Mapping chromosomal regions affecting flowering time in a spring wheat RIL population

Flowering time is an important trait for the adaptation of wheat to its target environments. To identify chromosome regions associated with flowering time in wheat, a whole genome scan was conducted with five sets of field trial data on a recombinant inbred lines (RIL) population derived from the cross of spring wheat cultivars ‘Nanda 2419’ and ‘Wangshuibai’. The identified QTLs involved seven chromosomal regions, among which QFlt.nau-1B and QFlt.nau-2B were homoeologous to QFlt.nau-1D and QFlt.nau-2D, respectively. Nanda 2419, the earlier flowering parent, contributed early flowering alleles at five of these QTLs. QFlt.nau-1B and QFlt.nau-7B had the largest effects in all trials and were mapped to the Xwmc59.2–Xbarc80 interval on chromosome 1BS and the Xgwm537–Xgwm333 interval on 7BS. Most of the mapped QTL intervals were not coincident with known vernalization response or photoperiod sensitivity loci and QFlt.nau-1B seems to be an orthologue of EpsA ^m 1. Four pairs of loci showed significant interactions across environments in determining flowering time, all of which involved QFlt.nau-1B. These findings are of significance to wheat breeding programs.     

Genetic control of photoperiodic sensivity and maturity in spring wheat within narrow limits of adaptation

Summary Photoperiodic respose, as assessed by a regression technique, exhibited complete dominance averaged over the crosses of an eight parent diallel in the vernalized condition. Photoperiodic response as final leaf number for the vernalized 8-hour photoperiod diallel was closely related to photoeriodic response of the regression method. However, the diallel analyses of both sets of data showed little agreement in terms of respectieve array positions.The inheritance of photoperiodic response in diallels using regression values showed little agreement between the vernalized and unvernalized conditions. This difference was postulated to be due to interaction of vernalization and photoperiodic response in the unvernalized situation. In the unvernalized condition photoperiodic response exhibited non-allelic interaction, attributable mainly to the cultivar Pinnacle in general behaviour in its crosses. Its removal gave a situation of high average dominance for photoperiodic response with a clear indication that high photoperiodic sensitivity was dominant to comparative insensitivity.Days to ear emergence (vernalized and 18-hour photoperiod) exhibited non-allelic interaction in its expression, due mainly to the general behaviour of the cultivar Pinnacle in its crosses. Removal of its array gave a situation of a moderately strong degree of overdominance in the expression of days to ear emergence. Maturity differences amongst parents and F₁'s, vernalized and under 18-hour photoperiod, are postulated to be due to a factor other than vernalization or photoperiodic response beheved to be growth temperature in differentially in fluencing growth and/or developmental rates between genotypes.     

Genetic systems regulating flowering response in wheat

Genetic systems regulating bread wheat ontogenesis have been studied at Ukraine's Plant Breeding and Genetics Institute, for more than two decades. The influence of Vrn genes is the most obvious; dominant alleles of Vrn genes inhibit the vernalisation requirement. The Vrn genotypes of more than 1000 cultivars were determined and the peculiarities of gene geography were shown. Dominant Vrn1 or Vrn2 seemed to be replaced by Vrn3 in regions closer to the equator. In the developed sets of near-isogenic (congenic) lines, the value of different genes was characterised for certain environments (favourable – phytotron, natural – early or late drought) based on their effects. Methods of Vrn gene manipulation were elaborated, including methods for winter genotype selection from spring x spring crosses. The possibility of alien homoeologous Vrn loci introgression was shown. In the introgressed lines, the new genes were identified and found to be nonallelic to known Vrn genes in wheat. In studying congenic lines for three Ppd genes, differences were observed in duration and intensity of photoperiodic response, vernalisation requirement and effects on agronomic traits. For typical winter wheats, two loci were identified that influenced the duration of the vernalisation requirement. One system, controlling intrinsic earliness, might be responsible for the differences in reaction to light intensity, as selection of earlier genotypes is supposed to be more effective at lower light intensity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic analysis without replications: model evaluation and application in spring wheat

Genetic data collected from various plant breeding and genetic studies may not be replicated in field designs although field variation is always present. In this study, we addressed this problem using spring wheat (Triticum aestivum L.) trial data collected from two locations. There were no intralocation replications and an extended additive-dominance (AD) model was used to account for field variation. We numerically evaluated the data from simulations and estimated the variance components. For demonstration purposes we also analyzed three agronomic traits from the actual spring wheat data set. Results showed that these data could be effectively analyzed using an extended AD model, which was more comparable to a conventional AD model. Actual data analysis revealed that grain yield was significantly influenced by systematic field variation. Additive effects were significant for all traits and dominance effects were significant for plant height and time-to-flowering. Genetic effects were predicted and used to demonstrate that most spring wheat lines developed by the South Dakota State University breeding program (SD lines) exhibited good general combining ability effects for yield improvement. Thus, this study provides a general framework to appropriately analyze data in situations where field crop data are collected from non-replicated designs.     

Genetic mapping of a new flowering time gene on chromosome 3B of wheat

The single chromosome substitution lines of chromosome 3B of the Czech alternative wheat variety Česká Přesívka (CP 3B) into two spring varieties Zlatka and Sandra, revealed clear differences in flowering time compared to the recipient varieties. To map this gene(s), recombinant substitution lines for chromosome 3B were produced from crosses of the substitution lines with their recipient parents and genetic maps developed using SSR markers. Two populations were mapped, Sandra//Sandra 3B/Sandra (CP 3B) and Zlatka//Zlatka/Zlatka (CP 3B). Combining the genotype data with phenotype data on flowering time in five independent experiments under natural long day or controlled short day conditions revealed a single flowering time QTL. This gene had an additive effect of 1–6 days, depending on environment and genetic background, and was mapped in both populations to a position in the region of marker Xbarc164 near the centromere on the long arm of 3B. Comparisons of the genetic maps with other 3B maps developed by the authors indicated that the QTL may be homologous to a QTL segregating in UK germplasm.     

Quantitative trait analysis of flowering time in spring rapeseed (B. napus L.)

The inheritance of flowering time trait in spring-type rapeseed (Brassica napus L.) is poorly understood, and the investigations on mapping of quantitative trait loci (QTL) for the trait are only few. We identified QTL underlying variation for flowering time in a doubled haploid (DH) mapping population of nonvernalization-responsive canola (B. napus L.) cultivar 465 and line 86 containing introgressions from Houyou11, a Chinese early-flowering cultivar in Brassica rapa L. Significant genetic variation in flowering time and response to photoperiod were observed among the DH lines from 465/86. A molecular linkage map was generated comprising three types of markers loci. QTL analysis indicated that flowering time is a complex trait and is controlled by at least 4 major loci, localized on four different linkage groups A6, A7, C8 and C9. These loci each accounted for between 9.2 and 12.56 % of the total genotypic variation for first flowering. The published high-density maps for flowering time mapping used different marker systems, and the parents of our crosses have different genetic origins, with either spring-type B. napus or B. rapa. So we cannot determine whether the QTL on the same linkage groups were in the same region or not. There was evidence of additive × additive epistatic effects for flowering time in the DH population. Epistasis existed not only between main-effect QTLs, but also between QTLs with minor effects. Four pair of epistasis effects between minor QTLs explained about 20 % of the genetic variance observed in the DH population. The results indicated that minor QTLs for flowering time should not be ignored. Significant genotypes × environment interactions were also found for the quantitative traits, and with significant change in the ranking of the DH lines in different environments. The results implied that FQ3 was a non-environment-specific QTL and may control flowering time by autonomous pathway. FQ4 were winter-environment-specific QTL and may control flowering time by photoperiod-pathway. Identification of the chromosomal location and effect of the genes influencing flowering time may hasten the development of canola varieties having an optimal time for flowering in target environments such as for high altitude areas, via marker-assisted selection.     

Characterization of flowering time and SSR marker analysis of spring and winter type Brassica napus L. germplasm

Flowering dates and life forms of all available Brassica napus accessions conserved at the North Central Regional Plant Introduction Station (NCRPIS) were characterized, and a survey of molecular variation was conducted by using simple sequence repeats (SSR) in order to support better management of accessions with diverse life forms. To characterize flowering phenology, 598 B. napus accessions from the NCRPIS collection were planted in Iowa and Kansas field sites together with a current commercial cultivar and observed for days to flowering (first, 50% and 100% flowering) in 2003. Days from planting to 50% flowering ranged from 34 to 83 in Iowa and from 53 to 89 in Kansas. The mean accumulated growing degree days (GDD) to 50% flowering were 1,997 in Iowa, and 2,106 in Kansas. Between locations, the correlation in flowering time (r = 0.42) and the correlation in computed GDD (r = 0.40) were both significant. Differences in flowering-time rank were observed for several accessions. Accessions that failed to flower in Iowa in a single growing season comprised 28.5% of the accessions; of the flowering accessions, 100% plant flowering was not always achieved. Accessions were grouped according to flowering time. A stratified sample of 50 accessions was selected from these groups, including 10 non-flowering and 40 flowering accessions of diverse geographic origins and phenological variation. The flowering time observed in the sampled accessions when grown in the greenhouse were found to be significantly correlated to the flowering time observed in the field locations in Iowa (r = 0.79) and Kansas (r = 0.49). Thirty SSR markers, selected across 18 Brassica linkage groups from BrassicaDB, and 3 derived from Brassica expressed sequence tags (ESTs) were scored in the stratified sample. An average of three bands per SSR primer pair was observed. Associations of SSR marker fragments with the life forms were determined. Analysis of molecular variation by using cluster analysis and ordination resulted in recognizable, distinct groups of annual and biennial life-form types, which may have direct applications for planning and management of future seed regenerations. Mention of commercial brand names in this paper does not constitute an endorsement of any product by the U.S. Department of Agriculture or cooperating agencies.     

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.     

甘肃省春小麦新品系丰产稳产性分析

利用2007-2008年甘肃省西片水地春小麦区域试验资料,对甘肃省新育春小麦品种(系)的丰产性和稳定性进行综合分析.结果表明:9075-2、E32-1、7095和8972-14是丰产性优良、稳产性较好的小麦新品系.适宜甘肃河西灌区和沿黄灌区种植.     

Simultaneous selection for early maturity, increased grain yield and elevated grain protein content in spring wheat

High grain yield and grain protein content, and early maturity are important traits in global bread wheat ( Triticum aestivum L.)-breeding programmes. Improving these three traits simultaneously is difficult due to the negative association between grain yield and grain protein content and the positive association between maturity and grain yield. We investigated the genetic relationship between maturity, grain yield and grain protein content in a population of 130 early maturing spring wheat lines in a high latitude (52–53°N) wheat-growing region of Canada. Grain protein content exhibited negative genetic correlation with maturity (−0.87), grain fill duration (−0.78), grain fill rate (−0.49), grain yield (−0.93) and harvest index (−0.71). Grain yield exhibited positive genetic correlation with maturity (0.69), rate (0.78) and duration (0.49) of grain fill, and harvest index (0.55). Despite the positive association between maturity and grain yield, and negative association between grain yield and grain protein content, higher yielding lines with medium maturity and higher grain protein content were identified. Broad-sense heritabilities were low (<0.40) for rate and duration of grain fill, grain protein content, spike per m², grains per spike, harvest index and grain yield, and medium to high (>0.40) for grain weight, days to anthesis and maturity, and plant height. Selection for longer preanthesis and shorter grain fill periods may help circumvent the negative association between grain yield and grain protein content. Selection for shorter grain fill periods and higher grain fill rate may be a useful strategy for developing early maturing cultivars with acceptable grain yields in northern wheat-growing regions.     

QTL analysis on plant height and flowering time in Brassica napus

To identify quantitative trait loci (QTL) controlling plant height (PH) and flowering time (FT), a high stalk/later bloom Brassica napus line '2091' was crossed with a dwarf/early bloom mutant '99CDAM'. A segregating population with 145 F_2:3 lines was constructed and grown in field for 2 years. Based on this population, a linkage map consisting of 199 amplified fragment length polymorphism and 42 simple sequence repeat loci was constructed. The LOD threshold of 3.0 was used for declaring the existence of putative QTL. In total, seven QTL related to PH were identified, accounting for 8.5–28.6% of phenotypic variation, respectively, of which two QTL were identified in both years. Six QTL for FT were detected, accounting for 8.1–30.4% of phenotypic variation individually, of which two QTL were identified in both years. The main QTL of PH and FT were both mapped on linkage group 13, with overlapped creditable regions. QTL ph17 and ft17 existed at the same location. These might be the genetic base for the significant correlation observed between PH and FT.     

Genetic analysis of bread-making quality in wheat and spelt

Bread‐making quality in wheat and spelt reflects the combination of several, mostly quantitatively inherited parameters. The aim was to find molecular markers linked to quantitative trait loci (QTL) for quality parameters. Zeleny sedimentation values (Zel), protein (Prot), kernel hardness (KH) and 1000‐kernel weight (TKW) of 226 F₅ recombinant inbred lines (RILs) from a cross between wheat and spelt were assessed in different environments. The dough properties of 204 RILs were assessed with an alveograph. Based on a genetic map of 187 loci, nine QTL were found for Zel and Prot, explaining 47% and 51% of the phenotypic variance, respectively. Fifty‐four per cent of the variance was explained by 10 QTL for KH and eight for TKW. For the alveograph parameters 10 QTL were found for baking strength, nine for tenacity, seven for configuration ratio, and four for elasticity index and extensibility. The phenotypic variance explained ranged from 25% to 48%. The population mean of the dough parameters was shifted towards the spelt parent. It is concluded that non‐additive effects are crucial in the expression of high bread‐making quality of wheat. The consequences for wheat and spelt breeding programmes are discussed.     

Russian wheat aphid-induced protein alterations in spring wheat

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), has become a perennial, serious pest of wheat (Triticum aestivum L.) in the western United States. Current methodologies used to enhance RWA resistance in wheat germplasm could benefit from an understanding of the biochemical mechanisms underlying resistance to RWA. This study was initiated to identify specific polypeptides induced by RWA feeding that may be associated with RWA resistance. The effects of RWA feeding on PI 140207 (a RWA-resistant spring wheat) and Pavon (a RWA-susceptible spring wheat) were examined by visualizing, silver-stained denatured leaf proteins separated by two-dimensional polyacrylamide gel electrophoresis. Comparisons of protein profiles of noninfested and RWA-infested Pavon and PI 140207 revealed a 24-kilodalton-protein complex selectively inhibited in Pavon that persisted in PI 140207during RWA attack. No other significant qualitative or quantitative differences were detected in RWA-induced alterations of protein profiles. These results suggest that RWA feeding selectively inhibit synthesis and accumulation of proteins necessary for normal metabolic functions in susceptible plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of in vitro wheat somatic embryogenesis

Summary A spring wheat genotype which produces somatic embryos in vitro, after short and long-term culture, was tested for its ability to sexually transmit this embryogenic trait. Reciprocal crosses were performed between a embryogenic line and a nonembryogenic variety.Immature embryos were cultured on Murashige and Skoog medium plus 2 mg/l 2,4-dichlorophenoxyacetic acid, gelled with 5.5 g/l agarose. Somatic embryogenesis was not expressed in the F₁'s. In contrast, from several hundred immature embryos of the F₂ generation of one cross, 10.7% and 1.6% expressed somatic embryogenesis in short and long-term cultures respectively. These percentages of embryogenic: non-embryogenic fits a model of a few complementary genes. The embryogenic capacity of the F₂ genotypes depends on the presence of recessive alleles at these gene loci. The long-term wheat somatic embryogenesis capacity requires a more complex mechanism than the short-term one.Abbreviations CS Chinese Spring - Aq Aquila - E Embryogenic - NE Nonembryogenic - SC Subculture     

Genetic control of acquired high temperature tolerance in winter wheat

Summary The development of high temperature-tolerant wheat (Triticum aestivum L.) germplasm is necessary to improve plant productivity under high-temperature stress environments. The quantification of high temperature tolerance and the characterization of its genetic control are necessary for germplasm enhancement efforts. This study was conducted to determine the genetic control of acquired high temperature tolerance in common bread wheat cultivars. Reduction of 2,3,5-triphenyltetrazolium chloride (TTC) by heat-stressed seedling leaves was used as a quantitative measure to characterize acquired high temperature tolerance. Eleven-day-old seedlings of 20 F₁ progeny produced through a complete 5×5 (Payne, Siouxland, Sturdy, TAM W-101, and TAM 108) diallel mating design were acclimated at 37° C for 24 hours, followed by a 2-hour incubation at 50° C. Under these test conditions, acquired high temperature tolerance ranged from a high of 75.7% for the genotype TAM W-101 × TAM 108, to a low of 37.3% for the genotype Payne × Siouxland. Partitioning of genotypic variance revealed that only the general combining ability component effect was statistically highly significant, accounting for 67% of the total genotypic variation. These results suggest that enhancing the level of high temperature tolerance in wheat germplasm is feasible utilizing existing levels of genetic variability and exploiting additive genetic effects associated with high temperature tolerance.Contribution of the Texas Tech College of Agric. Sci. Journal no T-4-386. This work was supported by USDA specific agreement No. 58-7MNI-6-114 from the Plant Stress and Water Conservation Laboratory, USDA-ARS, Lubbock, Texas, USA     

A comparison of marker-assisted and phenotypic selection for high grain protein content in spring wheat

Wheat grain protein content (GPC) is a primary end-use quality determinant for hard spring wheat (Triticum aestivum L.), and marker-assisted selection (MAS) could help plant breeders to develop high GPC cultivars. Two experiments were conducted using two populations developed by crossing low GPC cultivars (Ember) and (McVey) with (Glupro), which contains a high GPC QTL from Triticum dicoccoides (DIC). In one experiment, MAS and phenotypic selection (PS) were employed to select high GPC genotypes, and the selected genotypes were grown in six North Dakota (ND), USA environments. In a second experiment, molecular markers were used to select BC₂F₂ plants from each marker class for the DIC allele from each population. These plants were twice self-pollinated to produce BC₂F₄ plants, which were grown in single ND and Minnesota (MN) environments. Mean GPC was highest among lines using PS at two environments and not significantly different between MAS and PS in the other four environments. Lines presumably homozygous for DIC alleles had significantly higher GPC than their respective low GPC parents. The phenotypic GPC variation explained by the markers (r ²) was 30% at the ND and 15% at the MN environment. The use of PS was as effective as MAS in selecting for high GPC genotypes and more effective in some environments. This likely can be attributed to PS enabling selection for both the major QTL and other genes contributing to GPC. The use of molecular markers might be more advantageous for transferring the high GPC DIC QTL in a backcrossing program during parent development.     

Quantitative genetic analysis of flowering time in the Davis Population of gerbera

Summary Phenotypic and genetic correlations of flowering time (FT) with cut-flower yield (Y) were estimated from six generations of the Davis Population of gerbera (Gerbera hybrida, Compositae). The phenotypic correlation was –0.34; the genetic correlation was –0.47 when estimated from ANOVA of a NCII design and –0.72 when estimated from parent-offspring analysis. An indirect selection model was constructed to assess the efficiency of indirect selection for Y using FT as a marker. This model includes population size and generation time as variables because they differ for FT and Y. The results indicate that indirect selection will be more efficient than direct selection.Correlations of FT with flower quality traits, including scape length (SL), flower diameter (FD), scape dry weight (SDW) and flower dry weight (FDW), were also estimated. FT was phenotypically independent of these traits. However, statistically significant estimates of genetic correlation indicate that FT may be correlated with flower quality traits. Thus, indirect selection on FT to increase Y may result in undesirable correlated responses for flower quality.     

Generation mean analysis of spring wheat (Triticum aestivum L.) seedlings tolerant to high levels of manganese

Effective utilisation of wheat (Triticum aestivum L.) germplasm tolerant to high manganese (Mn) in a breeding program requires an understanding of the genetics of Mn tolerance. Five wheat cultivars differing in their response to high Mn were crossed in a half diallel design with no reciprocals. Seedlings of parents and progeny generations were phenotyped in high Mn nutrient solutions. Total chlorophyll concentration, which was positively correlated with leaf elongation rate during recovery from Mn stress, was used for phenotyping Mn tolerance. Means of chlorophyll concentration of P₁, P₂, F₁, F₂, BC₁, and BC₂ generations, in all crosses which showed significant variation among generations, were subjected to line crosses analysis to estimate gene effects. The continuous frequency distribution of seedlings with differential Mn tolerance, the similarity of the F₁ and F₂ means, and the high and significant levels of additive gene action indicated quantitative inheritance for Mn tolerance at seedling stage. A preponderance of additive effects indicated that selection for Mn tolerance in early generations should be effective.     

Evaluation of winter wheat as a source of high yield potential for the breeding of spring wheat

Grain yield components of high yielding European winter wheat varieties and of the best spring varieties grown in Israel were compared and their growth was analyzed. F₁- and F₂-populations of crosses between winter and spring varieties were tested. Under conditions in which winter wheat attained its normal kernel size which was similar to that of the spring varieties tested, it markedly outyielded spring wheat by means of its greater number of spikelets per spike. This advantage was also expressed in the F₂-populations and, was apparently, not linked with cold requirement. Winter wheat had a longer growing period and a greater leaf-area but a lower net assimilation rate than spring wheat. The higher total dry matter yield of winter wheat was owing to its longer growing period. The higher grain yield, however, was induced by a higher ratio of grain to total dry matter accumulated during the period of kernel development. The inheritance of several characters is discussed and it is concluded that winter wheat should be able to contribute to an increase in yield of progenies of its crosses with spring wheat.Contribution from The National and University Institute of Agriculture, Rehovot, No. E-1072. This research was supported by a grant of the Ford Foundation, Project Ford 4(A-3).