs, such as S120 and S76, may provide important information about the most significant genes and markers for selection in commercial breeding. Among the statistically significant markers selected in the Kruskal-Wallis test (P?相似文献   

Effects of an intercultivaral chromosome substitution on winterhardiness and vernalization in wheat

During a study on the genetic control of winterhardiness in winter wheat (Triticum aestivum L. group aestivum), a gene that affected vernalization was found on chromosome 3B in the winter wheat cultivar `Wichita.' When chromosome 3B from Wichita was substituted into the winter wheat cultivar `Cheyenne,' the resultant substitution line exhibited a spring growth habit. This is unusual since a cross between the cultivars Wichita and Cheyenne results in progeny that exhibit the winter growth habit. The F(2) plants from a cross of the 3B substitution line to Cheyenne, the recipient parent, segregated 3:1 for heading/no heading response in the absence of vernalization (χ(2) = 2.44). Earliness of heading appeared to be due to an additive effect of the 3B gene as shown by the segregation ratio 1:2:1 (early heading-later heading-no heading) (χ(2) = 2.74). This vernalization gene differs from previously described vernalization genes because, while dominant in a Cheyenne background, its expression is suppressed in Wichita. The gene may have an effect on winter hardiness in Wichita. In a field test for winter survival the 3B substitution line had only 5% survival, while Wichita and Cheyenne had 50 and 80% survival, respectively. No other substitution line significantly reduced winter survival. The difference between Wichita and Cheyenne in winterhardiness may be due to the vernalization gene carried on the 3B chromosome.     

Genetic Map of Diploid Wheat, Triticum Monococcum L., and Its Comparison with Maps of Hordeum Vulgare L

A genetic map of diploid wheat, Triticum monococcum L., involving 335 markers, including RFLP DNA markers, isozymes, seed storage proteins, rRNA, and morphological loci, is reported. T. monococcum and barley linkage groups are remarkably conserved. They differ by a reciprocal translocation involving the long arms of chromosomes 4 and 5, and paracentric inversions in the long arm of chromosomes 1 and 4; the latter is in a segment of chromosome arm 4L translocated to 5L in T. monococcum. The order of the markers in the inverted segments in the T. monococcum genome is the same as in the B and D genomes of T. aestivum L. The T. monococcum map differs from the barley maps in the distribution of recombination within chromosomes. The major 5S rRNA loci were mapped on the short arms of T. monococcum chromosomes 1 and 5 and the long arms of barley chromosomes 2 and 3. Since these chromosome arms are colinear, the major 5S rRNA loci must be subjected to positional changes in the evolving Triticeae genome that do not perturb chromosome colinearity. The positional changes of the major 5S rRNA loci in Triticeae genomes are analogous to those of the 18S-5.8S-26S rRNA loci.     

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.     

Quantitative trait loci controlling vernalisation requirement, heading time and number of panicles in meadow fescue (Festuca pratensis Huds.)

The “BF14/16×HF2/7” mapping population of meadow fescue (Festuca pratensis Huds.) was characterised for number of panicles produced by non-vernalised plants in the field, vernalisation requirement (number of weeks at 6°C and 8 h photoperiod), as well as days to heading, number of panicles and proportion of shoots heading after a 12 weeks vernalisation treatment. Quantitative trait loci (QTLs) were identified and compared to QTLs and genes related to the induction of flowering in cereals and grasses. A region on chromosome 1F affected days to heading and the proportion of shoots heading. Chromosome 4F appeared to have several genes with a strong effect on vernalisation requirement. The strongest effects were located in the proximal end of 4F and may correspond to the earliness per se (eps) QTL eps6L.2 in barley and a heading time QTL in perennial ryegrass. A part of the meadow fescue orthologue of VRN1 was sequenced and mapped to another region of 4F that also had a strong effect on vernalisation requirement. The proximal end of chromosome 5F had QTLs for days to heading and proportion of heading shoots. Syntenic regions in wheat and barley contain eps-loci. A QTL for number of panicles in the field and a QTL for proportion of heading shoots were present on chromosome 6. A region on 7F affected the variation in number of panicles among plants without a vernalisation requirement, and is syntenic to regions in perennial ryegrass, barley and rice containing orthologues of Arabidopsis thaliana CO.